Biol 413- Island Biogeography

Question 1

Petran Islands

Answer 1

along the rocky mountains: at the area where it breaks and there are individual peaks at the “cordilleran” these areas are isolated from each other and the valleys below.
They have oaky forests that house temperate flora and fauna (much different to the deserts below)

Question 2

Why study islands?

Answer 2

Isolated - principal factor in driving evolutionary change

Smaller and maybe simpler ecosystems that are easier to study (in regards to ecological and evolutionary processes)

Question 3

Three major approaches of Island biogeography

Answer 3

1) Describe diversity and composition (and diff between continental flora and fauna), and describe adaptations that influenced dispersal and colonization of islands
2) Indentify and quantifies factors that affect rate of dispersal to islands, extinction and numbers and kinds of species that islands can support
3) Understand evolution and communities in novel environments following colonization

Question 4

Species area relationship

Answer 4

Thomas Schoener- one of community ecology’s universal regularities
S = cA^z , log[S]=log[c]+z(log[A])
S= richness, c= fitted parameter constant, A= habitat or island area, z= fitted parameter, represents slope of species area relationship (log= log scale)

As area increases #species increases

Question 5

Example of Species area relationship

Answer 5

• Diversity of conifer and flowering plant genera in the Pacific islands
• Butterflies on the islands off the british isles- a marginally significant relationship with substantial scatter
• Mammal and bird diversity in the great basin mountains
• Fresh water fish in African lakes (old) and North american lakes (young) : african lakes have a higher slope (i.e. higher increase of species to area)

Question 6

Explanations of Species area relationship (6)

Answer 6

• Larger areas hold more individuals, random sampling gives more species on larger islands
• Since larger areas hold more individuals and extinction is less likely in large populations there will be less extinction on larger islands
• Target effect: larger islands have a larger shoreline which leads to higher immigration rates
• Higher geographic/habitat diversity on larger islands (eg elevation and precipitation)
• Higher likelihood of abiotic disturbance on smaller islands, therefore higher extinction rate
• More evolutionary diversification on larger islands (more opportunity for within-island allopatry)

Question 7

Difference between sampling larger areas of continuous habitat vs sampling islands independently

Answer 7

Species richness increases with a higher slope with increasing island area than compared to increasing continuous habitat.

Question 8

Example of Difference between sampling larger areas of continuous habitat vs sampling islands independently

Answer 8

Comparing the ants of Moluccan and Melanesian Islands
The isolated islands had a higher slope than the single landmass ones.

Also the landmass has a higher y-intercept than the islands - indicating that there are more species in smaller “areas” on the large land mass than small islands.

Question 9

Species-isolation relationship

Answer 9

Increase in isolation = decrease in species richness
Decline in richness results from decline in dispersal with isolation
S=k1 * e^(-k2*l^2)
S=species richness, I=isolation, k1,k2= fitted constants

Question 10

Example of species of species-isolation relationship

Answer 10

• Butterflies off the British Isles (lots of scatter)
• Number of high andean bird species on each mountain island (with respect to distance from main andes) Sierras Pampeanas

Question 11

Explanation of species-isolation relationship (4)

Answer 11

-Low immigration rates prevent far islands from attaining equilibrium
-Low immigrations rates lead to a lower number of species at equilibrium
-Lower diversity of habitats on isolated islands
Rescue effect: populations on near islands are less likely to go extinct due to immigration from the mainland

Question 12

Example of dispersal into islands (Melanesian ant fauna)

Answer 12

1) Ants adapt to marginal habitat on mainland
2) cross water gap to Melanesian island
3) Some go extinct
4) others colonize inner rain forest
5) those that colonize diversify in forest habitat and then
6) continue cycle on further islands

Question 13

Equilibrium Theory of Island Biogeography (ETIB)

Answer 13

3 Characters of island biotas

1) species area relationship
2) species isolation relationship
3) species turnover

Question 14

Equilibrium Theory of Island Biogeography explannation

Answer 14

• A larger island has a lower sloped extinction slope therefore a higher #species equilibrium
• A farther island has a lower immigration rate and therefore a lower #species equilibrium

Question 15

Assumptions of ETIB

Answer 15

1) Rate of immigration of new species decreases with increasing species on the island (i.e. because the more species on the island the less chance there is a new arriving species). Reaches 0 when all species in the source area are on the island.
2) Rate of extinction increases with increasing number of species on the island

Question 16

Why are the ETIB lines concave?

Answer 16

• As more species arrive the chance of having deleterious (extinction inducing) interactions increases
• Variation in extinction/immigration probabilities between species:
• best dispersers arrive quickly, poorer and poorer dispersers arrive later
• when many species are present the more extinction-prone species are lost first

Question 17

Significance of the ETIB

Answer 17

1) Interest in the role of contemporary processes to explain species distributions and diversity
2) Conservation biology: relevant to design of wildlife reserves- higher species richness occurs with large area, small edge effects
3) ETIB gives testable predictions (S=species richness, l=large, n=near, f=far, s=small, T=turnover rate) eg
Sln>Slf> = Ssn>Ssf
Tsn>Tln=Tsf>Tlf