Abstract
Comparative influences of minnows (mainly fathead minnow Pimephales promelas), black bullhead Ameiurus melas, and common carp Cyprinus carpio on shallow lake ecosystems are poorly known, as are factors driving patterns of distribution of these species among lakes. We explored these relationships by studying 67 shallow lakes in three study regions in the southern half of Minnesota (USA) during 2010. We used ordinal regression to test for effects of lake size, watershed area, lake depth, and connection to another fish source on four types of fish communities: fishless (FISHLESS), minnows-dominant (MINNOWS), minnows + black bullhead (BULLHEADS), and minnows + black bullhead + common carp (CARP). We also used redundancy analysis to test whether the four types of fish communities differed in invertebrate community composition, water quality, and abundance of submerged plants. Results showed FISHLESS lakes were the least common and occurred in lakes with the smallest watersheds and no connection to a fish source. As watersheds became larger, fish communities became increasingly complex, starting with MINNOWS, then BULLHEADS, and finally CARP in the largest watersheds in lakes connected to a fish source. Ecosystem characteristics differed among the fish communities and reflected the same ordinal change in fish communities with increasing watershed area, as invertebrate and plant abundance was the highest, and phytoplankton and nutrient levels the lowest, in FISHLESS lakes. These variables changed in concert along the gradient to lakes with MINNOWS, then BULLHEADS, and ending with CARP having the lowest invertebrate and plant abundance and the highest phytoplankton and nutrient levels. Our results showed that lake connectivity and watershed area indirectly influence shallow lake characteristics by influencing fish community composition.