BIOB50 Ch.3

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Biological Sciences
Marc Cadotte

Chapter 3 The Biosphere Introduction y What do these largescale environmental changes have to do biology differences The physical environment ultimately determines where organisms can live and the resources that are available to them y Living things are found on every part of the Earth from the highest mountains to the deepest oceans y Bacteria and archaea are found everywhere even on dust high in the atmosphere y But most organisms occur within a thin veneer on Earths surface from the tops of trees to the surface soil layers and within 200 meters of the surface of the oceansy The biosphere the zone of life on Earth that lies bw the lithosphere Earths surface crust and upper mantle that includes the tectonic plates and the troposphere the lowest layer of the atmospherey Biological communities can be categorized at multiple scales of varying complexityTerrestrial Biomesy Terrestrial biomes are characterized by the dominant growth forms of vegetationy Biomes are large biological communities shaped by the physical environment particularly climatic variation Based on similarities in the morphological responses how organisms physically depend on the environmentof organisms to the physical environmenty Terrestrial biomes are classified by the growth form of the most abundant plantsy Characteristic of leaves may be used Deciduousness seasonal shedding of leaves ThicknessSucculence development of fleshy water storage tissuesTerrestrial biomes reflect global patterns y The locations of terrestrial biomes are correlated w these variations in temp and precipitationy Temperature influences the distribution of plant growth forms directly through its effect on the physiological functioning of plantsy The association bw climatic variation and terrestrial biome distribution can be visualized using a graph of avg annual precipitation and tempThe potential distributions of terrestrial biomes differ from their actual distributions due to human activitiesy Human activities influence the distribution of biomes y Land use change conversion of land to agriculture logging resource extraction urban developmenty The potential and actual distributions of biomesare markedly different The potential distributions of biomes differ from their actual distributions bc human activities have altered so much of Earths land surfaceBiomes Tropical Rainforests Tropical Seasonal Forests and Savannas Hot Deserts Temperate Grasslands Temperate Shrublands and WoodlandsTemperate Deciduous Forests Temperate Evergreen Forests Boreal Forests Tundra y Biome has constant temp and high rainfalloy Found in lowlatitude regions 10 N and S with precipitation exceeding 200cm annuallyy Warm seasonally invariant temperaturesy Contain substantial amount of living plant biomass and they include the most productive ecosystems on Earth y They contain an estimated 50 of Earths species in only about 11 of its terrestrial vegetation covery Occur in central and south America Africa Australia and Southeast Asiay Characterized by broadleaved evergreen and deciduous treesy Globally tropical rainforests are disappearing rapidly due to logging and conversion to pasture and croplands y About half of the tropical rainforest biome has been alteredy Recovery of rainforests is uncertain soils are often nutrientpoor and recovery of nutrient supplies may take a long timey Temp is constant but high and there is a change in rainfall therefore organisms need to adapt to the environment based on the amount of rainfally Located to the N and S of the wet tropics towards the Tropics of ooCapricorn 235 S and Cancer 235 N y Rainfall is seasonally wet and dry seasonsy Vegetation response to this climatic gradient includes shorter stature lower tree densities and an increasing degree of drought deciduousness w leaves dropping from the trees during the dry season y There is a greater abundance of grasses and shrubs w fewer trees relative to rainforestsy Includes a complex of treedominated systems Tropical dry forests Thorn woodlands trees have heavy thorns to protect from herbivores Tropical savannas grasses w intermixed trees and shrubsy Fires promote establishment of savannas some are set by humansy In Africa large herds of herbivores wildbeasts zebras elephants and antelopes also influence the balance of grass and treesy On the Orinoco River floodplain seasonal flooding promotes savannas
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