The SLOSS Debate

Two Burchell's Zebras in morning light Two
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One of the most heated controversies in conservation history is known as the SLOSS Debate. SLOSS stands for "Single Large or Several Small" and refers to two different approaches to land conservation in order to protect biodiversity in a given region.

The "single large" approach favors one sizeable, contiguous land reserve.

The "several small" approach favors multiple smaller reserves of land whose total areas equal that of a large reserve.

Area determination of either is based on the type of habitat and species involved.

New Concept Spurs Controversy:

In 1975, an American scientist named Jared Diamond proposed the landmark idea that a single large land reserve would be more beneficial in terms of species richness and diversity than several smaller reserves. His claim was based on his study of a book called The Theory of Island Biogeography by Robert MacArthur and E.O. Wilson.

Diamond's assertion was challenged by ecologist Daniel Simberloff, a former student of E.O. Wilson, who noted that if several smaller reserves each contained unique species, then it would be possible for smaller reserves to harbor even more species than a single large reserve.

Habitat Debate Heats Up:

Scientists Bruce A. Wilcox and Dennis L. Murphy responded to an article by Simberloff in The American Naturalist journal by arguing that habitat fragmentation (caused by human activity or environmental changes) poses the most critical threat to global biodiversity.

Contiguous areas, the researchers asserted, are not only beneficial to communities of interdependent species, they are also more likely to support populations of species that occur at low population densities, particularly large vertebrates.

Harmful Effects of Habitat Fragmentation:

According to the National Wildlife Federation, terrestrial or aquatic habitat fragmented by roads, logging, dams, and other human developments "may not be large or connected enough to support species that need a large territory in which to find mates and food.

The loss and fragmentation of habitat make it difficult for migratory species to find places to rest and feed along their migration routes."

When habitat is fragmented, mobile species that retreat into smaller reserves of habitat can end up crowded, increasing competition for resources and disease transmission.

The Edge Effect:

In addition to interrupting contiguity and decreasing the total area of available habitat, fragmentation also magnifies the edge effect, resulting from an increase in the edge-to-interior ratio. This effect negatively impacts species that are adapted to interior habitats because they become more vulnerable to predation and disturbance.

No Simple Solution:

The SLOSS Debate spurred aggressive research into the effects of habitat fragmentation, leading to conclusions that the viability of either approach may depend on the circumstances.

Several small reserves may, in some cases, be beneficial when indigenous species' extinction risk is low. On the other hand, single large reserves may be preferable when extinction risk is high.

In general, however, the uncertainty of extinction risk estimates leads scientists to prefer the established habitat integrity and security of a single larger reserve.

Reality Check:

Kent Holsinger, Professor of Ecology and Evolutionary Biology at the University of Connecticut, contends, "This whole debate seems to have missed the point. After all, we put reserves where we find species or communities that we want to save. We make them as large as we can, or as large as we need to protect the elements of our concern. We are not usually faced with the optimization choice poised in the [SLOSS] debate. To the extent we have choices, the choices we face are more like … how small an area can we get away with protecting and which are the most critical parcels?"

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Bove, Jennifer. "The SLOSS Debate." ThoughtCo, Mar. 28, 2017, thoughtco.com/overview-of-the-sloss-debate-1181943. Bove, Jennifer. (2017, March 28). The SLOSS Debate. Retrieved from https://www.thoughtco.com/overview-of-the-sloss-debate-1181943 Bove, Jennifer. "The SLOSS Debate." ThoughtCo. https://www.thoughtco.com/overview-of-the-sloss-debate-1181943 (accessed January 22, 2018).