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Chapter 5

BIO120 Notes - The Economy of Nature Textbook 6th ed Chapter 5

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Doug Thomson

CHAPTER 5 THE BIOME CONCEPT convergence process by which unrelated organisms evolve a resemblance to each other in response to similar environmental conditions y Explains why we recognize association bw the forms of organisms and their particular environments eg all tropical rain forest trees have same general appearance biomes categories of biological ecosystems and communities based on climate and dominant plant form y Ecosystems in the same biome type in different parts of world develop similar vegetation structure and similar ways of functioning eg productivity rates of nutrient cycling etc under similar environmental conditions y Each biome is immediately recognizable by distinctive vegetation growth form physical structure biomes establish the fact that no single type of plant can endure the whole range of conditions on earth unique growth forms suited for a particular environment two other factors other than environment influence distributions of species and growth forms interactions bw species and chance and history y Competition predation mutualism etc determine whether a speciesgrowth form can persist in a certain place y Most species dont occupy many suitable environments bc they had not been able to travel to all ends of earth demonstrated by the successful introduction of humans of species to parts of the world that have suitable environmental conditions but are far outside the natural distributions of the species y Unique biomes may be formed bc evolution has proceeded independently in some areas eg Australia has been isolated from other continents for a long time leading to unusual flora and faunaImportance of Climate on Plant Growth Form and Distribution vegetation of temperate seasonal forest and subtropical desert differs y leaves of deciduous forest trees are broad and thin large surface area for light absorption and little protection from dryness or frost leaves of desert species are small and finely divided to dissipate heat spacing of plants differs in addition to form y trees form closed canopies in temperate forests in drier environments trees are more widely spaced bc of competition among their root systems for water ranges of species are limited by the same physical conditions to which they are adapted to in terrestrial environments temperature and moisture are the most important variables especially for plantsBoundaries of Terrestrial Biomes are Defined by Climate climate zone system popular climate classification scheme developed by Heinrich Walter has nine major divisions based on the annual cycle of temperature and precipitation Robert Whittaker defined biomes first by vegetation type and devised a climate diagram to determine the approximate boundaries of biomes with respect to avg temperature and precipitation y on the diagram most locations on earth fall within a triangle with three corners represent warm moist warm dry and cool dry cold regions dont have rainfall bc water does not evaporate quickly at low tempsat higher latitudes precipitation varies so little from one locality to another that vegetation types are poorly differentiated by climate boreal forest bw 0C and 5C tundra below 5C in dry areas with highly seasonal moisture availability grassland and shrubland fire is important in shaping plant communities y desertsmoist forests burn infrequently bc desert dont have enough plan debris for fire and moist forests have moisture
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