Persistence of species in trophic chains depends on temperature-size responses of individuals

Body size reductions of ectotherms–such as insects, fish and bacteria–are among the main responses of organisms to climate change. However, the ecological consequences of this phenomenon are little explored. An international tem lead by researchers at the Institute of Entomology of the Biology Centre CAS and University of South Bohemia has simulated long-term consequences of changes in body size on the persistence and structure of trophic chains. They show that body size reductions can increase the survival of populations and hence mitigate the consequences of climate change. Their findings published in the July issue of Ecology Letters underlie the importance of phenotypic responses of individual organisms to changing temperature and show that these changes must be considered if we want to fully understand how climate change will affect biodiversity and ecosystem functioning.

Example of the effect of temperature on individuals across three trophic levels: dragonfly larvae feeding on cladocerans that in turn feed on green algae. Size of all individuals decreases with temperature.

Three main organismal responses to climate change are currently recognized: (1) changes in the spatial distribution of species, (2) changes in phenology and (3) changes in body size of ectotherms. While the first two phenomena have been widely recognized and studied, the ecological consequences of body size reductions are relatively little understood. At the same time, temperature-dependent changes in body size depend on the body size itself and differ between unicellular and multicellular organisms and between terrestrial and aquatic ectotherms. This makes general predictions of the impact of these changes on ecosystems difficult.

The new study by Arnaud Sentis, Amrei Binzer and David Boukal used simulation modelling to unravel the effect of temperature, habitat productivity, body size and temperature-size responses on the stability and persistence of a simple food chain. The food chain consisted of three ectotherm populations–consumers, intermediate predators and top predators–that potentially differed in body size and size response to warming. The results revealed that changes in body size can substantially increase (but also decrease) the probability that the predator populations will survive increased temperatures predicted by the current climate change scenarios. The predicted effects were strongest for aquatic ectotherms and for food chains with high body size ratios at adjacent trophic levels.

In summary, this study shows that individual phenotypic plasticity can have strong effects on the community level, and that temperature-size responses should be included in future models of climate change effects on ecosystems and biodiversity.

A. Sentis, A. Binzer, D. S. Boukal (2017) Temperature-size responses alter food chain persistence across environmental gradients. Ecology Letters 20: 852-862.