22. Community ecology: dispersal, metapopulations, and island biogeography

Question 1

Dispersal allows organisms to

Answer 1

• Colonize new areas
• Escape competition
• Avoid inbreeding depression

Question 2

inbreeding depression

Answer 2

reduced survival and fertility of offspring of related individuals

Question 3

Source-sink dynamics

Answer 3

‘Sinks’: are populations in small habitat patches that would go extinct, except migrant populations from ‘source’ populations rescue these population

Question 4

A metapopulation

Answer 4

a collection of spatially distinct populations that are connected via dispersal

Question 5

A patch

Answer 5

each spatially distinct population a patch

Question 6

Patch Dynamics

Answer 6

instead of individuals in a population, we track patch occupancy through time

Question 7

Colonization rate

Answer 7

c P (1 - P)

C = constant
P= The fraction of currently occupied patches

Question 8

Metapopulation dynamics

Answer 8

1. prey colonize empty patch
2. prey grow quickly towards carrying capacity
3. some predators arrive and reproduce rapidly
4. predators drive prey to extinction
5. predators starve, island is empty

Question 9

Levin’s patch occupancy model

Answer 9

dP/dt = cP (1 - P) - eP
eP = overall extinction rate
dP/dt = 0 at equilibrium thus, P= 1 - e/c

Question 10

Local coexistence is impossible because…

Answer 10

A always outcompetes B within a habitat patch

Question 11

Global coexistence requires…

Answer 11

• A must sometimes go extinct OR new patches must be created from time to time
• B must be a better disperser than A (B is a weedy species)
• a competition-colonization tradeoff

Question 12

competition-colonization tradeoff

Answer 12

a mechanism explaining patterns of species coexistence and diversity in nonequilibrium

Question 13

Stochasticity

Answer 13

Relating to or characterized by random, chance, or probability

Question 14

Ways populations can be driven to extinction…

Answer 14

1) stochasticity
2) competitive exclusion
3) preator-pray or host-parasite interactions
4) allee effects at low density

Question 15

Ways extinction are countered (and the paradox of the plankton is resolved by):

Answer 15

1) Predation keeping competitive exclusion from going to completion (as in Paine’s sea star removal experiment)
2) Non-equilibria conditions, habitat patchiness, rescue-by-migration, variation in life-history strategy (as in a competition-colonization trade-off)

Question 16

competitive exclusion

Answer 16

two species or populations cannot inhabit the same niche: one will consistently out-compete the other

Question 17

Metacommunity

Answer 17

a set of local communities linked by the dispersal of one or more of their constituent species

Question 18

MacArthur & Wilson’s Theory of Island Biography

Answer 18

Was made to predict the number of species on an island based on island size and isolation (distance from mainland)
Ignored in-situ speciation; only considered colonization and extinction

Question 19

What determines the number of species on an island?

Answer 19

Colonization (A species can arrive on an island from elsewhere)

Extinction (A species can go locally extinct on an island)

In-situ speciation (A lineage can split in 2 on an island (very slow process))