Lecture 22

Question 1

why is dispersal important

Answer 1

1. colonize new areas
2. escape competition (to a new area with no competition)
3. avoid inbreeding depression (neg conseq of breeding with relatives)

Question 2

how has the plant taxa evolved to help them disperse

Answer 2

they evolved sweet fruit to attract animal seed dispersers
- other seeds are dispersed by wind or water

Question 3

T/F dispersal is the same thing as colonization

Answer 3

true

Question 4

metapopulation

Answer 4

a collection of spatially distinct populations that are connected via dispersal
- each distinct population = a patch

Question 5

T/F metapopulation structure can allow the overall population to thrive even when individual populations are ____

Answer 5

doomed
- they can be rescused
local populations can be reestablished by colonists from other populations after being empty

Question 6

source-sink dynamics

Answer 6

sinks = populations in small habitat patches that would go extinct
- but migrants from other sources (patches) can rescue these populations

Question 7

explain the process of how a patch can become empty

Answer 7

1. prey colonize the empty island
2. prey quickly grows toward carrying capacity
3. some predators arrive and reproduce rapidly
4. predators drive prey to extinction
5. predators starve - die - island is empty
   - this is unstable - both species go extinct

Question 8

how can species that is locally weak be globally stable

Answer 8

dispersal
- occasional dispersal between islands
- recolonizing an empty patch = maintains the population dynamics by the use of metapopulations

Question 9

what are the colonization of patches affected by

Answer 9

• the fraction of currently occupied patches = P
• the fraction of empty patches = 1 - P
  higher P = more sources for colonizers
  as more patches fill up there is less spots for colonizers to occupy

Question 10

what is levins patch occupancy model

Answer 10

ROC = cP (1-P) - eP
at equilibrium, the derivative is = to 0
when the 2 lines intersect = equilibrium where colonization = the patches that are empty - happens at the same rate

Question 11

what happens when P - the colonization of occupied patches = 1?

Answer 11

no empty patches left to colonize
this leads to the colonization rate to be zero

Question 12

how can species A and B have global coexistence but not locally

Answer 12

if A always outcompetes B then B must be a better disperser than B to colonize new patches and ensure persistence across the globe
A has a competition and colonization trade-off - it is good at being a strong competitor but it does not have good colonization skills

Question 13

how do pikas use metapopulation dynamics

Answer 13

in the north they have cooler climates, patches are closer together = stable populations

in the middle region, they have a bit higher temperatures, and the overall quality of the patches becomes reduced - patches are farther apart = low patch occupancy

in the south = high temperatures = habitat degradation = patches become too far and isolated = decline in pikas overtime = they cant be replaced

Question 14

how can populations be driven to extinction

Answer 14

1. stochasticity = random fluctuations that impact the population numbers
2. competitive exclusion - one will outcompete the other eventually bc they cannot live with
3. predator-prey interactions
4. allee effects at low density - growth rate decreases when the size becomes too small

Question 15

what is a metacommunity

Answer 15

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

Question 16

what determines the number of species on an island

Answer 16

1. colonization - migrations
2. extinction - locally extinct on an island
3. in-situ speciation - a lineage can split into 2 on this island but it is a very slow process so we can ignore

Question 17

what was the goal of MacArthur and Wilson’s theory of island biogeography

Answer 17

predict the number of species on an island from the size of the island and its distance from the mainland

Question 18

what did the island biogeography theory say about the colonization rate

Answer 18

species increase = colonization decreases
when a new species colonizers there is less of a chance that it is a new species on this island
- if the island is near the mainland = there is a higher colonization rate bc it is easier to get to
- if the island is far from the mainland = lower colonization rate bc it is harder to get to

Question 19

what did the island biogeography theory say about the extinction rate

Answer 19

increasing the number of species on an island = more extinction
- if it’s a small island - the extinction happens when there is a relative small amount of species bc there are less resources, food, and space
- if it’s a large island - the extinction happens later on when there is more species on the island than small bc there are more resources

Question 20

explain the species richness on real islands with Anolis lizards

Answer 20

• large islands = more lizards
• if the island is more geographically isolated = less species

Question 21

T/F smaller and more isolated habitats have the highest species richness

Answer 21

false
Larger, less isolated habitats tend to have the highest species richness.
Smaller, more isolated habitats have the lowest species richness.