Conservation in the Anthropocene: Using Genetics to Understand the Past and Manage for the Future of the Threatened Stephens' Kangaroo Rat

Abstract

Habitat loss and fragmentation are major drivers of biodiversity decline, reducing connectivity among populations and leading to genetic isolation, loss of diversity, increased inbreeding, and reduced fitness. Translocations that promote gene flow by introducing genetically distinct individuals—a process known as genetic rescue—can mitigate these effects by increasing genetic diversity, alleviating inbreeding, and improving adaptive capacity. However, a limited understanding of a population's demographic history, genetic differentiation, and connectivity can hinder the effective application of genetic rescue. We used the Stephens' kangaroo rat (Dipodomys stephensi), a species threatened by habitat loss and fragmentation in southern California, as a model for developing range-wide genetic management strategies. We analyzed mitochondrial DNA and microsatellite data to investigate genetic structure and estimate both historical and recent demographic patterns, and we used landscape resistance modeling to assess the impacts of natural and anthropogenic barriers on gene flow. Genetic analyses suggest a relatively recent diversification of Stephens' kangaroo rat populations, with higher allelic diversity concentrated in central populations and reduced diversity in isolated northern and southern populations. Although natural geographic features explain much of the genetic structure, landscape resistance models showed that anthropogenic barriers (e.g., roads, development) play a key role in current genetic isolation and are expected to continue driving population differentiation. To guide management, we used population viability simulations to test translocation strategies aimed at reversing genetic erosion. Repeated translocations were far more effective than single events at boosting heterozygosity and population persistence. The frequency and size of translocations were less important than their continued implementation. For very small populations, concurrent habitat restoration to increase carrying capacity was essential to prevent extirpation. Our findings highlight the value of integrating genetic, demographic, and landscape data into conservation planning. This approach is broadly applicable to other species experiencing habitat fragmentation and population isolation.