Lecture 22: Dispersal, Metapopulations, and Island Biogeography Flashcards
How is sweet, fleshy fruit an adaptation?
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)
Dispersal allows organisms to
- colonize new areas
- escape competition
- avoid inbreeding depression
metapopulation and metacommunity
- collections of spatially distinct populations connected via dispersal
- set of local communities linked by the dispersal of one or more of their constituent species
patch
each spatially distinct population within a metapopulation
source-sink dynamics
one patch is a source the other is a sink (locally extinct without being globally extinct)
Areas which can often be locally unstable but globally stable
archipelagos (each island can have different population dynamics) so long as there is occasional dispersal between islands
What is tracked with patch dynamics
patch occupancy through time (instead of individuals)
Colonization of patches is affected by…
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
Metapopulation structure facilitates
species persistence and coexistence
If species A always outcompetes species B within a habitat patch…
local coexistence is impossible, but global coexistence could be possible
Global coexistence of species A and B requires (when A always outcompetes B in a patch)
- 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
When local coexistence is impossible but global coexistence is, this is known as a…
competition-colonization tradeoff
populations can be driven to extinction by…
- stochastic forces: chance fluctuations in population numbers
- competitive exclusion
- predator prey interactions
- Allee effects at low density
Without migration…
patches that went extinct would stay extinct
What determines the number of species on an island?
- 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
Goal of the Theory of Island Biogeography
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
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?
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)
Species richness tends to…
increase with area, decrease with isolation
habitat fragmentation
suitable habitat in an inhospitable matrix (kind of like an island but on land; island of suitable habitat)
How are metapopulations used to describe disease dynamics?
Hosts are like islands, area (or usable resources) and isolation matters for population dynamics of the disease.
Environmental Stochasticity
Seemingly random events caused by environmental changes that influence how a population changes in size through time.
Demographic Stochasticity
chance sequences of births or deaths in a small populations
Variability increases around the…
carrying capacity (K) in the discrete logistic growth model as the growth rate (lambda) increases.
Deterministic Chaos
make population dynamics looks very noisy but the value in one timestep depends exactly on the value in the preceding timestep
