Chapter Twenty-Six - Climate change, phenology and the nature of consumer–resource interactions

Summary

Introduction

Understanding how species cope with ecological and environmental variation is a fundamental concern of ecology. Over the course of their lives, many organisms alter their phenotypes in response to biotic and abiotic pressures (Miner et al. 2005), responses that cascade through the food web to, in turn, affect the dynamics of species interactions. These effects, called trait-mediated effects, are pervasive in ecological communities, and their study has offered new insights into community ecology, a subject previously dominated by a density-mediated understanding of species interactions (Werner and Peacor 2003). Most analyses of trait-mediated effects take a top-down perspective where variation in consumer traits causes phenotypic responses by prey species. These phenotypic responses include behavioural, morphological and/or physiological plasticity that have ramifying consequences for the food web by influencing how predators and prey interact (Werner and Peacor 2003). This top-down perspective on the influence of traits in communities suggests that it is consumers that determine the nature and strength of the mediated effects.

Climate change is an ongoing global perturbation that also affects the densities and traits of interacting species, although these effects are not necessarily related to food web trade-offs. Cohesive shifts in phenology – the timing of periodic biological events, such as migration, flowering or mating – reveal the global scale of climate change’s influence on species’ traits (Parmesan and Yohe 2003; Root et al. 2003). These phenological changes affect conditions that influence the relative fitness contributions of life-history traits, traits such as age-structured growth, reproductive timing or developmental rates. For some species, these traits are plastic to fitness trade-offs created by phenological shifts. In this way, climate change can affect the expression of traits that have an overwhelming influence on species interactions. Unlike the top-down influence of consumers, this non-trophic forcing can affect food webs via bottom-up processes. Phenology not only affects the nature and timing of species interactions, but also influences the very likelihood that two species will interact at all. In this manner, it can conflate or confound prey trait responses to immediate food web trade-offs, like those mediated by predators. Climate-driven phenological variability provides new context for understanding the interaction between trophic and non-trophic traits and how this influences overall food web dynamics.