Lake size and fish diversity determine resource use and trophic position of a top predator in high-latitude lakes.

Antti P Eloranta,Kimmo K Kahilainen,Per‐Arne Amundsen,Roger I Jones,Chris Harrod,Rune Knudsen

doi:10.1002/ece3.1464

Abstract

Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food-web stability. In lakes, littoral and pelagic food-web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high-latitude lakes. We analyzed food-web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5–1084 km2) and fish species richness (2–13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food-chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate-dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high-latitude lakes.

Highlights

Ecological research has increasingly recognized the fundamental importance of habitat linkages to the structure and function of aquatic and terrestrial ecosystems (Polis et al 1997; Vadeboncoeur et al 2002; Marcarelli et al 2011)
Ecology and Evolution published by John Wiley & Sons Ltd
Littoral benthic macro-invertebrate d13C values were on average 6.7–14.3 & higher than those of zooplankton, whereas mean d15N values differed by only 0.09–1.9 &

Summary

Introduction

Ecological research has increasingly recognized the fundamental importance of habitat linkages to the structure and function of aquatic and terrestrial ecosystems (Polis et al 1997; Vadeboncoeur et al 2002; Marcarelli et al 2011). Terrestrial predators can use terrestrial, marine and/or freshwater prey depending on seasonal and spatial availability of different resources (Helfield and Naiman 2006; Killengreen et al 2011; Middleton et al 2013). Generalist fish top predators in lakes can use both littoral (benthic) and pelagic food resources and thereby link these different habitats and food-web compartments (Schindler and Scheuerell 2002; Vander Zanden and Vadeboncoeur 2002; Eloranta et al 2013a). Such cross-habitat linkages by top a 2015 The Authors.

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Conclusion