L13: Islands

Question 1

Different types of insularity (islands)?

Answer 1

Islands
Mountain summits
Lakes
Forest fragments

Question 2

What is the main difference between continental and oceanic islands?

Answer 2

The main difference is that continental islands have the same geology as a continental crust, oceanic hsa the same as oceanic crust.

Question 3

What are continental islands?

Answer 3

Part of the continent shelf, and of the same geologic composition as the continent, but separated from the mainland by water.
Rifts, erosion, subsidence, or a rise in sea level.
E.g Madagascar

Question 4

What are oceanic islands?

Answer 4

Islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
Fairly recent origin that have emerged from the ocean floor.
Islands formed at mid-oceanic ridges Ascension Island Azores, Tristan da Cunha, Hawai’i
E.g Hawaii

Question 5

Body size and Islands!

Answer 5

Small mammals in continent are bigger in islands (insular gigantism)
Larger mammals in continent are smaller in islands (insular dwarfism)

Question 6

What is adaptive radiation?

Answer 6

(Gillespie, 2009).

A rapid evolutionary radiation!
The term is taken here to refer to the evolutionary development of distinct species from a single ancestral form, where the radiation is distinguished by niche differentiation among the members of the lineage. The most widely recognized “trigger” for adaptive radiation is the opening up of ecological space

Question 7

What does radiation mean?

Answer 7

A radiation refers to the process by which one species rapidly speciate into a number of different species

Question 8

What is the most widely recognized “trigger” for adaptive radiation?

Answer 8

The opening up of ecological space!

Question 9

Genetic drift

Answer 9

• Change in allele frequencies (genes) in a population due to chance event.
• More likely to occur in small population (ISLANDS!).
• Unlike natural selection (favors beneficial traits) genetic drift is random. Can cause an increase of: beneficial, detrimental, or neutral traits.

Question 10

Types of genetic drift

Answer 10

1) Founder effect: change in gene frequency due to colonization of a new area by a limited number of individuals. Founder populations are essential to the study of island biogeography and island ecology.
2) Population bottleneck: change in gene frequency due to a drastic reduction in the size of the population. For example, a natural disaster.

Question 11

Conservation

Islands are known to have a lot of extinctions

Answer 11

Islands contribute disproportionately to global biodiversity and species extinctions since around 1500, the point from which we have reasonably good data on human impact on islands as European naturalists accompanied the voyages of exploration and conquest.

In this time, about 60% of known terrestrial species extinctions have been island endemics.

But for those birds, invertebrates, mammals and plants for which we can reasonably estimate the timing of species extinctions, we can see that the losses have shown a pattern of increase over time.

This reflects increased pressures placed by human activity on many island ecosystems around the world.

Question 12

What is immigration?

Answer 12

The process of arrival of a propagule on an island not occupied by the species.

Question 13

Immigration decreases with…

Answer 13

isolation.

Question 14

Successful colonisation decreases with…

Answer 14

species richness, due to increased competition (i.e fewer available niches).

Question 15

Function of island area:

Answer 15

Smaller islands have higher extinction rates
Smaller islands provide fewer resources & lower habitat heterogeneity
Smaller islands support fewer individuals within a species: more vulnerable to extinction!

Question 16

Mac Arthur and Wilson’s theory embraces two very general and long-known patterns in Island Biogeography:

Answer 16

1) Number of species to increase with island area.

2) Number of species to decrease with island isolation.

Question 17

Species-area relationship

Answer 17

1) One of the best documented community ecology’s few laws.
2) Regardless of the taxonomic group or type of ecosystem, species
number tends to increase with increasing area.
3) This relationship is NOT linear: richness increases less rapidly for larger islands.

Question 18

Species number

S =

Answer 18

S = cA^Z

Where...
S = species number/ richness
c = constants 
A = Island area
Z =

Question 19

Why is the species-area relationship important?

Answer 19

The species–area relationship is widely used in conservation science to predict the number of species likely to go extinct as a result of habitat loss.

Question 20

Species-isolation relationship: less clearly established than species-area relationship

Answer 20

Species should decline as a function with isolation

Influences immigration!

Question 21

The Equilibrium Theory of Island Biogeography

Answer 21

Species richness on an island represents a dynamic equilibrium controlled by the rate of immigration of new species and the rate of extinction of previously established species.

Question 22

Species turnover (T) concept
Species composition is constantly changing on islands!

Answer 22

The composition of the community is dynamic and changing even if the number of species is reliably stable about some equilibrium point.

Question 23

Assumptions

Answer 23

1) Extinction is only influenced by island size
2) Immigration is only influenced by island isolation.
3) Continued turnover occurs.

Question 24

MacArthur and Willson’s 1963 equilibrium model of island biogeography summary

Answer 24

• They suggested (A) that islands typically reach an equilibrium species diversity, set by opposing rates of natural immigration by dispersing organisms, and species extinction by natural population declines within the island
• As the island fills with species extinction rates increase to balance the tendency to increase through immigration and speciation (which happens especially on more isolated islands)
• Larger islands hold more individuals per population, so have slower rates of extinction; more distant islands have lower immigration rates
• They also saw (B) that over time, distant islands would show gradual increase in diversity as evolution filled more empty niches through speciation, leading to (C) gradual increase in the equilibrium diversity pattern

Question 25

MacArthur and Willson’s 1963 equilibrium model of island biogeography strengths

Answer 25

Produce clear hypotheses and indicates the kind of data needed to test them.

Question 26

MacArthur and Willson’s 1963 equilibrium model of island biogeography weaknesses

Answer 26

• Too simple?
• More factors will affect species richness?
• How to measure isolation?
• Importance of speciation?
• Paid no attention to the life cycle of islands
and has not done so well in explaining the diversity patterns of remote oceanic islands?