Friday, February 5, 2010

Global change in species interactions of terrestrial ecosystems

There is lots of talk about the impact of climate change on ecosystems such that it affects the distribution of plant and animal species. Thus, for example, we know the production of wheat will move further north in North America and we see the impact of warmer winters on the lifecycle of the mountain beetle that is currently destroying the forests of BC.

Less appreciated by social scientists is the fact that climate change is only one of several major drivers affecting terrestrial ecosystem change. The others are CO2 enrichment, nitrogen deposition, biotic exchanges, and land-use change. In an important recent paper, Global change and species interactions in terrestrial ecosystems, biologist Jason Tylianakis reports the results of a metanalysis of 700 papers about terrestrial ecosystem change.

Tylianakis describes the significance of his work as follows:

Global changes to the Earth's ecosystems are possibly the greatest combined challenge that humanity must face. These changes are often studied independently, but their effects are likely to be interactive, which could exacerbate or even mitigate the effect of each driver in isolation, and have potentially devastating consequences for the structure and functioning of communities and ecosystems. Our paper brings together a large body of research on how these changes affect interactions between different species from different systems, and thus it provides an insight into what we may expect in the future.

There are no longer any ecosystems on Earth that are untouched by human influence. Global environmental changes drive extinctions and alter species distributions, and recent evidence now shows pervasive impacts on a variety of interactions between species. Species interactions are critically important for ecosystem stability and functioning, yet their fragility makes them vulnerable to environmental changes.

Each of the major drivers of global change (CO2 enrichment, nitrogen deposition, climate change, biotic exchanges, and land-use change) have direct effects on species interactions, but the interactions between multiple drivers acting simultaneously hinder predictions of future responses. Summing up these individual changes across entire networks of species interactions yields unanticipated effects on ecosystems and the services they provide.

Thus, much like Charles Perrow's analysis of technological systems (Normal Accidents), Tylianakis has realized that the interactions among different causes create unexpected complications that generate uncertainties.

The paper can be found in Ecology Letters, (2008) 11: 1351–1363 doi: 10.1111/j.1461-0248.2008.01250.x

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