Ecosystem Decay

Ecosystem decay is a term coined by the conservation biologist Thomas Lovejoy to describe the process by which species become locally extinct and ecosystem functions deteriorate following habitat fragmentation. The term has become synonymous with an ongoing, ambitious study of ecosystem decay in the Amazon rain forest, initiated by Lovejoy and colleagues in the 1980s. In this study, forest fragmentation has been found to have unexpected and cascading impacts on species remaining in forest fragments. This entry first describes the process of ecosystem decay and then examines impacts on the Amazon rain forest that have been identified by researchers with the Biological Dynamics of Forest Fragments Project.

It has been long recognized that habitat fragmentation is a leading cause of species loss worldwide. This widespread threat is also referred to as “islandization,” whereby a fragment of untouched habitat is isolated in a sea of altered habitat. Nature reserves have been ongoing testament to the negative effects of islandization; for example, populations of mammals with large home ranges visibly decrease within reserves, and this decrease is relative to the size of the reserve. Nonetheless, the mechanisms by which most species cease to exist in such habitat fragments have been difficult to isolate within the complexities of an ecosystem, a difficulty recognized by Lovejoy when he labeled this complex process as ecosystem decay.

To grasp the impacts of habitat fragmentation, biogeographers turned to island biogeographic theory soon after it emerged in the 1960s. By understanding the impacts of area, isolation, species immigration, and extinction within virtual islands, conservation biogeographers aimed to improve nature reserve selection. However, debates over optimal sizes of reserves ensued, a well-known one being the SLOSS (single large reserve or several small) debate. The questions driving such debates were based on the unknown complexities of ecosystem decay.

Today, the term ecosystem decay is often replaced by habitat degradation or habitat loss, reflecting the tendency of biogeographers and conservation scientists to focus on habitats rather than ecosystems. Because we are still far from understanding the inner workings of ecosystems and because biodiversity loss is occurring at an unprecedented rate, it is generally more manageable to work toward the preservation of habitats when making conservation decisions. Habitats can be defined at many scales and do not necessarily require in-depth knowledge of entire systems.