BIOB50 ch.8

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University of Toronto Scarborough
Biological Sciences
Marc Cadotte

Chapter 8 Population Distribution and Abundance Introduction y Distribution geographic area where individuals of a species occur y Abundancetheof individuals in a species that are found in a given areay Ecologists often seek to understand the factors that determine the distributions and abundances of organismsy The abundances and distributions of populations can change greatly over time and space in other words populations are dynamicy Populations of many species are decreasing due to human actions such as habitat destruction and pollutionWe can best prevent the decline of populations we want to protect if we have a clear understanding of what determines their distribution and abundancePopulationsy Population a group of individuals of the same species that live within a particular area and interact w one anothery We can report population abundance either as population size theof individuals in the population or as population density theof individuals per unit of area If there were 2500 lizards on a 20hectare island the population size would be 2500 lizards and the population density would be 125 lizards per hectarey In some cases the total area occupied by a population is not knownIt is often difficult to know how far organisms or their gametes can travel When the area isnt fully known an area is delimited based on best available knowledge of the species Abundances change over time and space y Abundance can change over time and space and some species vary more than others Eg a 6year study of 23 species of insects that fed on goldenrod showed that although the sites had similar climatic conditions every year insect abundances varied greatlyDispersal links populationsy Organisms differ greatly in their capacity for movement y In plants dispersal occurs when seeds which contain the embryo of an individual of the next generation move away from the parent plant Although events such as storms can transport seeds long distances dispersal distances in plants are usually smally Other species such as whales can move thousands of kilometres in a year y Populations may exist in patches that are spatially isolated but linked by dispersal This can result from physical features of the environment and from human activities that subdivide populations Eg heathlands in England have been fragmented by human development What are individuals y For many species whose dispersal capabilities are poorly understood it can be challenging to determine the spatial extent of a populationIn addition for many organisms it can be hard to determine what constitutes the individuals of the population Eg Aspen trees can produce clones genetically identical copies of themselves by forming new plants from root buds A grove of aspens may all be from the same individual
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