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Transcript
Biomes Ecology of Ecosystems Biomes are large-scale, regional ecosystems • Biomes: the Earth’s ecosystems – These ecosystems are dominated by their forms of vegetation – Boundaries are largely determined by climate – The same biomes can occur on two different continents and have different species; usually the two regions will bear striking similarities • Energy transfer in ecosystems • Cycling of major elements Ice • • • • Water is frozen all year No plants Microscopic algae Penguins, Polar bears, etc. • Threatened by global warming Tundra • • • • • • At high altitude or latitude Cold and dry few or no trees Short growing season Low species diversity Low productivity Taiga (Boreal Forest) • cold with much snow • dominated by evergreens • Longer growing season than tundra, but still short • birds immigrate during summer and emmigrate during winter 1 Tropical Rainforest • • • • Warm and wet low seasonality highest diversity evergreen • • • • • Moderate diversity Brushy areas composed of shrubs Mild winters and very dry summers Poor in nutrients Ecosystem depends on fire Temperate Forest • • • • moderate temperature and precipitation high seasonality deciduous trees shaded understory • good diversity Temperate Grassland Chaparral • dominated by grasses • dry and prone to fire • seasonal in temperature Tropical Savannah • • • • scattered trees in grassland high temperature and low rainfall many herbivores Impacted by grazing and fire Mountains • Tropical Montane forests: – cool but constant year round. – In Central America, dominated by oaks. • Alpine – at an altitude of about 10,000 feet or more. – just below the snow line of a mountain. 2 Desert • • • • • Common at 30° N and S of equator low rainfall, but may be cold to hot many succulents Spiny plants Small rodents, lizards, snakes, jackrabbits, etc. Determinants of the Ecosytem • Temperature – – – – Tilt of the Earth Oceanic Circulation Latitude Altitude • Precipitation – Oceanic Circulation – Mountain Shadows Atmospheric circulation creates deserts. Earth’s tilt creates seasons. Latitudinal Patterns of Rainfall 3 Efficiency of Energy Transfer • Energy is transferred between species ina community by predation, herbivory or parasitism. Decrease in energy available at each level • Organisms use about 90% of the energy in their food for their functions: • Cellular respiration • Excretion • Reproduction – Only 10% can be transferred to another species. The 10% Rule 1 10 100 1000 Abundance of Elements in Living Things • Applies to Biomass as well as energy – There are many more plants than herbivores – There are more herbivores than carnivores Producers • Our composition does not reflect the abundance of elements in the earth. • We are mostly Carbon, Hydrogen, Oxygen, Nitrogen. Elements in Living Things – Carbon used as the basis for all biological molecules The Carbon Cycle – Water is the solute for all of life’s reactions – Nitrogen is used to build proteins and DNA 4 The Water Cycle Transpiration The Nitrogen Cycle • Nitrogen Fixation – Bacteria convert N2 gas to NH3 (ammonia) – Occurs in the roots of certain plants • Nitrification – Bacteria convert NH3 to NO3 (plant food) • Denitrification – Bacteria remove NO3 to N2 in the air 5