For help, see the essay "Helping Your Students to Interpret Figures and Tables."
Figure 1A. A map of the Great Lakes including the St. Lawrence Seaway and the Erie Canal
(from Mills, E. L., J. H. Leach, J. T. Carlton, and C. l. Secor. 1994. Exotic species and the integrity of the Great Lakes.
BioScience 44: 666-676).
Figure 1B. A map showing the distribution of zebra mussels in the Great Lakes region in 1988
(USGS, 2003. Zebra Mussel Information: U.S. Distribution Maps, http://nas.er.usgs.gov/zebra.mussel/).
Figure 1C. A map showing the distribution of zebra mussels in the Great Lakes region in 1995
(USGS, 2003. Zebra Mussel Information: U.S. Distribution Maps, http://nas.er.usgs.gov/zebra.mussel/).
Figure 1D. A map showing the distribution of zebra mussels in the Great Lakes region in 2002
(USGS, 2003. Zebra Mussel Information: U.S. Distribution Maps, http://nas.er.usgs.gov/zebra.mussel/).