SLOSS debate

Last updated October 07, 2023

The SLOSS debate was a debate in ecology and conservation biology 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 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.

History

In 1975, Jared Diamond suggested some "rules" for the design of protected areas, based on Robert MacArthur and E. O. Wilson's book The Theory of Island Biogeography . 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 increases with habitat 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 — 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.^[1]

Simberloff and Abele expanded their argument in subsequent paper in the journal The American Naturalist stating neither ecological theory 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. 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 conservation biology.^[2] 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, Brazil in 1979 by Thomas Lovejoy and Richard Bierregaard.

Alternate theories

In 1986, Michael E. Soulé and Daniel Simberloff proposed that the SLOSS debate was irrelevant and that a three step process was the ideal way to determine reserve size.^[3] 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.^[3]

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.^[4] 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.^[5]^[6]

In the field of metapopulation 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.^[7]

In conservation biology and conservation genetics, metapopulations (i.e. connected groups of sub-populations) are considered to be more stable if they are larger, or have more populations.^[8] This is because although individual small populations may go extinct due to stochastic processes of environment or biology (such as genetic drift and inbreeding), 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, when the loss is dispersed, few large reserves are best, when the loss is in clusters, multiple small reserves are best.^[9]

Related Research Articles

<span class="mw-page-title-main">Theoretical ecology</span>

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 improve understanding of the natural world by revealing how the dynamics of species populations are often based on fundamental biological conditions and processes. Further, the field aims to unify a diverse range of empirical observations by assuming that common, mechanistic processes generate observable phenomena across species and ecological environments. Based on biologically realistic assumptions, theoretical ecologists are able to uncover novel, non-intuitive insights about natural processes. Theoretical results are often verified by empirical and observational studies, revealing the power of theoretical methods in both predicting and understanding the noisy, diverse biological world.

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 terms of any one ideology.

Biological dispersal refers to both the movement of individuals from their birth site to their breeding site, as well as the movement from one breeding site to another . Dispersal is also used to describe the movement of propagules such as seeds and spores. Technically, dispersal is defined as any movement that has the potential to lead to gene flow. The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved.

<span class="mw-page-title-main">Habitat fragmentation</span> Discontinuities in an organisms environment causing population 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 processes that slowly alter the layout of the physical environment, and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species. More specifically, habitat fragmentation is a process by which large and contiguous habitats get divided into smaller, isolated patches of habitats.

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 agricultural fields, but the idea has been most broadly applied to species in naturally or artificially fragmented habitats. In Levins' own words, it consists of "a population of populations".

Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness and diversification of isolated natural communities. The theory was originally developed to explain the pattern of the species–area relationship occurring in oceanic islands. Under either name it is now used in reference to any ecosystem that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, seamounts, oases, fragmented forests, and even natural habitats isolated by human land development. The field was started in the 1960s by the ecologists Robert H. MacArthur and E. O. Wilson, who coined the term island biogeography in their inaugural contribution to Princeton's Monograph in Population Biology series, which attempted to predict the number of species that would exist on a newly created island.

Ecology is a new science and considered as an important branch of biological science, having only become prominent during the second half of the 20th century. Ecological thought is derivative of established currents in philosophy, particularly from ethics and politics.

Reconciliation ecology is the branch of ecology which studies ways to encourage biodiversity in the human-dominated ecosystems of the anthropocene era. Michael Rosenzweig first articulated the concept in his book Win-Win Ecology, based on the theory that there is not enough area for all of earth's biodiversity to be saved within designated nature preserves. Therefore, humans should increase biodiversity in human-dominated landscapes. By managing for biodiversity in ways that do not decrease human utility of the system, it is a "win-win" situation for both human use and native biodiversity. The science is based in the ecological foundation of human land-use trends and species-area relationships. It has many benefits beyond protection of biodiversity, and there are numerous examples of it around the globe. Aspects of reconciliation ecology can already be found in management legislation, but there are challenges in both public acceptance and ecological success of reconciliation attempts.

<span class="mw-page-title-main">Biological Dynamics of Forest Fragments Project</span>

The Biological Dynamics of Forest Fragments Project is a large-scale ecological experiment looking at the effects of habitat fragmentation on tropical rainforest. The experiment which was established in 1979 is located near Manaus in the Brazilian Amazon rainforest. The project is jointly managed by the Amazon Biodiversity Center and the Brazilian Institute for Research in the Amazon (INPA).

Daniel Simberloff is an American biologist and ecologist. He earned his Ph.D. from Harvard University in 1969. He is currently Gore Hunger Professor of Environmental Science at the University of Tennessee, editor-in-chief of the journal Biological Invasions, and a member of the National Academy of Sciences.

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 patches and paths. Connectivity includes both structural connectivity and functional connectivity. Functional connectivity includes actual connectivity and potential connectivity in which movement paths are estimated using the life-history data.

Ilkka Aulis Hanski was a Finnish ecologist at the University of Helsinki, Finland. The Metapopulation Research Center led by Hanski, until his death, has been nominated as a Center of Excellence by the Academy of Finland. The group studies species living in fragmented landscapes and attempts to advance metapopulation ecology research. Metapopulation ecology itself studies populations of plants and animals which are separated in space by occupying patches.

Reserve design is the process of planning and creating a nature reserve in a way that effectively accomplishes the goal of the reserve.

A wildlife corridor, habitat corridor, or green corridor is an area of habitat connecting wildlife populations separated by human activities or structures. This allows an exchange of individuals between populations, which may help prevent the negative effects of inbreeding and reduced genetic diversity that often occur within isolated populations. Corridors may also help facilitate the re-establishment of populations that have been reduced or eliminated due to random events. This may potentially moderate some of the worst effects of habitat fragmentation, wherein urbanization can split up habitat areas, causing animals to lose both their natural habitat and the ability to move between regions to access resources. Habitat fragmentation due to human development is an ever-increasing threat to biodiversity, and habitat corridors serve to manage its effects.

Patch dynamics is an ecological perspective that the structure, function, and dynamics of ecological systems can be understood through studying their interactive patches. Patch dynamics, as a term, may also refer to the spatiotemporal changes within and among patches that make up a landscape. Patch dynamics is ubiquitous in terrestrial and aquatic systems across organizational levels and spatial scales. From a patch dynamics perspective, populations, communities, ecosystems, and landscapes may all be studied effectively as mosaics of patches that differ in size, shape, composition, history, and boundary characteristics.

<i>The Theory of Island Biogeography</i> 1967 book by Robert MacArthur and Edward O. Wilson

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 book in 2001 as a part of the "Princeton Landmarks in Biology" series. The book popularized the theory that insular biota maintain a dynamic equilibrium between immigration and extinction rates. The book also popularized the concepts and terminology of r/K selection theory.

In ecology, extinction debt is the future extinction of species due to events in the past. The phrases dead clade walking and survival without recovery express the same idea.

Ecosystem decay is a term coined by Thomas Lovejoy to define the process of which species become extinct locally based on habitat fragmentation. This process is what led to the extinction of several species, including the Irish Elk. Ecosystem decay can be mainly attributed to population isolation, leading to inbreeding, leading to a decrease in the population of local species. Another factor is the absence of competition, preventing the mechanisms of natural selection to benefit the population. This leads to a lack of a skill set for the animal to adjust and adapt to a new environment. Habitat fragmentation and loss lead to smaller habitat sizes, and ecosystem decay predicts ecological processes are changed so heavily in smaller habitats that the loss in diversity is more extreme than expected by fragmentation alone.

The rescue effect is a phenomenon which was first described by Brown and Kodric-Brown, and is commonly used in metapopulation dynamics and many other disciplines in ecology. This populational process explains how the migration of individuals can increase the persistence of small isolated populations by helping to stabilize a metapopulation, thus reducing the chances of extinction. In other words, immigration can lead to the recolonization of previously extinct patches, promoting the long-term persistence of the network of populations.

Lenore Fahrig is a Chancellor's Professor in the biology department at Carleton University, Canada and a Fellow of the Royal Society of Canada. Fahrig studies effects of landscape structure—the arrangement of forests, wetlands, roads, cities, and farmland—on wildlife populations and biodiversity, and is best known for her work on habitat fragmentation. In 2023, she was elected to the National Academy of Sciences.

References

↑ Baz, Arturo; Garcia-Boyero, Antonio (1996-04-01). "The SLOSS dilemma: a butterfly case study". Biodiversity & Conservation. 5 (4): 493–502. doi:10.1007/BF00056393. ISSN 1572-9710.
↑ Laurance, William F., and R.O. Bierregaard. 1997. Tropical Forest Remnants: Ecology, Management, and Conservation of Fragmented Communities. University of Chicago Press.
1 2 Soulé, Michael E.; Simberloff, Daniel (1986-01-01). "What do genetics and ecology tell us about the design of nature reserves?". Biological Conservation. 35 (1): 19–40. doi:10.1016/0006-3207(86)90025-X. hdl: 2027.42/26318 . ISSN 0006-3207.
↑ Valente, Donatella; Pasimeni, Maria Rita; Petrosillo, Irene (2020-01-01). "The role of green infrastructures in Italian cities by linking natural and social capital". Ecological Indicators. 108: 105694. doi:10.1016/j.ecolind.2019.105694. ISSN 1470-160X.
↑ Tjørve, Even (2010-05-21). "How to resolve the SLOSS debate: Lessons from species-diversity models". Journal of Theoretical Biology. 264 (2): 604–612. doi:10.1016/j.jtbi.2010.02.009. ISSN 0022-5193. PMID 20152842.
↑ Lindenmayer, David B.; Wood, Jeff; McBurney, Lachlan; Blair, David; Banks, Sam C. (2015-03-01). "Single large versus several small: The SLOSS debate in the context of bird responses to a variable retention logging experiment". Forest Ecology and Management. 339: 1–10. doi:10.1016/j.foreco.2014.11.027. ISSN 0378-1127.
↑ Ovaskainen, Otso (2002). "Long-Term Persistence of Species and the SLOSS Problem". Journal of Theoretical Biology. 218 (4): 419–433. doi:10.1006/jtbi.2002.3089. ISSN 0022-5193.
↑ Hanski, Ilkka. 1999. Metapopulation Ecology. Oxford University Press. ISBN 0-19-854065-5
↑ Liu, Haoqi; Li, Weide; Lv, Guanghui (2019-04-01). "How nonrandom habitat loss affects nature reserve planning strategies". Ecological Modelling. 397: 39–46. doi:10.1016/j.ecolmodel.2018.12.014. ISSN 0304-3800.