Biodiversity provides a hedge for Earth’s biota from a variety of assaults. Ecosystems have always been buffeted by natural occurrences such as extreme heat and cold, storms, natural disasters, and epidemics, but they withstand such onslaughts because of the diversity contained within them. Ecosystems survive disruptions according to what was
described in 1955 by Princeton University biologist Robert MacArthur as the Diversity-Stability Hypothesis. According to the hypothesis, less complex food webs with fewer interactions between species are more vulnerable than more complex food webs with more interactions between species. This is because in simple food webs each predator’s livelihood depends on a small variety of prey. If the predator’s habitat becomes threatened, it has few alternatives for survival. Complex food webs, by comparison, contain greater diversity of species and more alternatives for food chains to function. In other words, complicated ecosystems withstand threats better than simple ecosystems, which can also be thought of as sensitive ecosystems. Complex ecosystems possess what is called a buffering effect against potentially harmful environmental changes. The sidebar “Zebra Mussels” examines a situation in which native species lack a buffering effect and cannot adapt to an invasion.
The great horned owl is such a skillful predator it might also be considered an invasive species. It dominates almost all of North and Central America and is moving south through South America. Many less adaptive owls disappear from territory invaded by the great horned owl. In addition to other bird species, the great horned owl eats reptiles, amphibians, fish, insects, invertebrates, and mammals such as rodents, rabbits, skunks, and cats. (Gary M. Stoltz, U.S. Fish and Wildlife Service)
