Abstract
Understanding the physiological tolerances of ectotherms, such as thermal limits, is important in predicting biotic responses to climate change. However, it is even more important to examine these impacts alongside those from other landscape changes: such as the reduction of native vegetation cover, landscape fragmentation and changes in land use intensity (LUI). Here, we integrate the observed thermal limits of the dominant and ubiquitous meat ant Iridomyrmex purpureus across climate (aridity), land cover and land use gradients spanning 270 km in length and 840 m in altitude across northern New South Wales, Australia. Meat ants were chosen for study as they are ecosystem engineers and changes in their populations may result in a cascade of changes in the populations of other species. When we assessed critical thermal maximum temperatures (CTmax) of meat ants in relation to the environmental gradients we found little influence of climate (aridity) but that CTmax decreased as LUI increased. We found no overall correlation between CTmax and CTmin. We did however find that tolerance to warming was lower for ants sampled from more arid locations. Our findings suggest that as LUI and aridification increase, the physiological resilience of I. purpureus will decline. A reduction in physiological resilience may lead to a reduction in the ecosystem service provision that these populations provide throughout their distribution.
Highlights
As temperature and rainfall patterns are becoming less predictable and more variable across many parts of the world (Coumou & Rahmstorf, 2012; Harris et al, 2018), understanding population and species responses are critical to understanding how ecosystem structure will change (Smith, 2011a, 2011b)
There was no consistent relationship between critical thermal minimums (CTmin) and critical thermal maximum temperatures (CTmax) across the 11 sites sampled (Fig. 1), suggesting no causal relationship between the two endpoints
The preferred model proposed for explaining meat ants CTmax across the landscape is: CTmax $ land use intensity (LUI) þ Canopy þ Exotic þ Clay þ Aridity þ ðCTminjSITE IDÞ
Summary
As temperature and rainfall patterns are becoming less predictable and more variable across many parts of the world (Coumou & Rahmstorf, 2012; Harris et al, 2018), understanding population and species responses are critical to understanding how ecosystem structure will change (Smith, 2011a, 2011b). Understanding the impacts on species from exposure to extreme temperatures is critical, for ectotherms and poikilotherms. Changes in precipitation patterns occur with rising temperatures, increasing rates of evapotranspiration (Dai, 2011) which can lead to aridification (Girvetz & Zganjar, 2014). In ecosystems with high temperatures and low available moisture (e.g. more arid environments), most individuals are less likely to perform well (Punzo, 1991) unless they have adapted to environmental water scarcity (Huang et al, 2015). We use the composite Aridity index which incorporates data on both rainfall and evaporation
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