The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species

Abstract

Resource polymorphism is common across taxa and can result in alternate ecotypes with specific morphologies, feeding modes, and behaviors that increase performance in a specific habitat. This can result in high intraspecific variation in the expression of specific traits and the extent to which these traits are correlated within a single population. Although metabolic rate influences resource acquisition and the overall pace of life of individuals it is not clear how metabolic rate interacts with the larger suite of traits to ultimately determine individual fitness.We examined the relationship between metabolic rates and the major differences (habitat use, morphology, and resource use) between littoral and pelagic ecotypes of European perch (Perca fluviatilis) from a single lake in Central Sweden.Standard metabolic rate (SMR) was significantly higher in pelagic perch but did not correlate with resource use or morphology. Maximum metabolic rate (MMR) was not correlated with any of our explanatory variables or with SMR. Aerobic scope (AS) showed the same pattern as SMR, differing across habitats, but contrary to expectations, was lower in pelagic perch.This study helps to establish a framework for future experiments further exploring the drivers of intraspecific differences in metabolism. In addition, since metabolic rates scale with temperature and determine predator energy requirements, our observed differences in SMR across habitats will help determine ecotype-specific vulnerabilities to climate change and differences in top-down predation pressure across habitats.

Keywords: Perca fluviatilis; intraspecific variation; metabolic rate; morphometrics; plasticity; resource use; respirometry; stable isotopes.

FIGURE 1

Visualization (with 4x magnification) of the morphological differences between littoral (green, open circles) and pelagic (blue, closed circles) perch from lake Erken, based on a discriminate function analysis (DFA).

FIGURE 2

Stable isotope bi‐plot showing the mean (± standard deviation) and individual δ¹³C and δ¹⁵N stable isotope values of each perch in addition to littoral and pelagic primary consumers.

FIGURE 3

Residual standard metabolic rate (mg O₂ h⁻¹) across (a) habitat, (b) habitat + resource use, and (c) resource use groups in perch. Asterisks indicate significant differences (*p < .05, **p < .01, ***p < .001) based on pairwise comparisons controlling for sex. Boxplots depict median, 25th and 75th percentile, and whiskers extend to the maximum and minimum values with the exception of plots with outliers (>1.5 * interquartile range) which are represented by dots.

FIGURE 4

Residual maximum metabolic rate (mg O₂ h⁻¹) across (a) habitat, (b) habitat + resource use, and (c) resource use groups in perch. There were no significant differences based on pairwise comparisons controlling for sex. Boxplots depict median, 25th and 75th percentile, and whiskers extend to the maximum and minimum values with the exception of plots with outliers (>1.5 * interquartile range) which are represented by dots.

FIGURE 5

Residual factorial aerobic scope (mg O₂ h⁻¹) across (a) habitat, (b) habitat + resource use, and (c) resource use groups in perch. Asterisks indicate significant differences (*p < .05, **p < .01, ***p < .001) based on pairwise comparisons controlling for sex. Boxplots depict median, 25th and 75th percentile, and whiskers extend to the maximum and minimum values with the exception of plots with outliers (>1.5 * interquartile range) which are represented by dots.

FIGURE 6

Residual absolute aerobic scope (mg O₂ h⁻¹) across of (a) habitat, (b) habitat + resource use, and (c) resource use groups in perch. Asterisks indicate significant differences (*p < .05, **p < .01, ***p < .001) based on pairwise comparisons controlling for sex. Boxplots depict the median, 25th^, and 75th percentile, and whiskers extend to the maximum and minimum values except for plots with outliers (>1.5 * interquartile range) which are represented by dots.