The SLOSS debate was a debate in

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

and

conservation biology Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an i ...

during the 1970's and 1980's as to whether a single large or several small (SLOSS) reserves were a superior means of conserving

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

in a fragmented habitat. Since its inception, multiple alternate theories have been proposed. There have been applications of the concept outside of the original context of

habitat conservation Habitat conservation is a management practice that seeks to conserve, protect and restore habitats and prevent species extinction, fragmentation or reduction in range. It is a priority of many groups that cannot be easily characterized in ter ...

History

In 1975,

Jared Diamond Jared Mason Diamond (born September 10, 1937) is an American scientist, historian, and author. In 1985 he received a MacArthur Genius Grant, and he has written hundreds of scientific and popular articles and books. His best known is '' Guns, G ...

suggested some "rules" for the design of protected areas, based on Robert MacArthur and

E. O. Wilson Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, ecologist, and entomologist known for developing the field of sociobiology. Born in Alabama, Wilson found an early interest in nature and frequ ...

's book ''

The Theory of Island Biogeography ''The Theory of Island Biogeography'' is a 1967 book by the ecologist Robert MacArthur and the biologist Edward O. Wilson. It is widely regarded as a seminal work in island biogeography and ecology. The Princeton University Press reprinted the b ...

''. One of his suggestions was that a single large reserve was preferable to several smaller reserves whose total areas were equal to the larger. Since

species richness Species richness is the number of different species represented in an community (ecology), ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the Abundance (ecology), abunda ...

increases with

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

area, as established by the species area curve, a larger block of habitat would support more species than any of the smaller blocks. This idea was popularised by many other ecologists, and has been incorporated into most standard textbooks in conservation biology, and was used in real-world conservation planning. This idea was challenged by Wilson's former student Daniel Simberloff, who pointed out that this idea relied on the assumption that smaller reserves had a '' nested''

species composition Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community.Hubbell, S. P. 2001. ''The unified neutral theory of biodiversity and biogeog ...

— it assumed that each larger reserve had all the species presented in any smaller reserve. If the smaller reserves had unshared species, then it was possible that two smaller reserves could have more species than a single large reserve. Simberloff and Abele expanded their argument in subsequent paper in the journal ''

The American Naturalist ''The American Naturalist'' is the monthly Peer review, peer-reviewed scientific journal of the American Society of Naturalists, whose purpose is "to advance and to diffuse knowledge of organic evolution and other broad biological principles so as ...

'' stating neither

ecological theory Theoretical ecology is the scientific discipline devoted to the study of ecological systems using theoretical methods such as simple conceptual models, mathematical models, computational simulations, and advanced data analysis. Effective models ...

nor empirical data exist to support the hypothesis that subdividing a nature reserve would increase extinction rates, basically negating Diamond as well as MacArthur and Wilson. Bruce A. Wilcox and Dennis D. Murphy responded with a key paper "Conservation strategy - effects of fragmentation on extinction" pointing out flaws in their argument while providing a comprehensive definition of

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...

. Wilcox and Murphy also argued that habitat fragmentation is probably the major threat to the loss of global biological diversity. This helped set the stage for fragmentation research as an important area of

. The SLOSS debate ensued as to the extent to which smaller reserves shared species with one another, leading to the development of ''nested subset theory'' by Bruce D. Patterson and Wirt Atmar in the 1980s and to the establishment of the Biological Dynamics of Forest Fragments Project (BDFFP) near

Manaus Manaus () is the List of capitals of subdivisions of Brazil, capital and largest city of the States of Brazil, Brazilian state of Amazonas (Brazilian state), Amazonas. It is the List of largest cities in Brazil, seventh-largest city in Brazil, w ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

in 1979 by

Thomas Lovejoy Thomas Eugene Lovejoy III (August 22, 1941December 25, 2021) was an American ecologist who was President of the Amazon Biodiversity Center, a Senior Fellow at the United Nations Foundation and a university professor in the Environmental Science a ...

and Richard Bierregaard.

Alternate theories

In 1986,

Michael E. Soulé Michael Ellman Soulé (May 28, 1936 – June 17, 2020) was an American biologist, known for his work in promoting the idea of conservation biology. Soulé was born in San Diego, California, the son of Berenice (Ellman) and Herman Herzoff. His fath ...

and Daniel Simberloff proposed that the SLOSS debate was irrelevant and that a three step process was the ideal way to determine reserve size. The proposed steps were to firstly decide the species whose presence was most important to the reserves biodiversity, secondly, decide how many of the species were required for the species to survive, and lastly, based on other metapopulation densities, estimate how much space is needed to sustain the required number of individuals.

Other considerations

* Dispersal and genetics, the consideration of which alternate theories often center on as the original debated tended to ignore them. * Habitat connectivity or

Landscape connectivity In landscape ecology, landscape connectivity is, broadly, "the degree to which the landscape facilitates or impedes movement among resource patches". Alternatively, connectivity may be a continuous property of the landscape and independent of patche ...

Applications

Conservation park planning

The purpose of the debate itself is in regards to conservation planning and is currently used in most spatial allotment planning.

Urban areas

The SLOSS debate has come in to play in urban planning concerning green spaces with considerations extending beyond biodiversity to human well being. The concept can also be applied to other aspects of city planning.

Current status of debate

The general consensus of the SLOSS debate is that neither option fits every situation and that they must all be evaluated on a case to case basis in accordance to the conservation goal to decide the best course of action. In the field of

metapopulation A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in a ...

ecology, modelling works suggest that the SLOSS debate should be refined and cannot be solved without explicit spatial consideration of dispersal and environmental dynamics. In particular, a large number of small patches may be optimal to long-term species persistence only if the species range increases with the number of patches. In

and

conservation genetics Conservation genetics is an interdisciplinary subfield of population genetics that aims to understand the dynamics of genes in a population for the purpose of natural resource management, conservation of genetic diversity, and the prevention of ...

metapopulations A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in a ...

(i.e. connected groups of sub-populations) are considered to be more stable if they are larger, or have more populations. This is because although individual small populations may go extinct due to stochastic processes of environment or biology (such as

genetic drift Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...

and

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely genetic distance, related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genet ...

), they can be recolonized by rare migrants from other surviving populations. Thus several small populations could be better than a single large: if a catastrophe wipes out a single big population, the species goes extinct, but if some regional populations in a large metapopulation get wiped out, recolonization from the rest of the metapopulation can ensure their eventual survival. In cases of

habitat loss Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...

, when the loss is dispersed, few large reserves are best, when the loss is in clusters, multiple small reserves are best.

References

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