Elevation alters outcome of competition between resident and range‐shifting species

Abstract

Species’ geographic range shifts toward higher latitudes and elevations are among the most frequently reported consequences of climate change. However, the role of species interactions in setting range margins remains poorly understood. We used cage experiments in ponds to test competing hypotheses about the role of abiotic and biotic mechanisms for structuring range boundaries of an upslope range‐shifting caddisfly Limnephilus picturatus. We found that competition with a ubiquitous species Limnephilus externus significantly decreased L. picturatus survival and emergence at subalpine elevations supporting the notion that species interactions play a critical role in determining upslope range limits. However, without competitors, L. picturatus survival was greater at high‐elevation than low‐elevation sites. This was contrary to decreases in body mass (a proxy for fecundity) with elevation regardless of the presence of competitors. We ultimately show that species interactions can be important for setting upslope range margins. Yet, our results also highlight the complications in defining what may be abiotically stressful for this species and the importance of considering multiple demographic variables. Understanding how species ranges will respond in a changing climate will require quantifying species interactions and how they are influenced by the abiotic context in which they play out.

Competition mediates understorey species range shifts under climate change

“…For all focal species, the SDMs predicted substantial amounts of suitable habitat beyond their current ranges, indicating that species' potential ranges are considerably larger than their realized ranges. These results corroborate previous modelling and experimental work, suggesting that also non‐climatic factors are important in setting range limits (Louthan et al, 2015; Sanczuk et al, 2022; Shepard et al, 2021). For example, Svenning et al (2008) showed that the ranges of many plants native to European forests are still subject to post‐glacial dispersal limitation (Svenning et al, 2008).…”

“…These results corroborate previous modelling and experimental work, suggesting that also non-climatic factors are important in setting range limits (Louthan et al, 2015;Sanczuk et al, 2022;Shepard et al, 2021). For example, Svenning et al (2008) showed that the ranges of many plants native to European forests are still subject to post-glacial dispersal limitation (Svenning et al, 2008).…”

“…This conclusion contests Species Interaction—Abiotic Stress hypothesis, posing that at the environmental stressful end of a species' distribution, mainly abiotic factors determine range limits, while in environmentally suitable areas, mainly biotic interactions regulate the spatial distribution of species (Darwin, 1859; Louthan et al, 2015). However, Shepard et al, 2021 recently formulated an alternative ‘Apparent Climatic Exclusion’ (ACE) hypothesis based on the idea that both abiotic conditions biotic interactions act in concert to determine species distributions (Shepard et al (2021), and references therein). Under this hypothesis, populations growing in abiotic stressful environments have inherent slow growth rates (with λ marginally larger than 1).…”

“…Although one would expect structured patterns in range shifts that closely match the unidirectional upslope and poleward moving isotherms, documented range responses to climate change are more complex, with slower, absent or even disparate trends frequently observed (Chen et al, 2011; Lenoir et al, 2020). This suggests that factors other than macroclimate change are also mediating species redistributions (De Frenne et al, 2013; Nathan et al, 2011; Sanczuk et al, 2022; Shepard et al, 2021; Zellweger et al, 2020). Based on the idea that mainly abiotic factors structure range limits at the cold ends of a species' distribution (Darwin, 1859; Louthan et al, 2015), macroclimate has been traditionally identified as the key driver of the distribution of species at large spatial scales (>10,000–200 km), whereas biotic interaction effects were considered more important at smaller scales (<10 km–0.1 m) (Wisz et al, 2013).…”

“…Based on the idea that mainly abiotic factors structure range limits at the cold ends of a species' distribution (Darwin, 1859; Louthan et al, 2015), macroclimate has been traditionally identified as the key driver of the distribution of species at large spatial scales (>10,000–200 km), whereas biotic interaction effects were considered more important at smaller scales (<10 km–0.1 m) (Wisz et al, 2013). A growing body of research now points towards the importance of local‐scale microclimatic conditions (De Frenne et al, 2013; Lembrechts et al, 2019) and biotic interactions (Alexander et al, 2015; Araújo & Luoto, 2007; Sanczuk et al, 2021; Shepard et al, 2021) in shaping species ranges at large scales. Hence, not only the macroclimate, but also microclimatic conditions biotic interactions should be considered to accurately predict species distributions (Pearson & Dawson, 2003).…”