Extinction, Substitution, and Ecosystem Services

Synopsis

Humanity is driving populations and species to extinction at an unprecedented rate. There are many controllers at any given level in an ecosystem, ranging from a single species in the redwood forest to a guild of many species in the rainforest. The structure of an ecosystem is determined by the interactions among the species in an ecosystem, weather, competition, predators, and other factors. Extinctions occur continuously as part of evolutionary and ecological processes, and ecosystems can sustain some amount of loss without suffering serious impairment. The deletion of one element in an ecosystem can affect the ecosystem in the long run, but the immediate impact can be judged by its involvement in the control of various functions. Deforestation and strip mining are examples of the permanent loss of a guild of dominant trees and an entire biota. Deforestation cancels numerous services such as flood control, erosion prevention, filtration of atmospheric pollutants, and the continuous supplying of firewood and timber, and can even be disastrous for populations dependent upon them. When a large area of tropical moist forest is cleared, climate change and soil and nutrient loss make natural succession unlikely or impossible or extend the time scale of restoration of the original ecosystem beyond the period of reasonable human interest. Ease of substitution for a keystone mutualist would be a long process, based on the impact of loss. This is because keystone mutualists are often long-lived, and every species that goes extinct takes with it an average of 10 to 30 other species. Looking to the future, one might imagine that genetic engineering would eventually produce crops with desirable properties without using wild plants. This is unlikely, because of the lack of information about the ecological roles of many organisms. Aldo Leopold (1953, p. 190) wrote that if we are to preserve ecosystem services, we must save every cog and wheel that the biota built. If we do not save more of the parts, we will eventually need to make substitutions. At some point, substitution will become unbearable. Therefore, preserving ecosystems and populations within them is important.

I agree that with enough human effort deserts can be made to bloom and forests to grow. Deforestation is a major contributor to climate change, and the restoration of forest ecosystems is a major human activity. Many studies show that single-species tree plantations do not replace the services provided by an original forest ecosystem. This is crucial in indicating that we need to do our part in preserving ecosystems and populations.

Citation

Ehrlich, P. R., & Mooney, H. A. (1983). Extinction, Substitution, and Ecosystem Services. BioScience, 33(4), 248-254.