Some like it hot: from individual to population responses of an arboreal arid‐zone gecko to local and distant climate

Abstract

Accumulating evidence has demonstrated considerable impact of climate change on biodiversity, with terrestrial ectotherms being particularly vulnerable. While climate‐induced range shifts are often addressed in the literature, little is known about the underlying ecological responses at individual and population levels. Using a 30‐yr monitoring study of the long‐living nocturnal gecko Gehyra variegata in arid Australia, we determined the relative contribution of climatic factors acting locally (temperature, rainfall) or distantly (La Niña induced flooding) on ecological processes ranging from traits at the individual level (body condition, body growth) to the demography at population level (survival, sexual maturity, population sizes). We also investigated whether thermoregulatory activity during both active (night) and resting (daytime) periods of the day can explain these responses. Gehyra variegata responded to local and distant climatic effects. Both high temperatures and high water availability enhanced individual and demographic parameters. Moreover, the impact of water availability was scale independent as local rainfall and La Niña induced flooding compensated each other. When water availability was low, however, extremely high temperatures delayed body growth and sexual maturity while survival of individuals and population sizes remained stable. This suggests a trade‐off with traits at the individual level that may potentially buffer the consequences of adverse climatic conditions at the population level. Moreover, hot temperatures did not impact nocturnal nor diurnal behavior. Instead, only cool temperatures induced diurnal thermoregulatory behavior with individuals moving to exposed hollow branches and even outside tree hollows for sun‐basking during the day. Since diurnal behavioral thermoregulation likely induced costs on fitness, this could decrease performance at both individual and population level under cool temperatures. Our findings show that water availability rather than high temperature is the limiting factor in our focal population of G. variegata. In contrast to previous studies, we stress that drier rather than warmer conditions are expected to be detrimental for nocturnal desert reptiles. Identifying the actual limiting climatic factors at different scales and their functional interactions at different ecological levels is critical to be able to predict reliably future population dynamics and support conservation planning in arid ecosystems.

Functional traits determine the different effects of prey, predators, and climatic extremes on desert reptiles

“…Climatic data from the weather station closest to Kinchega (station 047019 Menindee Post Office; Bureau of Meteorology, Australian Government) matched the local conditions very well (Grimm‐Seyfarth et al. ). We chose climatic parameters that likely affect the lizards and the biotic conditions in late summer (Table ; see for details): summer mean maximum temperature; the number of days warmer than 45°C reflecting the number of days exceeding all species’ critical thermal maxima (Table ); the summed summer and the summed previous winter rainfall, both known to affect vegetation in summer (Robertson ); and the averaged summer and winter river heights of the adjacent Darling River at the closest weir (weir 32; Department of Primary Industries, Office of Water, New South Wales Government) since both vegetation (Shmida et al.…”

“…Higher summer temperatures usually increased occupancy, suggesting potential strategies on individual level that compensate effects on population level (Adolph and Porter , Grimm‐Seyfarth et al. ). Eremiascincus richardsonii was the only species that declined in occupancy with increasing temperature, but it was also the only habitat generalist whose favorite habitat, an adjacent sand dune, was not included in the three study plots (Henle ).…”

“…) and lizard species (Grimm‐Seyfarth et al. ) are likely affected by floodplain dynamics. Previous analyses indicated that Darling River heights were strongly related to the ENSO phenomenon (Grimm‐Seyfarth et al.…”

“…), or a combination thereof (Barrows , Grimm‐Seyfarth et al. ). However, no climatic factor will affect reptiles only directly but rather through multiple pathways (Ockendon , Deguines et al.…”

“…We expected that biotic factors are at least as important as climatic factors (Ockendon ), but that the effects differ between the individual level and the population level (Grimm‐Seyfarth et al. ). The eight lizard species differed in their functional traits (Table ), which could potentially explain different reactions among species (Read et al.…”