A decline spiral is the destruction of a species , ecosystem , or biosphere in a continuing downward trend, leading to ecosystem disruption and impoverishment. The term is sometimes used to describe the loss of biodiversity , when a catastrophic event has led to a sharp decline in the number of organisms in a biological community .
In areas where the habitat is highly fragmented either due to human intervention or natural disaster, the loss of species is markedly accelerated. Loss of species diversity often initiates a downward spiral, as the weakening of even one plant or animal in an ecosystem, especially a keystone species , can lead to the malfunctioning of the biological community as a whole.
Biodiversity exists at several levels within the same community; it can include ecosystem diversity, species diversity, and genetic diversity. Ecosystem diversity refers to the different types of landscapes that are home to living organisms. Species diversity refers to the different types of species in an ecosystem. Genetic diversity refers to the range of characteristics in the DNA of the plants and animals of a species. A catastrophic event that affects any aspect of the diversity in an ecosystem can start a decline spiral.
Any major catastrophe that results in a decline in biospheric quality and diversity, known as an ecocatastrophe, may initiate a decline spiral. Herbicide and pesticide used in agriculture, as well as other forms of pollution ; increased use of nuclear power , and exponential population growth are all possible contributing factors. The Lapp reindeer herds were decimated by fallout from the nuclear accident at Chernobyl in 1986. Similarly, the oil spill from the Exxon Valdez in 1989 led to a decline spiral to the Gulf of Alaska ecosystem.
The force that begins a decline spiral can also be indirect, as when acid rain , air pollution , water pollution , or climate change kill off many plants or animals in an ecosystem. Diversity can also be threatened by the introduction of non-native or exotic species , especially when these species have no natural predators and are more aggressive than the native species. In these circumstances, native species can enter into a decline spiral that will impact other native species in the ecosystem.
Restoration ecology is a relatively new discipline that attempts to recreate or revive lost or severely damaged ecosystems. It is a hands-on approach by scientists and amateurs alike designed to reverse the damaging trends that can lead toward decline spirals. Habitat rebuilding for endangered species is an example of restoration ecology . For example, the Illinois chapter of The Nature Conservancy has reconstructed an oak-and-grassland savanna in Northbrook, Illinois, and a prairie in the 100-acre (40-ha) ring formed by the underground Fermi National Accelerator Laboratory at Batavia, Illinois. Since it is easier to reintroduce flora than the fauna into an ecosystem, practitioners of restoration ecology concentrate on plants first. When the plant mix is right, insects, birds, and small animals return on their own to the ecosystem.
[Linda Rehkopf ]
Ehrlich, P., and J. Roughgarden. The Science of Ecology. New York: Macmillian, 1987.
May, R. M. Stability and Complexity in Model Ecosystems. Princeton, NJ: Princeton University Press, 1973.