Nationwide trophic cascades: changes in avian community structure driven by ungulates.

Georgina Palmer,Philip A Stephens,Stephen G Willis,Alastair I Ward

doi:10.1038/srep15601

Georgina Palmer, Philip A Stephens + Show 2 more

Open Access

https://doi.org/10.1038/srep15601

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Abstract

In recent decades, many ungulate populations have changed dramatically in abundance, resulting in cascading effects across ecosystems. However, studies of such effects are often limited in their spatial and temporal scope. Here, we contrast multi-species composite population trends of deer-sensitive and deer-tolerant woodland birds at a national scale, across Britain. We highlight the divergent fates of these two groups between 1994 and 2011, and show a striking association between the calculated divergence and a composite population trend of woodland deer. Our results demonstrate the link between changes in deer populations and changes in bird communities. In a period when composite population trends for deer increased by 46%, the community population trend across deer-sensitive birds (those dependent on understory vegetation) declined much more than the community trend for deer-tolerant birds. Our findings suggest that ongoing changes in the populations of herbivorous ungulates in many countries worldwide may help explain patterns of community restructuring at other trophic levels. Ungulate impacts on other taxa may require more consideration by conservation practitioners than they currently receive.

Highlights

In recent decades, many ungulate populations have changed dramatically in abundance, resulting in cascading effects across ecosystems
The most commonly studied trophic cascades are of predator-consumer-producer[9], these cascades can, and have, been extended to include the indirect effect of the consumer on other species. This is exemplified by the wolf-elk-tree system in Yellowstone National Park, USA; Ripple & Beschta[2] demonstrated that the restoration of riparian habitats as a result of increased predation of consumers by predators, resulted in further cascades to beavers Caster Canadensis and bison Bison bison
The composite population trend for deer increased by 46% between 1996 and 2010 (Fig. 1a)

Summary

Introduction

Many ungulate populations have changed dramatically in abundance, resulting in cascading effects across ecosystems. Herbivorous ungulates exert cascading effects on components of biodiversity in ecosystems they inhabit, including birds, small mammals, meso-herbivores and invertebrates[1,2,3,4] These effects are commonly mediated through changes to vegetation abundance, structure, and diversity[1]. Gregory et al.[16] created a ‘Climate Impact Indicator’, which measured the divergence of population trends of birds in two groups: those expected to be favourably, or adversely, affected by climate change. Such indicators are easy to interpret and highly useful for describing general patterns of change in impacts over time, raising awareness of the environmental driver, and assisting in setting strategies to reduce negative impacts[16]

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