Potential Inland Distribution of
Invasive Species
in the Lake Michigan Basin
Abstract | Introduction | Data and Methods | Results | Discussion | Contact
Data and Methods
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Data Data were obtained through the Great Lakes Information Network, which compiles various spatial data sets relevant to the Great Lakes basin. The following data layers were used in the analysis:
Methods
Analyses
were performed using ArcGIS 10. All data layers were projected with
NAD_1983_Great_Lakes_Basin_Albers and clipped to the appropriate
area using the Lake Michigan Basin outline as a mask. Determining where invasive species are able to disperse Appropriate buffer distances were determined for sea lampreys, quagga mussels, and zebra mussels based on their previous ability to disperse inland. Zebra mussel points generally covered to the edge of the basin, and data points extended beyond the boundary before clipping the layer, so their buffer was made to extend the entire basin. For sea lamprey and quagga mussels, their dispersal distance in the area was taken to be the distance of the furthest point from the boundary of Lake Michigan, found with Point Distance in Arc Toolbox. The buffer distances were as follows:
The potential dispersal distance buffers were intersected with accessible spawning routes in the basin, which could serve as suitable habitat to facilitate their spread. The selected area for sea lampreys , quagga mussels , and zebra mussels were mapped. To determine where the different species' likely dispersal areas overlapped with each other, the Intersect tool was used to determine the overlap of areas for zebra mussel & sea lamprey only , zebra mussel & quagga mussel only , and all three . To determine where only zebra mussels were likely to be, the Clip tool was used to remove areas that were relevant to the other two species from the zebra mussel area.
Comparing invasive species in the different states and counties The original species points were mapped according to county. All counties were aggregated into a single polygon using the Overlay tool. A Spatial Join was used to associate the species occurrence points with the counties. State polygons were created by clipping the Lake Michigan Basin polygon to each state's county polygon and used for the purpose of showing state outlines. V alues displayed on the maps are of invasive species occurence by county, and represent [absolute number of species points]/[area of the county within the basin]. The generated potential species dispersal areas were also mapped by county. Four different maps were created -- one for each for the potential distribution of "zebra mussels only," "zebra mussels & sea lampreys only," "zebra mussels & quagga mussels only," and "all three invasive species". To accomplish this, a Spatial Join was used to link counties with the potential distributions generated earlier. Values mapped represent the the percent of the total potential habitat in the entire basin to show the relative weight that should be put on emphasizing monitoring efforts in each county. |
