Dynamics of fish communities and populations in five northern Wisconsin lakes from 1981--2001

Freshwater fish research has produced a large and divided literature concerning factors that influence fish population dynamics. Many studies have indicated thermal conditions, prey consumption, and predation pressure are key influences on year-class strength and fish communities. I explored a 21 year, five lake data set to identify critical life stages and causal drivers of fish temporal dynamics at the population, community and species scales. Variables used described aspects of temperature, predation, prey, competition, and species stock.; Explanatory models of fish year-class strength varied between populations. No single variable or group of variables was a universal element for any species or lake. Based on age 1 explanatory models I determined that fish of age 0 were more important in establishing temporal population dynamics. Variables referring to age 0 abundance and condition occurred more often than other variables in age 1 models. Age 0 temporal dynamics were influenced most strongly by thermal conditions and prey abundance.; Invasive species were identified as overarching drivers of fish community dynamics in lakes with high abundances of non-native crayfish (Orconectes rusticus and/or O. propinquus) or rainbow smelt (Osmerus mordax). Natural variation in abundances of native fishes related to climate variation may have helped invasive species become established. Fish species that competed with invasive species for prey (benthic invertebrates or zooplankton) became less abundant in the fish community as invasive species increased, while small, short lived generalist species ( Cyprinidae) and smallmouth bass increased in abundance.; A stream connection between two of the five lakes facilitated metapopulation dynamics between largemouth bass (Micropterus salmoides) and black crappie (Pomoxis nigromaculatus). Age 0 bass and crappie moved from the upstream uninvaded lake into the downstream invaded lake. Populations were synchronous and demographic data showed that only the upstream populations were self supporting, indicating that the downstream populations were in a sink habitat.; The five lakes were chosen as reference systems in 1981, but have changed in fish composition well beyond what was expected for relatively “pristine” lakes. If these lakes do represent reference systems then freshwater fish biodiversity in this and other “wilderness” lake districts may be at risk.