Niche width collapse in a resilient top predator following ecosystem fragmentation.

Craig A Layman,John P Quattrochi,Caroline M Peyer,Jacob E Allgeier

doi:10.1111/j.1461-0248.2007.01087.x

Abstract

Much research has focused on identifying species that are susceptible to extinction following ecosystem fragmentation, yet even those species that persist in fragmented habitats may have fundamentally different ecological roles than conspecifics in unimpacted areas. Shifts in trophic role induced by fragmentation, especially of abundant top predators, could have transcendent impacts on food web architecture and stability, as well as ecosystem function. Here we use a novel measure of trophic niche width, based on stable isotope ratios, to assess effects of aquatic ecosystem fragmentation on trophic ecology of a resilient, dominant, top predator. We demonstrate collapse in trophic niche width of the predator in fragmented systems, a phenomenon related to significant reductions in diversity of potential prey taxa. Collapsed niche width reflects a homogenization of energy flow pathways to top predators, likely serving to destabilize remnant food webs and render apparently resilient top predators more susceptible to extinction through time.

Highlights

Organisms differ in their susceptibility to ecosystem fragmentation and other anthropogenic impacts (McKinney 1997; Henle et al 2004; Cardillo et al 2005)
Is the trophic ecology of resilient top predators altered in fragmented habitats? If so, how is this related to overall food web architecture and what are implications for ecosystem function and stability?
We demonstrate that trophic niche width of a dominant top predator collapses following aquatic ecosystem fragmentation, and we discuss how this collapse may further decrease food web stability in fragmented habitats

Summary

Introduction

Organisms differ in their susceptibility to ecosystem fragmentation and other anthropogenic impacts (McKinney 1997; Henle et al 2004; Cardillo et al 2005). Trophic generalists may be less susceptible to extinction (or extirpation) because of their ability to shift among alternative food resources (Purvis et al 2000; Hopkins et al 2002). As such, those organisms with a broad trophic niche may be expected, other factors being equal, to be most resilient to the detrimental impacts associated with fragmentation. Due to the wellknown limitations of these approaches, stable isotopes have become a common alternative for study of trophic niches, providing for time- and space-integrated representations of the trophic ecology of organisms (Post et al 2000b; Bearhop et al 2004; Layman et al 2007).

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Conclusion