Lecture 22

Question 1

Dispersal

Answer 1

movement from one population to another

Question 2

dispersal allows organisms to:

Answer 2

• colonise new areas
• escape competition
• avoid inbreeding depression

Question 3

in animals, dispersal relies on

Answer 3

active movement - running, flying, etc

Question 4

how are plants able to disperse?

Answer 4

they have evolved traits that aid dispersal:
- sweet, fleshy fruit is an adaptation that attracts animal seed disperses
- other seeds are dispersed by wind or water

Question 5

Describe how dispersal is important for colonisation of new habitats

Answer 5

• postglacial colonisation depends on plant and animal dispersal
• most of Canada was under ice ~12,000 years ago
• range shifts in response to climate change depend on dispersal
• islands

Question 6

Metapopulation

Answer 6

a population of populations - a collection of specially distinct populations that are connected via dispersal

Question 7

how is dispersal involved in the formation of metapopulations?

Answer 7

• dispersal connects populations
• We call each spatially distinct population a patch

Question 8

describe how metapopulation structure can allow population persistence even when individual populations are doomed

Answer 8

• local populations can be reestablished by colonists from other populations after going extinct

Question 9

source-sink dynamics

Answer 9

Source-sink dynamics:
* ‘Sinks’ are populations in small habitat
patches that would go extinct, except …
* Migrants from ‘source’ populations ‘rescue’
these populations

Question 10

Oceanic Island - single island level

Answer 10

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

Question 11

single island system

Answer 11

At the island level, this
system is inherently
unstable: both species
go extinct

Question 12

archipelago of many such islands, each at a different stage, with some dispersal possible

Answer 12

• a group of weakly coupled, locally unstable
  systems can be globally stable
• The coupling is provided by occasional dispersal between islands

Question 13

patch dynamics

Answer 13

• akin to population dynamics, except:
• instead of individuals in a population, we track patch occupancy through time

Question 14

colonisation of patches is affected by:

Answer 14

• the fraction of currently occupied patches, P
• higher P = more sources for colonisers
• the fraction of empty patches, 1-P
• as patches fill up, there are few patches available to colonise

Question 15

give a simple case for patch dynamics

Answer 15

• a large number of identical patches
• ignore population size within patches
• populations within patches go extinct at some constant rate e
• colonisation of patches is affected by P and 1-P
• colonisation rate is thus cP(1-P), where c is a constant

Question 16

Levin’s patch occupancy model

Answer 16

differential equations

Question 17

equilibrium patch occupanc7

Answer 17

when overall colonisation rate and overall extinction rate intersect

Question 18

what does meta population structure facilitate?

Answer 18

species persistence and coexistence
- of a single species (eg tiger salamanders)
- of predators and prey
- of competitors

Question 19

describe how meta population structure facilitates coexistence of competitors

Answer 19

• say A always outcompetes B within a habitat patch, so local coexistence is impossible
• global coexistence requires:
• A must sometimes go extinct in a patch or new patches must be created from time to time
• B must be a better disperser than A
• so B must be a fugitive, tramp, weedy, opportunistic, transient species
• a competition-colonisation trade-off

Question 20

Pikas as an example of meta populations

Answer 20

• Bodie, California
• mining ghost town
• Andy smith’s pika research site
• 1972 - present
• tailing piles from hard-rock mining create many small replicated patches of pika habitat

Question 21

general conclusions on species coexistence

Answer 21

• populations can be driven to extinction in several ways
• but these tendencies are countered and the paradox of the plankton is resolved

Question 22

• populations can be driven to extinction in several ways

Answer 22

Stochasticity: chance fluctuations in population numbers
- Competitive exclusion
- Through predator-prey (or host-parasite, etc.) interactions
- Allee effects at low density

Question 23

but these tendencies are countered and the paradox of the plankton is resolved

Answer 23

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

Question 24

meta community

Answer 24

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

Question 25

What determines the number of species on an island?

Answer 25

Three processes: * 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 two on an island, but this is a very slow process ...

Question 26

MacArthur and Wilson’s theory of island biogeography

Answer 26

Goal: predict the number of species on an island from the island’s size and isolation (distance from mainland) * Ignored in-situ speciation; only considered colonization and extinction

Question 27

draw theory of island biogeography in graphs

Question 28

why colonisation rate decreases as no of species increases

Answer 28

- the fewer the number of species, the more likely a migrant will be a new species

Question 29

why extinction rate increases as no of species increases

Answer 29

more competition

Question 30

near island vs far island

Answer 30

- near island has higher colonisation rate than far island as it is easier to get to - so has more species at equilibrium

Question 31

large island vs small island

Answer 31

- extinction rate higher at small islands - have fewer resources and can support smaller population sizes - so have less species at equilibrium

Question 32

is this model effective for species richness?

Answer 32

- Mahler studied anolis lizards - species richness of anoles increase with area and decrease with isolation

Question 33

when else does island biodiversity apply?

Answer 33

habitat fragmentation creates 'islands' of suitable habitat within an inhospitable matrix