Bioclimatic variables
Yearly and seasonal patterns in temperature and precipitation are known to influence behaviour and life history in bats around the world (Conenna et al., 2019; Gorman et al., 2021; Kohyt et al., 2021; Weinberg et al., 2022). To capture these conditions and test the hypothesis that macroclimatic effects can determine occurrence of bats, the 19 standard current bioclimatic variables were sourced at 2.5 arc-minute resolution from the WorldClim v2.1 database for the period of 1970 to 2000 (Fick & Hijmans, 2017). We focused on this resolution (~4x4 km) considering, in the absence of detailed species-level information, that such distances are within the average foraging range and mobility of these species. Our study covers large taxonomic, spatial, and temporal scales that aim to capture broad environmental effects that are best detected using moderately coarse resolutions (Wiens et al., 2009). Finer resolutions are more suitable to detect smaller-scale behavioural effects (Pulliam, 2000) including movement, territoriality, and inter-species interactions in mixed colonies.
Four future climate predictions were obtained combining two different models and two different scenarios to capture uncertainty. We considered the Canadian Earth System Model 5 (CanESM5; Swart et al., 2019) and Hadley Centre Global Environment Model 3 (HadGEM3; Good, 2019; Good, 2020) available in the Coupled Model Intercomparison Project 6 (CMIP6) from which we obtained 2.5 arc-minute climate predictions for a near-future time (2050, averaged from 2041-2060). From each model, data were obtained for the shared socioeconomic pathways 2 and 5 (SSP2, equivalent to Representative Concentration Pathway RCP4.5; and SSP5, equivalent to Representative Concentration Pathway RCP8.5). These pathways, used by the International Panel on Climate Change, characterise an optimistic ‘middle of the road’ socioeconomic scenario representing an ideology towards sustainable development, and a pessimistic ‘fossil-fuelled development’ scenario of climate change based on development almost entirely based on fossil fuels in the future, and little development towards sustainability and an emphasis on resource- and energy-intensive lifestyles (Kriegler et al., 2017). The two CanESM5 models are hereafter referred to as Can2-45 for SSP2-RCP4.5 and Can5-85 for SSP5-RCP8.5, and the two HadGEM3 models as Had2-45 for SSP2-RCP4.5 and Had5-85 for SSP5-RCP8.5.
To allow for accuracy in model transfer and clarity in interpretation, bioclimatic variables in ENM models are usually selected a priorito avoid multicollinearity and variance inflation. The bioclimatic variables were first filtered using an assessment of ecological relevance based on field knowledge and literature (Stones & Wiebers, 1965; Grindal et al., 1992; Bates & Harrison, 1997; Appel et al., 2019; Corro et al., 2021). Then the variables were further filtered based on collinearity - noting that available ENM algorithms are not greatly impacted or can account for correlation and interaction between variables (Muñoz & Felicísimo, 2004; Dormann et al., 2012; Junior & Nobrega, 2018; Feng et al., 2019), and in some cases, correlated variables may be used if they are considered ecologically relevant. An analysis of multicollinearity was conducted using a combined variance inflation factor (VIF) and pairwise correlation test in the usdmpackage (Naimi et al., 2014) in R. Variables with an absolute pairwise Pearson’s r < 0.85 were selected for the analysis. When a variable pair had high correlation (r 0.85|), we removed the variable deemed to have least ecological relevance, but if both variables were considered ecologically relevant, the variable with the highest VIF was excluded instead. Additionally, collinearity shifts between current and future predictions were measured using paired t-tests of VIF scores for each variable, as these tend to impact model transferability (Feng et al., 2019). All climate data were cropped and masked to the extent of the study area defined above. A final set of 10 climate variables was selected for the analysis, which were considered ecologically relevant for South Asian bats, and showed no significant collinearity shifts between current and future scenarios (Supplementary Material 1). The same variables were used for all species for consistent interpretations.