Doubts about integrity and stability of ecosystems
With flux taken to be the norm on a variety of levels, it becomes more difficult to interpret natural systems as well-integrated, persisting wholes, much like organisms. Ecosystem integrity becomes problematic when species relationships are opportunistic. Noting that co-occurrence of species is determined by abiotic factors as much as by species interactions and that typical interactions between species involve competition, predation, parasitism, and disease, one well-known conservation biologist claims that “the idea that species live in integrated communities is a myth.” Evidence suggests that species groupings are historically contingent and are not fixed packages that come and go as units. Insofar as species associations are transient, individualistic, biotic assemblages, we must begin to question the ideas that ecosystems are supposed to have certain species, that without all of its species an ecosystem is “incomplete,” and that exotic species do not belong.
Indeed, the very notion of an ecosystem has become suspect in some quarters. A number of ecologists now investigate the dynamics of “patches” of land, giving up on the idea of homogenous ecosystems. Others retain the notion of an ecosystem, but drop the organismic assumptions often associated with it. We will follow the latter course, recognizing that without these assumptions, what counts as an ecosystem depends on our purposes as well as on the empirical facts.
Looking at the fossil record of the last 50,000 years, David Jablonski says, “The most important message . . . is that ecological communities do not respond as units to environmental change. . . . Species are highly individualistic in their behavior, so that few, if any, modern terrestrial communities existed in their present form 10,000 years ago.” See Jablonski’s “Extinction: A Paleontological Perspective,” Science 253 (1991): 756. In a similar vein, Michael Soule suggests that historical “studies are undermining typological concepts of community composition, structure, dynamics, and organization by showing that existing species once constituted quite different groupings or ‘communities’.” See Soule’s, “The Onslaught of Alien Species, and Other Challenges in the Coming Decades,” Conservation Biology 4 (1990): 234.
Are Ecosystems Moral Communities?
One intriguing response to these worries has been advanced by J. Baird Callicott. Callicott points out that, like biotic communities, human communities are neither stable, nor typological, that is, they change over time and do not come and go as units. Human communities are also composed of individualistic, self-promoting, and competitive individuals. Callicott concludes that biotic communities are no less integrated and no harder to demarcate than are human communities, and thus that if human communities are sufficiently coherent to generate obligations to them, then so are biotic communities.
One problem with this argument is that human communities are held together by shared purpose and meaning. That people see themselves as part of a human community is essential to its unity. Self-seeking individualism, predatory competition, and parasitism, unchecked by community spirit and identity, tear apart human communities. Sprawl development characterized by vacant strip malls, big-box stores adjacent to diseased local merchants, and aggressive automobile traffic hardly constitutes a community that generates preservationist obligations. Callicott's analogy ignores that the shared purpose and meaning that bind together changing, self-seeking individuals into human communities are lacking in biotic communities.
Callicott also suggests that the Leopoldean response to the ecology of instability should be to modify Leopold’s dictum to say: “A thing is right when it tends to disturb the biotic community only at normal spatial and temporal scales. It is wrong when it tends otherwise.” This implausibly suggests that it is morally permissible to intentionally extirpate other species, so long as we do so at rates comparable to normal extinction frequencies in evolutionary history. It also has the unfortunate consequence that extensive restoration projects are impermissible insofar as they disturb nature at nonnormal scales.
We want to stress that there are important ways in which many natural systems display significant degrees of integrity and stability in various respects. Ecosystems are certainly not mere jumbles of self-sufficient individuals. No one denies the existence of causal connections between individuals in ecosystems or dependencies between species. Species adapt to each other, to disturbances, and to changing environments. Sometimes these adaptations can make ecosystems more resistant (and persistent), as when a keystone tree species on hurricane-prone barrier islands evolves a thicker trunk and begins to hug the ground. Selective pressures also put a brake on species self-aggrandizement, for example, by working against predator species that drive their prey to extinction and parasites that destroy their hosts. Many dimensions of natural systems clearly persist on human time scales.