Slide Set 2 Distribution of Species & Communities

What major factors influence the distribution of species and communities?

Evolutionary history, changes in geography, and environmental conditions.

What are biogeographic regions?

Large-scale regions characterized by distinct species compositions.

How many major biogeographic regions are there?

Eight.

How are boundaries between biogeographic regions determined?

Where species composition changes dramatically over short distances.

What are biogeographic regions based on?

Taxonomic similarities of organisms living in each region.

What is climate?

Long-term average atmospheric conditions over time, including temperature, precipitation, and wind velocity.

What is weather?

Short-term atmospheric conditions at a specific place and time.

Why does climate vary across Earth?

Differences in the amount of solar energy received, which drives global atmospheric and oceanic circulation.

What causes daily temperature cycles?

Earth's rotation on its axis (24-hour cycle).

What causes seasonal temperature cycles?

Earth's fixed axial tilt of 23.5° and its annual orbit around the sun.

Why do seasonal temperature differences occur between hemispheres?

Changes in sunlight intensity and day length between the northern and southern hemispheres.

Why does solar radiation hit the tropics more directly?

Sunlight strikes near right angles at the equator but at obtuse angles near the poles.

How does radiant heat concentration differ between tropics and poles?

The same amount of heat is concentrated over a smaller area in the tropics.

Why do polar regions receive less effective solar radiation?

Sunlight passes through a thicker layer of atmosphere, increasing reflection, absorption, and scattering.

What are the three major global air circulation cells?

Hadley cell, Ferrel cell, and Polar cell.

What happens at the equator in global air circulation?

Warm, moist air rises (low pressure), cools, and rains, forming tropical rainforests.

What occurs at about 30° N and 30° S latitude?

Cool air descends, creating high pressure and hot deserts.

What happens at about 60° N and S latitude?

Air rises, cools, and rains, forming temperate rainforests.

What characterizes polar regions in air circulation?

Cold, dry air descends, forming polar deserts.

What determines the distribution of biomes?

Climate.

How are terrestrial biomes classified?

By the structure of dominant vegetation.

How are aquatic biomes classified?

By physical and chemical differences.

Why can vegetation in the same biome look similar but be unrelated?

Similar traits evolve independently due to similar environmental pressures.

What two main questions are asked about species distribution?

Why does a species not occur, and what is the source of limitation?

Why don't large-scale patterns predict small-scale patterns?

Climate predicts broad patterns but not specific species occurrences.

What variables can predict large-scale distribution patterns?

Temperature, precipitation, and wind.

What is the purpose of transplant experiments?

To determine factors limiting a species' distribution.

How are transplant experiments conducted?

Move organisms to a new environment and observe survival and reproduction over at least one generation.

What does a successful transplant indicate?

The potential range is larger than the actual range.

What does an unsuccessful transplant indicate?

The potential range equals the actual range.

Why might a species not occupy its full potential range?

Inaccessibility, lack of dispersal, or inability to recognize habitat.

What factors can cause transplant failure?

Predators, competitors, parasites, disease, physical/chemical factors, or habitat selection.

What is dispersal?

Movement of organisms from one geographic location to another.

Are most organisms capable of dispersal?

Yes, most organisms are mobile.

Are geographic barriers common in nature?

Yes.

What species was studied in Southern California intertidal zones?

The barnacle Balanus cariosus.

Where is the southern limit of B. cariosus?

Point Conception.

How do barnacle larvae disperse?

Via plankton.

What were the two hypotheses explaining the southern limit?

Larvae die due to poor conditions, or Point Conception blocks dispersal.

What was done in the transplant experiment?

Barnacles were transplanted to UCSB.

What were the results of the barnacle transplant?

Barnacles survived and reproduced.

What conclusion was reached?

Dispersal barrier (water currents) limits distribution.

When and why was Tasmanian blue gum introduced to California?

1850s Gold Rush; used for construction, furniture, and railroad ties.

Why does blue gum thrive in Southern California?

Favorable abiotic conditions, no native predators, and competitive advantage.

What limited its distribution originally?

Dispersal barriers breached by human introduction.

How were black rats introduced to Hawaii?

By humans in the late 1700s.

Why was the mongoose introduced?

To control black rat populations.

Why did the mongoose fail to control rats?

Rats are nocturnal; mongooses are diurnal.

What unintended effect did mongooses have?

Predation on native birds and eggs.

What is habitat selection?

When organisms choose not to live in certain habitats despite being able to disperse there.

How can habitat selection limit distribution?

Through behaviorally constrained choices.

How does habitat selection affect dragonfly distribution?

Male territorial behavior determines where females lay eggs.

What is the result of this behavior?

Reproductive habitat is smaller than available habitat.

Which two species are compared in the pipit example?

Tree pipit (Anthus trivialis) and meadow pipit (Anthus pratensis).

What do these two species have in common?

Ground breeding and similar diets.

Why is the tree pipit absent from treeless areas?

It needs a tree perch to end its mating song.

Why can meadow pipits live in treeless areas?

Their mating song ends on the ground.

What limits the distribution of tree pipits?

Behavioral habitat selection.

Why does habitat selection evolve?

Because individuals in certain habitats leave more descendants than those in others.