Edge effects

In ecology, edge effects are changes in population or community structures that occur at the boundary of two 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.

Height can create borders between patches as well.

Environmental conditions enable certain species of plants and animals to colonize habitat borders. Plants that colonize tend to be shade-intolerant 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, elk, 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 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:

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