Patterns of Divesity and Island Biogeography

biogeography

the study of how species and populations are distributed geographically across the planet

Diversity

Variety of life in an area; includes species richness and evenness.

Continental Drift

Movement of Earth's continents over time due to plate tectonics.

Pangea

A supercontinent containing all of Earth's land that existed about 225 million years ago.

Laurasia

Northern part of Pangea after the split

Gondwana

The large southern land mass that existed from pangea. Present-day remnants are South America, Africa, India, Australia, and Antarctica.

Biogeographic Regions

Subdivide earth on basis geographic distributions of related species, genera or families

neararctic region

North America

Palearctic

Europe / N. Asia / N. Africa

Neotropical

Central and South America

Afrotropical

Sub-saharan africa

Indomalayan

India + Southeast Asia

Australian

Australia, New Guinea-- had highly unique fauna

Endemism

species found in only one location and nowhere else

Biodiversity Hotspots

regions with:

Extremely high numbers of endemic species

High threat of destruction

Example: Madagascar, Polynesia, California Floristic Province

Latitude

Distance from the equator. Low latitude = high diversity (closer to equator) especially in tropics.

area

size of habitat

species richness

the number of species in a given area

species-area curve

The larger the geographic area, the greater the number of species.

fragments

small, isolated pieces of habitat left after fragmentation

edge habitats

Border zones between habitats.

Edges have:

More disturbance

More predators

Different light & microclimate

Usually bad for interior-dependent species.

Island Biogeography Theory

Explains species richness on islands using:

Habitat size (bigger = more species)

Isolation (closer to mainland = more species)

Habitat Size

larger habitats contain more species

-lower extinction

- higher immigration

Isolation

closer islands recieve more colonists --> higher diversity

farther island --> fewer species

Equilibrium Point ( Ŝ )

Where immigration rate = extinction rate.Determines the number of species expected on an island.

Discuss evidence for historical influences on regional differences in species richness

Historical events like continental drift, the breakup of Pangea, and long periods of isolation explain why different regions have different groups of species.

Laurasia and Gondwana created distinct northern vs. southern faunas.

Long isolation of places like Australia led to high endemism (marsupials, monotremes).

Past climate shifts and glaciation shaped which species survived or colonized regions.

Key idea: Past geography determines present biodiversity.

Describe the relationship between area of the habitat and the number of species found within that area.

Larger habitats contain more species.

This is the species-area relationship:

Larger areas = more niches

Larger populations = lower extinction rates

Higher probability of colonization

Graph shows a rising curve: as area ↑, species ↑.

What are the predictions of the Island Biogeography Theory?

Species richness is highest on islands that are:

Large (low extinction)

Close to the mainland (high immigration)

Therefore:

Small, far islands have fewest species.

Large, near islands have most species.

Species number reaches an equilibrium where immigration = extinction.

What are the effects of fragmentation of a large contiguous habitat?

Fragmentation results in:

- Smaller habitats (higher extinction risk)

- More isolation (reduced immigration/gene flow)

- More edge habitat (predators, disturbance)

- Loss of interior species

- Smaller, more vulnerable populations

It acts like creating many tiny “islands” in a “sea” of unsuitable habitat.

How can we apply island biogeography theory to design better nature reserves?

Size

Bigger reserves support more species and lower extinction rates.

BEST = one large reserve rather than several small ones.

Number

Fewer, larger reserves generally better than many small ones.

Proximity

Reserves should be close together to allow movement.

Spatial Arrangement

Clustered reserves > widely spaced reserves.

Connectivity

Wildlife corridors (bridges, forest strips, riverbanks) increase immigration and gene flow.

Boosts long-term survival.

Shape

Round or compact shapes are best because they reduce harmful edge habitat.

Long, skinny reserves have more edges → worse.

SPECIES AREA CURVE FORMULA

S= cA^z