Technical Options
Policy Tools
Actual Practices

Theory v. Practice
Theory v.




Biodiversity and Species Protection
the economic perspective

Causes of Species Extinction

Increased Vulnerability to Extinction:
Because of some aspect of their natural history, some species have a higher risk of extinction than others.  Species that fit into the following categories are under greater extinction pressures than other species.  In addition, species that that fall into multiple categories have an even greater risk.

  • narrow geographical ranges--if the entire range is affected by human activity (not unlikely with smaller, more narrow ranges), then the species no longer has a supportive habitat and may go extinct

  • only one or a few populations--any one population may go extinct from human or natural causes (earthquakes, fires, disease, loss of habitat); the fewer populations comprising a species, the greater the risk of a population extinction leading to the species going extinct

  • population size is small--greater vulnerability to demographic and environmental changes and to loss of genetic variability; fewer individuals to provide genetic resistance to disease or environmental changes

  • low population density--these species will have fewer individuals per unit area and thus tend to have only small populations remaining if habitat is fragmented;

  • require a large home range--these species are more prone to extinction when part of their range is degraded or fragmented and range is thus reduced; the species will not have the required habitat size necessary for survival and could be subjected to increased extinction pressures.  Example: the brown bear of North America or the North American mountain lion both require large ranges for roaming and hunting.  When these ranges are reduced, the species is often forced to continue hunting and roaming in human-occupied areas.  This often results in injury or death of the animals.

  • low rates of population increase--these species tend to have delayed reproduction to an advanced age and tend to produce fewer, larger young; they are often unable to rebuild populations to a viable size fast enough after a sudden decrease, possibly due to disease or hunting/predation pressures;  Example:  elephants produce their first offspring nearly 10 to 15 years into life and may have only 10 to 12 young in a lifetime.  If the young of an elephant population are killed, then the population has only the older, less reproductively active individuals to increase the herd size.  Once these older individuals are dead, there may be too few elephants left for the population to remain viable.

  • migratory behaviors--migratory species depend on two or more distinct habitats; if any one of these habitats is destroyed, reproduction may be seriously impaired because food resources or reproductive habitats have been destroyed.  Example:   the sea turtle migrates back to land for breeding purposes.  Many of the beaches used for breeding have been developed by humans, and the turtles can no longer lay their eggs there or the young that hatch are in jeopardy because of the human contact.

  • little genetic variability--reduced genetic variability can result in reduced adaptability to changes in the environment;  it also reduces resistance to diseases and/or predators.  Example:  the cheetah of Africa exhibits exceptionally low levels of genetic diversity (levels that are expected only after 10-20 generations of brother-sister matings only).  Consequently, the cheetah suffers from a serious lack of disease resistance, reduced litter sizes, and weak or infertile offspring.

  • specialized niche requirements--these species often require one or two particular resources, generally a habitat type or food item; if these resources are altered or destroyed, the environment may no longer be suitable for the species survival.   Example:  the giant panda of Asia subsists solely on a diet of bamboo.   If the bamboo forests are cleared for farming or livestock, the panda will go extinct.

  • hunted or harvested by people--the selfish, utility-maximizing behavior of humans often leads to overhunting and overharvesting because of the "more is better" and "now" mentality.  Example:  the buffalo of the American West were hunted to near extinction because of the economic value of their hides and tongues.

Habitat Destruction, Degradation, and Fragmentation:
Habitat is necessary for any species to survive.  It provides the necessary elements of life--shelter, food, etc.   Without a healthy habitat, the species will not have those necessary elements. 

A study by Elizabeth Losos found that "natural resource extraction activities are wholly or partly responsible for endangering 62 to 68 percent of all species formally listed as at risk of extinction" in this country.  These extraction activities are subsidized at an estimated $1 billion annually.  Taxpayers also fund the species protection activities, costing many millions more.  This perverse policy amounts to a "double burden" on society.

Exotic Species Introduction:
All too often exotic species (species that are not native to the area) are introduced into habitats in which the native species cannot compete.  The exotic species monopolizes the resources for survival and the native species, without access to required resources, cannot reproduce.

The School of Public and Environmental Affairs
Copyright 1999 Indiana University Bloomington
Comments: kenricha@indiana.edu