Habitat mediates coevolved but not novel species interactions.

Joshua P Twining,Neil Reid,Chris Sutherland,David G Tosh

doi:10.1098/rspb.2021.2338

Abstract

Ongoing recovery of native predators has the potential to alter species interactions, with community and ecosystem wide implications. We estimated the co-occurrence of three species of conservation and management interest from a multi-species citizen science camera trap survey. We demonstrate fundamental differences in novel and coevolved predator–prey interactions that are mediated by habitat. Specifically, we demonstrate that anthropogenic habitat modification had no influence on the expansion of the recovering native pine marten in Ireland, nor does it affect the predator's suppressive influence on an invasive prey species, the grey squirrel. By contrast, the direction of the interaction between the pine marten and a native prey species, the red squirrel, is dependent on habitat. Pine martens had a positive influence on red squirrel occurrence at a landscape scale, especially in native broadleaf woodlands. However, in areas dominated by non-native conifer plantations, the pine marten reduced red squirrel occurrence. These findings suggest that following the recovery of a native predator, the benefits of competitive release are spatially structured and habitat-specific. The potential for past and future landscape modification to alter established interactions between predators and prey has global implications in the context of the ongoing recovery of predator populations in human-modified landscapes.

Highlights

Determining the mechanisms underpinning species occurrence and how perturbations can alter species coexistence and biodiversity patterns is a fundamental goal in ecology
We expect: (i) the impact of the pine marten on grey squirrels to be consistent regardless of local habitat owing to the naivety of the invasive species to the native predator [19]; (ii) the interactions between the pine marten and the red squirrel to be dynamic and dependent on habitat, with more structurally complex and diverse habitats resulting in lower impacts on the native prey species; and (iii) the competitively linked native-invasive prey species interactions to be mediated by habitat [20]
Using Akaike information criterion (AIC) to compare the multi-species models, we found clear evidence of interspecific dependence among all three species, and habitat mediation of coevolved but not novel predator–prey interactions

Summary

Introduction

Determining the mechanisms underpinning species occurrence and how perturbations can alter species coexistence and biodiversity patterns is a fundamental goal in ecology. The planetary-scale influence of human activity has brought into sharp focus the need to predict how whole communities respond to multiple anthropogenically driven stressors This requires an explicit focus on how specific species respond to change, and how interactions and interdependencies among species are affected by changing environments. Invasive species have been associated with increased vertebrate extinctions more than any other factor [3,4] and provide compelling examples of how novel indirect interactions can alter established species interactions, with potential outcomes ranging from complete exclusion and species extirpation to fugitive coexistence [5]. The consequences of failing to predict novel species interactions are exemplified by numerous ill-fated attempts to introduce non-native generalist predators as biological control agents to island ecosystems, leading to disastrous impacts on naive native prey species, often resulting in severe decline, extirpation, or extinction [18]. We expect: (i) the impact of the pine marten on grey squirrels to be consistent regardless of local habitat owing to the naivety of the invasive species to the native predator [19]; (ii) the interactions between the pine marten and the red squirrel to be dynamic and dependent on habitat, with more structurally complex and diverse habitats resulting in lower impacts on the native prey species; and (iii) the competitively linked native-invasive prey species interactions to be mediated by habitat [20]

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Discussion