Lecture 22 Flashcards
why is dispersal important
- colonize new areas
- escape competition (to a new area with no competition)
- avoid inbreeding depression (neg conseq of breeding with relatives)
how has the plant taxa evolved to help them disperse
they evolved sweet fruit to attract animal seed dispersers
- other seeds are dispersed by wind or water
T/F dispersal is the same thing as colonization
true
metapopulation
a collection of spatially distinct populations that are connected via dispersal
- each distinct population = a patch
T/F metapopulation structure can allow the overall population to thrive even when individual populations are ____
doomed
- they can be rescused
local populations can be reestablished by colonists from other populations after being empty
source-sink dynamics
sinks = populations in small habitat patches that would go extinct
- but migrants from other sources (patches) can rescue these populations
explain the process of how a patch can become empty
- prey colonize the empty island
- prey quickly grows toward carrying capacity
- some predators arrive and reproduce rapidly
- predators drive prey to extinction
- predators starve - die - island is empty
- this is unstable - both species go extinct
how can species that is locally weak be globally stable
dispersal
- occasional dispersal between islands
- recolonizing an empty patch = maintains the population dynamics by the use of metapopulations
what are the colonization of patches affected by
- 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
what is levins patch occupancy model
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
what happens when P - the colonization of occupied patches = 1?
no empty patches left to colonize
this leads to the colonization rate to be zero
how can species A and B have global coexistence but not locally
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
how do pikas use metapopulation dynamics
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
how can populations be driven to extinction
- stochasticity = random fluctuations that impact the population numbers
- competitive exclusion - one will outcompete the other eventually bc they cannot live with
- predator-prey interactions
- allee effects at low density - growth rate decreases when the size becomes too small
what is a metacommunity
a set of local communities linked by the dispersal of one or more of their constituent species
what determines the number of species on an island
- colonization - migrations
- extinction - locally extinct on an island
- in-situ speciation - a lineage can split into 2 on this island but it is a very slow process so we can ignore
what was the goal of MacArthur and Wilson’s theory of island biogeography
predict the number of species on an island from the size of the island and its distance from the mainland
what did the island biogeography theory say about the colonization rate
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
what did the island biogeography theory say about the extinction rate
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
explain the species richness on real islands with Anolis lizards
- large islands = more lizards
- if the island is more geographically isolated = less species
T/F smaller and more isolated habitats have the highest species richness
false
Larger, less isolated habitats tend to have the highest species richness.
Smaller, more isolated habitats have the lowest species richness.
