Effects of warming on intraguild predation communities with ontogenetic diet-shifts

Viktor Thunell and Max Lindmark, Department of aquatic resources, Swedish University of Agricultural Sciences, SLU, Öregrund, Sweden, Magnus Huss and Anna Gårdmark, Department of Aquatic Resources, Swedish University of Agricultural Sciences, Öregrund, Sweden

Background/Question/Methods
Temperature influences individual growth by affecting energetic demand and supply, and can influence population structure. Species interactions in animal communities mediate feedbacks between individual growth and population structure and thus effects of warming on community composition. Theoretical predictions on how temperature- and body size dependence of individual-level rates affect community composition have so far focused mainly on linear (food chain) communities, disregarding mixed interaction communities despite their ubiquity in nature. Mixed competition-predation interactions, such as intraguild predation, often result from changes in diet over ontogeny (‘ontogenetic diet-shifts’) and strongly affect community composition and dynamics. Here we study how warming mechanistically affects a community of intraguild predators with ontogenetic diet-shifts by analyzing a stage-structured bioenergetics model with temperature- and body size-dependent individual-level rates.
Results/Conclusions
We find that warming strengthens competition and decreases predation and ultimately predator collapse, via loss of the cultivation mechanism that supports predator growth rate. Cultivation is the feedback between competition with predator juveniles from intermediate consumers, and the predation on those consumers exerted by the adult predators. Furthermore, we show that the effect of temperature on community composition depends on the extent of the predators ontogenetic diet shift. If a predator undergoes a partial, rather than complete diet-shift, warming may induce species shifts from predator to consumer dominated communities. We highlight the importance of accounting for how interspecific interactions mediate feedbacks between temperature- and size-dependent processes and intraspecific size-structure for understanding warming induced shifts in community composition. With mean temperatures increasing globally, our findings suggests changes in species composition, possible steep declines and abrupt loss of intraguild predator species and biodiversity.