Thèses sur le sujet « Community ecology and stability »
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1
Liautaud, Kevin. « Community stability and turnover in changing environments ». Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30264.
Texte intégralRésumé :
Les communautés d'êtres vivants peuvent elles êtres considérées comme des organismes complexes, ou au contraire comme de simples groupes d'espèces, individuelles ? Cette question est à l'origine de nombreux débats en écologie, ces deux visions impliquant notamment des prédictions très différentes dans les patrons spatiaux et temporels de communautés. Lorsque l'environnement change graduellement dans l'espace ou dans le temps, la vision individualiste implique des changements graduels dans la composition des communautés, tandis que la vision du "super-organisme" prédit des changements davantage abrupts. L'objectif principal de cette thèse est de comprendre et déterminer sous quelles conditions ces différents types de réponse des communautés aux changements de l'environnement peuvent advenir. Dans une première partie, nous étudions le rôle que la compétition inter-spécifique peut jouer dans l'émergence de différents patrons spatiaux de communautés. Nous étudions notamment les conditions théoriques sous lesquelles la compétition peut faire apparaître des patrons graduels ou discontinus dans la composition des espèces. Dans une deuxième partie, nous étudions l'influence des interactions entre les espèces et leur environnement sur les patrons spatiaux de communautés. Nous montrons notamment comment des phénomènes de construction de niche peuvent mener à l'émergence de changements brutaux dans la composition des communautés, mais également dans les conditions de l'environnement. Enfin, dans une dernière partie, nous illustrons le rôle que peut jouer la biodiversité dans la protection des écosystèmes face à des effondrements écologiques, et notamment le rôle que peut jouer la biomasse dans cette protectionThe question whether communities should be viewed as superorganisms or loose collections of individual species has been the subject of a long-standing debate in ecology. Each view implies different spatial and temporal community patterns. When environment gradually changes in space or in time, the organismic view predicts that species turnover is discontinuous, while the individualistic view predicts gradual changes in species composition. The main objective of this thesis is to understand the theoretical conditions under which these various types of community response can occur. First, I study the role of interspecific competition can play in the emergence of various spatial community patterns. I investigate the theoretical conditions in competition under which smooth or discrete spatial patterns can emerge. Then, I study how interactions between species and their environment can lead to various community patterns in space. I notably show how ecological niche construction can lead to the emergence of abrupt changes in species composition and in the environment, and the role biodiversity plays therein. Finally, I focus on the role biodiversity can play against ecosystem collapse. In this section, I illustrate how diversity loss, through its effects on total biomass, can lead to ecosystem collapse
2
Rodgers, Erin V. « Scales of Resilience : Community Stability, Population Dynamics, and Molecular Ecology of Brook Trout in a Riverscape after a Large Flood ». Antioch University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=antioch1422195420.
Texte intégral
3
Li, Wei. « The effect of resource availability on community dynamics and properties in experimental microcosms ». Oxford, Ohio : Miami University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1218118890.
Texte intégral
4
n, Hussin Wan Mohd Rauhan. « Measurement of changes in marine benthic ecosystem function following physical disturbance by dredging ». Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2838.
Texte intégralRésumé :
Measuring the impact of physical disturbance on macrofaunal communities and sediment composition is important given the increased demand for the exploitation and disturbance of marine ecosystems. The aim of the present investigation was to provide a comprehensive study about the extent to which the disturbance (especially aggregate dredging) may affect benthic ecosystem function. The first part of the thesis concerns a field investigation of the impacts of dredging on the benthic community and related ecosystem function which was measured by different approaches including traditional methods based on benthic community structure and a more novel approach based on the functional traits of benthic organisms. The assessment was done by comparing dredged sites (Area 222, southeast England) with nearby undisturbed reference sites from the years 2001 to 2004 and in 2007. In general, low dredging intensity did not appear to impose great impacts on the benthic community and related ecosystem function compared to the higher intensity activity. Most of the analyses suggested that the community at the high dredging intensity site had yet to recover at the end of this study period. Among many factors related to the recovery of the benthic community was sediment composition where gravel deposits appeared to support a faster biological recovery. Meanwhile, the recovery of species with specific traits, such as tube-building and filter feeding also indicate a faster recovery for the whole community. The experimental work to determine different impacts of Hediste diversicolor on its surrounding depending on its relative size is discussed in Appendix 1.
5
Lurgi, Rivera Miguel. « The assembly and disassembly of ecological networks in a changing world ». Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/133289.
Texte intégralRésumé :
El
ensamblaje,
estructuración
y
funcionamiento
de
las
comunidades
naturales,
compuestas
de
muchas
especies
que
forman
redes
complejas
de
interacciones
ecológicas,
ha
desconcertado
a
los
ecólogos
durante
muchas
generaciones.
Investigación
ecológica
pionera
determinó
que
el
tamaño
de
la
comunidad
y
su
complejidad
(medida
como
la
conectividad
en
la
red
de
interacciones
ecológicas)
limita
la
estabilidad
de
la
comunidad,
y
por
lo
tanto
impiden
que
las
comunidades
sean
indefinidamente
complejas
o
ricas
en
especies.
Investigación
sobre
el
ensamblaje
y
la
estabilidad
en
comunidades
naturales
ha
descubierto
que
la
arquitectura
de
la
red
trófica
es
la
clave
para
la
estabilidad
de
la
comunidad
y
su
persistencia.
Así,
los
científicos
comenzaron
a
centrarse
en
la
comprensión
de
las
complejas
redes
de
interacciones
entre
especies,
y
pronto
se
dieron
cuenta
de
que
la
dinámica
de
las
poblaciones
de
las
comunidades
naturales
se
rigen
por
la
estructura
de
estas
redes.
Por
otra
parte,
ciertas
características
observadas
en
la
estructura
de
las
redes
ecológicas
son
responsables
del
mantenimiento
de
la
estabilidad
en
diferentes
tipos
de
comunidades
ecológicas.
El
siguiente
paso
en
la
investigación
de
las
redes
ecológicas
es
incorporar
varios
tipos
de
interacción
en
un
escenario
ecológico
más
amplio.
Esto
incrementará
el
conocimiento
de
la
estructura
y
la
estabilidad
de
la
comunidad.
El
cambio
global
está
afectando
los
ecosistemas
de
todo
el
mundo,
con
profundos
impactos
sobre
el
delicado
equilibrio
de
la
naturaleza.
Ya
ha
causado
un
número
sin
precedentes
de
extinciones,
y
el
consiguiente
daño
en
la
estructura
y
funcionamiento
del
ecosistema
ha
llevado
a
muchos
a
sugerir
que
en
estos
momentos
estamos
presenciando
la
sexta
extinción
masiva
en
la
historia
de
la
Tierra.
El
principal
desafío
para
la
investigación
ecológica
que
tenemos
por
delante
es
entender
y
predecir
cómo
el
cambio
global
está
afectando,
y
es
probable
que
afecte
en
el
futuro,
los
ecosistemas
complejos.
En
esta
tesis
enfrento
este
desafío
utilizando
una
aproximación
empírico-‐teórica
integradora
para
explorar
los
efectos
del
cambio
global
-‐cambio
climático,
pérdida
de
biodiversidad
e
invasión
de
especies-‐
en
comunidades
compuestas
por
múltiples
especies.
Adicionalmente,
investigo
qué
hace
que
las
comunidades
ecológicas
sean
estables
durante
su
ensamblaje,
y
cómo
esta
estabilidad
puede
verse
afectada
por
el
cambio
global.
En
concreto,
he
empleado
una
combinación
de
revisión
de
resultados
y
análisis
de
datos
empíricos,
un
novedoso
marco
conceptual
para
el
análisis
de
las
relaciones
entre
diferentes
dimensiones
de
la
estabilidad
ecológica,
modelos
teóricos
fundamentados
en
redes
tróficas
con
estructuras
realista
y
ecuaciones
diferenciales
ordinarias
para
simular
la
dinámica
de
las
poblaciones,
y
modelos
espacialmente
explícitos
basados
en
el
individuo
con
una
mezcla
de
tipos
de
interacciones
ecológicas;
con
el
fin
de
obtener
una
visión
predictiva
de
los
efectos
de
los
diferentes
componentes
del
cambio
global
sobre
las
comunidades
naturales
y
sobre
los
factores
que
explican
la
estabilidad
de
estos
conjuntos
de
especies.
Algunos
de
mis
principales
hallazgos
son:
(1)
cambios
de
distribuciones
de
especies
provocados
por
el
cambio
climático
están
generando
comunidades
nuevas
.
Estas
últimas
se
caracterizan
por
nuevos
patrones
en
que
las
distribuciones
de
tamaño
corporal
dentro
de
las
redes
tróficas
se
están
desplazando
hacia
tamaños
más
pequeños,
las
interacciones
especialistas
se
están
perdiendo,
y
las
fuerzas
de
interacción
son
cada
vez
más
fuertes
en
general,
con
consecuencias
importantes
para
la
dinámica
de
la
comunidad.
(2)
Las
diferentes
dimensiones
de
la
estabilidad
ecológica
se
correlacionan
de
manera
no
trivial.
La
pérdida
de
biodiversidad
lleva
a
un
desacoplamiento
de
estas
correlaciones.
Esto
conduce
a
dinámicas
altamente
impredecibles
en
comunidades
ecológicas
sujetas
a
perturbaciones.
(3)
Enfocándonos
en
las
invasiones
biológicas
vemos
que
la
estructura
de
la
red
trófica
es
un
factor
determinante
para
éxito
de
la
invasión.
Comunidades
menos
conectadas,
más
modulares,
y
más
heterogéneas
en
términos
de
amplitud
de
la
dieta
de
las
especies
que
las
componen
son
más
robustas
a
las
invasiones
biológicas.
Las
invasiones
hacen
a
las
comunidades
más
conectadas
y
menos
modulares
en
general,
lo
que
las
hace
aún
más
frágiles
a
las
invasiones.
Algunos
rasgos
de
las
especies
invasoras,
como
su
tamaño
corporal
y
su
capacidad
de
capturar
la
presa,
también
son
fuertes
determinantes
del
éxito
de
la
invasión.
(4)
Por
último,
las
interacciones
mutualistas
incrementan
tanto
la
estabilidad
temporal
como
la
estabilidad
espacial,
mediante
el
mantenimiento
de
una
agregación
espacial
más
constante.
Las
distribuciones
de
las
fuerzas
de
interacción
en
la
red
se
desplazan
hacia
valores
más
bajos
a
medida
que
la
fracción
de
mutualismos
en
la
comunidad
aumenta.The assembly, structuring and functioning of natural communities, composed of many species forming complex networks of ecological interactions, has puzzled ecologists for many generations. Early ecological research determined that community size and complexity (measured as connectivity in the network of ecological interactions) limit community stability, and hence impose constraints to communities to become indefinitely complex or speciose. Community assembly and stability research uncovered the fact that food web architecture is the key to community stability and persistence. Scientists thus started to focus on the understanding of complex networks of interactions between species, and it was soon realised that species population dynamics are influenced by biotic interactions within the overall network. Moreover, certain features observed in the structure of ecological networks are responsible for the maintenance of stability and species persistence in different kinds of ecological communities. The next step in ecological networks research is to incorporate several interaction types into a broader ecological scenario. This will further our knowledge in community structure and stability. Global change is affecting all ecosystems across the globe, having profound impacts over the delicate balance of nature. It has already caused an unprecedented number of extinctions, and the consequent damage to ecosystem structure and functioning has prompted many to suggest that we are currently witnessing the sixth mass extinction in the history of the Earth. The main big challenge for ecological research that lies ahead is to understand and predict how different components of global change are affecting and will likely affect complex ecosystems. In this thesis I tackle this challenge following an integrative empirical-‐theoretical approximation exploring the effects of global change –climatic warming, biodiversity loss and species invasion-‐ on multispecies communities. In addition, I investigate what makes ecological communities stable through their assembly, and how this stability may be affected by global change. Specifically, I employed a combination of empirical results review and data analysis, a novel conceptual framework for the analysis of relationships between different dimensions of stability, theoretical models grounded on realistic food web structure and ordinary differential equations to simulate populations dynamics, and individual-‐based spatially explicit models with a mixture of ecological interaction types in order to gain predictive insights on the effects of different components of global change on natural communities and several factors behind the stability of these assemblages of species. Some of my key findings are: (1) Species range shifts triggered by climate change are generating novel communities. These are characterized by consistent novel patterns where body size distributions within the food webs are getting shifted towards smaller sizes, specialised interactions are getting lost, and interaction strengths are getting stronger in general, with further consequences for community dynamics. (2) Different dimensions of ecological stability are correlated in non-‐trivial ways. Biodiversity loss leads to a decoupling of the correlations previously observed between stability measures. This leads to highly unpredictable dynamics of ecological communities after major disturbances. (3) When focusing on biological invasions I find that food web structure is a strong determinant of invasion success. Less connected, more modular, and more heterogeneous communities in terms of diet breadth are more robust to biological invasions. Invasions make communities more connected and less modular in general, rendering them even more fragile to invasions. Species traits of the invasive species, such as body size and the ability to capture prey, are also strong determinants of invasion success. (4) Finally, mutualistic interactions increase both temporal stability and spatial stability, by keeping spatial aggregation more constant. Distributions of interaction strengths across the entire food web are shifted towards lower values as mutualism increases.
6
Maurent, Eliott. « Des forêts tropicales et des humains dans les Amériques : trajectoires de réponse aux perturbations anthropiques de la diversité et de la composition des arbres. Of tropical forests and humans in the Americas : response trajectories of tree diversity and composition to anthropogenic disturbances ». Electronic Thesis or Diss., Paris, AgroParisTech, 2023. http://www.theses.fr/2023AGPT0014.
Texte intégralRésumé :
Les forêts tropicales sont confrontées à des perturbations anthropiques fréquentes et intenses, telles que l'exploitation sélective - l'abattage de quelques arbres dans des forêts anciennes, tandis que le reste du peuplement se régénère naturellement. De nombreuses études ont été menées sur la reconstitution des stocks de carbone et de bois, en raison d'un intérêt pour l'atténuation du changement climatique et la rentabilité de l'exploitation. Malgré le rôle crucial de la biodiversité pour le maintien et le fonctionnement des écosystèmes - et sa valeur intrinsèque - peu d'études ont été menées sur l'impact de l'exploitation sélective sur la biodiversité. Par conséquent, cette thèse vise à caractériser la réponse de la diversité et de la composition des arbres à l'exploitation forestière dans les forêts tropicales américaines.Grâce aux inventaires forestiers (1986-2021, diamètre à hauteur de poitrine ≥ 10 cm) de la station de Paracou (Guyane française), nous avons construit un cadre bayésien de modélisation des trajectoires de la diversité et de la composition des arbres après exploitation : Paracou a été perturbé par des traitements sylvicoles de différentes intensités en 1986-1987. Nous avons propagé l'incertitude associée à la détermination botanique et aux mesures des traits fonctionnels, et modélisé les trajectoires de diversité et de composition taxonomique, phylogénétique et fonctionnelle des arbres au niveau de l'espèce, par rapport à leurs niveaux pré-perturbation. En outre, nous avons évalué l'effet des caractéristiques des communautés d'arbres pré-perturbation, des conditions biophysiques et des propriétés de la perturbation sur nos trajectoires d'attributs forestiers. Deuxièmement, nous avons utilisé une version simplifiée du cadre de modélisation susmentionné sur des inventaires forestiers à long terme provenant de parcelles situées au Costa Rica et dans trois pays amazoniens (Observatorio de los Ecosistemas Forestales de Costa Rica et Tropical managed Forest Observatory). Nous avons modélisé leurs trajectoires de diversité et de composition taxonomique et fonctionnelle après exploitation au niveau du genre, à partir desquelles nous avons extrait des indicateurs sur la période d'inventaire de chaque site. Nous avons ensuite évalué l'effet de la structure de la communauté d'arbres pré-perturbation et des propriétés de la perturbation sur ces indicateurs. Bien que plus variables dans la seconde étude ayant une portée géographique plus large, nous avons observé des tendances similaires dans les deux études : la diversité a majoritairement augmenté après exploitation et les communautés d'arbres sont principalement passées de stratégies de conservation à des stratégies d'acquisition des ressources. Ces changements semblent provenir du recrutement abondant et momentané d'espèces de début de succession présentant des caractéristiques d'acquisition des ressources, ce qui leur confère un avantage compétitif lorsque l'intensité de perturbation - i.e., disponibilité de la lumière et de l'espace - augmente. En effet, les changements de diversité et composition ont augmenté dans les deux études avec l'intensité de perturbation, alors que les autres descripteurs n'ont pas eu d'effet significatif. Troisièmement, suite à l'importance de l'intensité de perturbation dans les études précédentes, nous avons développé un cadre commun de modélisation des trajectoires de forêts perturbées à travers un gradient d'intensité de perturbation. Nous avons testé notre approche de modélisation sur des inventaires forestiers de long-terme du Costa Rica et de Guyane française, après exploitation sélective, agriculture, et coupe à blanc suivie d'un feu.Ces résultats ouvrent des perspectives sur les méthodes d'évaluation de la réponse forestière aux perturbations, la réponse des forêts elle-même et ses processus écologiques sous-jacents, et l'intérêt des forêts perturbées pour les plans de gestion et de conservation forestièresTropical forests face more frequent and intense anthropogenic disturbances, such as selective logging, namely the felling and harvesting of a few commercially valuable trees in old-growth forests, while the remaining stand is left for natural regeneration. Many studies focused on this regeneration, particularly on the recovery of carbon and timber stocks, most likely due to a strong interest in climate change mitigation and logging profitability. However, despite the crucial role of biodiversity for ecosystem maintenance and functioning - and its intrinsic value - there have been few studies on the impact of selective logging on biodiversity. Therefore, this thesis - organised in three studies - aimed at characterising the response of tree diversity and composition to logging in tropical American forests.First, we drew upon the long-term forest inventories (1986-2021, trees with a diameter at breast height ≥ 10 cm) from Paracou experimental station to build a Bayesian modelling framework of tree diversity and composition trajectories after selective logging. Paracou is located in French Guiana and was disturbed by silvicultural treatments of different intensities in 1986-1987. We propagated in our Bayesian framework the uncertainty associated with botanical determination and functional trait measurements, and modelled Paracou trajectories of taxonomic, phylogenetic and functional tree diversity and composition at the species level, relatively to their pre-disturbance levels. Additionally, we assessed the effect of pre-disturbance tree community characteristics, biophysical conditions and disturbance properties on our forest attribute trajectories. Second, we used a simplified version of the aforementioned Bayesian modelling framework on long-term forest inventories from sample plots located in Costa Rica and three Amazonian countries (respectively belonging to the Observatorio de los Ecosistemas Forestales de Costa Rica and the Tropical managed Forest Observatory). We modelled their post-logging trajectories of taxonomic and functional tree diversity and composition at the genus level, from which we extracted indicators solely over the inventory timespan of each site. We then assessed the effect of pre-disturbance tree community structure and disturbance properties on such indicators. While more variable in the second study with a broader geographical scope than in the first one, we observed similar trends in both studies: diversity mostly increased after logging and tree communities mainly shifted from resource-conservative strategies to resource-acquisitive strategies. Such changes appeared to be driven by the abundant and transient recruitment of early-successional species with acquisitive trait values, which provided them with a competitive advantage as disturbance intensity - i.e., light and space availability - increased. Indeed, changes in diversity and composition increased in both studies with disturbance intensity whereas disturbance selectivity, pre-disturbance tree community characteristics and biophysical conditions had no significant effect. Third, building up on the paramount importance of disturbance intensity in the two previous studies, we developed an original Bayesian hierarchical model of recovery trajectories, considering disturbed forests in a common framework, through a disturbance intensity gradient. We tested our modelling approach on data from two long-term experiments in Costa Rica and French Guiana, set up after selective logging, agriculture, and clearcutting and fire.Overall, these results opened various perspectives on the methods used to evaluate forest response to disturbance, the forest response itself and the ecological processes underlying forest succession, and how disturbed forests could be considered in forest management and conservation plans
7
Masterman, Richard. « Vegetation effects on river bank stability ». Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358028.
Texte intégral
8
Memmott, Jane. « The community ecology of phlebotomine sandflies ». Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235646.
Texte intégral
9
Averis, Alison Margaret. « Ecology of an Atlantic liverwort community ». Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/10681.
Texte intégral
10
Golladay, Stephen W. « The effects of forest disturbance on stream stability ». Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53695.
Texte intégralRésumé :
This project was designed to examine the stability of stream ecosystems in response to forest disturbance and subsequent succession. Stability was defined as the ability of streams to retain particulate organic matter and nutrients during storms. I hypothesized that forest streams are least stable during the intermediate stages of forest succession because particulate organic matter accumulations in streams are lowest at that time. This hypothesis was tested by examining stream stability in relation to forest succession.
Stream surveys indicated fewer debris dams and organic matter accumulations in streams draining early and intermediate successional forests compared to reference sites. The abundance of large wood declined within 10 years of forest disturbance and continued to decline for at least 30-40 years through the intermediate stages of forest succession. Comparisons of inputs with standing stocks of organic matter indicated that streams draining early and intermediate successional sites receive less litter from their watersheds and processed it faster. Decreases in stream obstructions combined with changes in litter inputs and processing resulted in relatively high storm transport of fine organic matter from disturbed streams. Storm organic matter export from disturbed streams averaged 4.22 g AFDW/m² and from reference streams averaged 1.83 g AFDW/m². Storm nutrient budgets, constructed by measuring nutrient inputs (soil water, throughfall) and outputs (stream discharge) during individual storms indicated that streams draining early and intermediate successional forest were less retentive of nitrogen and phosphorus than reference sites. Nitrogen loss from disturbed streams averaged 58.04 mg/m²/storm and from reference streams averaged 16.52 mg/m²/storm. Phosphorus loss from disturbed streams averaged 32.52 mg/m²/storm and from reference sites averaged 7.14 mg/m²/storm. A majority of the nitrogen and phosphorus loss was in association with organic particles. There was no difference between disturbed and reference streams in potassium, calcium, or sulfate retention during storms. However, disturbed streams tended to lose more particulate organic potassium and calcium than reference sites. These results indicate that forest disturbance has a Iong-term impact on stream ecosystems by reducing their stability for many years following forest clearing.Ph. D.
11
Danczak, Robert E. « Dynamics in Microbial Ecology Across an Environmental Stability Gradient ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1530878203337741.
Texte intégral
12
Williams, Trevor J. « Synthesizing Phylogeography and Community Ecology to Understand Patterns of Community Diversity ». BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9176.
Texte intégralRésumé :
Community ecology is the study of the patterns and processes governing species abundance, distribution, and diversity within and between communities. Likewise, phylogeography is the study of the historic processes controlling genetic diversity across space. Both fields investigate diversity, albeit at different temporal, spatial and taxonomic scales and therefore have varying assumptions. Community ecology typically focuses on contemporary mechanisms whereas phylogeography studies historic ones. However, new research has discovered that both genetic and community diversity can be influenced by contemporary and historic processes in tandem. As such, a growing number of researchers have called for greater integration of phylogeography and ecology to better understand the mechanisms structuring diversity. In this dissertation I attempt to add to this integration by investigating ways that phylogeography and population genetics can enhance studies on community ecology. First, I review traditional studies on freshwater fish community assembly using null model analyses of species co-occurrence, which shows that fish are largely structured by deterministic processes, though the importance of different mechanisms varies across climates, habitats, and spatial scales. Next, I show how phylogeographic data can greatly enhance inferences of community assembly in freshwater fish communities in Costa Rica and Utah respectively. My Costa Rican analyses indicate that historic eustatic sea-level change can be better at predicting community structure within a biogeographic province than contemporary processes. In comparison, my Utah analyses show that historic dispersal between isolated basins in conjunction with contemporary habitat filtering, dispersal limitation, and extinction dynamics both influence community assembly through time. Finally, I adapt a forward-time population genetics stochastic simulation model to work in a metacommunity context and integrate it with Approximate Bayesian Computation to infer the processes that govern observed community composition patterns. Overall, I show that community ecology can be greatly enhanced by including information and methods from different but related fields and encourage future ecologists to further this research to gain a greater understanding of biological diversity.
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Gregory, Richard D. « Host-parasite interactions : population and community ecology ». Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276582.
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Frid, C. L. J. « Community ecology of inter-tidal invertebrate faunas ». Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380953.
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Roach, Ty Noble Frederick. « Nonequilibrium Thermodynamics, Microbial Bioenergetics, and Community Ecology ». Thesis, University of California, San Diego, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10827422.
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While it is clear that thermodynamics plays a nontrivial role in biological processes, exactly how this affects the macroscopic structuring of living systems is not fully understood. Thus, the objective of this dissertation was to investigate how thermodynamic variables such as exergy, entropy, and information are involved in biological processes such as cellular metabolism, ecological succession, and evolution. To this end, I have used a combination of mathematical modelling, in silico simulation, and both laboratory- and field-based experimentation.
To begin the dissertation, I review the basic tenets of biological thermodynamics and synthesize them with modern fluctuation theory, information theory, and finite time thermodynamics. In this review, I develop hypotheses concerning how entropy production rate changes across various time scales and exergy inputs. To begin testing these hypotheses I utilized a stochastic, agent-based, mathematical model of ecological evolution, The Tangled Nature Model. This model allows one to observe the dynamics of entropy production over time scales that would not be possible in real biological systems (i.e., 106 generations). The results of the model’s simulations demonstrate that the ecological communities generated by the model’s dynamics have increasing entropies, and that this leads to emergent order, organization, and complexity over time. To continue to examine the role of thermodynamics in biological processes I investigated the bioenergetics of marine microbes associated with benthic substrates on coral reefs. By utilizing both mesocosm and in situ experiments I have shown that these microbes change their power output, oxygen uptake, and community structure depending upon their available exergy.
Overall, the data presented herein demonstrates that ecological structuring and evolutionary change are, at least in part, determined by underlying thermodynamic mechanisms. Recognizing how physical processes affect biological dynamics allows for a more holistic understanding of biology at all scales from biochemistry, to ecological succession, and even long-term evolutionary change.
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Swallow, Kelly A. « Ancient woodland vegetation : distinctiveness and community ecology ». Thesis, University of Gloucestershire, 2018. http://eprints.glos.ac.uk/5800/.
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The high floristic biodiversity value of ancient woodland is widely acknowledged, as is its status as a fragmented habitat of limited spatial extent. The distinctive vegetation of ancient woodland is an important factor in its conservation. Specifically, Ancient Woodland Indicator (AWI) species have been shown to be poor dispersers and incompatible with a fragmented habitat that is subject to environmental change. In recognition of their ecological importance, both Ancient Semi-Natural Woodland (ASNW) and Ancient Replanted Woodland (ARW) are protected by legislation. This thesis took the novel approach of examining the distinctiveness and community ecology of vegetation communities in all three woodland types of ASNW, ARW, and recent woodland. Importantly, analyses were based on new high-granularity primary vegetation and soil data. To address questions raised in the literature regarding the accuracy of ancient woodland and AWI identification, this research examined the metrics used to distinguish these habitats and species. Increasingly, the literature calls for further understanding of the ecological drivers of ancient woodland vegetation distinctiveness. In response, this research tested for differences in species composition of canopy, shrub, herb layer, AWI, and moss communities across all three woodland types. For AWI species, biotic, abiotic, and biogeographical variables were analysed for their contribution to community distinctiveness. Results highlighted the importance of consistency in metric selection when assessing the distinctiveness of ancient woodland and determining indicator species. In addition to the usual alpha scale measure of distinctiveness, assessing richness and community composition at the beta and gamma scales is recommended to inform conservation. Life traits and dispersal mechanisms were important differentiators for herb layer community composition among the woodland types. AWI richness was equally strongly explained by biogeographical variables as by ASNW, ARW, and recent status. Overall, this thesis supported ecological and biogeographical explanations for the distinctiveness of ancient woodland vegetation.
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Kuhn, Nicola. « Community ecology of small-mammal pollinated proteas ». Bachelor's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/14252.
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The floral characteristics of small-mammal pollinated (SMP) Protea species have been assessed in a number of previous studies. This study aimed to determine whether the inflorescences of Protea canaliculata, Protea sulphurea and Protea humiflora possess these traits and are pollinated by small mammal species. An additional aim of this study was to determine whether there is a variation in pollinator efficiency of different animal species. Floral characteristics that may influence plantpollinator interactions were measured, including floral dimensions, nectar production and spectral reflectance. Live-trapping was conducted using Sherman traps and mean facial and faecal pollen load was determined for the different species caught. Furthermore pollinators were observed through footage from motion sensor cameras placed facing the inflorescences of SMP proteas. The results of this study confirmed that Protea canaliculata, Protea sulphurea and Protea humiflora are pollinated by small mammal pollinators. The evidence supporting this is that the afore-mentioned species have traits that correspond to those possessed by known small-mammal pollinated proteas including: bowlshaped inflorescences, high nectar concentrations (ranging between 24.1-42.9%), sucrose-rich nectar composition, a "yeasty" scent, floral colours that are visible to small mammals, and a winter flowering season. These proteas were found to have separated peak flowering times, providing a nectar source throughout winter for small mammals at this site. Fifty-eight small mammals of seven different species, were trapped in P. canaliculata and P. sulphurea stands over 98 hours. The average nighttrapping success was 22.7% and day-trapping success was 5.7%, indicating a relatively abundant nocturnal small-mammal population. A separation in pollinator efficiency was observed for different small mammal species, with Elephantulus edwardii identified as the most effective pollinator as it showed the greatest pollen removal (highest faecal pollen load) and spent the longest time foraging on inflorescences (±28 seconds per inflorescence). Another important pollinator was Aethomys namaquensis because it visited flowers 75% more frequently than any of the other pollinators. Camera trapping was shown to be a superior method than conventional trapping for assessing pollination by providing insight into pollinator behaviour, identifying new pollinators of 'trap-shy' species and also due to its more animal-friendly disposition.
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Bergh, Maria G. « Community Ecology : Social Capital in Public Space ». University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337352062.
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KINYAGU, NEEMA. « Political Ecology : Local Community on Water Justice ». Thesis, Linnéuniversitetet, Institutionen för organisation och entreprenörskap (OE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-85884.
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Tourism is often promoted as growing industries that make an important economic contribution especially to marginalized communities in rural areas. But taking a Political Ecology approach, what sort of contribution does tourism really make? Why are its benefits spread unevenly? And have communities necessarily need to give up access and use rights to certain natural resources? This study provides an insight on understanding the different dimensions of justice on water access by local community from a tourism perspective. In understanding the issues of justice on water, environmental justice has been a central focus of this research. Justice issuesrelated to water access is still a complex phenomenal due to the truth that, it is embedded to historical and socio-cultural context and linked to integrity of ecosystem. However, justice issues can be viewed differently from different people in relation to different perspective. Therefore, Schlosberg framework of justice is adopted in this research to understand and explore water issues in three realms of justice i.e distributive, recognition and participation. Qualitative research method was employed in data collection and findings were presented based on three realms of Schlosberg's theory. However, researcher concluded that, there are mixed feelings and perceptions on understanding the sense of justice to local people in water access. Lastly, due to the fact that, the researches related to justice in tourism studies are still very limited , further research need to be done in investigating the access rights local people have on accessing their natural resources for instance water.
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Yiannakis, Eleni. « Human reproductive cloning community, identity, stability : reinventing creation ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0020/MQ55112.pdf.
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Roddy, Jackie Ann. « Retention Strategies for Financial Stability in Community Colleges ». ScholarWorks, 2016. https://scholarworks.waldenu.edu/dissertations/2687.
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Tennessee education leaders must improve their student retention strategies to increase financial stability and enhance the state's ability to support businesses and jobs through a well-educated workforce. The focus of this qualitative multiple case study was on 6 Tennessee community colleges where leaders had demonstrated successful strategies for retaining students resulting in increased revenues and financial stability. The advocacy/ participatory worldview provided a conceptual framework for identifying and comparing themes regarding Tennessee higher education leaders' retention strategies. Data collection included interviews and review of organizational retention reports on strategies as well as college, state, and federal findings on retention. Federal government websites contained information about Tennessee community colleges having the highest retention rates. Methodological triangulation provided the opportunity to identify similarities in retention strategies used by the community college leaders. Using the concept of classical data analysis, responses were categorized according to the program, activity, or initiative college administrators used to increase retention. Based on mind mapping of the clusters of information, findings revealed 3 primary themes: effects of retention on college revenues; challenges in retaining at-risk students; and strategies for retaining students, including new student orientation, counseling and advising, tutoring, and freshman seminars. The potential for social change includes the opportunity to increasing the college-educated workforce to provide more opportunities for local business leaders and find viable applicants to fill open positions and enhance the economic sustainability of local communities.
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Larocque, Allen. « Untangling mechanisms behind the stability-diversity relationship in experimental grasslands ». Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96711.
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The mechanisms underlying the positive relationship between species richness (diversity) and temporal variability in community biomass (stability) are not well understood. Here a model incorporating density dependence and environmental and demographic stochasticity is fit to experimental data from two European and two American experimental grassland sites. The parameterization of this model allows for the calculation of an approximation of community variability which explicitly separates two mechanisms: 1. asynchrony in environmental responses, and 2. overyielding. Analysis shows that this approximation accounts for much of the underlying variation and that both these mechanisms are important in stabilizing systems. Comparison of the estimated parameters highlights differences and similarities between datasets and suggests that this can be explained by species identity, experimental design and protocol, and geographical location. This thesis provides support for the view that different systems are stabilized by different mechanisms and this emphasizes the importance of examining a diversity of large, long-term ecological experiments.Les mécanismes qui soutiennent la relation positive entre la richesse en espèces (biodiversité) et la variabilité temporelle de la biomasse de la communauté (la stabilité) ne sont pas bien compris. Ici un modèle qui intègre densité dépendance, stochasticité environnementale, et stochasticité démographique est ajusté aux données expérimentales de quatre sites expérimentaux: deux européens et deux américains. Le paramétrage de ce modèle permet le calcul d'une approximation de la variabilité de la communauté qui sépare explicitement deux mécanismes: 1. asynchronie dans les réponses a l'environnement, et 2. surproduction due a la diversité des espèces. L'analyse montre que cette approche explique une grande partie de la variation de la variabilité de la communauté et que ces deux mécanismes sont importants dans la stabilisation des systèmes écologiques. La comparaison des paramètres estimés révèle les différences et les simililarités entre les jeux de données et démontre l'importance des espèces clés dans la médiation des relations entre la stabilité et la diversité. Ce travail soutient la thèse qu'une diversité de facteurs influence les fluctuations écologiques et met l'accent sur l'importance des grands expériences écologiques à grand durée.
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Pfeifer-Meister, Laurel. « Community and ecosystem dynamics in remnant and restored prairies/ ». Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2008. http://hdl.handle.net/1794/9497.
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Nishimoto, Atsushi. « Ecology of sunken wood community in the ocean ». 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188518.
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Dewsbury, Bryan. « The Ecology and Economics of Seagrass Community Structure ». FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1237.
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Coastline communities have experienced a marked increase in human populations over the last few decades. This increase in population places disproportionate pressure on coastal ecosystems to provide economic services to support local economies. At the same time, overuse of these services can aid in the destruction of the ecosystems responsible for them. Seagrass ecosystems are mainly found near coastlines, and are typically a chief provider of some of these economic goods and services. Many previous studies have documented the ecological functions of this seagrasses. Unfortunately, our increasing knowledge of seagrass structure and function has not been fully incorporated into economic models estimating their value. In this dissertation, I focus on the seagrass ecosystem in southern Biscayne Bay, and simultaneously study the ecological dynamics of the seagrass beds, and estimate its economic value. This value is based on recent ecological models in the literature as well as data I collected from the system. I focused on Biscayne Bay due to, 1) the relevance that this question had to the relationship between Biscayne Bay and the Miami metropolis, and 2) the lack of existing reliable models that explore this relationship in this area. More specifically, I became very interested in this question while working for Biscayne National Park, where such a model would have improved seagrass restoration work taking place there.
I found that southern Biscayne Bay is dominated by Thalassia testudinum, with other seagrasses following a spatial pattern primarily determined by salinity and water column nutrient distribution. Syringodium filiforme was mostly found east of the islands, Halodule wrightii was mostly found near the shoreline, and Halophila engelmenii was spotted at only two of the 190 sites visited. T. testudinum distribution was largely unaffected by nutrient enrichment at all sites, but it appeared to induce severe herbivory further from the coastline. For the calendar year 2004, we deduced using a Total Ecosystems Valuation (TEV) model that seagrass ecosystems potentially contributed over $198 million US dollars to the local economy. We argue that a simultaneous understanding and use of both ecological and economic models is important for future conservation efforts of seagrass ecosystems.
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Wilson, Jenny, et mikewood@deakin edu au. « Flowering ecology of a Box-Ironbark Eucalyptus community ». Deakin University. School of Ecology and Environment, 2002. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20050826.113429.
Texte intégralRésumé :
Box-Ironbark forests occur on the inland hills of the Great Dividing Range in Australia, from western Victoria to southern Queensland. These dry, open forests are characteristically dominated by Eucalyptus species such as Red Ironbark E. tricarpa, Mugga Ironbark E. sideroxylon and Grey Box E. microcarpa. Within these forests, several Eucalyptus species are a major source of nectar for the blossom-feeding birds and marsupials that form a distinctive component of the fauna.
In Victoria, approximately 83% of the original pre - European forests of the Box-Ironbark region have been cleared, and the remaining fragmented forests have been heavily exploited for gold and timber. This exploitation has lead to a change in the structure of these forests, from one dominated by large 80-100 cm diameter, widely -spaced trees to mostly small (≥40 cm DBH), more densely - spaced trees.
This thesis examines the flowering ecology of seven Eucalyptus species within a Box-Ironbark community. These species are characteristic of Victorian Box-Ironbark forests; River Red Gum E. camaldulensis, Yellow Gum E. leucoxylon, Red Stringybark E. macrorhyncha, Yellow Box E. melliodora, Grey Box E. microcarpa, Red Box E. polyanthemos and Red Ironbark E. tricarpa. Specifically, the topics examined in this thesis are: (1) the floral character traits of species, and the extent to which these traits can be associated with syndromes of bird or insect pollination; (2) the timing, frequency, duration, intensity, and synchrony of flowering of populations and individual trees; (3) the factors that may explain variation in flowering patterns of individual trees through examination of the relationships between flowering and tree-specific factors of individually marked trees; (4) the influence of tree size on the flowering patterns of individually marked trees, and (5) the spatial and temporal distribution of the floral resources of a dominant species, E. tricarpa. The results are discussed in relation to the evolutionary processes that may have lead to the flowering patterns, and the likely effects of these flowering patterns on blossom-feeding fauna of the Box-Ironbark region.
Flowering observations were made for approximately 100 individually marked trees for each species (a total of 754 trees). The flower cover of each tree was assessed at a mean interval of 22 (+ 0.6) days for three years; 1997, 1998 and 1999. The seven species of eucalypt each had characteristic flowering seasons, the timing of which was similar each year. In particular, the timing of peak flowering intensity was consistent between years. Other spatial and temporal aspects of flowering patterns for each species, including the percentage of trees that flowered, frequency of flowering, intensity of flowering and duration of flowering, displayed significant variation between years, between forest stands (sites) and between individual trees within sites. All seven species displayed similar trends in flowering phenology over the study, such that 1997 was a relatively 'poor' flowering year, 1998 a 'good' year and 1999 an 'average' year in this study area.
The floral character traits and flowering seasons of the seven Eucalyptus species suggest that each species has traits that can be broadly associated with particular pollinator types. Differences between species in floral traits were most apparent between 'summer' and 'winter' flowering species. Winter - flowering species displayed pollination syndromes associated with bird pollination and summer -flowering species displayed syndromes more associated with insect pollination. Winter - flowering E. tricarpa and E. leucoxylon flowers, for example, were significantly larger, and contained significantly greater volumes of nectar, than those of the summer flowering species, such as E. camaldulensis and E. melliodom.
An examination of environmental and tree-specific factors was undertaken to investigate relationships between flowering patterns of individually marked trees of E. microcarpa and E. tricarpa and a range of measures that may influence the observed patterns. A positive association with tree-size was the most consistent explanatory variable for variation between trees in the frequency and intensity of flowering. Competition from near-neighbours, tree health and the number of shrubs within the canopy area were also explanatory variables.
The relationship between tree size and flowering phenology was further examined by using the marked trees of all seven species, selected to represent five size-classes. Larger trees (≥40 cm DBH) flowered more frequently, more intensely, and for a greater duration than smaller trees. Larger trees provide more abundant floral resources than smaller trees because they have more flowers per unit area of canopy, they have larger canopies in which more flowers can be supported, and they provide a greater abundance of floral resources over the duration of the flowering season.
Heterogeneity in the distribution of floral resources was further highlighted by the study of flowering patterns of E. tricarpa at several spatial and temporal scales. A total of approximately 5,500 trees of different size classes were sampled for flower cover along transects in major forest blocks at each of five sample dates. The abundance of flowers varied between forest blocks, between transects and among tree size - classes. Nectar volumes in flowers of E. tricarpa were sampled. The volume of nectar varied significantly among flowers, between trees, and between forest stands. Mean nectar volume per flower was similar on each sample date.
The study of large numbers of individual trees for each of seven species was useful in obtaining quantitative data on flowering patterns of species' populations and individual trees. The timing of flowering for a species is likely to be a result of evolutionary selective forces tempered by environmental conditions. The seven species' populations showed a similar pattern in the frequency and intensity of flowering between years (e.g. 1998 was a 'good' year for most species) suggesting that there is some underlying environmental influence acting on these aspects of flowering.
For individual trees, the timing of flowering may be influenced by tree-specific factors that affect the ability of each tree to access soil moisture and nutrients. In turn, local weather patterns, edaphic and biotic associations are likely to influence the available soil moisture. The relationships between the timing of flowering and environmental conditions are likely to be complex.
There was no evidence that competition for pollinators has a strong selective influence on the timing of flowering. However, as there is year-round flowering in this community, particular types of pollinators may be differentiated along a temporal gradient (e.g. insects in summer, birds in winter). This type of differentiation may have resulted in the co-evolution of floral traits and pollinator types, with flowers displaying adaptations that match the morphologies and energy requirements of the most abundant pollinators in any particular season.
Spatial variation in flowering patterns was evident at several levels. This is likely to occur because of variation in climate, weather patterns, soil types, degrees of disturbance and biotic associations, which vary across the Box-Ironbark region. There was no consistency among sites between years in flowering patterns suggesting that factors affecting flowering at this level are complex.
Blossom-feeding animals are confronted with a highly spatially and temporally patchy resource. This patchiness has been increased with human exploitation of these forests leading to a much greater abundance of small trees and fewer large trees. Blossom-feeding birds are likely to respond to this variation in different ways, depending upon diet-breadth, mobility and morphological and behavioural characteristics.
Future conservation of the blossom-feeding fauna of Box-Ironbark forests would benefit from the retention of a greater number of large trees, the protection and enhancement of existing remnants, and revegetation with key species, such as E. leucoxylon, E. microcarpa and E. tricarpa. The selective clearing of summer flowering species, which occur on the more fertile areas, may have negatively affected the year-round abundance and distribution of floral resources. The unpredictability of the spatial distribution of flowering patches within the region means that all remnants are likely to be important foraging areas in some years.
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Koslow, Jennifer Marie. « Mixed mating systems, pathogens, and plant community ecology ». [Bloomington, Ind.] : Indiana University, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3232578.
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Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2006."Title from dissertation home page (viewed July 11, 2007)." Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4208. Advier: Keith Clay.
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Raine, Nigel. « The pollination ecology of a Mexican Acacia community ». Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393473.
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Bergh, Maria. « Community Ecology : Public Interventions for Communities at Risk ». University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337085243.
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Lello, Joanne. « The community ecology of rabbit (Oryctolagus cuniculus) parasites ». Thesis, University of Stirling, 2003. http://hdl.handle.net/1893/25418.
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This thesis investigates aspects of the community ecology of rabbit parasites with particular emphasis upon the gut helminths, utilising a 23 (later extended to 26) year time series of rabbits and their parasites. A clearer understanding of parasite communities can lead to more effective biological control strategies. Rabbits are regarded as a serious pest species throughout Europe and the Antipodes and the use of the myxomatosis virus, as a biological control agent, has already been tried and failed. However, a clearer picture of the parasite community may offer future possibilities for control. Additionally, the rabbit is a good model for other grazing species, as it carries a similar gut helminth community. Drug resistance is an increasing problem in a wide range of parasites. A clearer appreciation of parasite communities could also aid in the search for effective and environmentally sound pathogen control strategies (e.g. via cross immunity or competition with benign species). Theoretical models have revealed the importance of aggregation to the stability of the host parasite relationship, to parasite evolution and to interspecific parasite interactions. A number of models have considered the effect of varying aggregation upon these dynamics with differing outcomes to those where aggregation was a fixed parameter. Here the stability of the distribution for each of the rabbit helminths was examined using Taylor's power law. The analyses revealed that aggregation was not a stable parameter but varied with month, year, host sex, host age, and host myxomatosis status. Evidence for the existence of interspecific parasite interactions in natural systems has been equivocal. Factors influencing parasite intensity were evaluated for the gut helminth. A network of potential interactions between the parasites was revealed. Only month was shown to be of greater influence on the community. Following, from the above analyses, a community model was constructed which incorporated both seasonal forcing and interspecific parasite interactions, with interaction mediated via host immunity. One unexpected emergent property was an interaction between the seasonality and the immune decay rate with slower immune decay resulting in a shift of the immune response out of phase with the species against which it was produced. The model was also used to assess the potential effects of two control strategies, an anticestodal and a single species vaccine. The vaccine had greater effects on the whole community than the anticestodal because of the immune- mediated interactions. The host is also an integral part of the community as the parasite dynamics are linked with that of their host. Therefore an assessment of the parasites' impact upon host condition and fecundity was also undertaken. This revealed a variety of positive and negative associations between the parasites and their host, with potential implications for future host control strategies. This study has shown that ignoring parasite-parasite or parasite-host interactions and interactions of both the host and the parasite with the external environment, could result in a poor description of the community dynamics. Such complexities need to be considered and incorporated into theory if future control strategies for either host or parasites are to be effective.
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Victorsson, Jonas. « Community Assembly and Spatial Ecology of Saproxylic Coleoptera ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-88765.
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Enwall, Karin. « Community ecology of denitrifying bacteria in arable land / ». Uppsala : Dept. of Microbiology, Swedish University of Agricultural Sciences, 2008. http://epsilon.slu.se/200858.pdf.
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Pitman, Sheryn Dee. « Community participation in environmental rehabilitation / ». Title page, contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09ENV/09envp685.pdf.
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Wales, Shea B. « MECHANISMS UNDERLYING PRODUCTION STABILITY IN TEMPERATE DECIDUOUS FORESTS ». VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5803.
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A persistent and reliable future terrestrial carbon (C) sink will depend on how stable forest production is under more variable climate conditions. We examined how age, forest structure, and disturbance history relate to the interannual variability of above-ground wood net primary production (NPPw). Our site in northern Michigan spans two experimental forest chronosequences and three late successional stands; the chronosequences have distinct disturbance histories, originating following either clear cut harvesting (“Cut Only”) or clear cut harvesting and fire (“Cut and Burn”), and range from 21 to 108 years old. Annual NPPw was estimated using dendrochronology and site specific allometric equations. We used a portable canopy LiDAR (PCL) system to derive canopy rugosity, a measure of the variability and heterogeneity of vertical and horizontal leaf arrangement, to quantify plot level canopy complexity. Counter to our hypothesis, we found that NPPw stability was greatest in the most frequently disturbed, Cut and Burn stands and lowest in less recently disturbed, late successional forest communities. Opposing trends in chronosequence interannual variation of NPPw indicated that stand age and canopy complexity are not consistently related to production stability. Furthermore, sub-canopy leaf trait properties and breadth were not, as hypothesized, correlated with canopy complexity or NPPw stability. Our mixed findings suggest that multiple factors, including stand age and disturbance history, interact to influence NPPw stability, but also highlight an unexpected dichotomy in which disturbance legacies at our site negatively impact the long-term trajectory of annual forest NPPw, but enhance its interannual stability.
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Ward, Jessica MacKay. « Community-level effects of nonindigenous aquatic ecosystem engineers ». Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=92244.
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Levy, Ruth. « Community structure of ants in Brunei rain forest ». Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240586.
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Weatherby, Anita J. « Species coexistence and community assembly in protist microcosms ». Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322945.
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Jumeau, Philippe J. A. M. « Arthropod predation in a simple Antarctic terrestrial community ». Thesis, University of York, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277219.
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Morton, Richard Daniel. « An investigation of sequential community assembly using permanence ». Thesis, University of York, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319458.
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Milne, Judith May. « Plant community ecology of a major subtropical riverine floodplain ». Thesis, University of Glasgow, 2004. http://theses.gla.ac.uk/4057/.
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This project described the vegetation of a stretch of the Parana River and investigated which natural or human-imposed factors might be controlling its characteristics, its capacity for biodiversity support and its potential to provide an economic resource. This information is of value in the planning of management strategies aiming to conserve biodiversity and develop sustainable ways in which the floodplain resources can be utilised. Central to this study were the surveys of vegetation and environmental characteristics of aquatic, terrestrial and transitional habitats of the Parana floodplain near Porto Rico. These produced extensive data sets which helped to reveal the types of vegetation-environment relationships structuring the floodplain plant communities. To complement this investigative approach, three aspects of the functioning of floodplain vegetation were chosen for closer study. These were the impacts of livestock grazing on wetland and island vegetation, competitive interactions between pairs of free-floating aquatic plant species and the role of aquatic macrophytes in contributing carbon to aquatic food webs. Three major community types were identified in the aquatic habitats of the floodplain, one which included Eichhornia azurea in mixture with several free-floating and emergent species, a second in which E. azurea was strongly dominant and a third comprised purely of submerged species. Two strongly contrasting broad vegetation communities were identified at bank and shore environments. Polygonum and Ludwigia species were important in one group and Poaceae, creepers, woody plants and ferns in the other group. Sub-groups of these communities could also be suggested, but these are less distinct. Most of the floodplain sites supported a Poaceae-creeper community type with the remaining sites supporting a community indicated by Polygonum species. The Poaceae group was comprised of a number of sub-communities in which the importance of Poaceae relative to other species varied. The aquatic vegetation communities differed structurally with contrasting community biomass, canopy height, canopy cover, species richness and stem density. They were associated with waterbodies with different water depth and pH and different sediment nitrogen and phosphorus contents. Water flow rate category and underwent light availability also differed between the sites that tended to support the different vegetation types. The two major bank and shore vegetation communities differed in canopy cover, in the soil nitrogen, phosphorus and calcium levels with which they were associated and in the steepness of the bank on which they tended to grow. Floodplain vegetation communities contrasted in species richness and differed in the soil nitrogen and calcium levels and river systems with which they were associated.
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Cuthbertson, Leah Forbes. « The microbial community ecology of the cystic fibrosis lung ». Thesis, King's College London (University of London), 2015. https://kclpure.kcl.ac.uk/portal/en/theses/the-microbial-community-ecology-of-the-cystic-fibrosis-lung(7ae2ec94-0325-4d0c-93a3-449da53f6b1f).html.
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Respiratory failure, due to infection and concomitant inflammation is the major cause of morbidity and mortality in people suffering from the genetic disorder, cystic fibrosis (CF). Consequently, the CF Foundation currently estimates that patients with CF have a median predicted life expectancy of only 41.1 years. Understanding the relationship between the complex and diverse bacterial community present within the lower respiratory tract and patient outcomes has therefore become a top priority. Through the use of next generation sequencing technologies (Roche 454 and Illumina MiSeq) and ecological statistics and modelling, the complex relationships between the bacterial community within the CF lung and host related clinical factors were investigated. By first establishing guideline methodologies for the reduction of bias in the collection, storage and treatment of respiratory samples, this thesis aimed to use large scale spatial and longitudinal studies to investigate key relationships between the bacterial community and clinical factors. It has been well established that a complex and diverse bacterial community exists within the CF lung. Spatial sampling revealed key relationships between the bacterial community and other diagnostic parameters including, FEV1, gender, and clinic location. Longitudinal sampling aimed principally to investigate CF pulmonary exacerbations (CFPE), implicated in the progressive loss of lung function associated with CF lung disease. Over the course of a CFPE the common bacterial taxa show resistance to perturbations while the rare taxa show resilience. Through this investigation, Veillonella parvula was identified as a potential bioindicator of CFPE, introducing the potential for a rapidly testable parameter for clinicians to identify a CFPE. This finding could provide one of the most important recent developments in CF therapy.
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Yanoviak, Stephen P. « Community ecology of water-filled tree holes in Panama / ». Full-text version available from OU Domain via ProQuest Digital Dissertations, 1999.
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Nguyen, Tung Shen Wenxian Hetzer Georg. « A-stability for two species competition diffusion systems ». Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Summer/Dissertations/NGUYEN_TUNG_28.pdf.
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Proulx, Marc. « The effects of planktivorous fish on phytoplankton community structure ». Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6640.
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The response of phytoplankton to nutrient loading and planktivorous fish additions was investigated in large experimental enclosures installed in lac Croche at the Station de Biologie des Laurentides de l'Universite de Montreal. During the summer period (July and August), phytoplankton biomass significantly increased with fertilization and the presence of fish in the deep, thermally stratified, enclosures. The presence of fish increased algal biomass, particularly under the fertilized conditions. In the shallow, thermally mixed enclosures, total phytoplankton biomass was significantly affected by fertilization but not by the presence of fish. The taxonomic composition at both the species and the division levels differed in all treatments. In the deep stratified enclosures, both the addition of nutrient (p .001) and fish (p =.003) favored a large increase in Chlorophyta biomass which was composed of 1 or 2 species. Pyrrhophytes increased slightly with the presence of fish. In the shallow enclosures, nutrient additions significantly affected the division composition of total algal biomass, whereas presence of fish did not. The presence of planktivorous fish influenced phytoplankton community structure by modulating total algal biomass, the distribution of biomass according to size classes and the overall taxonomic composition. The impacts of fish were more numerous in the deep than in the shallow enclosures. Thermal stratification may thus be an important factor influencing the impact of planktivorous fish on phytoplankton. (Abstract shortened by UMI.)
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Radovski, Monica. « Testing a trait-based model of fern community assembly ». Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97187.
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The MaxEnt (maximum entropy) approach is a recently introduced analytic framework that utilizes plant traits to predict community assembly along environmental gradients. I aimed to provide a rigorous test of this approach using forest understory fern communities. I executed the MaxEnt algorithm by inputting observed community-aggregated traits (CATs), and accurately determined species abundance distributions (SADs). These results support the notion that trait-based environmental filtering at least in part drives fern community assembly, but a more general application of the MaxEnt approach depends on its ability to predict SADs using CATs independently estimated from environmental data. In an initial exploration of this predictive ability I was unable to accurately predict SADs for fern communities despite screening many measures of environmental conditions. Very recent studies, however, provide new tools that can be used to further analyze my data and may yet establish the utility of the MaxEnt approach in predicting SADs.Le modèle MaxEnt (entropie maximale) est un nouveau cadre analytique qui utilise des caractéristiques de plantes afin de prédire l'assemblage de communautés suivant un gradient environnemental. J'ai voulu tester cette approche de façon rigoureuse en utilisant des communautés de fougères de sous-bois. En exécutant l'algorithme du modèle MaxEnt avec des traits biologiques agrégés au niveau des communautés, j'ai pu déterminer la distribution et l'abondance des espèces. Ces résultats appuient la notion que l'assemblage des communautés de fougères est au moins en partie déterminé par un filtre environnemental reposant sur les traits biologiques. Toutefois, une application plus générale de l'approche MaxEnt dépend de son habileté à prédire la distribution et l'abondance des espèces en utilisant les traits agrégés estimés indépendamment des données environnementales. Dans une première évaluation des capacités prédictives du modèle, il fut impossible de prédire les distributions et abondances des espèces pour des communautés de fougères malgré l'essaie de multiples mesures de conditions environnementales. Néanmoins, plusieurs études récentes fournissent de nouveaux outils qui peuvent être utilisés dans des analyses plus poussées de mes données et pourraient établir l'utilité du modèle MaxEnt pour prédire la distribution et l'abondance des espèces.
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Lancaster, Jill. « Invertebrate predation and community structure in an acid stream ». Thesis, Queen Mary, University of London, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284801.
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Cotton, Peter Angus. « The hummingbird-plant community of a lowland Amazonian rainforest ». Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334213.
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Stewart, Gavin. « Grazing management and plant community composition on Bodmin Moor ». Thesis, University of Plymouth, 2002. http://hdl.handle.net/10026.1/2362.
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Background information, essential to a full appreciation of the research presented in the thesis, is submitted in Chapters Two, Three and Four in the form of literature reviews. Chapter Two includes a review of the geology, climate, soils, past management, vegetation history and nature conservation value of Bodmin Moor. The chapter culminates by discussing the proposed future management of grazing on Bodmin Moor. Chapter Three comprises a review of the mechanisms by which grazing affect vegetation. Particular reference is made to the effects of 7 General Introduction variation in grazing practices and interactions between grazing and other environmental variables. Chapter Four provides a review of successional processes with particular reference to the effects of grazing on upland plant community succession and the limits of current knowledge of grazing management in upland habitats. Chapter Five presents the results of phytosociological classification and explores the relationships between environmental variables and vegetation. Chapter Six examines spatial variation in the seed bank of Bodmin Moor in a range of communities at different depths. Chapter Seven presents the results of a Countryside Stewardship monitoring scheme established on Bodmin Moor North SSSI. Chapter Eight investigates the effects of variation in timing, frequency and severity of defoliation, on Molütia caerulea, along a soil moisture gradient. Chapter Nine reviews the preceeding work focusing on the overall implications of the thesis. The structure of the thesis is presented diagrammatically in Figure 1.1.
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Chisholm, Chelsea. « Cryptogam community structure and functioning along an elevational gradient ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119427.
Texte intégralRésumé :
Biodiversity studies have recently focused on incorporating measures of phylogenetic and functional diversity into examinations of community ecology. Functional diversity describes those traits that influence the interaction between a species and the environment, whereas phylogenetic diversity is a more derived measure that represents the evolutionary history of species, and might incorporate information on functional identity, taking into account multiple traits. This thesis examined patterns in cryptogam (bryophyte and lichen) diversity across an elevation gradient to (i) evaluate the interplay between species, phylogenetic, and functional lichen diversity within and between habitats and (ii) link diversity (species and phylogenetic) to bryophyte productivity across environmental gradients. We found that phylogenetic and functional turnover correlate strongly, despite low signal in measured traits. Within and between habitats, different beta diversity indices are driven by different environmental factors, and as such one metric cannot be used as a surrogate for another. By establishing a link between diversity and productivity within bryophytes, we highlight the importance of diversity in regulating biomass production within stressful environments. We also highlight the use of alternative phylogenetic measures as descriptors of the diversity-productivity relationship, as they provide more information on the underlying mechanisms that drive the relationship. Cryptogams are relatively understudied in comparison to their vascular counterparts, and as such the information from this study will provide valuable insights into their community structure and turnover across space.Les études sur la biodiversité ont récemment mis l'accent sur l'intégration des mesures de diversité phylogénétique et fonctionnelle dans les examens de l'écologie des communautés. La diversité fonctionnelle décrit les traits influençant l'interaction entre une espèce et l'environnement, alors que la diversité phylogénétique est une mesure dérivée représentant l'histoire de l'évolution d'une espèce et peut inclure des renseignements sur l'identité fonctionnelle d'une espèce. J'ai étudié les modèles de diversité des cryptogames (bryophytes et lichens) à travers un gradient d'altitude afin (i) d'examiner les interactions entre la diversité des espèces, la diversité phylogénétique et la diversité fonctionnelle des lichen au sein des habitats et entre eux, et (ii) de relier la diversité (des espèces et phylogénétique) à la productivité des bryophytes à travers les gradients environnementaux. Nous avons constaté que les changements de la composition phylogénétique et fonctionnelle sont fortement corrélés, malgré le faible signal dans les traits mesurés. Puisque les différents indices de diversité bêta sont entrainés par différents facteurs environnementaux au sein des habitats et entre eux, une unité de mesure ne peut être utilisée comme substitut à une autre. En établissant un lien entre la diversité et la productivité au sein des bryophytes, nous soulignons l'importance de la diversité dans la règlementation de la production de biomasse au sein d'environnements stressants. Nous appuyons également l'utilisation de mesures phylogénétiques alternatives comme descripteurs de la relation diversité-productivité, car celles-ci apportent plus d'information sur les mécanismes entrainant cette relation. Puisque les cryptogames sont relativement peu étudiés, cette étude fournit des indications précieuses sur la structure de leur communauté et leur changement de composition à travers l'espace.
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Colville, Sonia University of Ballarat. « Community response to shading a Phragmites australis reedbed ». University of Ballarat, 2005. http://archimedes.ballarat.edu.au:8080/vital/access/HandleResolver/1959.17/12753.
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The consequences of introducing riparian shade on in-stream community structure has not been well explored in south-eastern Australia. With catchment managers focusing on revegetation of riparian zones, there is a need to understand, monitor, and predict changes in ecological patters and processes that may take place as a system shifts from an open to a shaded stream community. Presented in this thesis is a conceptual model portraying possible responses of a macrophyte community to light reduction as a result of the introduction of riparian vegetation. This model was tested in the field by artificially shading sites (three shade treatments) to observe the direct effects of light reduction on Phragmites australis growth and structure and flow-on effects to associated in-stream biota."Doctor of Philosphy