Body size and tree species composition determine variation in prey consumption in a forest-inhabiting generalist predator

Due to physiological, behavioural or ecological mechanisms, generalist predators may show individual variation in prey consumption. This individual specialization can result from both environmental and trait variation, with especially body size strongly connected to diet. Environmental variation can thus affect consumer-predator interactions by the joint action of changes in prey community composition and predator size.We studied whether and how changes in forest environmental conditions, such as variation in tree species identity and forest fragmentation, affect predator-prey interactions. More specifically we anticipate tree diversity or spatial context to impact the predator diet directly via prey availability and prey size, but also indirectly through shifts in predator size. We used the orb-weaving spider Araneaus diadematus inhabiting forest fragments differing in edge distance, tree diversity and tree species as a model species. The species’ diet was quantified by an unprecedented metabarcoding campaign. A total of 983 spiders were subjected to molecular diet analysis, from in total of 53 forest plots.A. diadematus showed to be a generalist predator, with 298 prey items detected in total. At the individual level, we found large spiders to consume less different species, but consistently larger species. Tree species composition affected both prey species richness and size in the spider’s diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey.We attribute the structural complexity of the understory related to tree species composition as a driver of prey composition and its size distribution as reflected in the predator’s diet. Although large spiders may specialize on large prey, we found no firm evidence for either ecological opportunism or strong specialization. Finally, we conclude that intraspecific size variation and tree species composition define the consumed prey of this generalist predator, and that the many feeding interactions of this spider underlie the species’ success in a large diversity of habitats.

Big and bad: how relative predator size and dietary information influence rusty crayfish (Faxonius rusticus) behavior and resource-use decisions

Prey animals use the information that they extract from predator cues to assess risk. Animals can obtain information about the relative size of predators and their dietary constituents from odor cues that predators deposit in the environment. However, it is currently unknown how prey animals respond when presented with two or more pieces of information about a predator. Rusty crayfish (Faxonius rusticus (Girard, 1852)) were exposed to odors from predatory largemouth bass (Micropterus salmoides (Lacepède, 1802)) that were fed four different diets and also varied in size relative to the crayfish subjects. A series of analyses of covariance (ANCOVA) indicated that rusty crayfish altered their macrophyte consumption, foraging behavior, and shelter-use behavior depending on the relative size and dietary information presented by the largemouth bass. This study demonstrates that prey consider and respond to multiple aspects of a predatory threat when making resource-use decisions.

Ontogenetic variation in the diet of the anuran community from a semi-arid environment in the southeastern Chihuahuan Desert

Although ontogeny influences dietary composition and trophic niche breadth in many anurans, its effects on diet have been little analyzed in sympatric species. In this study, we analyzed interspecific and ontogenetic variation in dietary composition and trophic niche width in an anuran community from a semi-arid environment. We found a more profound effect of species identity than body size on dietary composition, with the diet of four species dominated by formicids, that of two others by coleopterans and formicids, and that of the remaining species not dominated by specific prey types. We found ontogenetic changes in dietary composition in three of four species analyzed, in which consumption of some small insects decreased as predator size increased, regardless of species. Additionally, we did not find ontogenetic change in prey number consumed in any of the four species, but prey size increased with increasing predator size in all of them. Most species exhibited a narrow trophic niche, which was even narrower in adults in three of the four species analyzed. Costello’s modified plots revealed a high variation among individuals in termite consumption in Anaxyrus punctatus, and in more prey types in Spea multiplicata. Our results suggest that this community is not size-structured, and that ontogenetic diet shifts are mainly caused by passive sampling toward prey of different sizes. Finally, comparisons with previous data revealed an interpopulation pattern, in which trophic niche width contracts as aridity increases, possibly because of an increase in interspecific competition for trophic resources.