Analysis of fish communities in Illinois lakes

Fish community structure and the main environmental factors influencing community structure were studied using a database of fish population surveys and limnological information describing 144 Illinois lakes. Data were collected by Illinois Department of Conservation fisheries biologists in a standardized manner using electrofishing and gill nets. Population survey data were adjusted using equations estimating efficiency of the gears under varying conditions resulting in estimates of biomass and number of fish per hectare;Guild systems were used to describe the communities and to simplify the analysis of fish community data thus allowing for comparison of community structure between lakes of varying species compositions. I used Balon\u27s reproductive guilds and developed new guild systems based on selected life history characteristics. Data for these life history characteristics were taken from the literature and analyzed using cluster analysis and correspondence analysis. This resulted in guilds based on spawning characteristics, trophic position, and habitat utilization and combinations of each of these. Analysis of guild dynamics revealed that the number of guilds present in a lake increased with lake size. The number of species representing each guild increased with lake size in some guilds, but was unrelated in others;Eighteen environmental parameters were estimated for the 144 lakes including descriptors of water chemistry, lake morphometry, age, location in watershed, and growing season length. Using principal components analysis, the variables were summarized into four major factors: lake size, north-south gradient, depth, and percent of lake as littoral zone. When lakes were classified using hierarchical cluster analysis, 11 categories of lakes were described;Species richness was best correlated with lake surface area and, secondarily, with conductivity. There were significant differences in species richness among lake categories, but this was mainly attributed to lake size. Species rank-abundance curves showed differences in abundance patterns related to lake size. Equitability of species abundance was negatively related with lake size and species richness;Fish species abundance and biomass was related to environmental variables using canonical correspondence analysis. Lakes within the 11 categories exhibited characteristic fish communities. The lake size gradient indicated that large lakes contain characteristic guilds comprised of several species primarily associated with large rivers. The north-south gradient was important in separating a group of five more northerly species from the remaining 37 species. It is postulated that environmental factors act in a hierarchical manner in influencing fish communities. Large-scale processes (climate and geology), local processes (lake size, connectance, etc.), and in-lake processes (predation, competition, etc.) all act to modify the potential community at different levels and each must be accounted for when studying processes at the other levels