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BIO120 > Lecture 22 > Flashcards

Lecture 22 Flashcards

1
Q

Dispersal

A

movement from one population to another

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2
Q

dispersal allows organisms to:

A
  • colonise new areas
  • escape competition
  • avoid inbreeding depression
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3
Q

in animals, dispersal relies on

A

active movement - running, flying, etc

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4
Q

how are plants able to disperse?

A

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

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5
Q

Describe how dispersal is important for colonisation of new habitats

A
  • 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
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6
Q

Metapopulation

A

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

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7
Q

how is dispersal involved in the formation of metapopulations?

A
  • dispersal connects populations
  • We call each spatially distinct population a patch
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8
Q

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

A
  • local populations can be reestablished by colonists from other populations after going extinct
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9
Q

source-sink dynamics

A

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

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10
Q

Oceanic Island - single island level

A
  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
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11
Q

single island system

A

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

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12
Q

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

A
  • a group of weakly coupled, locally unstable
    systems can be globally stable
  • The coupling is provided by occasional dispersal between islands
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13
Q

patch dynamics

A
  • akin to population dynamics, except:
  • instead of individuals in a population, we track patch occupancy through time
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14
Q

colonisation of patches is affected by:

A
  • 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
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15
Q

give a simple case for patch dynamics

A
  • 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
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16
Q

Levin’s patch occupancy model

A

differential equations

17
Q

equilibrium patch occupanc7

A

when overall colonisation rate and overall extinction rate intersect

18
Q

what does meta population structure facilitate?

A

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

19
Q

describe how meta population structure facilitates coexistence of competitors

A
  • 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
20
Q

Pikas as an example of meta populations

A
  • 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
21
Q

general conclusions on species coexistence

A
  • populations can be driven to extinction in several ways
  • but these tendencies are countered and the paradox of the plankton is resolved
22
Q
  • populations can be driven to extinction in several ways
A

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

23
Q

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

A

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)

24
Q

meta community

A

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

25
Q

What determines the number of
species on an island?

A

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 …

26
Q

MacArthur and Wilson’s theory
of island biogeography

A

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

27
Q

draw theory of island biogeography in graphs

A
28
Q

why colonisation rate decreases as no of species increases

A
  • the fewer the number of species, the more likely a migrant will be a new species
29
Q

why extinction rate increases as no of species increases

A

more competition

30
Q

near island vs far island

A
  • near island has higher colonisation rate than far island as it is easier to get to
  • so has more species at equilibrium
31
Q

large island vs small island

A
  • extinction rate higher at small islands
  • have fewer resources and can support smaller population sizes
  • so have less species at equilibrium
32
Q

is this model effective for species richness?

A
  • Mahler studied anolis lizards
  • species richness of anoles increase with area and decrease with isolation
33
Q

when else does island biodiversity apply?

A

habitat fragmentation creates ‘islands’ of suitable habitat within an inhospitable matrix

BIO120 (61 decks)

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