Costly neighbours: Heterospecific competitive interactions increase metabolic rates in dominant species

Matouš Janča,Lumír Gvoždík

doi:10.1038/s41598-017-05485-9

Abstract

The energy costs of self-maintenance (standard metabolic rate, SMR) vary substantially among individuals within a population. Despite the importance of SMR for understanding life history strategies, ecological sources of SMR variation remain only partially understood. Stress-mediated increases in SMR are common in subordinate individuals within a population, while the direction and magnitude of the SMR shift induced by interspecific competitive interactions is largely unknown. Using laboratory experiments, we examined the influence of con- and heterospecific pairing on SMR, spontaneous activity, and somatic growth rates in the sympatrically living juvenile newts Ichthyosaura alpestris and Lissotriton vulgaris. The experimental pairing had little influence on SMR and growth rates in the smaller species, L. vulgaris. Individuals exposed to con- and heterospecific interactions were more active than individually reared newts. In the larger species, I. alpestris, heterospecific interactions induced SMR to increase beyond values of individually reared counterparts. Individuals from heterospecific pairs and larger conspecifics grew faster than did newts in other groups. The plastic shift in SMR was independent of the variation in growth rate and activity level. These results reveal a new source of individual SMR variation and potential costs of co-occurrence in ecologically similar taxa.

Highlights

The energy costs of living constitute an important component of life histories
Standard metabolic rates were measured in juvenile newts of two different species experimentally exposed to the presence of con- and/or heterospecifics for two months (Fig. 1)
Our study demonstrated that two-month exposure to competitive interactions affected standard metabolic rate (SMR) in heterospecific but not conspecific pairs in newts

Summary

Introduction

The energy costs of living constitute an important component of life histories. These costs, consisting in the minimum energy requirements of a resting postabsorptive individual, are termed the basal metabolic rate in endotherms or standard metabolic rate (SMR) in ectotherms. According to the increased intake hypothesis[1, 2], a higher SMR is typical for active individuals with relatively larger internal organs[3]. Interacting individuals shift their SMR according to their body size differences, (i.e. the presence of a bigger individual increases SMR in smaller conspecifics)[12], and that may result from a hormonal stress response[15]. Competition-induced plastic responses in SMR have been studied mainly in conspecifics This is surprising, because individuals interact with members of their own species and with other species within an ecosystem. Due to greater size differences and relative competitive abilities between species as compared to within species, we predicted a more pronounced SMR shift in heterospecific than in conspecific pairs. In the case of association between the two traits, this allows for the comparison of SMR relative to growth rate in each group

Methods

Results

Conclusion