Linking human impacts to community processes in terrestrial and freshwater ecosystems

Human impacts such as habitat loss, climate change and biological invasions are radically altering biodiversity, with even greater effects projected into the future. Evidence suggests human impacts may differ substantially between terrestrial and freshwater ecosystems, but the reasons for these differences are poorly understood. We propose an integrative approach to explain these differences by linking impacts to the fundamental processes that structure communities: dispersal, speciation, ecological selection and ecological drift. Our goal is to provide process-based insights into why human impacts, and the responses to these impacts, may differ across ecosystem types within a mechanistic, eco-evolutionary comparative framework. To enable these insights, we review and synthesize i) how the four processes can influence diversity and dynamics in terrestrial and freshwater communities, focusing on whether their relative importance may or may not differ among ecosystems, and ii) how human impacts can alter terrestrial and freshwater biodiversity in different ways due to differences in process strength among ecosystems. Finally, we highlight research gaps and next steps, and discuss how this approach can provide new insights for conservation. By focusing on the processes that shape diversity in communities, we aim to mechanistically link human impacts to ongoing and future changes in ecosystems.

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Demonstration of the impact, process and response approach for a warming scenario. Focusing on the community processes of dispersal, speciation, selection and drift can provide mechanistic insights into how humans alter the dynamics of terrestrial and freshwater systems via effects on community structure and function. We demonstrate the utility of this approach for a hypothetical climate warming scenario in which terrestrial communities (red circle) are turning over towards more warm-adapted species (aka thermophilising) faster than freshwater communities (blue circle). Potential differences or similarities in the strength of each process among ecosystem types can then be examined to provide possible explanations for why responses may vary or not between terrestrial and freshwater habitats. In this hypothetical scenario, a pattern of slower community turnover in freshwater compared to terrestrial habitats may be explained by weaker warming impacts and greater effective dispersal limitation in freshwaters (see main text and Table 1).

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Published in Ecology Letters, 2022 (issued 2023)

Authors: Ian R McFadden, Agnieszka Sendek, Morgane Brosse, Peter M Bach, Marco Baity-Jesi, Janine Bolliger, Kurt Bollmann, Eckehard G Brockerhoff, Giulia Donati, Friederike Gebert, Shyamolina Ghosh, Hsi-Cheng Ho, Imran Khaliq, J Jelle Lever, Ivana Logar, Helen Moor, Daniel Odermatt, Loïc Pellissier, Luiz Jardim De Queiroz, Christian Rixen, Nele Schuwirth, J Ryan Shipley, Cornelia W Twining, Yann Vitasse, Christoph Vorburger, Mark KL Wong, Niklaus E Zimmermann, Ole Seehausen, Martin M Gossner, Blake Matthews, Catherine H Graham, Florian Altermatt, Anita Narwani

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