Edge effects
In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats.[1] 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.
Urbanization is causing humans to continuously fragment landscapes and thus increase the edge effect. This change in landscape ecology is proving to have consequences.[2] Generalist species, especially invasive ones, have been seen to benefit from this landscape change whilst specialist species are suffering.[3] For example, the alpha diversity of edge-intolerant birds in Lacandona rainforest, Mexico, is decreasing as edge effects increase.[4]
Height can create borders between patches as well.[5]
Environmental conditions enable certain species of plants and animals to colonize habitat borders. Plants that colonize forest edges tend to be shade-intolerant. [6] These plants also tend to be 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, elk, cottontail rabbits, blue jays, and robins. Some animals travel between habitats, while edge species are restricted to edges. Larger patches have increased native species biodiversity compared to smaller patches.[7] 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 levels.
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 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:
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:
Effects on succession[edit]
Edge effects also apply to succession, 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[edit]
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 assays 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.