Land-use following a middle-road socio-economic pathway (SSP2) is not enough to recover mammal populations in Southern-Asia

Land use is the main direct driver of biodiversity loss and Southern-Asia is, globally, one of the regions under the highest land-use change. Here we estimate how mammals that play a key role in the ecosystem functioning will cope with landscape transformations. We used the a state-of-the-art spatially-explicit agent-based model (RangeShifter) combining local density-dependence on fecundity, stage-structured demographics and dispersal to predict the occupancy and abundance for large-body size carnivorous species (Panthera tigris, Panthera pardus) mid-sized and small carnivorous (Cuon alpinus, Felis chaus, Vulpes vulpes and Prionailurus bengalensis) and two Cetartiodactyla species (Sus scrofa and Gazella benetti) in Southern Asia. In addition, we estimated how species-richness changed through time. The model was projected to the period 1850 to 2100 under two socio-economic pathways, representing an intermediate scenario (SSP2-4.5) and a fossil-fueled development scenario (SSP5-8.5). We found mixed-response to land-use across species. We estimate the mean total proportion of remaining individuals to be 0.60 (SD = 0.24) under SSP2 and 0.64 (SD = 0.37) under SSP5 compared to baseline land use in 1850. The drop in the total number of occupied cells is of lower magnitude (SSP2: mean = 0.82, SD = 0.27; SSP5: mean = 0.84, SD = 0.32). Mean species richness per cell followed a decline throughout the 20th century (mean = 0.90, SD = 0.15) followed by increase from current time up to 2100 under both scenarios (SSP2: mean = 0.95, SD = 0.18; SSP5: mean = 0.97, SD = 0.22). Our results support biotic homogenization with spread of widespread species and restriction of forest-specialists. We confirm a disproportionate and negative influence of loss of non-disturbed patches, and lower landscape permeability in large mammals, potentially leading to considerable change in mammalian biomass in the ecosystem. These findings suggest that a middle-road socio-economic pathway (SSP2) is not enough to maintain or recover populations compared to pre-disturbance levels.