Biotope network

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The biotope network or the biotope network is the creation of a network of (individual) biotopes , which ensures the survival of species . The biotope network exists when there is a functional contact between biotopes (habitats) that enables a network between populations of organisms . It works when the area between similar habitats can be surmounted by organisms, or is bridged by processes such as transport by grazing animals, so that a mutual exchange of individuals is possible.

In Germany biotope network and biotope network are u. a. Target aimed at by the Federal Nature Conservation Act (§21). In Bavaria, since the referendum on “Species diversity & natural beauty in Bavaria”, Article 19 of the Bavarian Nature Conservation Act stipulates a specific share of the area of ​​biotope network to be achieved.

Significance of the network in the life cycle

Roads as an obstacle to the networking of biotopes: road density per 100 km 2

Especially in the zoological area, the importance of the biotope network for defined individual species is based on its importance in the life cycle of the species. A distinction is made between:

  • Species that need a biotope network for their normal habitat, hunting or feeding grounds. Without a network, otherwise colonizable areas are devalued as living space and / or the minimum area for a viable population is not reached. This mainly applies to species with a very large space requirement, mostly vertebrates living as predators (e.g. the wolf or the wild cat )
  • Species that need a network of biotopes for regular migrations. Without a network, spatially separated sub-habitats are isolated from one another. Affected are z. B. Migrations between summer and winter habitats or between reproduction and food habitats. The migrations can be large-scale (e.g. intermediate roosts for migratory birds or bats), on a medium spatial level (e.g. summer and winter habitats of red deer ) or small-scale (e.g. amphibian migrations ).
  • Species that need a network of biotopes for spreading (dispersion) in order to be able to colonize new or vacated habitat "islands". If there is no connection, they die out, as all local populations gradually extinguish over a longer period of time, either for random reasons (stochastic fluctuations), as a result of succession processes (pioneer species) or because of large-scale area shifts ( global warming ). A genetic impoverishment due to inadequate allele exchange is also discussed (but has so far been very rarely proven).

While the first and second cases are relatively easy to understand, further justifications are required for the third case. It is usually assumed that restrictions on dispersion do not seem to have any obvious effects in the short term, but that in the long term the consequences of a lack of biotope network will primarily result from this. In the case of plant species, only the third way is significant.

Ecological basics

The requirement for a biotope network is based on the one hand on model statements derived from ecological theory, on the other hand on empirical observations, i.e. H. Case studies examining the survival of populations in more or less isolated habitats.

Island theory

(cf. island biogeography ) The island theory (actually: equilibrium theory of the biogeography of islands) represents an important basis for the biotope network. It is an influential ecological theory that the American theoretical ecologists Robert H. McArthur and Edward O. Wilson first established in 1963 and generalized in 1967. The researchers looked at the number of species on more or less isolated oceanic islands. They came up with a dependency pattern that can be represented in a mathematical formula, which they could interpret biologically as a balance between immigration and (local) extinction. Local populations are subject to a (stochastic) risk of extinction, which is dependent on the population size, which in turn depends on the island size (via the carrying capacity). Small populations die out randomly after a more or less long period (random population fluctuations). The island then represents a free habitat for the species. It can eventually be repopulated if it is discovered by immigrating individuals of this species. This colonization depends on the biological properties of the colonizing species, but above all on the isolation of the island, which (in addition to its shape and a few other parameters) results primarily from its distance. The actual number of species on an island then results as a state of equilibrium between extinction and the establishment of new populations. The species composition of the island here changes ( mode change , Eng. Species turnover). The number of species depends on the size of the island and its distance from other islands (or a continent).

The island theory was transferred early on from oceanic islands to isolated special biotopes, which can be interpreted as habitat islands in an "ocean" hostile to the survival of the species under consideration. This results in a number of predictions, some of which have been confirmed experimentally.

  • If the size of a habitat island decreases, numerous species die out, even if the habitat quality of the remaining area does not deteriorate at all ("relaxation"). In the transition period, the island has a species overhang that is gradually doomed to extinction. Which species actually survive depends in part on chance. In nature conservation, one speaks of "extinction debt". For the application cf. z. Federation.
  • If the remaining habitat islands are so far apart that a new colonization of "empty" islands is impossible or highly unlikely (colonization rate zero), sooner or later all species on all islands will die out (they only survive on very large islands and continents are so large that they have multiple independent populations, and their population size is so high that the stochastic risk of extinction drops to near zero.)
  • If the colonization rate of habitat islands can be increased, more species can survive, although neither the size nor the quality of the habitat islands has increased.

Metapopulations

A metapopulation describes a network of individual populations (subpopulations) that are partially, but not completely, isolated from one another. The subpopulations interact with each other through the exchange of individuals. The above Statements from the island theory can just as easily be derived from a population-biological approach. However, there are further hypotheses.

The Finnish population biologist Ilkka Hanski has put forward an influential theory, which takes into account that the population size of a species is included twice when colonizing islands or partial biotopes (mostly English: habitat patches); it increases the rate of colonization and decreases the rate of extinction. This results in a bimodal frequency distribution in his model: a few common species, which he calls "core species", are present on all islands. Most species ("satellite species") are rarer than one would expect from a purely random distribution. Due to this connection, the number of species increases more slowly with an increasing number of islands. Only the "core species" are present on almost all islands.

The Dutch ecologist Pieter J. den Boer has studied the influence of the dispersion on the ground beetle fauna of Dutch heather fragments over many years . With these predatory, ground-living beetles there are flightable species, non-flightable species and species in which some of the individuals are able to fly (wing-dimorphic species). He was able to show that the number of species in isolated heather fragments decreases in the long term. In addition, the proportion of individuals capable of flying is decreasing among the remaining. Den Boer interprets this as an evolutionary trend due to islanding. By isolating the heather fragments, the likelihood of successful immigration decreases. This gives species that no longer invest in the (energetically expensive) flight apparatus at an advantage in the short term. In the long term, however, almost all species are doomed to extinction in the long run.

Maintaining the genetic variability of species is also important in the metapopulation approach. On small islands and in populations newly established by a few colonizers, the variability is necessarily much lower than in large ones ("founder effect"). It is increased by immigrating individuals from other populations. This effect is also significant when these immigrants reach an island that is still inhabited by the species. The loss of genetic variability significantly increases the risk of extinction for a species because its plasticity to react to changes in habitat can be lost. If the population increases again after near extinction, this population is much more susceptible than the original one ("genetic bottleneck").

For very mobile animal species, e.g. B. many bird species, the metapopulation model is meaningless in practice. Here, individuals can easily switch between distant parts of the world. Due to the frequent exchange, they form a single large population.

Edge effects

Edge effects describe the influence of the surrounding landscape on biotope islands. In contrast to oceanic islands, biotope islands are embedded in a much more similar environment. Edge effects occur here in several ways. On the one hand, intensive land use also affects protected biotope islands by z. B. pesticides or fertilizers can be blown in and washed away. Therefore the value of very small or narrow biotope islands is sometimes greatly reduced in practice. Another kind of marginal effect comes from the species inventory of the agricultural landscape, which (in contrast to the oceanic species between real islands) can also colonize the biotope islands. Nature conservation tries to counteract marginal effects by establishing buffer zones. In the biotope network, they must be taken into account in order to be able to assess the effectiveness of biotope islands and corridors.

Edge effects at the population level can be intended by nature conservation under certain circumstances. In these cases, the network of linear biotopes (to be protected or newly created) should not primarily network near-natural biotope islands with one another, but rather specifically improve the value of the agricultural landscape in between by providing refuge or partial habitats for species of the agricultural landscape themselves (cf. z. B.) Although this goal can be legitimate and practicable, the argumentation sometimes becomes so blurred in practice that it is hardly possible to determine what the actual goal of the biotope network should be.

Edge effects can be effective on a larger scale than is often intuitively assumed. Investigations in New Zealand have shown that even small bugs living on the ground still had detectable effects on fauna at a distance of one kilometer from the border of a protected area. Naturally, stronger effects are to be expected with species that regularly cross the protected area boundaries, e.g. B. Carnivores. In addition to the negative, positive marginal effects have also actually been proven: There may be an enrichment of adjacent habitats with species. In rivers in Germany attempts are being made to make use of this effect under the name of "radiation effect", although reliable empirical evidence of its effectiveness is still pending.

Forms of the biotope network

Schematic representation (Dutch): stepping stones (stapstene) and green corridors between biotopes

The biotope network is thus defined by its effectiveness on selected target species. Strictly speaking, it is not biotopes that are networked, but populations . The biotope network must therefore meet different requirements depending on the biology of the species under consideration (especially its mobility and dispersal biology). For mobile species, especially those that are capable of flying or those with life stages capable of flying (especially birds, most insects, plants with wind-dispersed seeds), a network is usually sought via stepping stone biotopes . These are small, not necessarily interconnected, biotope "islands" within the surrounding landscape. Their distance should be measured according to the mobility of the target species. For immobile, ground-bound species (e.g. many mammals, but also plants of the forest floor without efficient long-distance distribution mechanisms), a biotope network via biotope corridors is sought. H. linear structures that physically connect the target biotopes to be connected. This can e.g. B. Hedge strips between two forest "islands" or one or more forest "islands" (so-called forest bridges ) between large forest areas. Important tasks for the biotope network are insurmountable landscape barriers, especially large roads (motorways). These are mostly insurmountable obstacles even for quite mobile but non-flightable species for which the normal agricultural landscape does not represent a turning point. This is particularly important for large mammal species. Contrary to intuition, depending on the design, such caesuras can also act as barriers for species capable of flying (e.g. bats). A biotope network is sought here using special connecting elements (e.g. green bridges ) at the landscape level.

Green Bridge (Ecoduct) in the Netherlands

The construction of green bridges can be seen in connection with a strategy of the biotope network that does not start so much with the islands, but more with the spaces in between. Targeted measures are intended to increase the permeability of the landscape between the biotope islands (mostly "connectivity"). Although this strategy would be well founded according to the theories of ecology, there are very considerable problems in practice, if z. B. the extensive extensification of agricultural land use is required. In practice, this approach does not yet play a role (except for the surmountability of linear obstacles, especially roads).

A special case of the biotope network, which is usually considered apart from the other discussion, is the lifting of the isolation of flowing water sections, e.g. B. by weirs, hydropower plants, reservoirs or piped waterways. One speaks here of the "ecological continuity" of the waters. If there is no patency, z. B. Migratory fish species do not reach water upper reaches that would actually be suitable as a habitat. Problems can also arise for invertebrate species, because sections of the water body cannot be repopulated after extinction events. By adopting the European Water Framework Directive , the member states have undertaken to restore the ecological continuity of all flowing waters where possible. Typical measures to establish patency include, for. B. the construction of fish ladders ( fish ladders) at hydropower plants and weirs, the construction of bypass channels ("bypasses") or the dismantling of pipes and falls (floor jumps).

Application in nature conservation and landscape planning

The demand for a biotope network only became stronger in the nature conservation discussion since the 1980s. Before that, nature conservation had concentrated on the preservation of particularly valuable individual biotopes. Because of his limited social influence, he probably had no other choice in practice. The nature conservationists became aware of the importance of the biotope network primarily through the decreasing suitability of the "normal" agricultural landscape due to the more intensive production methods. This made it increasingly clear that most species in small nature reserves cannot be preserved in the long term. In the international discussion, the topic was raised in efforts to conserve endangered natural habitats, e.g. B. the tropical rainforest, acute. A debate about the size and layout of the protected areas was held in the professional world, which is summarized under the catchphrase SLOSS ("single large or several small"). Today the importance of the biotope network in official and voluntary nature conservation is widely recognized.

The successes in the practical endeavors to implement the biotope network are still controversial. The networking of biotopes became a fashion and catchphrase, especially in the early 1990s, through which the actual issue has been rather obscured. In particular, there is a tendency to lose sight of the fact that a network of "biotopes" should actually only represent an abbreviated notation for the network of populations of animal and plant species in the planning implementation. Due to the definition of abstract "biotope types" the connection has occasionally been lost in practice.

Promotion of linear biotopes in the agricultural landscape

Line biotopes in the arable landscape are of particular importance in the networking of biotopes . The line biotopes include strips of field margins , creeks , stone walls , embankments , paths and roadsides, hedges , avenues and rivers . Line biotopes contribute to the diversity and networking of the island-like biotopes , especially in a heavily cleared landscape with little or no forest and grassland.

Promotion of the large-scale biotope network

A national strategy for a biotope network was first sought in Germany through a resolution of the Ministerial Conference for Spatial Planning on November 27, 1992. A working group with the participation of the Federal Agency for Nature Conservation developed a technical strategy. In the European Union, the topic has been debated in depth under the catchphrase “green infrastructure” since 2008 (a summary of the previous approaches under). Green Belt Germany is a current project for the large-scale, linear connection of different biotopes. It is part of the European Green Belt Europe initiative . The Netherlands has been striving for a national biotope network under the name Ecologische Hoofdstructuur (EHS) for around 20 years . In France, two connected protected area networks under the title Trame verte et bleue (TVB) have been sought since 2008 .

In 2007, the German Nature Conservation Union (NABU) drew up the national strategy of a federal wilderness route plan, primarily to counteract the fragmentation effect of the motorways. The Federation for the Environment and Nature Conservation Germany BUND created a wildcat path plan specifically for the target species wildcat, which he has implemented in several projects, e.g. B. in Thuringia, strives.

Political implementation

In the German state of Baden-Württemberg , the incumbent State Minister for Rural Areas and Consumer Protection in Baden-Württemberg Alexander Bonde ( Alliance 90 / The Greens Baden-Württemberg ) presented a concept for networking biotopes in the state in April 2012. The Bayern-Netz-Natur has existed in Bavaria since 1995 .

Disadvantages and criticism of the biotope network

The biotope network as a nature conservation strategy is generally considered to be well founded and recognized. Nevertheless, there is criticism of the application in numerous individual cases.

A more general criticism comes to the conclusion that the success of numerous previously implemented biotope networking measures has been questionable or undetectable. Due to the scarcity of nature conservation resources, they have been wasted and better invested in the direct preservation of high-quality biotopes. Most conservationists do not see this criticism as justified. Nevertheless, it should be pointed out that the concrete success of biotope-linking measures (like all nature conservation measures) must be checked and the measures improved if necessary. Although it was possible to prove the effect of corridors in careful studies, the actual failure of numerous measures that were supposed to support the biotope network is unfortunately well documented.

In addition, biotope networking problems are plausible in individual cases.

  • Networking enables epidemics and pathogens to spread faster. In flowing waters z. B. demanded the retention of weirs, the relic occurrences of the native noble crayfish ( Astacus astacus ) have so far protected from the cancer plague.
  • The biotope corridors can prevent the spread of undesirable species, e.g. B. neophytes and neozoa, as well as that of the target species. This can have a homogenizing effect.
  • Networking of biotopes can promote the migration of individuals to suboptimal habitats, which act as population sinks, and thus weaken a population that needs to be preserved.
  • The actual biology and speed of spread of many species is poorly known. This means that the design of biotope corridors can often only be carried out on the basis of assumptions. In some cases, living spaces that actually do not need to be networked may be networked.

Biotope networking and climate change

As an additional argument in favor of biotope networking, the mitigation (mostly "mitigation") of the effects of man-made climate change has been cited in the debate since around 2005. Due to climate change, numerous biotopes are changing in such a way that they will probably lose part of their current species population. Since the range of almost all species correlates well demonstrably with climatic factors, it can be assumed that the total range of many species will shift. They lose more or less large parts of their previous range; however, they could possibly make up for this by expanding them elsewhere, e.g. B. by moving their area northwards or uphill. Of course, this assumes that they can actually reach this new (initially only potential) area.

In this context, a strengthening of the biotope network is being debated in order to provide such escape and migration corridors for threatened species. No actual measures have yet been taken in this context. Whether this would be promising at all is controversial in research. One of the first projects to bring together the biotope network and climate impacts is currently being prepared in the Netherlands, the West European climate corridor on the Rhine (Province of Gelderland).

literature

  • Uwe Wegener (Ed.): Nature conservation in the cultural landscape, protection and care of habitats. Ulm 1998, ISBN 3-437-35250-4 .
  • E. Jedicke (Hrsg.): Biotope network: Basics and measures of a new nature conservation strategy. 2nd Edition. Ulmer Verlag, Stuttgart 1994, ISBN 3-8001-3324-5 .

Web links

Commons : Biotope network  - collection of images, videos and audio files

Individual evidence

  1. ↑ § 21 BNatSchG
  2. ↑ BayNatSchG: Art. 19 Biotope Network, Biotope Networking, Species and Biotope Protection Program - Citizen Service. Retrieved February 17, 2020 .
  3. ^ DJV project: "Overcoming barriers". In: jagdnetz.de. German Hunting Protection Association V. (DJV) Association of German State Hunting Associations, accessed on February 6, 2011 .
  4. ↑ H. Reck, K. Hänel, M. Hermann, J. Sachteleben: Association project “Overcoming barriers”. Target species of the regional biotope network. Pointer types for dissection and isolation. Preliminary draft. (PDF; 303 kB) (No longer available online.) September 2007, archived from the original on March 8, 2012 ; Retrieved February 6, 2011 .
  5. ^ Robert H. MacArthur, Edward O. Wilson: An Equilibrium Theory of Insular Zoogeography. Evolution . tape 17 , no. 4 , December 1963, p. 373–387 (English, unm.edu [PDF; 1.6 MB ]).
  6. ^ Robert H. MacArthur, Edward O. Wilson: The Theory of Island Biogeography . Princeton University Press, Princeton 1967.
  7. ^ Ilkka Hanski : Extinction debt in boreal forests. (PDF)
  8. ↑ Aveliina Helm et al: Extinction debt in Estonian calcareous grasslands ("alvars"). (PDF)
  9. ^ Ilkka Hanski : Dynamics of regional distribution: the core and satellite species hypothesis. In: Oikos. 38, Copenhagen 1982, pp. 210-221.
  10. ↑ PJ Den Boer: Dispersal power and survival: carabids in a cultivated countryside. (= Miscellaneous papers. 14). Landbouwhogeschool, Wageningen 1977, OCLC 923343497 .
  11. ^ PJ Den Boer: Density limits and survival of local populations in 64 carabid species with different powers of dispersal. In: Journal of Evolutionary Biology. 3 (1/2), Basel 1990, pp. 19-48.
  12. ↑ Baden-Württemberg biotope networking concept (Landwirtschaft-mlr.baden-wuerttemberg.de)
  13. ^ Robert M. Ewers, Raphael K. Didham: Pervasive impact of large-scale edge effects on a beetle community. In: Proceedings of the National Academy of Science (PNAS). 105 (14), 2008, pp. 5426-5429.
  14. ↑ Rosie Woodroffe, Joshua R. Ginsberg: Edge effects and the extinction of populations inside protected areas. In: Science. 280, 1998, pp. 2126-2128. (PDF)
  15. ↑ Lars A. Brudviga, Ellen I. Damschena, Joshua J. Tewksbury, Nick M. Haddad, Douglas J. Levey: Landscape connectivity promotes plant biodiversity spillover into non-target habitats. In: Proceedings of the National Academy of Science (PNAS). 106 (23), pp. 9328-9332. (pnas.org)
  16. ↑ Do cyclists prevent gene exchange? In: Frankenpost . May 13, 2019.
  17. ↑ Lenore Fahrig, Trina Rytwinski: Effects of Roads on Animal Abundance. (ecologyandsociety.org)
  18. ↑ R. Burkhardt and others: Recommendations for the implementation of § 3 BNatSchG 'Biotope network'. Results of the working group 'Transnational Biotope Network' of the federal state authorities with the BfN. (= Nature conservation and biological diversity. Issue 2). 2004, ISBN 3-7843-3902-6 .
  19. ^ Towards Green Infrastructure for Europe. In: Proceedings of the European Commission workshop 2009. green-infrastructure-europe.org ( Memento of July 13, 2011 in the Internet Archive )
  20. ^ The Green Belt Initiative. ( Memento from December 20, 2010 in the Internet Archive )
  21. ↑ V. Ecological Hoofdstructuur. ( uni-muenster.de ( Memento from July 9, 2016 in the Internet Archive ))
  22. ↑ NABU National Wildlife Trail Plan (PDF)
  23. ↑ Wildkatzenwegeplan of the BUND (wildkatzenwegeplan.de)
  24. ↑ phi: So that the praying mantis knows where to go. In: badische-zeitung.de, Nachrichten, Südwest, April 28, 2012. (May 2, 2012)
  25. ↑ Ellen I. Damschen, Nick M. Haddad, John L. Orrock, Joshua J. Tewksbury, Douglas J. Levey: Corridors increase plant species richness at large scales. In: Science. 313, 2006, pp. 1284-1286. (sciencemag.org)
  26. ↑ Axel Ssymank, Sandra Balzer, Karin Ullrich: Biotope network and coherence according to Article 10 of the Fauna-Flora-Habitat Directive. Federal Agency for Nature Conservation, 2005. (PDF)
  27. ↑ M. Kettunen, A. Terry, G. Tucker, A. Jones: Guidance on the maintenance of landscape features of major importance for wild flora and fauna - Guidance on the implementation of Article 3 of the Birds Directive (79/409 / EEC ) and Article 10 of the Habitats Directive (92/43 / EEC). Institute for European Environmental Policy (IEEP), Brussels 2007. (PDF)