Native and introduced fish species richness in Chilean Patagonian lakes: Inferences on invasion mechanisms using salmonid-free lakes

Aim: Geographic patterns of species richness have been linked to many physical and biological drivers. In this study, we document and explain gradients of species richness for native and introduced freshwater fish in Chilean lakes. We focus on the role of the physical environment to explain native richness patterns. For patterns of introduced salmonid richness and dominance, we also examine the biotic resistance and human activity hypotheses. We were particularly interested in identifying the factors that best explain the persistence of salmonid-free lakes in Patagonia. Location: Chile (39° to 54°S). Methods: We conducted an extensive survey of 63 lakes, over a broad latitudinal range. We tested for the importance of temperature, ecosystem size, current and historic aquatic connectivity as well as measures of human activity (road access and land use) in determining patterns of native and introduced richness. Results: Introduced species richness was positively correlated with native richness. Native and introduced richness declined with latitude, increased with temperature and ecosystem size. Variation in native richness was related to historic drainage connections, while introduced richness and salmonid dominance were significantly affected by current habitat connectivity. We found a total of 15 salmonid-free lakes, all located in remote areas south of 45°S, and all upstream of major naturally occurring physical barriers. Main conclusions: Temperature, as a correlate of latitude, and lake size were key determinants of native and introduced species richness in Chilean lakes and were responsible for the positive correlation between native and introduced richness. We found no evidence for biotic resistance by native species to salmonid expansion, and although the original introductions were human-mediated, current patterns of introduced richness were not related to human activity, as measured by road access or land use. Rather, environmental factors, especially habitat connectivity and temperature, appear to limit salmonid expansion within Chilean freshwaters.