Invasive Species Shifting Baselines
*A shifting baseline is a type of change to how a system is measured, usually against previous reference points (baselines), which themselves may represent significant changes from an even earlier state of the system.
A global map of commercial shipping, showing relative density (in color) against a black background. Ship ballast water discharge is one of the main ways invasive marine species are introduced.
Courtesy of http://www.nceas.ucsb.edu/globalmarine/impacts
Courtesy of http://www.nceas.ucsb.edu/globalmarine/impacts