• Biomes: the Earth’s ecosystems

• Energy transfer in ecosystems

• Cycling of major elements

Ecology of Ecosystems

Biomes

Biomes are large-scale, regional 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

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 immigrateduring summer and emmigrate during winter

Tropical Rainforest

• Warm and wet• low seasonality • highest diversity • evergreen

Temperate Forest• moderate temperature and precipitation • high seasonality • deciduous trees• shaded understory• good diversity

Chaparral• Moderate diversity• Brushy areas composed of shrubs • Mild winters and very dry summers • Poor in nutrients• Ecosystem depends on fire

Temperate Grassland• 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.

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

Earth’s tilt creates seasons.

Atmospheric circulation creates deserts.

Latitudinal Patterns of Rainfall

Efficiency of Energy Transfer • Energy is transferred between species ina

community by predation, herbivory or parasitism.

• 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.

Decrease in energy available at each level

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The 10% Rule

– There are many more plants than herbivores

– There are more herbivores than carnivores

Producers

• Applies to Biomass as well as energy

Abundance of Elements in Living Things

• 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

– Water is the solute for all of life’s reactions

– Nitrogen is used to build proteins and DNA

The Carbon

Cycle

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