Bruce J. Stephen

Woody Invasions of Urban Trails and the Changing Face of Urban Forests in the Great Plains, USA

Abstract Corridors such as roads and trails can facilitate invasions by non-native plant species. The open, disturbed habitat associated with corridors provides favorable growing conditions for many non-native plant species. Bike trails are a corridor system common to many urban areas that have not been studied for their potential role in plant invasions. We sampled five linear segments of urban forest along bike trails in Lincoln, Nebraska to assess the invasion of woody non-native species relative to corridors and to assess the composition of these urban forests. The most abundant plant species were generally native species, but five non-native species were also present: white mulberry (Morus alba), common buckthorn (Rhamnus cathartica), tree-of-heaven (Ailanthus altissima), honeysuckle (Lonicera spp.) and elm (Ulmus spp.). The distribution of two of the woody species sampled, common buckthorn and honeysuckle, significantly decreased with increasing distance from a source patch of vegetation (P  =  0.031 and 0.030). These linear habitats are being invaded by non-native tree and shrub species, which may change the structure of these urban forest corridors. If non-native woody plant species become abundant in the future, they may homogenize the plant community and reduce native biodiversity in these areas.

Fecundity of the Chinese mystery snail in a Nebraska reservoir

The Chinese mystery snail (Bellamya chinensis) is a non-indigenous, invasive species in freshwater ecosystems of North America. We provide fecundity estimates for a population of these snails in a Nebraska reservoir. We dissected 70 snails, of which 29 were females. Nearly all female snails contained developing young, with an average of 25 young per female. Annual fecundity was estimated at between 27.2 and 33.3 young per female per year. Based on an estimated adult population and the calculated fecundity, the annual production for this reservoir was between 2.2 and 3.7 million young.

A conservation assessment of the freshwater gastropods of South Dakota based on historical records and recent observations

In South Dakota, like most U.S. states, up-to-date knowledge of the distribution of freshwater gastropod species is lacking and historical data suffers from a host of synonyms. I consulted literature records and online museum databases to compile a list of freshwater gastropods historically recorded for South Dakota. I used systematic studies and regional records to evaluate each historically-listed species reducing 54 nominal species to 25 expected to inhabit South Dakota. This, along with recent survey data from across the state, enable a benchmark conservation status to be established for the freshwater gastropods of South Dakota. My preliminary conservation evaluation indicates Planorbula armigera is critically imperiled (S1), while three species; Ferrissia rivularis, Campeloma decisum, and Amnicola limosus are imperiled (S2). The status of historical species not observed recently, and suspected inhabitants known from adjacent states are discussed.

Thermal Tolerance Limits of the Chinese Mystery Snail (Bellamya chinensis): Implications for Management

Abstract: The Chinese mystery snail, Bellamya chinensis (Gray, 1834) is a gastropod native to East Asia and is considered an invasive species in North America where its impacts on native species and ecosystems are not well understood. Scientific literature describing its biology and life history are sparse. Thermal tolerance limits, or the maximum and minimum temperature under which a species can survive, are key to identifying the potential geographical range of a species. The ability of managers to control invasive species is directly impacted by the thermal tolerance limits of a species. We attempted to identify the thermal tolerance limits of B. chinensis in a laboratory setting. Using a random sampling design, we exposed groups of wild-caught B. chinensis to either extreme high or low temperature treatments. We identified the upper temperature tolerance limit as between 40 and 45 °C. This result indicates some hot water management techniques may successfully prevent spread of B. chinensis among waterways. Despite exposing B. chinensis to freezing temperatures for extended periods of time we did not identify a lower temperature limit. Identifying the thermal tolerance limits of this and other invasive species informs predictions of range expansion and identification of potential prevention efforts.

Species Composition of Nebraska's Freshwater Gastropod Fauna: A Review of Historical Records

Abstract: Freshwater gastropods are important components of aquatic ecosystems yet little is known of their distribution and abundance in most states. To clarify historical species presence in Nebraska, I created a database from literature and museum records to catalog each species of freshwater gastropod. Records provided a list of more than 80 provisional species of freshwater snails in the state. I then evaluated each species for possible misidentification and/or synonyms based on known geographic ranges and systematic studies thereby reducing the number of species expected to be present in Nebraska to 31, including one non-indigenous species. I suspect eight species are rare based on the number of records.