Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

A positive relationship has been documented for a wide diversity of taxa between the percentage of transects sampled in which a species is recorded (i.e., occupancy) and the average abundance of the species at transects where recorded. This positive relationship implies that abundance increases faster than occupancy, so populations that occupy more sites also tend to occupy them at higher abundances. Plainly, there is a limit to the sites available for a species to occupy, so as the population expands numerically, abundance at a site must also increase. The pattern may differ across species and geography depending on aspects such as species vital rates, resource use, and resource availability. I investigated abundance-occupancy patterns of three black basses Micropterus (Centrarchidae) in reservoirs of the mainstem Tennessee River, USA. The dataset included relative abundance estimates made at 7,237 sites in nine reservoirs sampled during 1997–2018 for 43,243 black bass including 67% Largemouth Bass M. salmoides, 14% Smallmouth Bass M. dolomieu, and 19% Spotted Bass M. punctulatus. As relative abundance increased due to natural annual population fluctuations, occupancy also increased but faster for Largemouth Bass and more slowly for Smallmouth Bass and Spotted Bass. Largemouth Bass abundance was spread more thinly over many sites, and Smallmouth Bass and Spotted Bass abundance was spread more thickly over fewer sites. The recognition that black bass populations that decline in occupancy face the additional burden of disproportionally larger decreases in abundance per site, or that black bass that decline in abundance per site face decreases in occupancy, has various conservation and habitat management implications