Hikers as hosts: human recreational activity is a primary driver of relative mosquito abundance at alpine lakes

Abstract: Human-driven global change is reshaping ecological communities and driving broad declines and extirpations across many taxa, while creating unexpected opportunities for some synanthropic taxa. Mosquitoes, in particular, may be well-suited to thrive under certain anthropogenic impacts, with consequences for both ecosystems and public health. However, little is known about how these dynamics unfold in remote alpine ecosystems, which historically have supported low mosquito abundance but are now experiencing a suite of changes - including increased recreation, invasive species, and climate change - that may facilitate mosquito persistence and expansion. Here, we examined the role of invasive species, human recreation, and seasonal climate dynamics in shaping mosquito populations across alpine lakes in the Sierra Nevada of California, using two years of surveys spanning 27 lakes. Unsurprisingly, we found that mosquito emergence was tightly linked to lake ice-off timing, with abundance peaking 15-20 days post-ice-off and varying across years depending on snowpack regime. Interestingly, after accounting for seasonality, human activity was the next-0 strongest predictor of mosquito abundance. In fact, relative mosquito abundance is predicted to double with a 25-50% increase in recreational use. Furthermore, human DNA was dominant in mosquito blood meals even at the most remote sites, suggesting that even low levels of recreation could have major impacts on mosquito populations. In contrast, the presence of nonnative trout, another common change in alpine lakes, had no detectable effect on adult relative mosquito abundance despite their known suppression of larval mosquito predators. Together, these results suggest that alpine mosquito populations are more limited by host availability than by aquatic food-web structure, and that human recreation is already reshaping mosquito ecology even in wilderness contexts.