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Warming undermines emergence success in a threatened alpine stonefly: A multi‐trait perspective on vulnerability to climate change

https://doi.org/10.1111/1365-2435.14284

Shah, Alisha A. ; Hotaling, Scott ; Lapsansky, Anthony B. ; Malison, Rachel L. ; Birrell, Jackson H. ; Keeley, Tylor ; Giersch, J. Joseph ; Tronstad, Lusha M. ; Woods, H. Arthur ( February 2023 , Functional Ecology)

Abstract

Vulnerability to warming is often assessed using short‐term metrics such as the critical thermal maximum (CT_MAX), which represents an organism's ability to survive extreme heat. However, the long‐term effects of sub‐lethal warming are an essential link to fitness in the wild, and these effects are not adequately captured by metrics like CT_MAX.

The meltwater stonefly,Lednia tumana, is endemic to high‐elevation streams of Glacier National Park, MT, USA, and has long been considered acutely vulnerable to climate‐change‐associated stream warming. As a result, in 2019, it was listed as Threatened under the U.S. Endangered Species Act. This presumed vulnerability to warming was challenged by a recent study showing that nymphs can withstand short‐term exposure to temperatures as high as ~27°C. But whether they also tolerate exposure to chronic, long‐term warming remained unclear.

By measuring fitness‐related traits at several ecologically relevant temperatures over several weeks, we show thatL. tumanacannot complete its life‐cycle at temperatures only a few degrees above what some populations currently experience.

The temperature at which growth rate was maximized appears to have a detrimental impact on other key traits (survival, emergence success and wing development), thus extending our understanding ofL. tumana's vulnerability to climate change.

Our results call into question the use of CT_MAXas a sole metric of thermal sensitivity for a species, while highlighting the power and complexity of multi‐trait approaches to assessing vulnerability.

Read the freePlain Language Summaryfor this article on the Journal blog.

Abstract

Climate change is altering conditions in high‐elevation streams worldwide, with largely unknown effects on resident communities of aquatic insects. Here, we review the challenges of climate change for high‐elevation aquatic insects and how they may respond, focusing on current gaps in knowledge. Understanding current effects and predicting future impacts will depend on progress in three areas. First, we need better descriptions of the multivariate physical challenges and interactions among challenges in high‐elevation streams, which include low but rising temperatures, low oxygen supply and increasing oxygen demand, high and rising exposure to ultraviolet radiation, low ionic strength, and variable but shifting flow regimes. These factors are often studied in isolation even though they covary in nature and interact in space and time. Second, we need a better mechanistic understanding of how physical conditions in streams drive the performance of individual insects. Environment‐performance links are mediated by physiology and behavior, which are poorly known in high‐elevation taxa. Third, we need to define the scope and importance of potential responses across levels of biological organization. Short‐term responses are defined by the tolerances of individuals, their capacities to perform adequately across a range of conditions, and behaviors used to exploit local, fine‐scale variation in abiotic factors. Longer term responses to climate change, however, may include individual plasticity and evolution of populations. Whether high‐elevation aquatic insects can mitigate climatic risks via these pathways is largely unknown.