Academic literature on the topic 'Life-history omnivore'

Abstract Tardigrades may be divided into the following feeding groups: herbivores, carnivores and omnivores. However, little is known about their specific feeding preferences. Here, we used a number of laboratory experiments with 18 potential food sources, representing a wide variety of organisms, to test feeding preferences, survival and fecundity of three tardigrade species, representing different feeding modes. We also tested for differences in preferences between juveniles and adults, and differences in survival between two age groups: one that started the experiment as juveniles and the other as adults. In our experiments, Milnesium inceptum is confirmed to be a carnivore, being able to reproduce only on animal prey. We also show that Hypsibius exemplaris is a herbivore, feeding on cyanobacteria, algae and fungi. Paramacrobiotus fairbanksi, on the other hand, is demonstrated to be an omnivore, feeding on cyanobacteria, algae, fungi and animals. In some cases, juveniles preferred different types of food than adults. Reproduction was strongly affected by food type. Finally, we demonstrate that tardigrades may ingest food types that they are not able to digest. Thus, gut content analysis may be misleading as a method of studying tardigrade feeding habits.

Monument Creek and West Fork, two interior Alaskan streams that are tributaries of the Chena River, are characterized by low water temperatures, low allochthonous input and periphyton biomass, and lengthy ice cover. Nine species of Trichoptera were found: Rhyacophila vofixa (Rhyacophilidae), Glossosoma verdona, Glossosoma alascense (Glossosomatidae), Brachycentrus americanus (Brachycentridae), Hydatophylax variabilis, Ecclisomyia conspersa, Onocosmoecus unicolor, Chyranda centralis, and Apatania crymophila (Limnephilidae). There were four shredders, three scrapers, one omnivore, and one predator. Within the shredder and scraper guilds, species had partially overlapping univoltine life histories, perhaps allowing functionally similar species to use the same food resources. The trichopteran fauna of interior Alaska seems to be composed of species typical of boreal forest, with arctic, western montane, and Siberian influences.

Examination of the reproductive biology of the abyssal seastar Dytaster grandis taken at different times of the year in the NE Atlantic suggests seasonal reproduction that is related to the seasonal pulse of phytodetritus to the deep-sea floor. Although this seastar is an omnivore, the availability of this labile organic material may fuel vitellogenesis during the summer and autumn months. The egg size suggests planktotrophic larval development. Spawning occurs in the early part of each year to allow the zygote to develop into a feeding larva to coincide with the downward flux of phytodetritus. Thus the flux of detritus may constitute an environmental forcing pressure at least at two points in the life history of D. grandis.

AbstractOmnivory is common among arthropods, but little is known about how availability of plant resources and prey affects interactions between species operating at the third and fourth trophic level. We used laboratory and field cage experiments to investigate how the provision of flowers affects an omnivorous lacewing, Micromus tasmaniae (Hemerobiidae) and its parasitoid Anacharis zealandica (Figitidae). The adult lacewing is a true omnivore that feeds on both floral resources and aphids, whereas the parasitoid is a life-history omnivore, feeding on lacewing larvae in the larval stage and floral nectar as an adult. We showed that the effect of floral resources (buckwheat) on lacewing oviposition depends on prey (aphid) density, having a positive effect only at low prey density and that buckwheat substantially increases the longevity of the adult parasitoid. In field cages, we tested how provision of flowering buckwheat affects the dynamics of a four trophic level system, comprising parasitoids, lacewings, pea aphids and alfalfa. We found that provision of buckwheat decreased the density of lacewings in the first phase of the experiment when the density of aphids was high. This effect was probably caused by increased rate of parasitism by the parasitoid, which benefits from the presence of buckwheat. Towards the end of the experiment when the aphid populations had declined to low levels, the effect of buckwheat on lacewing density became positive, probably because lacewings were starving in the no-buckwheat treatment. Although presence of buckwheat flowers did not affect aphid populations in the field cages, these findings highlight the need to consider multitrophic interactions when proposing provision of floral resources as a technique for sustainable pest management.

Abstract An individual’s early-life environment and phenotype often influence its traits and performance as an adult. We investigated whether such ‘carryover effects’ are associated with alternative, environmentally-induced phenotypes (‘polyphenism’), and, if so, whether they influence the evolution of polyphenism. To do so, we studied Mexican spadefoot toads, Spea multiplicata, which have evolved a polyphenism consisting of two, dramatically different forms: a carnivore morph and an omnivore morph. We sampled both morphs from a fast-drying and a slow-drying pond and reared them to sexual maturity. Larval environment (pond) strongly influenced survival as well as age and size at metamorphosis and sexual maturity; i.e. environment-dependent carryover effects were present. By contrast, larval phenotype (morph) did not affect life-history traits at sexual maturity; i.e. phenotype-dependent carryover effects were absent. These results are consistent with theory, which suggests that by amplifying selective trade-offs in heterogenous environments, environment-dependent carryover effects might foster the evolution of polyphenism. At the same time, by freeing selection to refine a novel phenotype without altering the existing form, the absence of phenotype-dependent carryover effects might enable polyphenism to evolve in the first place. Generally, carryover effects might play an underappreciated role in the evolution of polyphenism.

Abstract Falk-Petersen, J., Renaud, P., and Anisimova, N. 2011. Establishment and ecosystem effects of the alien invasive red king crab (Paralithodes camtschaticus) in the Barents Sea – a review. – ICES Journal of Marine Science, 68: . Since its introduction to the Barents Sea from the North Pacific in the 1960s, the red king crab (Paralithodes camtschaticus) has become invasive. The crab represents an important source of income, but also a potential threat to the highly productive fisheries in the region through its ecosystem impacts. A literature review was conducted, identifying factors contributing to the success of the crab as well as its interactions with native biota. Characteristics of the Barents Sea and the crab itself that may explain its success include suitable habitat for settlement and growth of the larvae; the wide range of habitats occupied throughout its life history, high mobility, generalist prey choice, low fishing pressure during establishment, and the lack of parasites. Being a large, bottom-feeding omnivore of great mobility, the king crab can significantly impact the ecosystem. Reduced benthic diversity and biomass have been registered in invaded areas. Important prey items include large epibenthic organisms whose structures also represent important habitat. Impacts on commercial and non-commercial fish species, through egg predation or indirect interactions, are difficult to detect and predict.

Arthropod species that have the potential to damage crops are food resources for communities of predators and parasitoids. From an agronomic perspective these species are pests and biocontrol agents respectively, and the relationships between them can be important determinants of crop yield and quality. The impact of biocontrol agents on pest populations may depend on the availability of other food resources in the agroecosystem. A scarcity of such resources may limit biological control and altering agroecosystem management to alleviate this limitation could contribute to pest management. This is a tactic of ‘conservation biological control’ and includes the provision of flowers for species that consume prey as larvae but require floral resources in their adult stage. The use of flowers for pest management requires an understanding of the interactions between the flowers, pests, biocontrol agents and non-target species. Without this, attempts to enhance biological control might be ineffective or detrimental. This thesis develops our understanding in two areas which have received relatively little attention: the role of flowers in biological control by true omnivores, and the implications of flower use by fourth-trophic-level life-history omnivores. The species studied were the lacewing Micromus tasmaniae and its parasitoid Anacharis zealandica. Buckwheat flowers Fagopyrum esculentum provided floral resources and aphids Acyrthosiphon pisum served as prey. Laboratory experiments with M. tasmaniae demonstrated that although prey were required for reproduction, providing flowers increased survival and oviposition when prey abundance was low. Flowers also decreased prey consumption by the adult lacewings. These experiments therefore revealed the potential for flowers to either enhance or disrupt biological control by M. tasmaniae. Adult M. tasmaniae were collected from a crop containing a strip of flowers. Analyses to determine the presence of prey and pollen in their digestive tracts suggested that predation was more frequent than foraging in flowers. It was concluded that the flower strip probably did not affect biological control by lacewings in that field, but flowers could be significant in other situations. The lifetime fecundity of A. zealandica was greatly increased by the presence of flowers in the laboratory. Providing flowers therefore has the potential to increase parasitism of M. tasmaniae and so disrupt biological control. A. zealandica was also studied in a crop containing a flower strip. Rubidium-marking was used to investigate nectar-feeding and dispersal from the flowers. In addition, the parasitoids’ sugar compositions were determined by HPLC and used to infer feeding histories. Although further work is required to develop the use of these techniques in this system, the results suggested that A. zealandica did not exploit the flower strip. The sugar profiles suggested that honeydew had been consumed by many of the parasitoids. A simulation model was developed to explore the dynamics of aphid, lacewing and parasitoid populations with and without flowers. This suggested that if M. tasmaniae and A. zealandica responded to flowers as in the laboratory, flowers would only have a small effect on biological control within a single period of a lucerne cutting cycle. When parasitoids were present, the direct beneficial effect of flowers on the lacewing population was outweighed by increased parasitism, reducing the potential for biological control in future crops. The results presented in this thesis exemplify the complex interactions that may occur as a consequence of providing floral resources in agroecosystems and re-affirm the need for agroecology to inform the development of sustainable pest management techniques.

Size-dependent differences between individuals in size-structured organisms have fundamental effect on population and community dynamics. Intraguild predation (IGP) is one specifically interesting constellation that often arises when two size-structured populations interact. Ontogenetic bottlenecks that determine population size-structure are affected by both population intrinsic as well as population extrinsic factors, and are therefore context-dependent. Surprisingly, size-structured IGP systems have mainly been investigated theoretically and especially long-term empirical studies are widely lacking. In this thesis I investigate empirically how habitat complexity, interaction strength, and stage-specific resource availabilities affect population processes and their effects on the dynamics of a size-structured IGP system. I conducted multi-generation experiments in a size-structured IGP system, with the Least Killifish (Heterandria formosa) as IG prey and the Common Guppy (Poecilia reticulata) as IG predator. With no alternative resource next to the shared resource, IG predator and IG prey could not coexist. Weak interactions only increased IG prey and IG predator persistence times and observed exclusion patterns depended on habitat complexity. An alternative resource for either the juvenile IG predator or the juvenile IG prey on the other hand promoted coexistence. However, this coexistence was context-dependent. Ontogenetic bottlenecks played a central role in the dynamics of the size-structured IGP system in general. In the final study I show that an ontogenetic bottleneck can, through changes in stage-specific resource availabilities, be affected in a way that leads to increased trophic transfer efficiency with potential effects on higher trophic levels. Overall, the results emphasize importance of the broader context in which size-structured communities are embedded. Especially, when managing natural communities it is important to account for the combined effects of size-structure, stage-specific resource availabilities, and habitat structure. Specifically, when managing species that connect habitats or ecosystems all life-stages’ environmental conditions must be consider in order to ensure strong predictive power of tools used for ecosystem management planning.

Predators with Pouches provides a unique synthesis of current knowledge of the world’s carnivorous marsupials—from Patagonia to New Guinea and North America to Tasmania. Written by 63 experts in each field, the book covers a comprehensive range of disciplines including evolution and systematics, reproductive biology, physiology, ecology, behaviour and conservation. Predators with Pouches reveals the relationships between the American didelphids and the Australian dasyurids, and explores the role of the marsupial fauna in the mammal community. It introduces the geologically oldest marsupials, from the Americas, and examines the fall from former diversity of the larger marsupial carnivores and their convergent evolution with placental forms. The book covers all aspects of carnivorous marsupials, including interesting features of life history, their unique reproduction, the physiological basis for early senescence in semelparous dasyurids, sex ratio variation and juvenile dispersal. It looks at gradients in nutrition—from omnivory to insectivory to carnivory—as well as distributional ecology, social structure and conservation dilemmas.