UCLA

Translocations are often necessary to reduce extinction risk for endangered species, but opportunities are usually constrained by limited available recipient habitat. In California, due to drastic declines in freshwater habitat, multiple aquatic species may require translocation to the same streams or ponds. However, interactions such as predation and competition could potentially impede the recovery of species translocated into the same sites. In this study we characterize interactions between two endangered species, the mountain yellow-legged frog (Rana muscosa) and unarmored threespine stickleback (Gasterosteus aculeatus williamsoni), to assess the potential for their coexistence following translocation. Using controlled laboratory experiments with R. muscosa tadpoles and a surrogate stickleback subspecies, the partially-armored threespine stickleback (Gasterosteus aculeatus microcephalus), we measured stickleback predation on tadpoles, tadpole interference in stickleback nesting, and impacts of both species on the habitat use of the other. Stickleback preyed on tadpoles that were small in size, but predation attempts on larger tadpoles were sub-lethal. Tadpoles had little to no impact on stickleback eggs and nesting behavior. In regard to interference in habitat use, when both species were present, stickleback moved to vegetated and shallower areas, while tadpoles shifted to deeper areas. This study is the first to describe interactions between these species and suggests that certain management strategies can facilitate the coexistence of translocated populations. Understanding how interactions among endangered species affect coexistence will inform co-management efforts and support species recovery.