Evolutionary potential but not extinction risk of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) is associated with stream characteristics

Abstract

Habitat fragmentation represents a major extinction threat for species of all taxa. Isolated populations have a higher risk of local extinction because of environmental variability and demographic processes associated with small populations. Here we examine the relationships among isolation, habitat size, habitat characteristics and variability, and genetic effective population size with extinction risk for 10 isolated and three interconnected populations of Lahontan cutthroat trout ( Oncorhynchus clarkii henshawi ) sampled from throughout their range. Contrary to expectations, we did not find a relationship between most habitat variables and extinction risk. However, we did find strong relationships between habitat variables and genetic effective population size, including a significant negative correlation between pool density and effective population size. Small effective population sizes can result in reduced genetic variation and losses of evolutionary potential and adaptability to changing environments. The absence of strong habitat correlates with extinction risk — despite an observed relationship with effective population size — highlights the need to consider habitat diversity at multiple spatial scales when considering management scenarios to both promote population persistence and maintain evolutionary relevance.