The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator

Community structure and collapses in multichannel food webs: Role of consumer body sizes and mesohabitat productivities

Multichannel food webs are shaped by the ability of apex predators to link asymmetric energy flows in mesohabitats differing in productivity and community traits. While body size is a fundamental trait underlying life histories and demography, its implications for structuring multichannel food webs are unexplored. To fill this gap, we develop a model that links population responses to predation, and resource availability to community-level patterns, using a tri-trophic food web model with two populations of intermediate consumers and a size-selective top predator. We show that asymmetries in mesohabitat productivities and consumer body sizes drive food web structure, merging previously separate theory on apparent competition and emergent Allee effects (i.e. abrupt population collapses) of top predators. Our results yield theoretical support for empirically observed stability of asymmetric multichannel food webs and discover three novel types of emergent Allee effects involving intermediate consumers, multiple populations or multiple alternative stable states.

Sex-specific plasticity in a trophic polymorphic aquatic predator: a modeling approach

Phenotypic plasticity is common among animal taxa. While there are clearly limits and likely costs to plasticity, these costs are unknown for most organisms. Further, as plasticity is partially genetically determined, the potential magnitude of exhibited plasticity may vary among individuals. In addition to phenotypic plasticity, various animal taxa also display sexual size dimorphism, a feature ultimately thought to arise due to differential size-dependent fitness costs and benefits between sexes. We hypothesized that differential selection acting on males and females can indirectly select for unequal genetically defined plasticity potential between the sexes. We evaluate this possibility for Eurasian perch (Perca fluviatilis), a species that displays modest sexual size dimorphism and habitat-related morphological plasticity. Using 500-year simulations of an ecogenetic agent-based model, we demonstrate that genetically determined morphological plasticity potential may evolve differently for males and females, leading to greater realized morphological variation between habitats for one sex over the other. Genetically determined potential for plasticity evolved differently between sexes across (a) various sex-specific life-history differences and (b) a variety of assumed costs of plasticity acting on both growth and survival. Morphological analyses of Eurasian perch collected in situ were consistent with model predictions: realized morphological variation between habitats was greater for females than males. We suggest that due to sex-specific selective pressures, differences in male and female genetically defined potential for plasticity may be a common feature across organisms.

Interspecific and interpopulation variation in individual diet specialization: Do environmental factors have a role?

Individual diet specialization (IS) has important community- and population-level implications and its ecological drivers are actively investigated. Here, to test the hypothesis that local environmental conditions may influence IS in wild populations, we analyzed the stomach contents of 395 individuals from eight populations of five allopatric species of European cave salamanders (genus Hydromantes). We assessed whether their degree of individual diet specialization (1) scaled positively with the respective niche widths, in agreement with Van Valen's niche variation hypothesis (NVH), and (2) could be predicted by satellite-derived climatic and vegetation characteristics of the sites where the populations live. Consistent with the NVH, the degree of individual diet specialization increased with the populations' total niche width. Furthermore, two variables describing local nonarboreal vegetation cover and habitat heterogeneity successfully predicted the variation in individual specialization across the eight populations. Climatic factors had a generally low predictive power, with individual specialization in low- and high-elevation populations showing contrasting patterns of co-variation with air temperature in the warmest quarter of the year. However, independently from elevation, specialization peaked under conditions of high nonarboreal vegetation cover and high precipitation regimes. We discussed the results against two mutually nonexclusive scenarios hypothesizing different mechanisms linking environmental factors to salamanders' trophic strategy at an individual and population level. We concluded that satellite-derived climatic and vegetation variables to date generally adopted to model Grinnellian niches might also be useful in predicting spatial variations in dietary habits of populations, that is, their Eltonian niches.

Sex, size, and prey caloric value affect diet specialization and consumption of an invasive prey by a native predator

Escaping the control of natural enemies is thought to heavily influence the establishment success and impact of non-native species. Here, we examined how the profitability of alternative prey in combination with the presence of a competitor and predator aggressive behavior explain individual differences in diet specialization and the consumption of the invasive green porcelain crab Petrolisthes armatus by the native mud crab predator Panopeus herbstii. Results from bomb calorimetry estimates show that invasive P. armatus has high caloric value relative to alternative native prey. Laboratory assays indicated that specialization and consumption of invasive P. armatus was mostly exhibited by large, female P. herbstii, but the presence of a competitor and predator aggressiveness did not influence diet and the consumption of P. armatus. Thus, intrinsic factors (e.g., sex and body size) seem to explain consumption of P. armatus and dietary specialization in P. herbstii, more generally. Although there are still many predator individuals that do not consume P. armatus, the proportion of individuals that have begun to specialize on P. armatus suggests that for some, it has become more profitable relative to alternative native prey. Given the high caloric value of P. armatus, we suggest that it is likely that differences in the cost of its consumption, including attack, capture, and handling times relative to alternative prey, determine its net profitability to individual predators.

Asymmetrical habitat coupling of an aquatic predator-The importance of individual specialization

Predators should stabilize food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here, we show clear asymmetry in the ability to couple habitats by Eurasian perch-a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats-pelagic and littoral zones-in Lake Erken, Sweden. Littoral perch showed stronger individual specialization, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialization but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilize spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialization.