Environmental & Ecological Modeling

Refugia

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Santa Catalina Mountains, Arizona, an ecological refugium. @ C.Michael Hogan

Refugia (singular Refugium) are geographical locations where natural environmental conditions have remained relatively constant or stable during times of great environmental change, such as eras of glacial advance and retreat. Refugia protect populations of geographically isolated organisms which may then re-colonize a region when the wider environment returns to levels within the organism's tolerance levels. This idea is commonly referred to as The Refugia Theory.

History

Haffer (1969) first proposed the idea of refugia to explain the high diversity of Amazonian bird species seen today. Haffer (1969) proposed that the Amazon Basin paleoclimate experienced several warm, dry periods during episodes of continental glacier advance in the Pleistocene. These glacially driven periods led to the conversion of forest to savanna, which resulted in the isolation of small fragments of forest separated by expanses of open plains. Birds within these forest patches were geographically isolated from each other, leading to allopatric speciation. When the forests returned to their previous range in conjunction with a changing climate, these newly evolved species of birds radiated with the forest. Where the forest ranges overlapped the bird species that evolved in the refugia were no longer in competition because they exploited different resource niches. The exploitation of different niches allowed for multiple species to occupy the same geographic area, leading to the present state of high bird diversity.

Although Hafer (1969)’s idea of refugia has gained widespread acceptance as an ecological concept, the idea faces significant opposition. Much of the opposition lies not with the idea itself, but with how it applies to a particular geogrphical research unit. Colinvaux (2008), in particular, disagreed with the hypothesis that the Amazonian forest was fragmented during the Pleistocene. He believes that the Amazon basin forests remained intact during the last glacial cycles and that there must therefore be an alternate explanation for the high species diversity found in the Amazon.

Although initially tied to glaciers and focused on a discussion of tropical diversity, the term refugia now applies to any isolated region where species may be able to survive during times of ecological change.

Discussion

In order to identify areas that may have been past refugia, it is common to look for centers of either species diversity or genetic diversity within a species. The thought is that the longer a genetically viable population has been present in an area the greater its genetic diversity will be. Additionally, the longer an area has remained climatically stable greater the diversity of species per unit area will be because there has been more time for species to evolve and specialize. Colonies outside the refugia area are likely to be less diverse in both species and genetics because they originate from a genetic or species subset of the original refugia population. In the USA, the Great Smoky Mountains have been relatively undisturbed by various climate changes during the last several million years and, as a result, harbors an extraordinarily diverse flora and fauna. Because of this diversity, the Great Smoky Mountains National Park has been proposed as a refugium for flora and fauna from temperate and boreal regions.

The U.S. National Park Service asserts the following:

"Some 100 species of native trees find homes in the Smokies, more than in any other North American national park. Almost 95% of the park is forested, and about 25% of that area is old-growth forest–one of the largest blocks of deciduous, temperate, old-growth forest remaining in North America. Over 1500 additional flowering plant species have been identified in the park. The park is the center of diversity for lungless salamanders and is home to more than 200 species of birds, 66 types of mammals, 50 native fish species, 39 varieties of reptiles, and 43 species of amphibians. Mollusks, millipedes, and mushrooms reach record diversity here."

Examples

Around the world there are numerous natural refugia of varying sizes. For example, the Klamath Mountains in Northern California, USA contains one of the highest diversities of conifers in the world and have been proposed as an acknowledged refugium. The dawn redwood and the monotypic gymnosperm, the ginkgo, are also common ornamental trees now, but each was brought to the western hemisphere from small refugia in East Asia. The dawn redwood (Metasequoia glyptostroboides) refugium in China is along the border between and Sichuan-Hubei provinces. The gingko (Ginkgo biloba) refugium is found in the Tian Mu Shan Reserve, Zhejiang province, China.

An important North American refugium are the Madean pine oak woodlands of Arizona and northern Mexico. These mountain peaks rise dramatically from the desert floor and provide a microclimate and geological niche for a variety of plants and animals that are no longer found in intervening topography. Thus this locale, termed the Madrean sky islands, is a site of high endemism.

caption Table Mountains refugium, California. @ C.Michael Hogan

The Table Mountains of California lie at the eastern verge of the California Central Valley with the foothill slopes of the Sierra Nevada Mountains rising in successive ridges to their east. The Table Mountain Range is floristically noted as one of the few extant refugia for the once vast native grasslands of  Central California. Unlike most of this original native grassland expanse, whose character was substantially altered beginning in the mid nineteenth century with waves of European settlers and gold prospectors, parts of the Table Mountain Range is substantially ecologically intact.

Conservation context

Despite the controversy surrounding the exact details of proposed and past refugia, the idea has become central to many conservation plans. With the current interest in studying the types and extent of climate variation, many areas are implementing long-term management plans with a clearly-stated purpose of preserving future refugia for present taxa. For example, Naxon (2009) developed a land conservation plan for San Francisco Bay, California with the explicit objective of protecting potential refugia. Conservation International also indicates that the search for or the artificial creation of refugia may be critical to maintaining biodiversity.

The idea of seeking out potential refugia for conservation efforts is a potentially valuable management tool, but predicting which areas will be refugia is challenging and relies on detailed ecological information.

Related terms

  • Biogeography
  • Center of Diversity
  • Allopatric Speciation
  • Geographic Speciation

Further reading

  • Colinvaux, P. 2008. Amazon expeditions: my quest for the ice-age equator. Yale University Press, New Haven, Connecticut, USA.
  • Great Smoky Mountains National Park, EOE
  • Great Smoky Mountains National Park, Nature and Science
  • Haffer, J. 1969. Speciation in Amazonian forest birds. Science 165:131-137.
  • Klamath Mountains (EPA ecoregion)
  • T.Naxon. 2009. Climate refugia in the protected areas of the San Francisco Bay area ESM 270: conservation planning. University of California, Santa Barbara, California, USA.
  • North America Regional Centre of Endemism: CPD Site NA16c Klamath-Siskyou region
  • D.I. Wagner and G.J. Saucedo. 1990. Age and Stratographic Relationships of Miocene Volcanic Rocks along the Eastern Margin of the Sacramento Valley, California. in Ingersoll, R.D. and T.H. Nelson eds., Sacramento Valley Symposium and Guidebook: Pacific Section, S.E.P.M. vol. 65, p. 143-151
  • Samantha Mackey and Albin Bills. 2004. Wildflowers of Table Mountain, Butte County, California. California State Univeristy, Chico, Studies from the Herbarium, number 13  ISBN 0-9761774-0-4
  • Salmon River restoration council Salmon River Watershed – a natural history
  • Secretariat of the Convention on Biological Diversity (2009). Connecting Biodiversity and Climate Change Mitigation and Adaptation: Report of the Second Ad Hoc Technical Expert Group.
  • Biodiversity and Climate Change. Montreal, Technical Series No. 41, 126 pages.
  • Willis, K. J., and Whittaker, R. J. 2000. Paleoecology: the refugial debate. Science 287:1406-1407.

This article was partially researched by Neahga Leonard, a student at the University of Vermont participating in the Encyclopedia of Earth's  Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors and independent experts on each topic.

 

Glossary

Citation

Leonard, N. (2013). Refugia. Retrieved from http://www.eoearth.org/view/article/51cbeec57896bb431f69a25c

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