3: Species area relationships & island biogeography

Question 1

Give some examples of different types of islands

Answer 1

Oceanic
Isolated mountain tops
Thermal tundra pools
Cryoconite holes in glaciers
Patches of habitat → due to human activity

Question 2

Why do larger islands have more species?

Answer 2

More area = more habitat diversity = more niches = more species
More area = More resources = larger pop. = reduced extinction risk = more species

Question 3

SARs are steeper for large _____ species and in the _____

Answer 3

bodied, tropics

Question 4

What does R^2 show about data?

Answer 4

A measure of how good your model is on predicting the data
- varies from 0-1
= values closer to 0 means more scatter around prediction lines

Question 5

What are the 2 hypotheses that explain SARs?

Answer 5

Environmental heterogeneity hypothesis

Energy availability hypothesis

Question 6

Describe the Environmental heterogeneity hypothesis

Answer 6

= Changes in land area, related to no. of niches and therefore species

In low lat. W. America, soil & rock types extremely diverse = diff plants niches and so species

Question 7

Describe the energy availability hypothesis

Answer 7

= Climate relationships, warmer/wetter is better for plant growth

Measures of mean annual temp
Potential evapotranspiration (PET) → energy in the system, how warm & wet it is
Suggestion that warmer /wetter climates have more species

Question 8

Describe the relationship between saturation and isolation in island biodiversity

Answer 8

• Saturation measures the number of species on an island relative to the possible species that could occur given the pool of species on the mainland
• More distant islands = less saturated than islands close to the mainland

→ observation that led to the development of the Equilibrium Theory of Island Biogeography

Question 9

Describe MacArthur & Wilson (1963) Island Biogeography theory

Answer 9

They devised a simple model predicting species richness on islands
- Species must arrive on an island (immigration)
- Species must persist on an island (extinction)
- Species richness is a balance of immigration and extinction

Question 10

Describe immigration on an island with few species vs many species (Island Geography theory)

Answer 10

E.g an island with very few species
Most colonising individuals will be from underrepresented species
Immigration rates of new species are high

E.g an island with many species
Many individuals that arrive will be from species already on the island
Immigration rates of new species are low

Question 11

Describe extinction on an island with no species vs many species (Island biogeography theory)

Answer 11

E.g an island with no species
No extinction rate
Extinction rates low

E.g an island with many species
By chance alone there will be local extinction
Increased interspecific competition reduces pop. sizes so species extinction rates increase

Question 12

Describe equilibrium according to Island Biogeography Theory

Answer 12

• No. of species present are roughly constant through time
• Immigration and extinction are balanced
• Species composition is dynamic: new species arrive and replace or drive resident species to extinction

Question 13

Why is Krakatoa a good case study for Island Biogeography theory?

Answer 13

• In 1883, catastrophic volcanic explosion devastated the island
• Flora and Fauna completely extinct
• Ecologists can study the recolonisation

Question 14

How does island isolation effect the rate immigration?

Answer 14

Rate is dependent on isolation level (distance from mainland)
= Immigration rates decrease with isolation

Question 15

How does island area effect immigration rate?

Answer 15

Larger islands (by chance) have a higher immigration rate and therefore colonisation rate
= immigration rates increase with area

Question 16

How does island area effect extinction rate?

Answer 16

Larger islands act as buffers against extinction as they can support larger pop. sizes
= Extinction rates decrease with area

Question 17

How does island isolation effect extinction rate?

Answer 17

Extinction rate increase with isolation

Question 18

How is species richness effected by area and isolation?

Answer 18

Species richness increases with increasing area and declines with increasing isolation

Question 19

What do species area relationship graphs describe?

Answer 19

a positive log-linear relationship between species and area

Question 20

The power law parameter(z) of the SAR depends on what?

Answer 20

• Sampling designs
• Organisms
• Body sizes
• Habitats
• Spatial scales

Question 21

What does island biogeography theory predict?

Answer 21

that equilibrium species richness depends on immigration and extinction rates

Question 22

On a SAR graph, what does a lower slope represent?

Answer 22

less environ heterogeneity

Question 23

Describe an environment with high heterogeneity

Answer 23

There is a wide range of different habitats or microhabitats e.g soil moisture, light availability, nutrient levels, or temperature gradients

Question 24

Describe the link between SAR and LDG

Answer 24

When SAR is applied to LDG, it means that larger geographic areas at lower latitudes (closer to the equator) generally have higher species richness

Question 25

What type of habitat often exhibits high levels of habitat heterogeneity

Answer 25

Tropics e.g rainforests, mangroves, and coral reefs