Drought-Mediated Transitions Between Invasive and Native Species Dominance in North Temperate Lakes

Invasive species abundance is variable, and understanding the mechanisms driving this variation is a major research and management goal.  The rusty crayfish (Orconectes rusticus) is an invasive species that impacts all trophic levels of aquatic ecosystems, although rusty crayfish do not always achieve high densities and negatively affect native biota.  Recent drought conditions in the north temperate region have reduced available rusty crayfish habitat via lowered water levels in some lakes, potentially modifying their interactions with native food webs. We used a stage-structured time series model to evaluate the drivers of rusty crayfish and native fish abundance using 30 years of time-series data from two northern Wisconsin lakes and a whole-lake experimental crayfish removal.  Rusty crayfish density was influnced by a combination of sunfish (Lepomis spp.) density and water level.  The best-fit model predicted an interaction between water level, native fishes, and invasive crayfish, where both rusty crayfish and Lepomis could thwart the invasion of the other under certain water level conditions. Furthermore, rusty crayfish may be vulnerable to suppression/eradication under drought conditions. Climate projections predict both higher and lower than average precipitation regimes within the invaded range of rusty crayfish, and water level will influence the appropriate management strategy for this invasive species.