One Migrant Too Many

Many endangered species have experienced rapid and dramatic population declines in the last century, resulting in severe fragmentation of the populations that remain. Nonetheless, much of the genetic diversity generated and maintained when populations were much larger still exists in extant meta-populations. Conservation plans typically recommend the facilitated transfer of one migrant per generation (OMPG) between isolated populations in order to maintain genetic diversity within populations and limit inbreeding depression. However, maintenance of meta-population connectivity via the OMPG strategy will result in the steady loss of historic genetic diversity in the meta-population as a whole. The loss of this genetic diversity may restrict the ability of populations to evolve when faced with new selective pressure. In contrast, the simple strategy of maintaining isolation between populations will retain the vast majority of diversity originally present in the species, thereby maximizing the supply of potentially adaptive variants when faced with environmental change. We evaluate the tradeoff between within-population diversity and total diversity using numeric calculations for various conservation scenarios and propose management strategies that account for this tradeoff in order to maximize the long-term survival of the species.