Habitat separation

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Habitat separation , also habitat fragmentation ( Latin fragmentum 'fragment') or habitat fragmentation , describes an environmental change process in biology that has a decisive influence on evolution and biodiversity and is also responsible for species loss. It is a division of the habitat of animal or plant species with the result that a genetic exchange between the resulting partial habitats is prevented. Habitat separation is caused on the one hand by geological or climatic processes such as rift fractures or glaciations, but on the other hand also by human activities such as clearing and construction of traffic routes . In the first case one speaks of geographical isolation , in the second of anthropogenic influences. The climatic-geological processes that cause the isolation of subpopulations over a long period of time are crucial prerequisites for speciation and for all extinction waves . These processes can occur once (such as mega floods , mega volcanic eruptions ), repeatedly or dynamically alternating. Humans can only be assumed to have participated in the last wave of extinction . The mostly much faster changes caused by human influences, also known as landscape fragmentation, have a similar effect , which must often be regarded as the cause of the extinction of many species.

The islanding of mainland habitats or their fragmentation leads to decreasing habitat sizes and increasing isolation of the species . Habitat fragmentation and habitat loss increase extinction rates and are among the main reasons for the local, regional and global loss of diversity .

Types of fragmentation and vulnerable types

Fragmentation can be caused by human intervention, e.g. B. be done by building roads or settlements . Habitat loss and habitat fragmentation usually does not affect all species equally within a species group. The following are particularly sensitive to fragmentation:

Edge effects increase sharply when a habitat is divided into many small parcels through fragmentation.

Effects

Habitat separation is usually associated with the following effects, which have an impact on species diversity :

  • Smaller habitat area: The population sizes in the sub-habitats inevitably decrease, in extreme cases the minimum size of stable populations is undershot, which in the long term leads to the population becoming extinct. Genetic impoverishment, the reduction in the gene pool, also has a negative effect .
  • Higher proportion of peripheral areas: Species usually only have optimal living conditions from a certain distance to the edge of their habitat, depending on their area of action . By separating habitats, the “more valuable” inner areas are disproportionately reduced and may even disappear completely.
  • Habitat destruction : In the area of ​​the dividing line, there is direct habitat destruction, often particularly valuable centrally located areas.

Corridors

Most species are able to reach suitable habitat islands via less suitable spaces (biogeographical corridors). However, such corridors must meet the minimum requirements of these species. Corridors are also called connecting routes in the case of new settlements, such as the "Beringia Corridor " in the case of the first human settlement in North America. Numerous plants and animals such as moose and dogs used the same corridor at the same time . One of the minimum requirements concerns the minimum width of a corridor.

Corridor closure is used when z. B. a land connection for grazing animals is no longer accessible due to mountain folds, water expansions, desertification or dense taiga development.

Refuges

The shrinking of habitat areas can mean that species survive in refuges that did not necessarily belong to the original habitat, but have similarities with it. For example, numerous plants and animals of the mammoth steppe were able to settle in polar tundras or alpine regions after the last glacial period .

Sometimes it is difficult to distinguish between refuges and corridors, as some habitat areas can be assigned to both functions in the case of habitat fragmentation.

Measures against anthropogenic fragmentation

Measures usually consist in the creation of refuge areas or corridors between habitat islands. For some measures it is unclear whether they are to be assessed more as a refuge or a corridor. In order to be successful, however, all measures must be coordinated with the existing inventory of species and have the requirements of the species particularly affected by habitat separation in mind.

In the run-up to the planning of refuge areas, interventions must be shifted to peripheral areas far away from particularly valuable natural habitats. As a result, at least one of the sub-habitats that will be created is still largely intact. The same goal of maintaining large contiguous habitats is achieved through the designation of compensation areas and their corresponding design (e.g. unsealing , abandonment of use, afforestation ).

The concept of corridors, which are intended to network the individual habitats and thus counteract the effects of fragmentation, requires that they be designed and equipped according to the species-specific requirements of the species to be protected. Concerted measures to overcome existing divisions are the creation of a biotope network through the establishment of bridging corridors between the sub-habitats. These include so-called “stepping stones”, smaller biotopes which cannot themselves accommodate a stable population, but which enable people to move from one habitat to another. Line-shaped networking elements such as hedges or field margins have the same function . Green bridges are occasionally created especially to bridge traffic routes . Although these measures do not create new core zones, they do counteract population death through genetic impoverishment. In the heavily populated regions of Central Europe, large-scale habitats such as B. large mammals (wolf, bear, lynx) would need, not enforceable.

literature

Individual evidence

  1. ↑ VR Baker : Global Late Quaternary Fluvial Paleohydrology: With Special Emphasis on Paleofloods and Megafloods. ( PDF; 1.2 MB ) In: John F. Shroder (ed.): Treatise on Geomorphology. Volume 9: Fluvial geomorphology. Elsevier, Amsterdam 2013, pp. 511-527.
  2. ↑ Keenan Lee: The Altai Flood. On: geology.mines.edu of October 4, 2004 ( PDF file ( Memento of August 11, 2011 in the Internet Archive )).
  3. ↑ Alexei N. Rudoy : Glacier-dammed lakes and geological work of glacial superfloods in the Late Pleistocene, Southern Siberia, Altai Mountains. In: Quaternary International. Vol. 87, No. 1, January 2002, pp. 119-140, doi : 10.1016 / S1040-6182 (01) 00066-0 .
  4. ↑ Alexei N Rudoy, ​​VR Baker: Sedimentary effects of cataclysmic late Pleistocene glacial outburst flooding, Altay Mountains, Siberia. In: Sedimentary Geology. Vol. 85, No. 1-4, May 1993, pp. 53-62, doi : 10.1016 / 0037-0738 (93) 90075-G ( full text online ).
  5. ↑ Victor R. Baker, Gerardo Benito, Alexey N. Rudoy: Paleohydrology of late Pleistocene superflooding, Altai Mountains, Siberia. In: Science. January 15, 1993, Vol. 259, pp. 348-352 ( PDF file ).
  6. ^ Philippe Huybrechts: Glaciological modeling of the late Cenozoic East Antarctic ice sheet: stability or dynamism ?. In: Geografiska Annaler. Series A. Physical Geography . 1993, pp. 221-238, doi : 10.2307 / 521202 .
  7. ↑ Dissertation by Jochen Krauß (2003): Effects of habitat fragmentation and landscape structure on butterflies and flowering plants
  8. ↑ Funk WC, Greene AE, Corn PS, Allendorf FW: High dispersal in a frog species suggests that it is vulnerable to habitat fragmentation . In: Biology Letters . 1, No. 1, 2005, pp. 13-6.
  9. ↑ Susan P. Bratton, Jeffrey R. Hapeman, Austin R. Mast: The lower Susquehanna River Gorge and floodplain (USA) as a riparian refugium for vernal, forest ‐ floor herbs. In: Conservation Biology , Vol. 8, No. 4, 1994, pp. 1069-1077, doi : 10.1046 / j.1523-1739.1994.08041069.x .
  10. ↑ Hannah J. O'Regan: The Iberian Peninsula – corridor or cul-de-sac? Mammalian faunal change and possible routes of dispersal in the last 2 million years. In: Quaternary Science Reviews , Volume 27, No. 23, 2008, pp. 2136-2144, doi : 10.1016 / j.quascirev.2008.08.007 .
  11. ↑ Knut R. Fladmark: Routes: Alternate migration corridors for early one in North America. In: American Antiquity , Vol. 44, No. 1, Jan 1979, pp. 55-69.
  12. ^ Susan C. Spackman, Jeffrey W. Hughes: Assessment of minimum stream corridor width for biological conservation: species richness and distribution along mid-order streams in Vermont, USA. In: Biological Conservation , Volume 71, No. 3, 1995, pp. 325-332, doi : 10.1016 / 0006-3207 (94) 00055-U .
  13. ↑ Glen M. MacDonald, T. Katherine McLeod: "The Holocene closing of the 'ice-free'corridor: A biogeographical perspective. In: Quaternary International , Volume 32, 1996, pp. 87-95, doi : 10.1016 / 1040- 6182 (95) 00055-0 .
  14. ↑ Calvin J. Heusser: Pollen profiles from the Queen Charlotte Islands, British Columbia. In: Canadian Journal of Botany , Vol. 33, No. 5, 1955, pp. 429-449, doi : 10.1139 / b55-036 .
  15. ↑ Alan N. Williams, Sean Ulm, Andrew R. Cook, Michelle C. Langley, Mark Collard: Human refugia in Australia during the Last Glacial Maximum and terminal Pleistocene: A geospatial analysis of the 25-12 ka Australian archaeological record. In: Journal of Archaeological Science , Volume 40, No. 12, 2013, pp. 4612-4625, doi : 10.1016 / j.jas.2013.06.015 .
  16. ^ Robert B. Kaul, Gail E. Kantak, and Steven P. Churchill: The Niobrara River Valley, a postglacial migration corridor and refugium of forest plants and animals in the grasslands of central North America. In: The Botanical Review , Vol. 54, No. 1, 1988, pp. 44-81, doi : 10.1007 / BF02858518 .
  17. ↑ James R. Sedell, Gordon H. Reeves, F. Richard Hauer, Jack A. Stanford, Charles P. Hawkins: Role of refugia in recovery from disturbances: modern fragmented and disconnected river systems. In: Environmental Management , Volume 14, No. 5, 1990, pp 711-724, doi : 10.1007 / BF02394720 .
  18. ↑ Brian C. Eversham, Mark G. Telfer: Conservation value of roadside verges for stenotopic heathland Carabidae: corridors or refugia ?. In: Biodiversity & Conservation , Volume 3, No. 6, 1994, pp. 538-545, doi : 10.1007 / BF00115159 .

See also