Will warming affect food web structure?

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  • PhD, School of Ocean Sciences

Abstract

The question is: Will warming affect food web structure? The rationale for asking this question comes from theories and laboratory observations that predict warming to decrease the quantity of producer relative to consumer biomass because rates of consumption increase more rapidly with warming than do rates of production. However, in natural ecosystems this is seldom observed. To explain this dichotomy, I posit the hypothesis that organisms adapt to their environment in many ways, and over various timescales such that the way in which individuals respond to temperature is contextual and dependent upon many other variables. Beginning with the contextual effects on the individuals themselves, in Chapters 2 and 3 I conduct laboratory experiments to investigate the effects of warming upon individual level rates of production and consumption and I then investigate how those individual level effects of warming govern the ratio of producer to consumer biomass. These experiments demonstrate that the initial ratio of consumer to producer body size is more important than temperature in determining change in the ratio of consumer to producer biomass. I then conduct field observations of the rocky shore community to investigate which key processes determine the ratio of consumer to producer biomass in this natural ecosystem. In Chapter 4, I observe that wave exposure affects the causal link between producer and consumer biomass, but also that producers and consumers respond to wave exposure in different, and apparently weakly connected ways. In Chapter 5, I observe that heterogeneity in the biomass of producers within communities is key in determining producer species richness and that the interaction between these two variables determines the abundance and group richness of consumers. Overall therefore, the results indicate that variation in individual attributes, and variation in individual responses to their environment and each other, are key in determining both community structure and whether it will be affected by warming. Thus the answer to the question is: I doubt it.

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Original languageEnglish
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Award dateJan 2016