Low desiccation and thermal tolerance constrains a terrestrial amphibian to a rare and disappearing microclimate niche

Abstract

Drier and hotter conditions caused by climate change threaten species that exist close to their physiological limits, as well as those with limited ability to move. Habitat specialists may also be particularly vulnerable if they have specific abiotic requirements. Here we assess whether thermal and hydric constraints can explain the highly restricted and declining distributions of the critically endangered terrestrial-breeding frog, Geocrinia alba. We also evaluate the species’ vulnerability to climate change based on the similarity of current microclimatic conditions to their physiological limits. We found that G. alba had low thresholds of thermal and desiccation tolerance relative to other anuran species. The estimated thermal optimum (Topt) and critical thermal maxima (CTmax) were 23.3°C and 29.6°C, respectively, and adult frogs had an absorption threshold (AT, the lowest water potential at which water can be absorbed from a substrate) of −50 kPa, the lowest recorded for an amphibian. Comparing environmental conditions and water loss in the field using agar models showed that riparian habitats where frogs occur provide a unique microclimate in the landscape, offering significantly lower desiccation risk during extreme summer conditions compared to immediately adjacent riparian and terrestrial habitats. Monitoring of microclimate conditions within occupied frog habitats over 2 years showed that in extreme dry and hot years the AT was exceeded at six of eight sites, and Topt was exceeded at two of eight sites. Given their specific physiological limits, the apparent rarity of suitable microclimates and a regional drying–warming trend, we suggest that G. alba occupies a potentially disappearing niche and may be indicative of other habitat specialists that rely on ephemeral drainages. More broadly, this study highlights that desiccation thresholds may tightly constrain amphibian distributions and need to be considered along with thermal tolerance thresholds when predicting the impacts of climate change.

Surviving on the edge: present and future effects of climate warming on the common frog (Rana temporaria) population in the Montseny massif (NE Iberia)

“…S5 ), they failed to confidently predict the local extinction of the species. Amphibians are mostly low vagile and small vertebrates which rely on microclimatic conditions ( Smith & Green, 2005 ; Hoffmann, Cavanough & Mitchell, 2021 ), far from the scope of the climatic niche analysis. Range contraction is frequently predicted by climatic niche modelling in analysis of the consequences of global warming in cold-adapted species ( Pauli et al, 2012 ; Ernakovich et al, 2014 ).…”

Heat-Induced Hatching of Red-Eyed Treefrog Embryos: Hydration and Clutch Structure Increase Behavioral Thermal Tolerance

“…Such information may be especially important for terrestrial-breeding tropical species, whose eggs are considered particularly vulnerable to climate change ( von May et al. 2017 ; Hoffmann et al. 2021 ).…”

Savanna vegetation increase triggers freshwater community shifts

“…The pond variables that we measured did consist of significant predictors of community structure and species occurrence, but the low coefficient of determination ( R 2 ‐value) associated with most of our models indicates that unmeasured factors, which likely include unmeasured terrestrial variables, may have contributed to freshwater community shifts. For example, changes in terrestrial habitats are expected to affect adult anuran survival by inducing changes in microclimate which can push amphibians to their physiological limits (Ernst & Rödel, 2005; Frishkoff et al, 2015; Hoffmann et al, 2021), or even result in altered predation rates on different species on land. Integrating information on coupled terrestrial–aquatic ecosystems can be challenging, but would be meaningful when studying organisms with complex life histories (Schreiber & Rudolf, 2008).…”

“…habitats are expected to affect adult anuran survival by inducing changes in microclimate which can push amphibians to their physiological limits (Ernst & Rödel, 2005;Frishkoff et al, 2015;Hoffmann et al, 2021), or even result in altered predation rates on different species on land. Integrating information on coupled terrestrial-aquatic ecosystems can be challenging, but would be meaningful when studying organisms with complex life histories (Schreiber & Rudolf, 2008).…”