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Ecology and People (BIOL 120) Lecture 4: Biomes; Population and Community Ecology Announcements Today’s Outline Biome Basics! Population Ecology Population Dynamics Human Impacts TERRESTRIAL BIOMES !Biomes - Areas sharing similar climate, topographic and soil conditions, and roughly comparable communities. "Temperature and precipitation are among the most important determinants in biome distribution. !Most terrestrial biomes are identified by the dominant plants of their communities. Grasslands ! Communities of grasses and seasonal herbaceous flowering plants. ! Large daily and seasonal temperature fluctuations. ! Frequent grass fires. ! Historic grazing by roaming herds of animals. Realm of Ecology! Biomes Populations Deserts ! Characterized by low moisture levels and precipitation. ! Wide daily and seasonal temperature fluctuations. ! Soils are easily disturbed by human activities, and slow to recover. ! Plants exhibit water conservation characteristics. Tundra ! Treeless ! Very short growing season, with cold harsh winters. 1 Conifer Forests !Cone-Bearing !Plants reduce water loss by evolving thin, needle-like evergreen leaves with thick waxy coating. Broad-Leaved Deciduous Forest !Temperate regions support lush summer plant growth when water is plentiful. "Deciduous leaves an adaptation to freezing temperatures. Conifer Forests !Boreal Forest - Northern Conifer Forest "Broad band of mixed coniferous and deciduous trees between 45° and 60° N latitude. "Moist and cool climate with abundant streams and wetlands. Tropical Moist Forests ! Humid tropical regions support one of most complex and biologically rich biomes. ! Ample rainfall and uniform temperatures. ! Tropical Rainforests - More than 200 cm annual rainfall with warm-hot temperatures year-round. " 90% nutrients tied up in living organisms. " Rapid decomposition and nutrient cycling. " Thin soil cannot support continued cropping, and cannot resist erosion. Population ecology Population Dynamics and Carrying Capacity **the basics** # What is a population? # The two basic characteristics of a population # Rate of growth # Birth rate minus death rate # Final size of the population -carrying capacity $ Population dynamics $ Biotic potential $ Exponential vs. Logistic Growth $ Carrying capacity $ Population Density 2 Exponential and Logistic Growth The Role of Predation in Controlling Population Size $ Predator-prey cycles $ Top-down control $ Bottom-up control Survivorship Curves Population ecology **Human Impacts** !Birth rate, death rate, carrying capacity !Utilization rate (= part of death rate) Human Impacts on Populations and communities $ Habitat degradation and fragmentation $ Ecosystem simplification $ Predator elimination $ Introduction of non-native species $ Over-harvesting renewable resources $ Interference with ecological systems 3