Consumer trait responses track change in resource supply along replicated thermal gradients.

E R Moffett,D C Fryxell,E P Palkovacs,F Lee,K S Simon

doi:10.1098/rspb.2021.2144

Abstract

Rising temperatures may alter consumer diets through increased metabolic demand and altered resource availability. However, current theories assessing dietary shifts with warming do not account for a change in resource availability. It is unknown whether consumers will increase consumption rates or consume different resources to meet increased energy requirements and whether the dietary change will lead to associated variation in morphology and nutrient utilization. Here, we used populations of Gambusia affinis across parallel thermal gradients in New Zealand (NZ) and California (CA) to understand the influence of temperature on diets, morphology and stoichiometric phenotypes. Our results show that with increasing temperature in NZ, mosquitofish consumed more plant material, whereas in CA mosquitofish shifted towards increased consumption of invertebrate prey. In both regions, populations with plant-based diets had fuller guts, longer relative gut lengths, superior-orientated mouths and reduced body elemental %C and N/P. Together, our results show multiple pathways by which consumers may alter their feeding patterns with rising temperatures, and they suggest that warming-induced changes to resource availability may be the principal determinant of which pathway is taken.

Highlights

Higher temperature is predicted to elevate consumer metabolic demand with important consequences for consumer feeding and food web dynamics [1]
Our aims were to (i) understand how resource availability and consumer diets shift with rising temperature, (ii) determine whether patterns of association with temperature are consistent across replicated introductions in New Zealand (NZ) and CA, and (iii) describe the relationship between dietary change, gut morphology and body nutrient stoichiometry
Using a space for time substitution approach, we observed that increased temperature was associated with altered resource availability

Summary

Introduction

Higher temperature is predicted to elevate consumer metabolic demand with important consequences for consumer feeding and food web dynamics [1]. The driver of shifts in diet with temperature change could be metabolic and stoichiometric constraints that shift consumption to foods with higher carbon : phosphorus ratios at higher temperatures [5,6]. Current theories on dietary shifts with rising temperature rest on shifting consumer demand from a physiological response to temperature, but they do not consider other changes in food webs that occur with warming. The dietary response of consumers is likely to depend on how temperature affects resource availability in addition to their physiological demand [7,8,9,10]. If animal-based resources decline with increased temperature [14,15]), consumers may be forced to consume plant material and increase their overall consumption If animal-based resources decline with increased temperature (e.g. [14,15]), consumers may be forced to consume plant material and increase their overall consumption

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Discussion

Conclusion