Edge effect

The edge effect in ecology is the effect of the juxtaposition or placing side by side of contrasting environments on an ecosystem Edge effects are especially pronounced in small habitat fragments where they may extend throughout the patch. Increasing edge effects allows more habitat structure to increase biodiversity within the area.

Edge species (biodiversity)

Environmental conditions enable certain species of plants and animals to colonize on the borders. Plants that colonize tend to be shade-intolerant and tolerable 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 may travel between habitats, while those that are restricted only to the edge are known as edge species. Larger patches include more individuals and therefore have increased biodiversity. The wideness of the patch influences diversity, a patch must be deeper than its border in order to develop interior conditions.

Advantages

They offer unique habitats with easy access to adjacent communities and therefore can support more plants and animals from these adjacent communities. These species can adapt and increase the areas biodiversity. The easy flow of animals to adjacent areas creates travel lanes along borders. There is an increased availability of light to plants along the borders that promotes primary production. For example, the increased availability of light can allow more plants to be supported, which increases herbivorous insects, and then nesting birds, and nest predators are attracted.

Disadvantages

The narrow borders act as travel lanes for predators and increase predation along the edges. Species can be restricted to one area if the border is too wide or overgrown. Edge effect can cause changes in abiotic and biotic conditions which can cause the natural variation to be lost and make the habitat unsuitable for the original ecosystem. Edge effect can also affect the physical and chemical conditions of the species on the borders. For example, fertilizer from an agricultural field can run off into a bordering forest and contaminate that habitat. The three factors affecting edges can be summarized:

1. Abiotic effect – involving changes in the environmental conditions that result from the proximity to a structurally dissimilar matrix

2. Direct biological effects – involves changes in the abundance and distribution of species caused directly by the physical conditions near the edge

3. Indirect biological effects which involve changes in species interactions such as predation, brood parasitism, competition, herbivory, and biotic pollination and seed dispersal[4]

Human effects on edges

Humans have created borders and fragmentation with development and agriculture. This causes habitat loss restricting species to a certain areas and thus creates lower biodiversity in the ecosystem. A few examples of human impacts are:

Introduction of invasive exotic vegetation Higher severity and frequency of fires

Companion animals acting as predators and competitors

Use of and creating trails

Introduction of exotic animals

Pollution, erosion

Loss of foraging habitats

Cooperation between landowners and environmental agencies is needed to maintain habitats and avoid fragmentation and edge effect[5]

Examples

When edges are expanded into 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. "Eugene P. Odum, professor of zoology, 1971: '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.'" quoted in William T. Vollmann, "Another Roadside Attraction," New York Times Book Review, at 9, February 21, 2010. In the case of 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 at the edge. Air temperature, vapor pressure deficit, soil moisture, light intensity and levels of photosynthetically active radiation (PAR) all change at edges.

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 assays refer to artifacts appearing in data which are caused by the position of the wells on a screening plate rather than a biological effect.

Edge effect in scanning electron microscopy is a phenomenon where a larger number of secondary and/or backscattered electrons are generated on a surface that is not purely horizontal.

As the angle relative to horizontal increases, so does the surface area hit by the beam of electrons and therefore the strength of the detected signal increases.