Bioclimatic context of species' populations determines community stability.

Clouded Yellow butterfly, by Mike Toms / BTO

Author(s): Evans, L. C., Melero, Y., Schmucki, R., Boersch-Supan, P. H., Brotons, L., Fontaine, C., Jiguet, F., Kuussaari, M., Massimino, D., Robinson, R. A., Roy, D. B., Schweiger, O., Settele, J., Stefanescu, C., van Turnhout, C. A., & Oliver, T. H.

Published: May 2022  

Journal: Global Ecology and Biogeography

Digital Identifier No. (DOI): https://doi.org/10.1111/geb.13527

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Projected increases in the magnitude and frequency of extreme weather events are likely to have important consequences for species and the wider communities of which they are a part. Understanding the impacts of such events on the complex relationships that exist between the species within a particular ecosystem, and which themselves influence the stability and functioning of that ecosystem, is a conservation priority.

Abstract

Aim: It is important to understand the factors affecting community stability because ecosystem function is increasingly at risk from biodiversity loss. Here, we evaluate how a key factor, the position of local environmental conditions within the thermal range of the species, influences the stability of butterfly communities at a continental scale.

Methods: We tested the following hypotheses about how species responses to temperature anomalies aggregate to influence stability: Hypothesis 1, species have contrasting responses to local temperature anomalies at opposing edges of their thermal range; hypothesis 2, communities with central thermal range positions have higher community stability; and the impacts of thermal range position on community stability are driven by hypothesis 3, population asynchrony, or hypothesis 4, additive population stability. Data were analysed at 876 sites for 157 species.

Results: We found some support for hypothesis 1, because there were interactions between thermal range and response to temperature anomalies such that species at different range edges could provide weak compensatory dynamics. However, responses were nonlinear, suggesting strong declines with extreme anomalies, particularly at the hot range edge. Hypothesis 2 was supported in part, because community stability increased with central thermal range positions and declined at the edges, after accounting for species richness and community abundance. Thermal range position was weakly correlated with asynchrony (hypothesis 3) and population stability (hypothesis 4), although species richness and population abundance had larger impacts.

Main conclusions: Future extreme heat events will be likely to impact species negatively across their thermal range, but might be particularly impactful on populations at the hottest end of the thermal range. Thermal range position influenced community stability because range edge communities were stable. However, the prediction of community stability from thermal range position is challenging because of nonlinear responses to temperature, with small temperature anomalies producing weak compensatory dynamics, but large extreme events synchronizing dynamics.

Butterflies, one of the most monitored and best-studied insect groups, are ideal for studying such questions, as this paper shows. Butterfly distributions are driven largely by abiotic factors, such as climate, and their population dynamics are driven by weather. We would expect their populations to be most abundant and stable near the centre of their niche range, and most sensitive to environmental variation at range edges. Using data collected through butterfly monitoring schemes operating in Finland, Spain and the UK, the team of researchers explored how the position of species within their thermal range influenced community stability when exposed to different temperature anomalies.

Four different hypotheses were tested: hypothesis one, species will have contrasting responses to temperature anomalies at different ends of their thermal ranges; hypothesis two, communities consisting of populations with central thermal range positions on average will be more stable; hypothesis three, communities composed of species from a mix of range positions will have contrasting population responses to temperature anomalies, leading to asynchrony in abundance and higher overall community stability; and hypothesis four, populations near the centre of species' thermal ranges will be more stable, meaning that communities with more populations at the thermal range centres will, overall, be more stable.

Hypothesis one was supported by the results, with the location of species within the thermal range influencing responses to local temperature anomalies, and populations at the hot edge of the range performing worse when faced with high-temperature anomalies. Hypothesis two was also supported by the results: after accounting for species richness and community abundance, community stability decreased towards the edges of the thermal range. The results provided less evidence in support of the remaining hypotheses; synchrony decreased only marginally towards the centre, and mean population stability declined towards the hotter range edge but did not noticeably peak at the range centre.

The results suggest that populations at the hot edge of the thermal range are, in general, more responsive to weather anomalies than those at the cold edge. The work demonstrates that the interaction of thermal range position and local anomalies influences both population change between years and community stability in butterflies at a broad biogeographical scale. The results imply that niche position is an important determinant of community and population stability, but also emphasise that the larger sensitivity of populations at the hot edge suggests that community stability at hot locations might be most impacted by climate change. Furthermore, the results suggest that relative niche position might be a simple but important indicator of the populations and communities most at risk from climate change.

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