Respond very rapidly to a massive disturbance

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respond very rapidly to a massive disturbance Ecological Succession Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession occurs where no soil exists when succession begins Secondary succession begins in an area where soil remains after a disturbance Early-arriving species and later-arriving species may be linked in one of three processes: + Early arrivals may facilitate appearance of later species by making the environment favorable
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They may inhibit establishment of later species 0 They may tolerate later species but have no impact on their establishment Retreating glaciers provide a valuable field-research opportunity for observing succession Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics Succession is the result of changes induced by the vegetation itself On the glacial moraines, vegetation lowers the soil pH and increases soil nitrogen content Human Disturbance Humans have the greatest impact on biological communities worldwide Human disturbance to communities usually reduces species diversity Humans also prevent some naturally occurring disturbances, which can be important to community structure Concept 54.4: Biogeographic factors affect community biodiversity Latitude and area are two key factors that affect a community’s species diversity Latitudinal Gradients Species richness generally declines along an equatorial-polar gradient and is especially great in the tropics Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate The greater age of tropical environments may account for the greater species richness Climate is likely the primary cause of the latitudinal gradient in biodiversity Two main climatic factors correlated with biodiversity are solar energy and water availability They can be considered together by measuring a community’s rate of evapotranspiration Evapotranspiration is evaporation of water from soil plus transpiration of water from plants Area Effects The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species A species-area curve of North American breeding birds supports this idea Island Equilibrium Model Species richness on islands depends on island size, distance from the mainland, immigration, and extinction The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at a dynamic equilibrium point Studies of species richness on the Galápagos Islands support the prediction that species richness increases with island size Concept 54.5: Community ecology is useful for understanding pathogen life cycles and controlling human disease Ecological communities are universally affected by pathogens , which include disease-causing
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