PARENT SESSION
Symposium #3: The role of spatial extent in ecological pattern and process.
Sponsored by ESA Vegetation Section
Organized by: J. Nekola and H.H. Wagner.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Madison Ballroom B
Landscape patterns of aquatic invaders: Assessing the extent of zebra mussel dispersal from spatial distributions.
Kraft, Clifford 1, Sullivan, Patrick 1, Karatayev, Alexander 2, Burlakova, Lyubov2, Nekola, Jeffrey3, Johnson, Ladd4, Padilla, Dianna 5, 1 2 3 4 5
ABSTRACT- Assessing the spatial pattern of organisms across landscapes is a key step in determining processes that produced those patterns. The spatial distribution of an invasive aquatic species, the zebra mussel Dreissena polymorpha, was examined in two lake-rich areas (Belarus and midwestern U.S.) with similar environmental conditions but contrasting invasion histories. Second-order spatial point pattern analysis techniques (Ripley's K) were used to determine spatial scales of aggregation and segregation of invaded lakes. Monte Carlo simulations were used to compare observed distributions to random selections from the underlying lake distribution pattern. Both study areas showed aggregation of invaded lakes at similar spatial scales: less than 80 km in Belarus and less than 50 km in the midwestern U.S. Segregation was found at spatial extents greater than 120 km for invaded Belarus lakes, and a trend towards segregation was found at spatial extents greater than 200 km for U.S. lakes. Observed spatial scales of aggregation likely reflect the maximal scale of secondary geographic spread operating in these landscapes, whereas the longer distances at which segregation was evident likely represent the spatial scale of the initial long-distance dispersal events from source populations. Isolated Belarus lakes were less likely to be invaded than those connected by waterways. An analysis of distances from invaded lakes to the nearest invaded lake among connected Belarus lakes indicated that within connected waterways, zebra mussel dispersal occurred at distances less than 15 km. A one-dimensional Ripley's K analysis of invaded lake distributions along connected Belarus waterway corridors failed to show aggregation of invaded lakes. Based on the observed spatial pattern, we conclude that this invasive species has not yet saturated European and North American lake landscapes, and many suitable Belarus lakes have not yet been invaded. A similar aggregated distribution in the U.S. suggests that similar processes are affecting zebra mussel spread in the North American landscape.
KEY WORDS: spatial patterns, invasive species, lakes, dispersal