Lecture_5 - Population Growth 5th 230 Ecology lecture 29...

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Population Growth 5 th 230 Ecology lecture 29 October 2009 th Ed. If you were to meander in the natural world you would continually encounter new species. Species are NOT distributed evenly at any spatial scale. Even at a small natural area like the James Woodworth prairie which is the size of a city block (2 ha = 1/16 x 1/8 mile) many plant species are located only in a small part of the site. At larger scales if one travels 50 miles in any direction one is likely to find species that do not occur in the starting area. Geographic range of a species is a map of the places that the species occurs. Even aquatic species that live in the oceans -which are all connected- are not found throughout the world. Humans are probably the only species that you might encounter anywhere on the earth, though some of the species that exploit human habitats (lice, mice & rats) or that humans deliberately spread (crops & other plants) are now much more widely distributed than they originally were. Figure 9.3 presents map which illustrates a typical spatial structure of individuals which also applies to subpopulations. Within the geographic range of a species the individuals and populations are not distributed uniformly. For sessile organisms such as plants the map has only a long temporal scale (> yr), but for organisms with mobility the same pattern is true at any one time but the locations of the patches change diurnally or seasonally. Birds are highly mobile and some species move between continents seasonally. Larger mammals also may move considerable distances to find more resources. The regular patterns of moving considerable distances are known as migration. During a migration the individuals of a species are often aggregated into large flocks or herds. One can always find a scale at which individuals/populations are aggregated (see Fig. 9.5). For plants, aggregation is mostly based on abiotic habitat requirements and dispersal of seeds from the individuals that produce seed. (dispersal limitation) In Figure 9.6 a grid has been superimposed on Fig. 9.5. How can we treat those data quantitatively? How do we know if the individuals are distributed randomly? The standard way is to count the individuals in each cell and then count the number of cells with each count from 0 up to the maximum. From the total number of individuals and the number of cells one calculates the mean number of individuals per cell. The Poisson distribution is used to calculate the expected proportion of cells with 0, 1, 2, …max. From
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This note was uploaded on 01/23/2010 for the course BIOS 230 taught by Professor Gibbons during the Fall '08 term at Ill. Chicago.

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Lecture_5 - Population Growth 5th 230 Ecology lecture 29...

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