The figure above shows how expected community productivity changes as species go extinct in communities of symmetric competitors.  In each panel, the black line shows the effect of extinction when all species have the same probability of going extinct, and the red, green, and blue lines show the effect of extinction when the correlation between extinction probability and per capita productivity is strongly positive (red), weakly positive (green), or strongly negative (blue).  Alpha scales the degree of resource partitioning (alternatively, interspecific competition): alpha=0 corresponds to species that use distinct resources, and alpha=1 corresponds to species that compete for identical resources.  Each community begins with 10 species.  For more details, see Gross & Cardinale (2005).

Aphids in North Carolina