Abstract
The trophic structure of species communities depends on the energy transfer between trophic levels. Primary productivity varies strongly through time, challenging the persistence of species at higher trophic levels. Yet resource variability has mostly been studied in systems with only one or two trophic levels. We test the effect of variability in resource productivity in a tritrophic model system including a resource, a size-structured consumer, and a size-specific predator. The model complies with fundamental principles of mass conservation and the body-size dependence of individual-level energetics and predator-prey interactions. Surprisingly, we find that resource variability may promote predator persistence. The positive effect of variability on the predator arises through periods with starvation mortality of juvenile prey, which reduces the intraspecific competition in the prey population. With increasing variability in productivity and starvation mortality in the juvenile prey, the prey availability increases in the size range preferred by the predator. The positive effect of prey mortality on the trophic transfer efficiency depends on the biologically realistic consideration of body size-dependent and food-dependent functions for growth and reproduction in our model. Our findings show that variability may promote the trophic transfer efficiency, indicating that environmental variability may sustain species at higher trophic levels in natural ecosystems.
Highlights
The transfer of energy between different trophic layers shapes the trophic structure of species communities
Previous studies have shown that resource variability can promote competitive coexistence and thereby increase the diversity of consumers (Armstrong and McGehee 1976; Sommer 1985; Chesson 2000)
The trophic transfer efficiency may be stimulated through this mechanism
Summary
The transfer of energy between different trophic layers shapes the trophic structure of species communities. The consequences of resource variability are intimately linked to the trophic transfer of energy, which results from the feeding of consumers on resources Such interactions occur between individuals and not between species (Clark et al 2011). In contrast to classic population models, size-structured population models are based on assumptions at the individual level regarding the intake and use of energy (Metz and Diekmann 1986; de Roos and Persson 2002, 2013) These assumptions lead to body size–dependent and food-dependent functions for growth, reproduction, and mortality (Kooijman 2000). We analyze the effect of variability in resource productivity on trophic transfer efficiency using a model system with three trophic layers including an unstructured resource, a size-structured consumer, and a size-specific predator. We test the robustness of our results to “pink” stochastic daily variation in the productivity of the resource as opposed to regular periodic variability using methods previously described by de Roos et al (2008a) and Vasseur (2007; see the appendix)
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