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Ecology Lec 4 (biosphere) summary.docx

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Western University
Biology 2483A
Hugh Henry

Ecology Lec 4: The Biosphere - Biosphere: zone of life on earth (mostly surface, also ocean) - Biomes: large scale biological communities shaped by physical environ (esp. climate) - Plants: non motile, long time- reflect climatic conditions biomes characterized by dominant plant (deciduous vs. succulent leaves) - Plant growth forms: 1. Deciduous 2. Cacti & shrubs (succulent) 3. Needle leaf evergreen Many forms in response to selection pressures: aridity, temp., 4. Grasses 5. Broad leaf evergreen sun, crowding, grazing 6. Forbs (non woody) 7. Sclerophyllous shrubs Convergence: similar growth forms on diff continents (NO genetic relation, BUT similar selection pressures) Temp & Precipitation: affect water loss & availability → in turn affects nutrient supply of soil E.g.: Tundra- ↓temp, ↓precip, Desert- ↑temp, ↓precip, Tropical rainforest- ↑temp, ↑precip Tundra- North (near poles), tropical rainforests- near equator But, humans influence the distribution of biomes 9 Major terrestrial biomes (w/ climate diagrams) 1) Tropical rainforest - High biomass; high diversity (50% of worlds species) - Light- plants must grow tall or adjust to low light - Emergents: rise above - Lianas/epiphytes: use trees for support - Understory: grow in shade - Shrubs/forbs: occupy forest floor - disappearing due to logging & converted to croplands (1/2 gone) - recovery takes long- nutrient poor soils 2) Tropical seasonal forests & savannas - low pressure band move N or S of equator = seasonal/cyclical rain - Wet & dry seasons - shorter trees (deciduous when dry), more grasses/shrubs (not shaded by big trees) - Trees → grass (fire, herbivores, Orinoco river floods)- trees burn but grass can resprout - Human influence- ½ gone, converted to cropland 3) Hot deserts - High pressure area- H cell air coming down (DRY) - High temp, low moisture - Low vegetation & animals (species with short life cycle or succulent leaves to store water) - Convergence eg. Cacti (west hemi) & euphorbs (east hemi) - agriculture- irrigation→ soil salinization - over grazing/drought→ desertification 4) Temperate grasslands - Warm/moist summer & cold/dry winter - grass dominates (frequent fires & large herbivores) - grass grows more roots (than leaves & stem)- cope with dryness → makes soil FERTILE - Agriculture- because fertile land→ sometimes soil sa
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