Lec #2: Distribution Species-Communities

The question that we ask ourselves

Why are particular species present in some places & absent in others?

Evolutionary history, changes in geography, environmental conditions

Large Scale Patterns: Biogeographic regions (8)

Based on the taxonomic similarities of the organisms living there

Boundaries are set where species composition changes dramatically over short distances (pinch-point of organisms)

Large Scale Patterns: Climate

The long-term average atmospheric conditions found over time (Temperature, Precipitation, Wind Velocity)

Ex: it is 2 degrees hotter every summer for 1000 years

Climate varies because of differences in the amount of solar energy (Drives global atmospheric and oceanic circulation) (time of the year)

Large Scale Patterns: Weather

The short-term state of atmospheric conditions at a particular place and time

Ex: it is hot this summer

Daily Temperature

Rotation of Earth on its axis (24-hour cycle); sun during the day and no sun at night

Seasonal Temperature

Annual Cycle (Fixed axial tilt at 23.5 )

Variation in sunlight intensity & day length give rise to seasonal variation in temp. in north & south hemispheres due to areas being closer or further away from the sun

The temp would be the same all around if there was no tilt

Tropics are hotter than temperate regions

1. solar radiation strikes at almost right angles near equator but at

obtuse angles near the poles

2. same amount of radiant heat concentrated over smaller area at tropics (more area is hit by the same sunlight, so there is more coverage making it less intense)

3. at poles solar radiation passes through deep layer of atmosphere (reflection, absorption, scattering)

Falling air

Cool air with high pressure

Rising air

Hot air with low pressure (like showers)

Climactic conditions

Water variability and temperature

From hot (high concentration) to cold (low concentration)

Global Air Circulation Pattern: 0 degrees

Radiant heat above equator warms the air at equator moist, hot air rises to cooler altitudes and rains (Tropical Rainforests)

Hot and wet

Low pressure

Sunlight on the water causes water vapor to go straight up

Global Air Circulation Pattern: 30 degrees

Cool air descends (high pressure) at latitudes of about 30 N and 30 S & heats (Hot Deserts)

Hot and dry (holding onto precipitation)

High pressure

Global Air Circulation Pattern: 60 degrees

Air picks up moisture and rises at 60 N and S & rains (Temperate Rainforests)

Cool and wet

Low pressure

Ex: redwoods

Global Air Circulation Pattern: 90 degrees

Drier air descends in polar regions (cold dry Polar Deserts)

Cold and dry

High pressure

Transitional zones

Between the 4 main biomes

Between desert and tropical rainforest: savannah

Between desert and temperate rainforest: prairie

Between temperate rainforest and polar desert: tundra

Large Scale Patterns: Biomes

Climate determine the distribution of biomes

Terrestrial biomes are based on the structure of their dominant vegetation (ex: tropics have the rainforest and the savannah has grass)

Aquatic biomes on their Physical/Chemical differences (temperature or pH)

In each terrestrial biome vegetation has similar traits, but may not be closely related (evolutionary)

Large Scale Patterns

Large scale distribution patterns can be predicted from climate conditions (Temperature, Precipitation, Wind)

Large scale distribution patterns do not predict small scale distribution patterns or what species will occur

Transplant experiments

Methods for Analyzing Distributions: the major conceptual/experimental techniques used to determine the factors limiting distribution

Move organism and see if it can survive and reproduce in new environment (at least one complete generation)

Successful: potential range of a species is larger than its actual range

Unsuccessful: potential range of a species is the same as its actual range