Browsing by Author "Toscano, Benjamin J."

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    Cannibalism and Intraguild Predation Community Dynamics: Coexistence, Competitive Exclusion, and the Loss of Alternative Stable States
    (The University of Chicago Press, 2017) Toscano, Benjamin J.; Hin, Vincent; Rudolf, Volker H.W.
    Predators often exert strong top-down regulation of prey, but in many systems, juvenile predators must compete with their future prey for a shared resource. In such life-history intraguild predation (LHIGP) systems, prey can therefore also regulate the recruitment and thus population dynamics of their predator via competition. Theory predicts that such stage-structured systems exhibit a wide range of dynamics, including alternative stable states. Here we show that cannibalism is an exceedingly common interaction within natural LHIGP systems that determines what coexistence states are possible. Using a modeling approach that simulates a range of ontogenetic diet shift scenarios along a productivity gradient, we demonstrate that only if the predator is competitively dominant can cannibalism promote coexistence by allowing prey to persist. If the prey is competitively dominant, cannibalism instead results in competitive exclusion of the predator and the loss of potential alternative stable states. Further, predator exclusion occurs at low cannibalistic preference relative to empirical estimates and is consistent across LHIGP systems in which the predator undergoes a complete diet shift or diet broadening over ontogeny. Given that prey is frequently competitively dominant in natural systems, our results demonstrate that even weak cannibalism can inhibit predator persistence, prompting exploration of mechanisms that reconcile theory with the common occurrence of such interactions in nature.
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    Ontogenetic development underlies population response to mortality
    (Wiley, 2021) Toscano, Benjamin J.; Figel, Alexandra S.; Rudolf, Volker H.W.
    Understanding demographic responses to mortality is crucial to predictive ecology. While classic ecological theory posits reductions in population biomass in response to extrinsic mortality, models containing realistic developmental change predict the potential for counterintuitive increase in stage‐specific biomass, i.e. biomass overcompensation. Patterns of biomass overcompensation should be predictable based on differences in the relative energetic efficiencies of juvenile maturation and adult reproduction. Specifically, in populations where reproduction is the limiting process, adult‐specific mortality should enhance total reproduction and thus juvenile biomass. We tested this prediction by inducing an array of stage‐specific harvesting treatments across replicate populations of Daphnia pulex. In accordance with reproductive regulation, the greatest biomass response occurred in the juvenile Daphnia stage and this response occurred most strongly in response to adult mortality. Nevertheless, we failed to detect significant biomass overcompensation and instead report largely compensatory effects. In total, our work demonstrates that knowledge of population structure is necessary to accurately predict population dynamics, but cautions that further research is needed to illuminate the factors generating over‐compensatory versus compensatory responses across natural populations.