Historical and Current Environmental Influences on an Endemic Great Plains Fish JESSE R. FISCHER 1 Kansas Cooperative Fish and Wildlife Research Unit, Division of Biology, Kansas State University, Manhattan 66506 AND CRAIG P. PAUKERT U.S. Geological Survey, Kansas Cooperative Fish and Wildlife Research Unit, Division of Biology, Kansas State University, Manhattan 66506 ABSTRACT.—Native fishes of the Great Plains are at risk of decline due to disturbances to physical habitat caused by changes in land and water use, as well as shifts in species assemblages driven by the invasion of introduced species with the loss of natives. We used historical and current fish assemblage data in conjunction with current habitat information to assess these influences on an endemic Great Plains stream fish, the plains topminnow (Fundulus sciadicus). Of the 31 sites where the plains topminnow occurred historically (1939– 1940), it was found in only seven of those sites in 2003–2005. Our results demonstrate a shift in fish assemblage over time that coincides with the loss of plains topminnow. Changes in fish assemblages were characterized by increases in occurrence of exotic, invasive and generalist species with declines in occurrences of native fishes. An information theoretic approach was used to evaluate candidate models of current fish assemblage and physical/chemical habitat on the presence of the plains topminnow. Candidate models that included both instream habitat (e.g., vegetation coverage, undercut banks) and the native fish species assemblage are important to predicting presence of the plains topminnow within its historic range. Conservation of Great Plains fishes including the plains topminnow will need a combination of habitat protection and enhancement. INTRODUCTION Freshwater fishes are at risk of decline in range and local abundance resulting in extirpation and eventual species loss due to widespread anthropogenic disturbances. Human impacts are the primary cause of decline and extinction of fishes (Miller et al., 1989; Williams et al., 1989; Richter et al., 1997; Ricciardi and Rasmussen, 1999). Disturbance to physical habitat (e.g., riparian vegetation alteration, impoundments; Gorman and Karr, 1978; Jones et al., 1999; Marchetti and Moyle, 2000; Quinn and Kwak, 2003), water quality (e.g., pollution, sedimentation; Tsai, 1973; Bonner and Wilde, 2002) and the introduction of nonnative species (Soule, 1990; Rahel, 2002) have resulted in fish assemblage shifts, decreased native species diversity, community homogenization, range reduction and extinction. The Great Plains, one of the largest biomes in North America, has been subjected to widespread disturbances to both its terrestrial and aquatic resources. The native grasslands (162 million ha) of the Great Plains are one of the nations most threatened ecosystems with losses of up to 99.9% in range (Samson and Knopf, 1994). However, the region’s aquatic ecosystems have received less attention compared to other regions (Matthews, 1988). 1 Present address: Department of Natural Resource Ecology and Management, Iowa State University, Ames 50011; e-mail: fischer@iastate.edu Am. Midl. Nat. 159:364–377 364