Lecture 22: Dispersal, Metapopulations, and Island Biogeography

Question 1

How is sweet, fleshy fruit an adaptation?

Answer 1

It attracts animal pollinators which can disperse the seeds in their stool (heavier seeds can be dispersed this way when they cannot be dispersed by wind or water)

Question 2

Dispersal allows organisms to

Answer 2

• colonize new areas
• escape competition
• avoid inbreeding depression

Question 3

metapopulation and metacommunity

Answer 3

• collections of spatially distinct populations connected via dispersal
• set of local communities linked by the dispersal of one or more of their constituent species

Question 4

patch

Answer 4

each spatially distinct population within a metapopulation

Question 5

source-sink dynamics

Answer 5

one patch is a source the other is a sink (locally extinct without being globally extinct)

Question 6

Areas which can often be locally unstable but globally stable

Answer 6

archipelagos (each island can have different population dynamics) so long as there is occasional dispersal between islands

Question 7

What is tracked with patch dynamics

Answer 7

patch occupancy through time (instead of individuals)

Question 8

Colonization of patches is affected by…

Answer 8

Fraction of currently occupied patches (P)

• higher P means more colonizers
• but also higher P means fraction of empty patches available to colonize is less

Question 9

Metapopulation structure facilitates

Answer 9

species persistence and coexistence

Question 10

If species A always outcompetes species B within a habitat patch…

Answer 10

local coexistence is impossible, but global coexistence could be possible

Question 11

Global coexistence of species A and B requires (when A always outcompetes B in a patch)

Answer 11

• that A must go extinct in a patch OR new patches must be created from time to time
• B must be a better disperser than A
• B must be a fugitive/tramp/weedy/opportunistic/transient species

Question 12

When local coexistence is impossible but global coexistence is, this is known as a…

Answer 12

competition-colonization tradeoff

Question 13

populations can be driven to extinction by…

Answer 13

• stochastic forces: chance fluctuations in population numbers
• competitive exclusion
• predator prey interactions
• Allee effects at low density

Question 14

Without migration…

Answer 14

patches that went extinct would stay extinct

Question 15

What determines the number of species on an island?

Answer 15

• colonization: species can arrive from elsewhere
• extinction: species can go locally extinct on an island
• in-situ speciation: a lineage can split in two on an island but it will be a very slow process

Question 16

Goal of the Theory of Island Biogeography

Answer 16

to predict the number of species on an island from the island’s size and isolation (distance from the mainland)
- only considers colonization and extinction

Question 17

Which island would you expect to have more species: an large island 3 km from mainland or a smaller island 10 km from the mainland? Why?

Answer 17

The larger island because it is easier to colonize something from closer by and equally so the large island because species are less likely to go extinct when there is more habitat (conducive to more species living there less comp)

Question 18

Species richness tends to…

Answer 18

increase with area, decrease with isolation

Question 19

habitat fragmentation

Answer 19

suitable habitat in an inhospitable matrix (kind of like an island but on land; island of suitable habitat)

Question 20

How are metapopulations used to describe disease dynamics?

Answer 20

Hosts are like islands, area (or usable resources) and isolation matters for population dynamics of the disease.

Question 21

Environmental Stochasticity

Answer 21

Seemingly random events caused by environmental changes that influence how a population changes in size through time.

Question 22

Demographic Stochasticity

Answer 22

chance sequences of births or deaths in a small populations

Question 23

Variability increases around the…

Answer 23

carrying capacity (K) in the discrete logistic growth model as the growth rate (lambda) increases.

Question 24

Deterministic Chaos

Answer 24

make population dynamics looks very noisy but the value in one timestep depends exactly on the value in the preceding timestep