Final Exam Review BIOGEO.docx

Three scales of the species area curve

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Three scales of the species-area curve - Interprovincial curve: relationship tends to be relatively steep for comparisons among provinces – they are evolutionary independent and share relatively few species - Within-province (mainland): at this scale, communities derived from a common pool of species (evolved within that province) – increase in richness as larger areas are sampled is largely function of ecological processes (availability of habitats and niches) but not evolution – therefore a relatively shallow curve - Among-island curves: sloped of curves tend to vary systematically with characteristics of the biota and archipelagoes – typically intermediate between those at other scales – function of tendency for habitat diversity to increase with island area and of interplay between processes of immigration and extinction - Island biogeography graphs represent the equilibrium species number on islands of different sizes and different degrees of isolation. Key Equilibrium Theory Terms - Colonization: the relatively lengthy persistence of an immigrant species on an island, especially where breeding and population increase are accomplished - Extinction: the total disappearance of a species from an island (which does not preclude recolonization) - Immigration: the process of arrival of a propagule on an island not occupied by the species (implying nothing concerning the subsequent duration of the propagule or of its descendants) - Propagule: the minimum number of individuals or a species capable of successfully colonizing a habitable island (the minimal input required – a single mated female, and adult female and a male or a whole social group, depending on the species Some exceptions of IBT (left target effect, right rescue effect) Small island effect - That decreasing species richness with island size might not hold on very small islands – in several cases if only the smallest islands of island groups are studied, there is often no relationship - Islands are so small that none can support large enough population to produce significant extinction rates Rescue effect - Proximity of islands to mainland also serves to decrease extinction rates –contrary to theory, islands near the mainland have significantly lower turnover rates than distant islands
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- The decreased turnover rats observed near islands have been attributed to a phenomenon called the rescue effects - Occurs when small populations of a species are rescued from the brink of extinction by the arrival of new immigrants of the same species - Shown to be important in maintaining some populations of continental bird species Target Area Effect - It has been suggested that island size will also influence rates of immigration, not just distance - Larger islands provide bigger target for dispersing organisms - The positive relationship between island size and immigration rates is called the target area effect - For actively dispersing animals that travel between the mainland and islands by flying,
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