Maintaining Local Adaptation Is Key for Evolutionary Rescue and Long-Term Persistence of Populations Experiencing Habitat Loss and a Changing Environment.

The Anthropocene is marked by increased population extirpations and redistributions driven primarily by human-induced climate change and habitat loss. Habitat loss affects populations by removing occupiable area, which reduces carrying capacity through a reduction in resources, and fragmenting the landscape, which can reduce gene flow with potential consequences for adaptation to changing environmental conditions. Real patterns of habitat loss are non-random, often clustered in space and within a subset of environmental conditions (e.g., primarily in the valleys of a mountain-valley region). Spatial clustering of habitat loss can alter population connectivity, and environmental clustering can shift the mean as well as decrease the variance in environmental conditions available to populations. We evaluate how spatial and environmental biases underlying habitat loss impact the survival of populations (as a proxy of evolutionary rescue) exposed to both habitat loss and environmental change. To do this, we simulated landscapes with a spatially autocorrelated temperature gradient to which individuals were locally adapted. These landscapes were then subjected to both nonrandom habitat loss (e.g., clustered based on the temperature) and increasing temperatures. We find that evolutionary rescue in response to increasing temperatures is hampered when habitat loss results in small patches, reduces the breadth of environmental conditions, and is concentrated on the cooler end of the temperature gradient. Our findings highlight the importance of maintaining a wide breadth of environmental conditions available to populations subjected to habitat loss, and the disproportionate role that colder sites play as a buffer to increasing temperatures, compared to warmer sites. Our findings also add a new dimension to the single large or several small (SLOSS) conservation discussion, stressing the importance of environmental diversity regardless of patch size.