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In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As the edge effects increase, the boundary habitat allows for greater
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
. Urbanization is causing humans to continuously fragment landscapes and thus increase the edge effect. This change in
landscape ecology Landscape ecology is the science of studying and improving relationships between ecological processes in the environment and particular ecosystems. This is done within a variety of landscape scales, development spatial patterns, and organizatio ...
is proving to have consequences. Generalist species, especially invasive ones, have been seen to benefit from this landscape change whilst specialist species are suffering. For example, the
alpha diversity In ecology, alpha diversity (α-diversity) is the mean species diversity in a site at a local scale. The term was introduced by R. H. WhittakerWhittaker, R. H. (1960) Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monograp ...
of edge-intolerant birds in Lacandona rainforest, Mexico, is decreasing as edge effects increase.


Types

* Inherent – Natural features stabilize the border location. * Induced – Transient natural disturbances (e.g., fire or flood) or human related activities, subject borders to successional changes over time. * Narrow – One habitat abruptly ends and another begins (e.g., an agricultural field.) * Wide ( ecotone) – A large distance separates the borders of two clearly and purely definable habitats based upon their physical conditions and vegetation, and in between there exists a large transition region. * Convoluted – The border is non-linear. * Perforated – The border has gaps that host other habitats. Height can create borders between patches as well.


Biodiversity

Environmental conditions enable certain species of plants and animals to colonize habitat
borders A border is a geographical boundary. Border, borders, The Border or The Borders may also refer to: Arts, entertainment and media Film and television * ''Border'' (1997 film), an Indian Hindi-language war film * ''Border'' (2018 Swedish film), ...
. Plants that colonize tend to be
shade-intolerant In ecology, shade tolerance is a plant's ability to tolerate low light levels. The term is also used in horticulture and landscaping, although in this context its use is sometimes imprecise, especially in labeling of plants for sale in commercial ...
and tolerant of dry conditions, such as shrubs and vines. Animals that colonize tend to be those that require two or more habitats, such as white-tailed and
mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...
,
elk The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. The commo ...
, cottontail rabbits, blue jays, and robins. Some animals travel between habitats, while edge species are restricted to edges. Larger patches include more individuals and therefore have increased biodiversity. The width of the patch also influences diversity: an edge patch must be more pronounced than just a stark border in order to develop gradients of edge effects. Animals traveling between communities can create travel lanes along borders, which in turn increases light reaching plants along the lanes and promotes primary production. As more light reaches the plants, greater numbers and sizes can thrive. Increased primary production can increase numbers of herbivorous insects, followed by nesting birds and so on up the
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
s. In the case of wide and/or overgrown borders, some species can become restricted to one side of the border despite having the ability to inhabit the other. Sometimes, the edge effects result in
abiotic In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them unde ...
and biotic conditions which diminish natural variation and threaten the original ecosystem. Detrimental edge effects are also seen in physical and chemical conditions of border species. For instance, fertilizer from an agricultural field could invade a bordering forest and contaminate the habitat. The three factors affecting edges can be summarized: * Abiotic effect—Changes in the environmental conditions that result from the proximity to a structurally dissimilar matrix * Direct biological effects—Changes in species abundance and distribution caused directly by physical conditions near the edge * Indirect biological effects which involve changes in species interactions such as predation, brood parasitism, competition, herbivory, and biotic pollination and
seed dispersal In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...


Human effects

Human activity creates edges through development and agriculture. Often, the changes are detrimental to both the size of the habitat and to species. Examples of human impacts include: * Introduction of invasives/exotics * Higher severity and frequency of fires * Companion animals (pets) acting as predators and competitors * Trails * Pollution, erosion *
Loss Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...
of foraging habitats *
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 process ...
* Deforestation and land use change


Examples

When edges divide any natural ecosystem and the area outside the boundary is a disturbed or unnatural system, the natural ecosystem can be seriously affected for some distance in from the edge. In 1971, Odum wrote, 'The tendency for increased variety and diversity at community junctions is known as the ''edge effect''... It is common knowledge that the density of songbirds is greater on estates, campuses and similar settings...as compared with tracts of uniform forest.'. In a forest where the adjacent land has been cut, creating an open/forest boundary, sunlight and wind penetrate to a much greater extent, drying out the interior of the forest close to the edge and encouraging growth of opportunistic
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
there. Air temperature, vapor pressure deficit, soil moisture, light intensity and levels of
photosynthetically active radiation Photosynthetically active radiation (PAR) designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more o ...
(PAR) all change at edges.


Amazon rainforest

One study estimated that the amount of
Amazon Basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Boliv ...
area modified by edge effects exceeded the area that had been cleared. "In studies of Amazon forest fragments, micro-climate effects were evident up to 100m (330ft.) into the forest interior." The smaller the fragment, the more susceptible it is to fires spreading from nearby cultivated fields. Forest fires are more common close to edges due to increased light availability that leads to increased desiccation and increased understory growth. Increased understory biomass provides fuel that allows pasture fires to spread into the forests. Increased fire frequency since the 1990s is among the edge effects that are slowly transforming Amazonian forests. The changes in temperature, humidity and light levels promote invasion of non-forest species, including invasive species. The overall effect of these fragment processes is that all forest fragments tend to lose native
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
depending on fragment size and shape, isolation from other forest areas, and the forest matrix.


North America

The amount of
forest edge A woodland edge or forest edge is the transition zone (ecotone) from an area of woodland or forest to fields or other open spaces. Certain species of plants and animals are adapted to the forest edge, and these species are often more familiar to hu ...
is orders of magnitude greater now in the United States than when the
European European, or Europeans, or Europeneans, may refer to: In general * ''European'', an adjective referring to something of, from, or related to Europe ** Ethnic groups in Europe ** Demographics of Europe ** European cuisine, the cuisines of Europe ...
s first began settling North America. Some species have benefited from this fact, for example, the
brown-headed cowbird The brown-headed cowbird (''Molothrus ater'') is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern ...
, which is a
brood parasite Brood parasites are animals that rely on others to raise their young. The strategy appears among birds, insects and fish. The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were its ow ...
that lays its
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
in the
nest A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materia ...
s of songbirds nesting in forest near the forest boundary. Another example of a species benefiting from the proliferation of forest edge is poison ivy. Conversely, Dragonflies eat mosquitoes, but have more trouble than mosquitoes surviving around the edges of human habitation. Thus, trails and hiking areas near human settlements often have more mosquitoes than do deep forest habitats.
Grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...
es,
huckleberries Huckleberry is a name used in North America for several plants in the family Ericaceae, in two closely related genera: ''Vaccinium'' and '' Gaylussacia''. The huckleberry is the state fruit of Idaho. Nomenclature The name 'huckleberry' is a Nor ...
, flowering currants and
shade-intolerant In ecology, shade tolerance is a plant's ability to tolerate low light levels. The term is also used in horticulture and landscaping, although in this context its use is sometimes imprecise, especially in labeling of plants for sale in commercial ...
trees such as the Douglas-fir all thrive in edge habitats. In the case of developed lands juxtaposed to wild lands, problems with
invasive exotic An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
s often result. Species such as
kudzu Kudzu (; also called Japanese arrowroot or Chinese arrowroot) is a group of climbing, coiling, and trailing deciduous perennial vines native to much of East Asia, Southeast Asia, and some Pacific islands, but invasive species, invasive in many ...
,
Japanese honeysuckle ''Lonicera japonica'', known as Japanese honeysuckle and golden-and-silver honeysuckle, is a species of honeysuckle native to eastern Asia. It is often grown as an ornamental plant, but has become an invasive species in a number of countries. Jap ...
and
multiflora rose ''Rosa multiflora'' — (syn. ''Rosa polyantha'') is a species of rose known commonly as multiflora rose, baby rose, Japanese rose, many-flowered rose, seven-sisters rose, Eijitsu rose and rambler rose. It is native to eastern Asia, in China, J ...
have damaged natural ecosystems. Beneficially, the open spots and edges provide places for species that thrive where there is more light and vegetation that is close to the ground. Deer and elk benefit particularly as their principal diet is that of grass and shrubs which are found only on the edges of forested areas.


Effects on succession

Edge effects also apply to
succession Succession is the act or process of following in order or sequence. Governance and politics *Order of succession, in politics, the ascension to power by one ruler, official, or monarch after the death, resignation, or removal from office of ...
, when vegetation spreads rather than losing to competitors. Different species are suited either to the edges or to central sections of the habitat, resulting in a varied distribution. Edges also vary with orientation: edges on the north or south receive less or more sun than the opposite side (depending on hemisphere and convex or concave relief), producing varying vegetation patterns.


Other usage

The phenomenon of increased variety of plants as well as animals at the community junction ( ecotone) is also called the edge effect and is essentially due to a locally broader range of suitable environmental conditions or ecological niches. Edge effects in
biological assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a ...
s refer to artifacts in data that are caused by the position of the wells on a screening plate rather than a biological effect. The edge effect in scanning electron microscopy is the phenomenon in which the number of secondary and/or backscattered electrons that escape the sample and reach the detector is higher at an edge than at a surface. The interaction volume spreads far below the surface, but secondary electrons can only escape when close to the surface (generally about 10 nm, although this depends on the material). However, when the electron beam impacts an area close to the edge, electrons that are generated below an impact point that is close to an edge but that is far below the surface may be able to escape through the vertical surface instead.


See also

* Ecotone *
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 process ...
*
Landscape ecology Landscape ecology is the science of studying and improving relationships between ecological processes in the environment and particular ecosystems. This is done within a variety of landscape scales, development spatial patterns, and organizatio ...
* Ruderal species * Spatial ecology *
Woodland edge A woodland edge or forest edge is the transition zone ( ecotone) from an area of woodland or forest to fields or other open spaces. Certain species of plants and animals are adapted to the forest edge, and these species are often more familiar to h ...


References


External links


Reducing Edge Effects in biological assays
{{DEFAULTSORT:Edge Effect Landscape ecology Ecological succession Habitats Ecology terminology Biology terminology Environmental terminology Habitat Systems ecology