474 Natural Resources Systems Copyright Goodheart-Willcox Co., Inc. Overhunting and Overfi shing As evident by the near extinction of the American bison from hunting, removing too many animals from an environment can quickly lead to a spe- cies’ extinction unless efforts are made to protect the species. Overhunting or overfi shing reduces the number of breeding animals and reduces the genetic variation among the remaining animals. These factors make it diffi cult for the species to repopulate and will likely lead to genetic defects in offspring. See Figure 19-10. The passenger pigeon (Ectopistes migratorius) is an example of overhunting leading to extinction. The passenger pigeon, numbering in the billions, was once a plentiful and popular food source for North Americans in the 1800s. The birds were hunted until no passenger pigeons were found in the wild. There were no efforts made to protect the birds and attempts to breed them in captivity were unsuccessful. The last known specimen died at the Cincinnati Zoological Garden in 1914. Biodiversity and Ecological Health Biodiversity is the variety of organisms living in an ecosystem. Scientists have long theorized that biodiversity is critical to the ability of an ecosystem to provide benefits, such as oxygen production, nutrients for the soil, and clean water. A diverse ecosystem is one in which each spe- cies receives services needed from other species to ensure mutual survival. Recent studies conducted by the USGS have proven that it is not possible to have a sustainable, productive ecosystem without biodiversity in the landscape. “Restoring nature to its natural state is a cause beyond party and beyond factions. It has become a common cause of all the people of this country,” —Richard Nixon, US President Petr Salinger/Shutterstock.com Figure 19-10. The muskox (Ovibos moschatus), hunted for its hide, nearly became extinct in the 1930s due to overhunting and the American crocodile (Crocodylus acutus), hunted for its skin, was close to extinction in the late 1960s. Hunting regulations and the Endangered Species Act have helped increase populations of both species in the wild. Fitawoman/Shutterstock.com