Articoli di riviste: "Low density populations of koalas"

1

Sullivan, B. J., W. M. Norris e G. S. Baxter. "Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. II. Distribution and diet". Wildlife Research 30, n. 4 (2003): 331. http://dx.doi.org/10.1071/wr00032.

Testo completo

Abstract (sommario):

This study used faecal pellets to investigate the broadscale distribution and diet of koalas in the mulgalands biogeographic region of south-west Queensland. Koala distribution was determined by conducting faecal pellet searches within a 30-cm radius of the base of eucalypts on 149 belt transects, located using a multi-scaled stratified sampling design. Cuticular analysis of pellets collected from 22 of these sites was conducted to identify the dietary composition of koalas within the region. Our data suggest that koala distribution is concentrated in the northern and more easterly regions of the study area, and appears to be strongly linked with annual rainfall. Over 50% of our koala records were obtained from non-riverine communities, indicating that koalas in the study area are not primarily restricted to riverine communities, as has frequently been suggested. Cuticular analysis indicates that more than 90% of koala diet within the region consists of five eucalypt species. Our data highlights the importance of residual Tertiary landforms to koala conservation in the region.

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Law, B., L. Gonsalves, R. Bilney, J. Peterie, R. Pietsch, P. Roe e A. Truskinger. "Using Passive Acoustic Recording and Automated Call Identification to Survey Koalas in the Southern Forests of New South Wales". Australian Zoologist 40, n. 3 (gennaio 2020): 477–86. http://dx.doi.org/10.7882/az.2019.033.

Testo completo

Abstract (sommario):

Cost-effective surveys of low density koala populations are challenging, but technological developments in the acoustics field offer great potential for landscape-scale surveys and monitoring. We assessed passive acoustic recording coupled with automated call identification as a survey method for koalas Phascolarctos cinereus . Surveys targeted areas of previously known koala activity based on scat surveys in southern forests of New South Wales where a low density of koalas is suspected. We set 24 Song Meters to record at night over a two week period (~3,696 hours) in the koala breeding season (October/November) in Murrah Flora Reserve. Recordings were scanned by a koala call recogniser and “matches” were manually verified. Across the 24 sites, 522 validated koala bellows were recorded at 21 sites (87.5 % detection rate). Three environmental variables had most influence on detection probability of koalas, including nightly rainfall (-ve), nightly temperature (-ve) and topographic position (lower on ridges). Calling activity peaked at midnight. Sustained site occupancy, at least in the short-term, was apparent as under optimal conditions (no rain) koalas were recorded, on average, for > 50 % of survey nights rather than for just a few nights. We suggest that only a modest survey effort (4–5 nights) in the breeding season, on nights with < 3 mm of rain, is required to achieve 90–95 % probability of koala call detection in an area of low koala density. Comparison with scat surveys at the same sites revealed that detection rates were more than three times greater with acoustic surveys. Technological advances will continue to provide improvements for wildlife survey, and perhaps most importantly, for collecting much needed long-term data to assess trends in occupancy or other population attributes over time.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Menkhorst, Peter, David Ramsey, Tim O'Brien, Emily Hynes e Desley Whisson. "Survival and movements of koalas translocated from an over-abundant population". Wildlife Research 46, n. 7 (2019): 557. http://dx.doi.org/10.1071/wr19090.

Testo completo

Abstract (sommario):

Abstract Context At some sites in southern Victoria, browsing pressure caused by high-density koala populations can result in defoliation of preferred browse trees. In extreme cases, this over-browsing can lead to widespread tree death and starvation of koalas. To reduce the potential for mortality of trees and koalas, a management strategy that includes fertility control of females and translocation of healthy individuals (male and female) has been adopted. AimsTo compare the short- to medium-term survival and body condition of koalas translocated from over-browsed habitat and released into unoccupied (or nearly so) habitat with that of koalas left in situ in compromised habitat. Methods We monitored survival and body condition of 36 translocated koalas for 4–5 months after translocation relative to that of a control group (24 animals) left in situ. Koalas were recaptured and body condition measured (as a scaled body-mass index) ~40 and 137 days after translocation. Additionally, GPS loggers were used to investigate patterns of koala movement. Key resultsSurvival rates of translocated koalas were not different from those of controls and females in both groups showed slightly higher survival rates than did males. After 137 days, control animals had lower scaled body mass, whereas translocated animals, after an initial reduction, had mostly regained, or increased their scaled body mass. Translocated females regained their original scaled body mass faster than did translocated males. Male koalas in both control and translocated groups had higher rates of movement than did females, and translocated koalas had slightly higher rates of movement than did control koalas. Translocated koalas moved farther from their release location than control koalas. ConclusionsOn the basis of the scaled body-mass index, translocated koalas fared better than those left in situ in compromised habitat, even though the density of koalas in the over-browsed habitat had been reduced by a wider salvage translocation program. The process used to identify potential release sites, including a spatial koala-habitat index, accurately predicted suitable koala habitat. ImplicationsThe current management strategy of translocating koalas out of over-browsed habitat is supported and could be more widely applied.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Masters, Pip, Toni Duka, Steve Berris e Graeme Moss. "Koalas on Kangaroo Island: from introduction to pest status in less than a century". Wildlife Research 31, n. 3 (2004): 267. http://dx.doi.org/10.1071/wr03007.

Testo completo

Abstract (sommario):

In less than a century the ecological profile of koalas on Kangaroo Island has shifted from that of a species introduced for conservation purposes to one of pest status. Between 1923 and 1925, 18 koalas were released on Kangaroo Island. Their numbers increased rapidly and in 1997 a population-control program was implemented based on a population estimate of 5000 koalas. During the course of this program, it became clear that the koala population on Kangaroo Island was much greater and more widely distributed than previously thought, hence a more comprehensive population survey was carried out.In 2000–01 the koala population size was calculated using a stratified sampling approach based on five 'catchment units' and three habitat classifications that were known to support koalas. The koala population was estimated to be ~27 000 koalas in 2001. There were substantial differences in koala density in the low-, medium- and high-quality habitat within each catchment unit, and therefore large differences in the spatial distribution of koalas across Kangaroo Island. This revised population estimate has substantial ramifications for the Kangaroo Island Koala Management Program that was set in place in 1997.

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Sullivan, B. J., G. S. Baxter, A. T. Lisle, L. Pahl e W. M. Norris. "Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. IV. Abundance and conservation status". Wildlife Research 31, n. 1 (2004): 19. http://dx.doi.org/10.1071/wr02037.

Testo completo

Abstract (sommario):

Urban encroachment on dense, coastal koala populations has ensured that their management has received increasing government and public attention. The recently developed National Koala Conservation Strategy calls for maintenance of viable populations in the wild. Yet the success of this, and other, conservation initiatives is hampered by lack of reliable and generally accepted national and regional population estimates. In this paper we address this problem in a potentially large, but poorly studied, regional population in the State that is likely to have the largest wild populations. We draw on findings from previous reports in this series and apply the faecal standing-crop method (FSCM) to derive a regional estimate of more than 59 000 individuals. Validation trials in riverine communities showed that estimates of animal density obtained from the FSCM and direct observation were in close agreement. Bootstrapping and Monte Carlo simulations were used to obtain variance estimates for our population estimates in different vegetation associations across the region. The most favoured habitat was riverine vegetation, which covered only 0.9% of the region but supported 45% of the koalas. We also estimated that between 1969 and 1995 ~30% of the native vegetation associations that are considered as potential koala habitat were cleared, leading to a decline of perhaps 10% in koala numbers. Management of this large regional population has significant implications for the national conservation of the species: the continued viability of this population is critically dependent on the retention and management of riverine and residual vegetation communities, and future vegetation-management guidelines should be cognisant of the potential impacts of clearing even small areas of critical habitat. We also highlight eight management implications.

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Hynes, E. F., K. A. Handasyde, Geoff Shaw e Marilyn B. Renfree. "Levonorgestrel, not etonogestrel, provides contraception in free-ranging koalas". Reproduction, Fertility and Development 22, n. 6 (2010): 913. http://dx.doi.org/10.1071/rd09253.

Testo completo

Abstract (sommario):

Management of high-density koala (Phascolarctos cinereus) populations is essential because of the browsing damage they inflict on their habitat. We have tested two types of gestagen implant, namely levonorgestrel and etonogestrel, as contraceptives for koalas. Free-ranging female koalas were given either a control, levonorgestrel (70 mg) or etonogestrel (34 or 68 mg) implant before the breeding season. Koalas were monitored every 4–12 weeks for births. Plasma progesterone was measured and a cytological smear of the urogenital sinus was taken. Fertility was high in the control group and the two etonogestrel-treated groups, with approximately 90% of females giving birth. In contrast, no levonorgestrel-treated female produced young during the study. Removal of levonorgestrel implants from six females reversed the contraceptive effect in the next breeding season, whereas the eight females in which the levonorgestrel implants were left in remained infertile for six breeding seasons. Vaginal cytology showed evidence of oestrous cycles during the breeding season in all females from all groups and there was no difference seen in the prevalence of cornified epithelial cells in the oestrous smears. This indirectly suggests that levonorgestrel does not prevent follicular development and oestrous cycling. Plasma progesterone in levonorgestrel-treated females remained low all year, but rose in controls concurrent with the onset of the breeding season. This suggests that levonorgestrel prevents pregnancy by blocking ovulation. Etonogestrel had absolutely no contraceptive effect at the two doses delivered and so is not suitable for controlling koala populations. In contrast, levonorgestrel was effective as a long-term, reversible contraceptive in wild koalas.

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Seabrook, Leonie, Clive McAlpine, Greg Baxter, Jonathan Rhodes, Adrian Bradley e Daniel Lunney. "Drought-driven change in wildlife distribution and numbers: a case study of koalas in south west Queensland". Wildlife Research 38, n. 6 (2011): 509. http://dx.doi.org/10.1071/wr11064.

Testo completo

Abstract (sommario):

Context Global climate change will lead to increased climate variability, including more frequent drought and heatwaves, in many areas of the world. This will affect the distribution and numbers of wildlife populations. In south-west Queensland, anecdotal reports indicated that a low density but significant koala population had been impacted by drought from 2001–2009, in accord with the predicted effects of climate change. Aims The study aimed to compare koala distribution and numbers in south-west Queensland in 2009 with pre-drought estimates from 1995–1997. Methods Community surveys and faecal pellet surveys were used to assess koala distribution. Population densities were estimated using the Faecal Standing Crop Method. From these densities, koala abundance in 10 habitat units was interpolated across the study region. Bootstrapping was used to estimate standard error. Climate data and land clearing were examined as possible explanations for changes in koala distribution and numbers between the two time periods. Key results Although there was only a minor change in distribution, there was an 80% decline in koala numbers across the study region, from a mean population of 59 000 in 1995 to 11 600 in 2009. Most summers between 2002 and 2007 were hotter and drier than average. Vegetation clearance was greatest in the eastern third of the study region, with the majority of clearing being in mixed eucalypt/acacia ecosystems and vegetation on elevated residuals. Conclusions Changes in the area of occupancy and numbers of koalas allowed us to conclude that drought significantly reduced koala populations and that they contracted to critical riparian habitats. Land clearing in the eastern part of the region may reduce the ability of koalas to move between habitats. Implications The increase in hotter and drier conditions expected with climate change will adversely affect koala populations in south-west Queensland and may be similar in other wildlife species in arid and semiarid regions. The effect of climate change on trailing edge populations may interact with habitat loss and fragmentation to increase extinction risks. Monitoring wildlife population dynamics at the margins of their geographic ranges will help to manage the impacts of climate change.

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Graham, C., L. Woolford, L. Johnson e K. N. Speight. "Age-dependent changes in gross and histological morphology of the thyroid gland in South Australian koalas (Phascolarctos cinereus)". Australian Journal of Zoology 62, n. 5 (2014): 360. http://dx.doi.org/10.1071/zo14011.

Testo completo

Abstract (sommario):

Studies characterising the thyroid gland structure of koalas are limited and have not previously been undertaken in South Australian populations. Hence, this study aimed to describe the thyroid gland morphology of koalas from the Mount Lofty region, South Australia. Results showed that thyroid gland morphology was highly variable between individual koalas (n = 36), ranging from that considered typical for healthy mammals, in which small colloid-filled follicles were lined by cuboidal epithelium, to that consistent with colloidal goitre, in which macrofollicles distended with colloid were lined by flattened epithelium. Juvenile koalas more frequently showed typical thyroid gland morphology than adults, with significantly higher thyroid follicle density (P < 0.05) and a higher proportion of follicles lined by cuboidal epithelium compared with flattened epithelium (P < 0.05). Thyroid glands of most adult koalas were characterised by colloidal macrofollicles (P < 0.01), and classified as colloidal goitre. There were no significant differences in thyroid gland morphology based on health status or sex of koalas. These findings suggest that an age-dependent colloidal goitre occurs in adult koalas, which is unlikely to have ill effects and may be associated with the low metabolic rate of this species, or exposure to a dietary goitrogen.

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Martin, R. W. "Overbrowsing, and decline of a population of the koala, Phascolarctos cinereus, in Victoria. III. Population dynamics". Wildlife Research 12, n. 3 (1985): 377. http://dx.doi.org/10.1071/wr9850377.

Testo completo

Abstract (sommario):

The demography of a population of koalas at Walkerville, Victoria, which was severely defoliating its preferred food trees was monitored for 3 yr from Aug. 1977. Population density declined from 3.0 animals/ha in winter 1978 to 0.7/ha in winter 1980. Population density also fluctuated seasonally, with a max. in autumn/winter and a min. in spring. Fertility rate was low compared with that of other populations and declined over the period of the study. This was due to depressed fertility among the younger females and substantial infertility among the older females. Mortality was heaviest in the winter, and the majority of carcasses found were of old females. A sharp decline in population density, caused by the dispersal of many of the residents, occurred in winter 1980 when the defoliation of the preferred food species, Eucalyptus ovata, was most advanced.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Lunney, Daniel, Mathew S. Crowther, Ian Shannon e Jessica V. Bryant. "Combining a map-based public survey with an estimation of site occupancy to determine the recent and changing distribution of the koala in New South Wales". Wildlife Research 36, n. 3 (2009): 262. http://dx.doi.org/10.1071/wr08079.

Testo completo

Abstract (sommario):

The present study demonstrates one solution to a problem faced by managers of species of conservation concern – how to develop broad-scale maps of populations, within known general distribution limits, for the purpose of targeted management action. We aimed to map the current populations of the koala, Phascolarctos cinereus, in New South Wales, Australia. This cryptic animal is widespread, although patchily distributed. It principally occurs on private property, and it can be hard to detect. We combined a map-based mail survey of rural and outer-urban New South Wales with recent developments in estimating site occupancy and species-detection parameters to determine the current (2006) distribution of the koala throughout New South Wales. We were able to define the distribution of koalas in New South Wales at a level commensurate with previous community and field surveys. Comparison with a 1986 survey provided an indication of changes in relative koala density across the state. The 2006 distribution map allows for local and state plans, including the 2008 New South Wales Koala Recovery Plan, to be more effectively implemented. The application of this combined technique can now be extended to a suite of other iconic species or species that are easily recognised by the public.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Sullivan, B. J., G. S. Baxter e A. T. Lisle. "Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. III. Broad-scale patterns of habitat use". Wildlife Research 30, n. 6 (2003): 583. http://dx.doi.org/10.1071/wr02036.

Testo completo

Abstract (sommario):

To date there have been few quantitative studies of the distribution of, and relative habitat utilisation by, koalas in the mulgalands of Queensland. To examine these parameters we applied habitat-accessibility and relative habitat-utilisation indices to estimates of faecal pellet density sampled at 149 sites across the region. Modelling the presence of pellets using logistic regression showed that the potential range of accessible habitats and relative habitat use varied greatly across the region, with rainfall being probably the most important determinant of distribution. Within that distribution, landform and rainfall were both important factors affecting habitat preference. Modelling revealed vastly different probabilities of finding a pellet under trees depending on the tree species, canopy size, and location within the region.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Lollback, Gregory W., J. Guy Castley, Alexa C. Mossaz e Jean-Marc Hero. "Fine-scale changes in spatial habitat use by a low-density koala population in an isolated periurban forest remnant". Australian Mammalogy 40, n. 1 (2018): 84. http://dx.doi.org/10.1071/am16036.

Testo completo

Abstract (sommario):

Koala (Phascolarctos cinereus) populations in south-east Queensland are in decline. Although various studies have looked at broad-scale tree preference and habitat quality, there has been little attempt to quantify fine-scale activity shifts from one year to the next or examination of activity at the mesoscale. This study quantified koala activity levels in a 909-ha forest patch at Karawatha Forest Park, in south Brisbane. The Spot Assessment Technique was used to quantify activity and tree selection on 33 long-term monitoring plots in 2009 and 2010. In total, 843 trees were searched and koala pellets were found underneath 34 and 47 trees in 2009 and 2010, respectively. A higher proportion of pellets was found underneath Eucalyptus tindaliae and E. fibrosa and there was weak selection for larger trees. A low occurrence of revisits and a minor shift in activity distribution from 2009 to 2010 indicate that the koala population exists at a low density. Rapid declines in koala populations are occurring in primary habitats. Hence, stable low-density koala populations are important for maintaining genetic diversity and connectivity in fragmented urban landscapes.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Mitchell, PJ, R. Bilney e RW Martin. "Population-Structure and Reproductive Status of Koalas on Raymond Island, Victoria". Wildlife Research 15, n. 5 (1988): 511. http://dx.doi.org/10.1071/wr9880511.

Testo completo

Abstract (sommario):

In December 1980, 87 adult (>1-year-old) koalas (36 males, 51 females) were captured and marked on Raymond Island, in the Gippsland Lakes of Victoria. A further 85 adults and 34 juveniles (6-12 months old) were sighted but not captured. In August 1985, 25 females and 24 males were captured and examined. The proportions of animals in the older age classes (age classes 4 and above) were 61% in 1980 and 39% in 1985, while the reproduction rates were 38 and 40%, respectively. The low reproduction rates, and the high proportions of older animals in 1980, were attributed to reproductive tract disease, although the presence of this disease did not prevent the population from increasing to a density at which trees were being overbrowsed.

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Sullivan, B. J., G. S. Baxter e A. T. Lisle. "Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. I. Faecal pellet sampling protocol". Wildlife Research 29, n. 5 (2002): 455. http://dx.doi.org/10.1071/wr00110.

Testo completo

Abstract (sommario):

Koala (Phascolarctos cinereus) populations in eastern Australia are threatened by land clearing for agricultural and urban development. At the same time, conservation efforts are hindered by a dearth of information about inland populations. Faecal deposits offer a source of information that is readily available and easily collected non-invasively. We detail a faecal pellet sampling protocol that was developed for use in a large rangeland biogeographic region. The method samples trees in belt transects, uses a thorough search at the tree base to quickly identify trees with koala pellets under them, then estimates the abundance of faecal pellets under those trees using 1-m2 quadrats. There was a strong linear relationship between these estimates and a complete enumeration of pellet abundance under the same trees. We evaluated the accuracy of our method in detecting trees where pellets were present by means of a misclassification index that was weighed more heavily for missed trees that had high numbers of pellets under them. This showed acceptable accuracy in all landforms except riverine, where some trees with large numbers of pellets were missed. Here, accuracy in detecting pellet presence was improved by sampling with quadrats, rather than basal searches. Finally, we developed a method to reliably age pellets and demonstrate how this protocol could be used with the faecal-standing-crop method to derive a regional estimate of absolute koala abundance.

Gli stili APA, Harvard, Vancouver, ISO e altri

15

TAYLOR, ANDREA C., JENNY MARSHALL GRAVES, NEIL D. MURRAY, STEPHEN J. O'BRIEN, N. YUHKI e BILL SHERWIN. "Conservation genetics of the koala (Phascolarctos cinereus): low mitochondrial DNA variation amongst southern Australian populations". Genetical Research 69, n. 1 (febbraio 1997): 25–33. http://dx.doi.org/10.1017/s0016672397002607.

Testo completo

Abstract (sommario):

Koala (Phascolarctos cinereus) populations in southern Australia have a history of bottlenecks – earlier this century the species became extinct in South Australia, and almost so in Victoria. Subsequently large numbers of animals from island populations (founded from very few animals) have been translocated back to mainland sites and to other islands in the region. As part of a larger study of the genetic structure of koala populations in southern Australia, we have undertaken a survey of mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) variability. Genomic DNA from 91 koalas from five populations was examined using 23 restriction enzymes, and mtDNA fragments were detected using a domestic cat full-length mtDNA clone. Only one of the enzymes, TaqI, revealed polymorphism – a relatively low amount of variation compared with other mammals, although low mtDNA-RFLP variation has also been reported in Queensland koalas. French Island and populations established predominantly from French Island immigrant koalas, either directly or via other island populations, were indistinguishable by haplotype frequencies. The mtDNA data are thus consistent with the interpretation that the koala translocation programme has homogenized gene frequencies amongst those populations involved. South Gippsland is not recorded as having received translocated koalas directly, and has significantly different mtDNA-RFLP haplotype frequencies from all other populations examined. The fact that this distinction was not previously observed in nuclear gene frequencies may reflect predominantly male-mediated dispersal in koalas.

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Stalenberg, Eleanor, Ian R. Wallis, Ross B. Cunningham, Chris Allen e William J. Foley. "Nutritional Correlates of Koala Persistence in a Low-Density Population". PLoS ONE 9, n. 12 (3 dicembre 2014): e113930. http://dx.doi.org/10.1371/journal.pone.0113930.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Wilmer, JMW, A. Melzer, F. Carrick e C. Moritz. "Low genetic diversity and inbreeding depression in Queensland Koalas". Wildlife Research 20, n. 2 (1993): 177. http://dx.doi.org/10.1071/wr9930177.

Testo completo

Abstract (sommario):

The amount of genetic variation in two natural populations of Queensland koalas (Phascolarctos cinereus adustus) was assessed by analysis of mitochondrial DNA. Levels and any adverse effects of inbreeding (inbreeding depression) were estimated from the pedigree of a well-characterised captive colony. Genetic diversity of mitochondrial DNA was found to be exceedingly low both within and between the two populations, but the variation detected was found to be strongly structured geographically. Inbreeding levels in the captive colony were moderate to high yet the only apparent evidence of inbreeding depression was a male-biased sex ratio. There was no evidence for decreased juvenile survivorship or growth rate with inbreeding. Because of the limited data it would be premature to conclude that koalas are relatively resistant to the effects of inbreeding. However, we suggest the hypothesis that koalas have a history of small population size, resulting in reduced susceptibility to inbreeding depression.

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Seddon, Jennifer M., Kristen E. Lee, Stephen D. Johnston, Vere N. Nicolson, Michael Pyne, Frank N. Carrick e William A. H. Ellis. "Testing the regional genetic representativeness of captive koala populations in South-East Queensland". Wildlife Research 41, n. 4 (2014): 277. http://dx.doi.org/10.1071/wr13103.

Testo completo

Abstract (sommario):

Context Captive breeding for release back to the wild is an important component of ex situ conservation but requires genetic diversity that is representative of the wild population and has the ultimate goal of producing ecologically sustainable and resilient populations. However, defining and testing for representativeness of captive populations is difficult. Koalas (Phascolarctos cinereus) are bred for educational and tourism purposes in zoos and wildlife parks in South-East Queensland, but there are drastic declines evident in some wild koala populations in this region. Aim We compared genetic diversity at microsatellite loci and mitochondrial DNA in two captive koala populations with that of the local, wild koalas of South-East Queensland, determining the degree to which genetic diversity of neutral loci had been preserved and was represented in the captive populations. Key results The expected heterozygosity and the allelic richness was significantly greater in one captive colony than one wild South-East Queensland population. There was low but significant differentiation of the captive from wild populations using FST, with greater differentiation described by Jost’s Dest. In contrast, a newly introduced Kullback–Leibler divergence measure, which assesses similarity of allele frequencies, showed no significant divergence of colony and wild populations. The captive koalas lacked many of the mitochondrial haplotypes identified from South-East Queensland koalas and possessed seven other haplotypes. Conclusions Captive colonies of koalas have maintained levels of overall neutral genetic diversity similar to wild populations at microsatellite loci and low but significant differentiation likely resulted from drift and founder effects in small captive colonies or declining wild populations. Mitochondrial DNA suggests that captive founders were from a wider geographic source or that haplotypes have been lost locally. Implications Overall, tested captive koalas maintain sufficient microsatellite diversity to act as an in situ reservoir for neutral genetic diversity of regional populations.

Gli stili APA, Harvard, Vancouver, ISO e altri

19

de Oliveira, S. M., P. J. Murray, D. L. de Villiers e G. S. Baxter. "Ecology and movement of urban koalas adjacent to linear infrastructure in coastal south-east Queensland". Australian Mammalogy 36, n. 1 (2014): 45. http://dx.doi.org/10.1071/am12046.

Testo completo

Abstract (sommario):

In Redland City, koalas (Phascolarctos cinereus) are in rapid decline as they are exposed to anthropogenic threats such as habitat clearing, dog attacks, vehicle collisions and disease. This study investigated the influence of linear infrastructure on the movement and habitat use of urban koalas. Seven koalas were tracked for up to 28 weeks during the breeding season. Home ranges were calculated for 95% Minimum Convex Polygon (MCP95%) and 95% fixed Kernel Density (FK95%). Koalas responded to the landscape in different ways. Linear infrastructure did not restrict the movements of most koalas. Home ranges varied from 1.1 to 31.5 ha MCP95% and from 5 to 55 ha for FK95%. Koalas mainly used Eucalyptus tereticornis throughout the study site. A variety of non-regionally endemic and regionally endemic trees in urban and remnant vegetation areas were used, suggesting that all trees are potentially koala habitat. At the completion of the study, four koalas remained alive, two were killed by trains and one died from a dog attack. Despite the small sample size and short duration, our results suggest that koalas are able to navigate linear infrastructure; however, the high rates of mortality associated with these movements puts the long-term viability of urban koala populations in doubt.

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Cristescu, Romane, Valma Cahill, William B. Sherwin, Kathrine Handasyde, Kris Carlyon, Desley Whisson, Catherine A. Herbert, Britt Louise J. Carlsson, Alan N. Wilton e Des W. Cooper. "Inbreeding and testicular abnormalities in a bottlenecked population of koalas (Phascolarctos cinereus)". Wildlife Research 36, n. 4 (2009): 299. http://dx.doi.org/10.1071/wr08010.

Testo completo

Abstract (sommario):

Habitat destruction and fragmentation, interactions with introduced species or the relocation of animals to form new populations for conservation purposes may result in a multiplication of population bottlenecks. Examples are the translocations of koalas to French Island and its derivative Kangaroo Island population, with both populations established as insurance policies against koala extinction. In terms of population size, these conservation programs were success stories. However, the genetic story could be different. We conducted a genetic investigation of French and Kangaroo Island koalas by using 15 microsatellite markers, 11 of which are described here for the first time. The results confirm very low genetic diversity. French Island koalas have 3.8 alleles per locus and Kangaroo Island koalas 2.4. The present study found a 19% incidence of testicular abnormality in Kangaroo Island animals. Internal relatedness, an individual inbreeding coefficient, was not significantly different in koalas with testicular abnormalities from that in other males, suggesting the condition is not related to recent inbreeding. It could instead result from an unfortunate selection of founder individuals carrying alleles for testicular abnormalities, followed by a subsequent increase in these alleles’ frequencies through genetic drift and small population-related inefficiency of selection. Given the low diversity and possible high prevalence of deleterious alleles, the genetic viability of the population remains uncertain, despite its exponential growth so far. This stands as a warning to other introductions for conservation reasons.

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Cristescu, Romane, Valma Cahill, William B. Sherwin, Kathrine Handasyde, Kris Carlyon, Desley Whisson, Catherine A. Herbert, Britt Louise J. Carlsson, Alan N. Wilton e Des W. Cooper. "Corrigendum to: Inbreeding and testicular abnormalities in a bottlenecked population of koalas (Phascolarctos cinereus)". Wildlife Research 39, n. 4 (2012): 374. http://dx.doi.org/10.1071/wr08010_co.

Testo completo

Abstract (sommario):

Habitat destruction and fragmentation, interactions with introduced species or the relocation of animals to form new populations for conservation purposes may result in a multiplication of population bottlenecks. Examples are the translocations of koalas to French Island and its derivative Kangaroo Island population, with both populations established as insurance policies against koala extinction. In terms of population size, these conservation programs were success stories. However, the genetic story could be different. We conducted a genetic investigation of French and Kangaroo Island koalas by using 15 microsatellite markers, 11 of which are described here for the first time. The results confirm very low genetic diversity. French Island koalas have 3.8 alleles per locus and Kangaroo Island koalas 2.4. The present study found a 19% incidence of testicular abnormality in Kangaroo Island animals. Internal relatedness, an individual inbreeding coefficient, was not significantly different in koalas with testicular abnormalities from that in other males, suggesting the condition is not related to recent inbreeding. It could instead result from an unfortunate selection of founder individuals carrying alleles for testicular abnormalities, followed by a subsequent increase in these alleles' frequencies through genetic drift and small population-related inefficiency of selection. Given the low diversity and possible high prevalence of deleterious alleles, the genetic viability of the population remains uncertain, despite its exponential growth so far. This stands as a warning to other introductions for conservation reasons.

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Lunney, Daniel, Carol Esson, Chris Moon, Murray Ellis e Alison Matthews. "A Community-based Survey of the Koala, Phascolarctos cinereus, in the Eden Region of South-eastern New South Wales". Wildlife Research 24, n. 1 (1997): 111. http://dx.doi.org/10.1071/wr94034.

Testo completo

Abstract (sommario):

A community-based postal survey (questionnaire and map) was undertaken in the Eden region of south-eastern New South Wales in 1991–92 to help determine the local distribution of koalas and to obtain information on which to base a regional plan of management for koalas. The 1198 replies from the II 600 households in the region represented all parts of the area surveyed. The survey responses suggest that koalas are rare in the Eden region, and that the number of koalas has been constantly low for the last four decades. The records are scattered both chronologically and geographically. National Parks and Nature Reserves have never been the stronghold of local koala populations, and freehold land, particularly farmland, is not a major reservoir of koalas. Most koalas reported were in, or adjacent to, State Forests, particularly Murrah–Berrnagui and Tantawangalo–Glenbog–Yurammie. These areas appear to contain the core of the surviving koala population of the region. An assessment of the vegetation where koalas were sighted indicated that dry forest is the preferred habitat. The once abundant and widespread local koala population of late last century has been reduced by habitat loss and fragmentation to a few small, isolated populations. This regional survey, which was undertaken by use of a carefully constructed questionnaire, revealed an invaluable source of records and contributed 70% of the records in the database used for this study. This study also laid a basis for assessing koala management options in south-eastern New South Wales.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Curtin, A., D. Lunney e A. Matthews. "A survey of a low-density koala population in a major reserve system, near Sydney, New South Wales.." Australian Mammalogy 23, n. 2 (2001): 135. http://dx.doi.org/10.1071/am01135.

Testo completo

Abstract (sommario):

cinereus) in Yengo National Park and Parr State Recreation Area, which together form a major reserve system where P. cinereus were known to be scarce. The first, a community survey which was distributed to 823 residences adjoining the reserves, yielded 139 responses. Of these, 31 responses provided information that allowed 26 P. cinereus locality records to be verified. A further eight P. cinereus locality records were obtained from interviews with neighbours. Most records were road-based. The second, a field survey based on scat searches, produced an additional 13 P. cinereus localities. P. cinereus scats were found under 11 tree species. Eucalyptus punctata was most frequently recorded with scats of those that were adequately sampled. A range of vegetation types and both ridges and gullies were used by P. cinereus. During field surveys, P. cinereus was found to be sparse and occurring throughout much of the survey area, concentrated in the eastern, southern and central parts of the reserve system. Both methods identified P. cinereus to be present before and after the extensive fires of January 1994, which burnt 60 % of the area. An appraisal of the methods revealed that they are complementary. The survey of residents provided recent and historical information and an indication of initial search areas for P. cinereus. The field survey yielded specific information about local P. cinereus habitat. The combination increased the number of P. cinereus records for the area more than four-fold. This study has provided the reserve managers with a clearer picture of the location of the local P. cinereus population.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Fitzpatrick, Matthew C., Evan L. Preisser, Aaron M. Ellison e Joseph S. Elkinton. "Observer bias and the detection of low-density populations". Ecological Applications 19, n. 7 (ottobre 2009): 1673–79. http://dx.doi.org/10.1890/09-0265.1.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Heinke, C. O., M. G. Ivanov, E. W. Koch, R. Andrews, L. Chomiuk, H. N. Cohn, S. Crothers et al. "The X-ray emissivity of low-density stellar populations". Monthly Notices of the Royal Astronomical Society 492, n. 4 (24 gennaio 2020): 5684–708. http://dx.doi.org/10.1093/mnras/staa194.

Testo completo

Abstract (sommario):

ABSTRACT The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally active binaries) varies between different environments. We compile calculations (largely from the literature) of the X-ray emissivity of old stellar populations, including open and globular clusters and several galaxies. We investigate three literature claims of unusual X-ray sources in low-density stellar populations. We show that a suggested quiescent neutron star in the open cluster NGC 6819 is a foreground M dwarf. We show that the suggested diffuse X-ray emission from an old nova shell in the globular cluster NGC 6366 is actually a background galaxy cluster. And we show that a suggested population of quiescent X-ray binaries in the Sculptor Dwarf Galaxy is mostly (perhaps entirely) background galaxies. We find that above densities of 104 M⊙ pc−3, the X-ray emissivity of globular clusters increases, due to dynamical production of X-ray emitting systems. Below this density, globular clusters have lower X-ray emissivity than the other populations, and we do not see a strong dependence of X-ray emissivity due to density effects. We find significant correlations between X-ray emissivity and binary fraction, metallicity, and density. Sampling these fits via bootstrap techniques gives less significant correlations, but confirms the effect of metallicity on low-density populations, and that of density on the full globular cluster sample.

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Liu, Zhenguo. "Oxidized low-density lipoprotein alters endothelial progenitor cell populations". Frontiers in Bioscience 20, n. 6 (2015): 975–88. http://dx.doi.org/10.2741/4351.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Crawley, Michael J. "Reduction of oak fecundity by low-density herbivore populations". Nature 314, n. 6007 (marzo 1985): 163–64. http://dx.doi.org/10.1038/314163a0.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Jiang, Alex, Andrew Tribe, Clive J. C. Phillips e Peter J. Murray. "Do Livestock Injure and Kill Koalas? Insights from Wildlife Hospital and Rescue Group Admissions and an Online Survey of Livestock–Koala Conflicts". Animals 11, n. 9 (13 settembre 2021): 2684. http://dx.doi.org/10.3390/ani11092684.

Testo completo

Abstract (sommario):

Koala populations in Australia are declining due to threats such as chlamydiosis, wild dog predation and vehicle collision. In the last decade, grazing livestock emerged anecdotally as a threat to koala survival in areas where koala habitat and livestock grazing land overlap. This is the first study investigating the significance of livestock-inflicted injuries and deaths in koala populations over a large spatial and temporal scale. We investigated the outcome, scale, and frequency of livestock–koala incidents via an online survey and analysed koala admission records in Queensland wildlife hospitals and a wildlife rescue group (Wildlife Victoria) in Victoria. The results provide evidence of both livestock-inflicted injuries and deaths to koalas, especially as these have been confirmed by witness statements. The outcomes for the koala victims of the incidents were severe with a 75% mortality rate. The reported frequency of livestock–koala incidents was low but increasing, with 72 cases (0.14% out of 50,873 admissions) in Queensland wildlife hospitals during 1997–2019, and 59 cases (0.8% of 7017 rescue records) in Wildlife Victoria during 2007–2019. These incidents were likely to be under-reported due to the remoteness of the incident location, possible mis-diagnoses by veterinarians and the possible reluctance of farmers to report them. Future research is encouraged to explore the mechanics and causes of livestock–koala incidents and to develop management strategies to minimise the livestock threat to koalas.

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Dreitz, Victoria J., Paul M. Lukacs e Fritz L. Knopf. "MONITORING LOW DENSITY AVIAN POPULATIONS: AN EXAMPLE USING MOUNTAIN PLOVERS". Condor 108, n. 3 (2006): 700. http://dx.doi.org/10.1650/0010-5422(2006)108[700:mldapa]2.0.co;2.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Willi, Y., P. Griffin e J. Van Buskirk. "Drift load in populations of small size and low density". Heredity 110, n. 3 (5 dicembre 2012): 296–302. http://dx.doi.org/10.1038/hdy.2012.86.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Dreitz, Victoria J., Paul M. Lukacs e Fritz L. Knopf. "Monitoring Low Density Avian Populations: An Example Using Mountain Plovers". Condor 108, n. 3 (1 agosto 2006): 700–706. http://dx.doi.org/10.1093/condor/108.3.700.

Testo completo

Abstract (sommario):

Abstract Declines in avian populations highlight a need for rigorous, broad-scale monitoring programs to document trends in avian populations that occur in low densities across expansive landscapes. Accounting for the spatial variation and variation in detection probability inherent to monitoring programs is thought to be effort-intensive and time-consuming. We determined the feasibility of the analytical method developed by Royle and Nichols (2003), which uses presence-absence (detection-nondetection) field data, to estimate abundance of Mountain Plovers (Charadrius montanus) per sampling unit in agricultural fields, grassland, and prairie dog habitat in eastern Colorado. Field methods were easy to implement and results suggest that the analytical method provides valuable insight into population patterning among habitats. Mountain Plover abundance was highest in prairie dog habitat, slightly lower in agricultural fields, and substantially lower in grassland. These results provided valuable insight to focus future research into Mountain Plover ecology and conservation.

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Kvasnes, Mikkel Andreas Jørnsøn, Hans Christian Pedersen, Torstein Storaas e Erlend Birkeland Nilsen. "Vegetation type and demography of low density willow ptarmigan populations". Journal of Wildlife Management 81, n. 1 (5 ottobre 2016): 174–81. http://dx.doi.org/10.1002/jwmg.21180.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Murray, Dennis L., James D. Roth, Ethan Ellsworth, Aaron J. Wirsing e Todd D. Steury. "Estimating low-density snowshoe hare populations using fecal pellet counts". Canadian Journal of Zoology 80, n. 4 (1 aprile 2002): 771–81. http://dx.doi.org/10.1139/z02-027.

Testo completo

Abstract (sommario):

Snowshoe hare (Lepus americanus) populations found at high densities can be estimated using fecal pellet densities on rectangular plots, but this method has yet to be evaluated for low-density populations. We further tested the use of fecal pellet plots for estimating hare populations by correlating pellet densities with estimated hare numbers on 12 intensive study areas in Idaho; pellet counts from extensive transects (n = 615) across northern Idaho enabled rectangular plots (0.155 m2) to be compared with paired small (0.155 m2) and large (1 m2) circular plots (metre-circle plots). Metre-circle plots had higher pellet prevalence, lower sample variance, and lower estimates of pellet density than the other plot types. Transects comprising circular plots required less establishment time, and observer training reduced the pellet-count bias attributable to plot shape. The number of hares occupying intensive study sites was correlated with pellet density on all plot types, but rectangular plots provided a slightly closer linear fit to hare numbers than did metre-circle plots. The relationship between pellet density and hare number may have been curvilinear rather than linear, but linear and nonlinear models provided similar numerical estimates over much of the range of pellet densities. These results indicate that pellet counts are a robust estimator of hare numbers in low-density populations, and that metre-circle plots represent an improvement over standard rectangular plots in terms of unbiased pellet counts, sacrificing little predictive power. We recommend using pellet counts in metre-circle plots for estimating populations of snowshoe hares in their southern distribution.

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Dennison, S., G. J. Frankham, L. E. Neaves, C. Flanagan, S. FitzGibbon, M. D. B. Eldridge e R. N. Johnson. "Population genetics of the koala (Phascolarctos cinereus) in north-eastern New South Wales and south-eastern Queensland". Australian Journal of Zoology 64, n. 6 (2016): 402. http://dx.doi.org/10.1071/zo16081.

Testo completo

Abstract (sommario):

Habitat loss and fragmentation are key threats to local koala (Phascolarctos cinereus) populations. Broad-scale management is suboptimal for koalas because distribution models are not easily generalised across regions. Therefore, it is imperative that data relevant to local management bodies are available. Genetic data provides important information on gene flow and potential habitat barriers, including anthropogenic disturbances. Little genetic data are available for nationally significant koala populations in north-eastern New South Wales, despite reported declines due to urbanisation and habitat loss. In this study, we develop 14 novel microsatellite loci to investigate koala populations in north-eastern New South Wales (Port Macquarie, Coffs Harbour, Tyagarah, Ballina) and south-eastern Queensland (Coomera). All locations were significantly differentiated (FST = 0.096–0.213; FʹST = 0.282–0.582), and this pattern was not consistent with isolation by distance (R2 = 0.228, P = 0.058). Population assignment clustered the more northern populations (Ballina, Tyagarah and Coomera), suggesting contemporary gene flow among these sites. For all locations, low molecular variation among (16%) rather than within (84%) sites suggests historical connectivity. These results suggest that koala populations in north-eastern New South Wales and south-eastern Queensland are experiencing contemporary impediments to gene flow, and highlight the importance of maintaining habitat connectivity across this region.

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Martin, R. W. "Overbrowsing, and decline of a population of the koala, Phascolarctos cinereus, in Victoria. II. Population condition". Wildlife Research 12, n. 3 (1985): 367. http://dx.doi.org/10.1071/wr9850367.

Testo completo

Abstract (sommario):

Juvenile and sub-adult koalas from a population at Walkerville, Victoria, which was severely defoliating its preferred food trees, had significantly lower growth rates than animals from a population on French Island, Victoria. Mature males from Walkerville were significantly smaller than French Island males in most age classes. There was no significant difference between the body weights of mature females of the 2 populations. Haematological tests on the females showed that nutritionally induced anaemia was significant in the Walkerville animals by Jan. 1981. Heavy tick loads probably exacerbated the effects of the food shortage on the animals' condition, but were not the cause of the anaemia. The low fertility rate of the Walkerville females appeared to be due to their poor nutritional state and to reproductive tract disease.

Gli stili APA, Harvard, Vancouver, ISO e altri

36

CORRÊA, F. F., R. H. MADAIL, S. BARBOSA, M. P. PEREIRA, E. M. CASTRO, C. T. G. SORIANO e F. J. PEREIRA. "Anatomy and physiology of Cattail as related to different population densities". Planta Daninha 33, n. 1 (marzo 2015): 01–12. http://dx.doi.org/10.1590/s0100-83582015000100001.

Testo completo

Abstract (sommario):

The objective of this work was to evaluate the effects of the population density of Typha angustifolia plants in the anatomical and physiological characteristics. Plants were collected from populations of high density (over 50% of colonization capacity) and low density (less than 50% of colonization capacity) and cultivated under controlled greenhouse conditions. Plants from both populations were grown in plastic trays containing 4 L of nutritive solution for 60 days. At the end of this period, the relative growth rate, leaf area ratio, net assimilatory rate, root/shoot ratio, leaf anatomy, root anatomy, and catalase and ascorbate peroxidase activities were evaluated. Plants from high density populations showed increased growth rate and root/shoot ratio. Low density populations showed higher values of stomatal index and density in leaves, as well as increased palisade parenchyma thickness. Root epidermis and exodermis thickness as well as the aerenchyma proportion of high density populations were reduced, these plants also showed increased vascular cylinder proportion. Only catalase activity was modified between the high and low density populations, showing increased values in low density populations. Therefore, different Typha angustifolia plants show differences in its anatomy and physiology related to its origins on high and low density conditions. High density population plants shows increased growth capacity related to lower apoplastic barriers in root and this may be related to increased nutrient uptake capacity.

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Järemo, P., M. Milovanovic, C. Buller, S. Nilsson e B. Winblad. "Low-density platelet populations demonstrate lowin vivoactivity in sporadic Alzheimer disease". Platelets 23, n. 2 (13 dicembre 2011): 116–20. http://dx.doi.org/10.3109/09537104.2011.593654.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Hart, Leslie C., Maurice C. Goodman, Ryan K. Walter, Laura Rogers-Bennett, Peter Shum, April D. Garrett, James M. Watanabe e Jennifer K. O'Leary. "Abalone Recruitment in Low-Density and Aggregated Populations Facing Climatic Stress". Journal of Shellfish Research 39, n. 2 (26 agosto 2020): 359. http://dx.doi.org/10.2983/035.039.0218.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Stacy, E. A., J. L. Hamrick, J. D. Nason, S. P. Hubbell, R. B. Foster e R. Condit. "Pollen Dispersal in Low-Density Populations of Three Neotropical Tree Species". American Naturalist 148, n. 2 (agosto 1996): 275–98. http://dx.doi.org/10.1086/285925.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Rodríguez-Barreras, Ruber. "Demographic implications of predatory wrasses on low-density Diadema antillarum populations". Marine Biology Research 14, n. 4 (26 febbraio 2018): 383–91. http://dx.doi.org/10.1080/17451000.2018.1426861.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Collobert, Maela, Marc Sarzi, Roger L. Davies, Harald Kuntschner e Matthew Colless. "Central stellar populations of early-type galaxies in low-density environments". Monthly Notices of the Royal Astronomical Society 370, n. 3 (5 luglio 2006): 1213–22. http://dx.doi.org/10.1111/j.1365-2966.2006.10538.x.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Stober, Jonathan M., Rocio Prieto-Gonzalez, Lora L. Smith, Tiago A. Marques e Len Thomas. "Techniques for Estimating the Size of Low-Density Gopher Tortoise Populations". Journal of Fish and Wildlife Management 8, n. 2 (1 giugno 2017): 377–86. http://dx.doi.org/10.3996/012017-jfwm-005.

Testo completo

Abstract (sommario):

Abstract Gopher tortoises (Gopherus polyphemus) are candidates for range-wide listing as threatened under the U.S. Endangered Species Act. Reliable population estimates are important to inform policy and management for recovery of the species. Line transect distance sampling has been adopted as the preferred method to estimate population size. However, when tortoise density is low, it can be challenging to obtain enough tortoise observations to reliably estimate the probability of detection, a vital component of the method. We suggest a modification to the method based on counting usable tortoise burrows (more abundant than tortoises) and separately accounting for the proportion of burrows occupied by tortoises. The increased sample size of burrows can outweigh the additional uncertainty induced by the need to account for the proportion of burrows occupied. We demonstrate the method using surveys conducted within a 13,118-ha portion of the Gopher Tortoise Habitat Management Unit at Fort Gordon Army Installation, Georgia. We used a systematic random design to obtain more precise estimates, using a newly developed systematic variance estimator. Individual transects had a spatially efficient design (pseudocircuits), which greatly improved sampling efficiency on this large site. Estimated burrow density was 0.091 ± 0.011 burrows/ha (CV = 12.6%, 95% CI = 0.071–0.116), with 25% of burrows occupied by a tortoise (CV = 14.4%), yielding a tortoise density of 0.023 ± 0.004 tortoise/ha (CV = 19.0%, 95% CI = 0.016–0.033) and a population estimate of 297 tortoises (95% CI = 210–433). These techniques are applicable to other studies and species. Surveying burrows or nests, rather than animals, can produce more reliable estimates when it leads to a significantly larger sample of detections and when the occupancy status can reliably be ascertained. Systematic line transect survey designs give better precision and are practical to implement and analyze.

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Bouchard, Mathieu, Véronique Martel, Jacques Régnière, Pierre Therrien e David Laginha Pinto Correia. "Do natural enemies explain fluctuations in low-density spruce budworm populations?" Ecology 99, n. 9 (30 luglio 2018): 2047–57. http://dx.doi.org/10.1002/ecy.2417.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

44

Hanberry, Brice B. "Compounded Heat and Fire Risk for Future U.S. Populations". Sustainability 12, n. 8 (17 aprile 2020): 3277. http://dx.doi.org/10.3390/su12083277.

Testo completo

Abstract (sommario):

Climate change is increasing the risk of extreme events, resulting in social and economic challenges. I examined recent past (1971–2000), current and near future (2010–2039), and future (2040–2069) fire and heat hazard combined with population growth by different regions and residential densities (i.e., exurban low and high densities, suburban, and urban low and high densities). Regional values for extreme fire weather days varied greatly. Temperature and number of extreme fire weather days increased over time for all residential density categories, with the greatest increases in the exurban low-density category. The urban high-density category was about 0.8 to 1 °C cooler than the urban low-density category. The areas of the urban and suburban density categories increased relative to the exurban low-density category. Holding climate change constant at 1970–2000 resulted in a temperature increase of 0.4 to 0.8 °C by 2060, indicating future population increases in warmer areas. Overall, U.S. residents will experience greater exposure to fire hazard and heat over time due to climate change, and compound risk emerges because fire weather and heat are coupled and have effects across sectors. Movement to urban centers will help offset exposure to fire but not heat, because urban areas are heat islands; however, urban high-density areas had lower base temperatures, likely due to city locations along coastlines. This analysis provides a timely look at potential trends in fire and heat risk by residential density classes due to the expansion and migration of US populations.

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Kellner, James R., e Stephen P. Hubbell. "Density-dependent adult recruitment in a low-density tropical tree". Proceedings of the National Academy of Sciences 115, n. 44 (15 ottobre 2018): 11268–73. http://dx.doi.org/10.1073/pnas.1800353115.

Testo completo

Abstract (sommario):

The Janzen–Connell hypothesis is a well-known explanation for why tropical forests have large numbers of tree species. A fundamental prediction of the hypothesis is that the probability of adult recruitment is less in regions of high conspecific adult density, a pattern mediated by density-dependent mortality in juvenile life stages. Although there is strong evidence in many tree species that seeds, seedlings, and saplings suffer conspecific density-dependent mortality, no study has shown that adult tree recruitment is negatively density dependent. Density-dependent adult recruitment is necessary for the Janzen–Connell mechanism to regulate tree populations. Here, we report density-dependent adult recruitment in the population of Handroanthus guayacan, a wind-dispersed Neotropical canopy tree species. We use data from high-resolution remote sensing to track individual trees with proven capacity to flower in a lowland moist forest landscape in Panama and analyze these data in a Bayesian framework similar to capture–recapture analysis. We independently quantify probabilities of adult tree recruitment and detection and show that adult recruitment is negatively density dependent. The annualized probability of adult recruitment was 3.03% ⋅ year−1. Despite the detection of negative density dependence in adult recruitment, it was insufficient to stabilize the adult population of H. guayacan, which increased significantly in size over the decade of observation.

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Hayashi, Hiromi, Hitomi Sakai, Wakako Minakuchi-Fujiwara, Miki Takayama, Michiko Nakamura-Murata, Ryoko Kamo, Kanako Funakoshi et al. "Cytokinesis Arrest and Nuclear Fission in Low Density Populations of Trichomonad Protozoan". Zoological Science 19, n. 10 (ottobre 2002): 1089–94. http://dx.doi.org/10.2108/zsj.19.1089.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

MacPherson, Laura M., Michael G. Sullivan, Lee Foote e Cameron E. Stevens. "Evaluating Sampling Techniques for Low-Density Populations of Arctic Grayling (Thymallus arcticus)". Northwestern Naturalist 93, n. 2 (settembre 2012): 120–32. http://dx.doi.org/10.1898/nwn11-04.1.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Kieckhefer, R. W., e J. L. Gellner. "Yield Losses in Winter Wheat Caused by Low‐Density Cereal Aphid Populations". Agronomy Journal 84, n. 2 (marzo 1992): 180–83. http://dx.doi.org/10.2134/agronj1992.00021962008400020011x.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Rohde, Klaus. "Intra- and Interspecific Interactions in Low Density Populations in Resource-Rich Habitats". Oikos 60, n. 1 (febbraio 1991): 91. http://dx.doi.org/10.2307/3544997.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Wang, Ying, Xinzhi Sheng, Yao Liu, Baolai Liang, Xiaoli Li, Qinglin Guo, Yuriy I. Mazur, Morgan E. Ware e Gregory J. Salamo. "PL of low‐density InAs/GaAs quantum dots with different bimodal populations". Micro & Nano Letters 12, n. 9 (settembre 2017): 599–604. http://dx.doi.org/10.1049/mnl.2016.0779.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Articoli di riviste sul tema "Low density populations of koalas"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili