HABITAT CHARACTERIZATION AND GEOSPATIAL METAPOPULATION DYNAMICS OF THREATENED FLOODPLAIN SPECIES BOLTONIA DECURRENS USING A GIS

The flood pulse of the Illinois River (Illinois, USA) has been distorted and the floodplain extensively modified as a result of human activity. This activity has changed the historic flood regime from moderate, late winter-early spring flood pulses, followed by a summer drawdown period, to a chaotic hydrology with floods occurring throughout the year. Boltonia decurrens (Torrey and Gray, Wood), federally listed as a threatened species, is endemic to the Illinois River floodplain. The species occurs as a large metapopulation; however, flood regime and habitat alteration have substantially reduced the size and number of populations within the metapopulation. We developed a geographic information system (GIS) to analyze habitat and geospatial population dynamics for B. decurrens. We analyzed floodplain land cover, identified specific wetland patches supporting B. decurrens, quantified habitat availability, habitat pattern, and analyzed the distribution of populations and individuals by wetland type and flood regime for the census period 1984– 2001. Our results show that floodplains of the navigation pools analyzed were dominated by row crop agriculture and forested wetlands with five land-cover types accounting for >90% of floodplain land-cover. Distribution analyses indicate that more populations and larger populations of B. decurrens occur on non-forested wetlands than forested wetlands. Habitat has been reduced for the species, and remaining habitat is highly fragmented with reduced connectivity. Patch occupancy rates were ≤ 1% for each pool and for all pools combined. Colonization and extinction rates fluctuated widely during this study, and there were no significant differences in the means of these rates for each individual pool and for all pools combined. Although during this study, there was relative stability between colonization and extinction rates, low patch occupancy combined with habitat reduction and reduced connectivity leaves the species vulnerable to extinction.