Can amphibians take the heat? Vulnerability to climate warming in subtropical and temperate larval amphibian communities

Abstract

Predicting the biodiversity impacts of global warming implies that we know where and with what magnitude these impacts will be encountered. Amphibians are currently the most threatened vertebrates, mainly due to habitat loss and to emerging infectious diseases. Global warming may further exacerbate their decline in the near future, although the impact might vary geographically. We predicted that subtropical amphibians should be relatively susceptible to warming-induced extinctions because their upper critical thermal limits (CT max ) might be only slightly higher than maximum pond temperatures (T max ). We tested this prediction by measuring CT max and T max for 47 larval amphibian species from two thermally distinct subtropical communities (the warm community of the Gran Chaco and the cool community of Atlantic Forest, northern Argentina), as well as from one European temperate community. Upper thermal tolerances of tadpoles were positively correlated (controlling for phylogeny) with maximum pond temperatures, although the slope was steeper in subtropical than in temperate species. CT max values were lowest in temperate species and highest in the subtropical warm community, which paradoxically, had very low warming tolerance (CT max -T max ) and therefore may be prone to future local extinction from acute thermal stress if rising pond T max soon exceeds their CT max . Canopy-protected subtropical cool species have larger warming tolerance and thus should be less impacted by peak temperatures. Temperate species are relatively secure to warming impacts, except for late breeders with low thermal tolerance, which may be exposed to physiological thermal stress in the coming years.

Effect of warming rate on the critical thermal maxima of crabs, shrimp and fish

“…Another important advantage of the CTMax method, in particular, is that it is sublethal, rather than lethal, and thus provides a reference for temperature tolerance that takes into account a more conservative thermal limit in which the organism does not die but is unable to escape predators and forage because of equilibrium loss. This means that CTMax results are more comparable to natural conditions, particularly those occurring in tidal pools and temporary ponds (Hiatt and Strasburg, 1960;Bennett and Judd, 1992;Mora and Ospina, 2001;Duarte et al, 2012;Vinagre et al, 2013). Climate change models predict that heat waves will increase in intensity, frequency and duration, this way tidal pools and temporary ponds will present a harder thermal challenge to their inhabitants.…”

“…It has also been widely used for other aquatic and non-aquatic organisms, such as shrimp, crabs, amphibians, molluscs and insects (e.g. McMahon 1990McMahon , 2001Terblanche et al, 2005;Deere and Chown, 2006;Hopkin et al, 2006;Duarte et al, 2012;Madeira et al, 2012a;Vinagre et al, 2013). It has also been applied in macrophysiological comparative studies in ectotherms (e.g.…”

“…Mora and Ospina, 2001;Duarte et al, 2012;Vinagre et al, 2013;Madeira et al, 2014aMadeira et al, , 2014b. The CTMax is quantified as the mean temperature at which individuals reach the critical point.…”

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

“…As a result, organisms across the globe will be more likely to experience temperatures beyond their physiological limits unless they can in some way buffer themselves from environmental change [2,3]. One mechanism that could greatly reduce the risk of overheating is physiological plasticity in thermal tolerance, such as the reversible changes in thermal tolerance known as acclimation (if measured in the laboratory) or acclimatization (if measured in the field) [4][5][6][7].…”

Physiological Stress Responses in Amphibian Larvae to Multiple Stressors Reveal Marked Anthropogenic Effects even below Lethal Levels

“…The introduction of novel predators may have a deep impact on local populations (Siesa et al 2011), in part because native prey are very likely to fail to recognize novel predators and hence fail to produce antipredator defenses, whether behavioral or morphological. Last, increased water temperature causes developmental acceleration, causing larvae to metamorphose smaller and with reduced hind limbs (Gomez-Mestre et al 2010;Duarte et al 2012).…”