Asymmetric competition shapes amphibian response to rapid environmental change

Abstract

Pond‐breeding amphibians experience climatic variability primarily in the form of seasonal temperature fluctuations and water availability, two factors that are strongly influenced by shifts in climate. Larval amphibians are concurrently exposed to biological stressors, such as competition and predation, as they often co‐occur in diverse, multi‐species assemblages. Thus, to accurately predict species’ response to climate change, we empirically tested the interaction between a biotic and abiotic driver. We focused on three amphibian species that overlap in distribution and phenology across high elevations of the Cascade Mountain Range of the U.S. Pacific Northwest: the Pacific chorus frog (Pseudacris regilla), Cascades frog (Rana cascadae), and Western toad (Anaxyrus boreas). Amphibians in this region are threatened by drought‐induced habitat loss resulting from the shortened hydroperiod and, in some areas, complete elimination of seasonal wetlands. We conducted a fully factorial experiment to determine the interactive effects of competition and drying on amphibian growth, development, and survival. We found that the impact of drying on each species was largely dependent upon interspecific competition dynamics. Competitive interactions, particularly in the three‐species competition treatment, exacerbated the effects of drying, with both competition‐ and context‐dependent responses to these stressors. Through an analysis of species‐level effects, as well as an examination of secondary productivity (i.e., total biomass across treatments), we determined that Cascades frogs are the dominant competitor in this system owing to their larger body size and relative ability to withstand the stress of a rapidly drying hydroperiod. Our results suggest that ignoring biotic interactions in predictions of species response to climate change factors may be misleading.

Climate change and the biodiversity of alpine ponds: Challenges and perspectives

“…Alpine pond species richness decreased with increasing altitude (Oertli, 2010 ), as a function of increasingly constrained drivers of temperature (Oertli, 2010 ), hydroperiod (He et al., 2016 ; Sandvik & Odland, 2014 ; Thurman & Garcia, 2019 ) and geographical connectivity (Hill et al., 2021 ; Oertli et al., 2008 ). Geographical connectivity of alpine ponds may be defined as the Euclidean distance from one pond to another, allowing direct comparison with species' dispersal distances, or the presence of tributaries connecting one pond to another.…”

“…Hydroperiod decrease can lead to modification of community composition, species traits and distribution, or to species disappearance. For example, mesocosm experiments linked lowered hydroperiod to reduced biomass of amphibian individuals at emergence (Thurman & Garcia, 2019 ). Reduced hydroperiod can also cause community composition modification and decrease of species distributions.…”

“…Annual hydroperiod—the timing and the length of time that there is standing water at a location (Convertino et al., 2013 )—is among the strongest filters for species persistence in alpine ponds (Ryan et al., 2014 ), and in ponds more generally (Wellborn et al., 1996 ). Hydroperiod decrease due to drying can affect species' size, phenology (Denoël, 2003 ; Galatowitsch & McIntosh, 2016 ), and geographical distribution (Sandvik & Odland, 2014 ; Thurman & Garcia, 2019 ). In addition to shrinking ecosystem surface area, drying reduces water volume and thermal inertia so that daily water temperature in shallow alpine ponds can fluctuate up to 30°C (Lund et al., 2016 ; Wissinger et al., 2016 ).…”

Numerical Analysis of Ordinary Differential Equations of Ecological Competing Species Across Diverse Environments

“…As stated above, species distributions can be influenced by the combined effects of biotic interactions and abiotic factors (Connell, 1961;Mittelbach, 2012;Ojonubah & Mohd, 2020). This is because the interactions of the biotic and abiotic factors are observed to determine how each factor affects the competing species (Amundrud & Srivastava, 2019;Gilman et al, 2010;Meier et al, 2011;Thurman & Garcia, 2019). For instance, environmental factor was demonstrated to mask the effect of biotic interactions among species (Godsoe et al, 2017).…”

Experimental warming and drying act independently on developmental responses for two amphibian species

“…Exploring and understanding the independent effects of climate‐mediated pressures, such as drying and temperature increases, on aquatic organisms and their habitats is an important step in predicting future responses to those pressures. However, many climate‐mediated pressures often co‐occur, and failing to account for their interactions may hinder efforts to predict amphibian response to climate change (Thurman & Garcia, 2019). As we continue to predict and assess the response of species to climate change, understanding the potentially diverse ways organisms with complex life cycles respond to climate change can help identify vulnerable life stages (Hodgson et al, 2016), disentangle relationships among biological drivers of vulnerability (Pearson et al, 2014), identify differences among species or within taxonomic groups (e.g., Foden et al, 2018; Mims et al, 2018), and improve mechanistic linkages among climate‐mediated environmental drivers and biological responses (e.g., Enriquez‐Urzelai et al, 2019).…”