Week 4-5 Flashcards
What is a metapopulation
Many populations of a single species in a region linked by immigrations and emigrations
What is the model for geometric growth for an open population
Nt+1= Nt+ B – D + I - E
What are the dynamics of a metapopulation determined by
by the
rate of colonization of empty patches and extinction of
individual subpopulations
What are the 3 stages of dispersal
emmigration, transfer and immigration
Define dispersal
The movement of individuals away from others
Define migration
the mass directional movement of large numbers of individuals of a species from one location to another
What is natal dispersal
the movement between the location where individuals are born and where it reproduces
What is breeding dispersal
movement between two successive breeding areas
What are the 4 dispersal mechanisms
passive dispersal
passive dispersal by mutualistic agent
active dispersal
clonal dispersal
What is passive dispersal
Non-exploratory, destination is a matter of chance, like dandelion seeds
What is passive dispersal by a mutualistic agent:
animals eating fruit and defecating the seed away from the original tree
what is active dispersal
dispersal controlled by the individual
What is a clonal dispersal
common on modular organisms, an individual branch spreads its parts around as it grows
What is random disperson
when an organism has the tendency to avoid other organisms or when organisms
What is aggregated dispersion
when individuals are attracted to parts of the
environment or by other individuals
Types of seed dispersal
- gravity,
- wind,
- ballistic,
- water and
- by animals
What is density dependent dispersal
Dispersal depends on local population size, availability of resources, habitat quality and habitat size
Example of density dependent dispersal
Large aphid populations have a lower growth rate than small ones as more aphids are dispersing
Example of inverse density dependent dispersal
Grey-tailed voles were found to disperse less when part of a large population than at as small due to males wanting to overlap several female territories
What species use density independent dispersal
All species that use
passive dispersal by wind, gravity or currents (plants,
spiders, some insects, fish)
What are the 3 main evolutionary consequences of dispersal
Inbreeding avoidance
Competition avoidance
Philopatry
Why is inbreeding avoidance important
Because when close related individuals breed they are likely to suffer from inbreeding depression in fitness -favours dispersal
What is philopatry
tendency of an organism to stay in or habitually return to a particular area`
Why is outbreeding depression a force against dispersal
long distance dispersal may bring together genotypes that are adapted to different environments and the resulting offspring may not be adapted to either environment
Example of a highly philopatric bird
lesser kestrel are highly philopatric, returning to very specific wintering sites
What are the general sex-related differences in dispersal across taxa
Insect males disperse more than,females (males look for females in large areas, while females look for host plants to lay eggs)
– Birds, usually the females
disperse (males compete for
territories and females select
the best territory/male)
– Mammals, usually the males disperse (males compete with other males for mates, so look for the places with most
females)
What is a source of variation in dispersal within a population
Age differences provide a lot of variation.
A lot of plants,mammals and birds use natal dispersal
Marine invertebrates the larval stage ismresponsible for dispersal
Insects, the adult disperses the eggs, the larva
move very little
Example when dispersal ability is a trade off
Glanville fritillary that the lifetime egg production is 4% smaller on average in the more dispersive butterflies due a trade off between high metabolic performance and reduced maximal life span.
What is population synchrony
The correlation of temporal fluctuations in population dynamics between different
localities
What factors promote synchrony
weather
predation
dispersal
Advantages of synchrony
Lower predation risk for each individual (linked to
aggregation and to the advantages of aggregation, e.g.
cicadas)
– Easier to find mates
Disadvantages of synchrony
In the case of disease it may wipe out all populations that are synchronised and connected by dispersal
In case of extreme weather event
Competition for resources
What is the population equation that that takes into account dispersal
Nt+1= Nt+ B – D + I - E
Why is dispersal important
subtract and add individuals to a population
alter the outcome of species interactions
provide crucial genetic variability
rescue populations from extinction
What dispersal studies do not include tagging
Detection of range expansion (in the case of
the butterflies it gives dispersal per generation)
Video cameras
Detection of animal tracks and signs
Dispersal studies with artificial markings
Mark-recapture Tracking paths (direct observation) Telemetry (Satellite, geolocators, etc) Vertical looking radar (VLR) Genetic markers
Why do we need more dispersal studies
The dispersal curves of many species are not
known
the tail of the distribution of
dispersal of many species is not known
For both insects and trees expanding their range after the last glaciation, long distance dispersal is essential to produce the patterns of distribution we see today
What is the relationship between dispersal and global environmental change
Thomas et al 2004 created a model which estimated percentage of extinctions depending on different climate projections. They found that in the worse case scenario, with no dispersal, 58% species will go extinct
What is the simple diffusion gradient
distance moved = Dn*(the square root of log e * R0)
D = average dispersal distance
n = number of generations
R0 = reproductive rate per generation
In terms of dispersal, what does modern DNA allow us to do
Modern DNA technology allows the identification of migration routes
When does a hybrid zone occur
Hybrid zones result from two
divergent genomes that have expanded from two different glacial refugia
What similarities did Hewitt find in dispersal pattern after the last glacier
(a) grasshopper, crested newt and alder
(b) hedgehog, oaks and beech
(c) bear shrews and water voles
What is a population
a discrete group of individuals living in an area with little immigration of emigration, generally the same gene pool
What are characteristics of a metapopulation
consists of many smaller local populations
small movements between sub-populations
can allow individuals to persist in fragments
What characteristics of metapopulations did Levins 1970 describe
Each local population has a substantial probability of extinction
Long term persistence can only occur at the regional or meta population level
What is a source population
A population in a good habitat that exports migrants
What is a sink population
A population in a poor quality habitat that receives migrants
Why do sink populations need migrants
Sinks have low breeding success or high mortality rate so their population growth rate is less than 1, so without migrants, sinks would become locally extinct
What does lambda represent
intrinsic rate of population growth
What is Levins metapopulation model equation and what does it show
The rate of change in the fraction of occupied habitat (patches, p)
dp/dt = mp(1 − p) − μp
μ is the rate of local extinction of patches
m is the rate of recolonization of empty patches
In Levins model, what is required to keep meta populations at a stable equilibrium
The intrinsic rate of recolonisation exceeds the intrinsic rate of extinction
Why is it important to look at trends in the metapopulation and not just local
Local populations can be very unstable and be susceptible to local extinction, and thus we need to look at metapopulations to understand long term persistence
Reasons why organisms would show philopatric behaviour
advantages of inhabiting a familiar environment;
individuals may cooperate with or tolerate related individuals in the natal habitat that share a high
proportion of their genes
Dispersers could meet a social fence from aggressive unrelated individuals
What are 3 necessary features of metapopulations
that individual subpopulations have a realistic chance of experiencing both extinction
and recolonization
The dynamics of the various subpopulations should be
largely independent, i.e. not synchronous
Why, for the metapopulation to persist, can’t the sub populations be dependent
little hope of stability if when one subpopulation went extinct they all did.
Does patchiness = metapopulations
No, for three reasons
Population may be patchily distributed but so much dispersal that the patches aren’t independent or
patches may be so isolated from one another that dispersal between them is negligible
all patches may simply
have a negligible chance of extinction, at least on observable
timescales. (so sig degree of extinction or recolonization.)
Why are corridors important
corridors facilitate exchange rates of organisms between otherwise isolated patches
Why are corridors important for pollinators
important for maintaining genetically viable populations of the plants that they pollinate
What is the Traditional Corridor Hypothesis
corridors function as movement conduits, channelling dispersing organisms between connected habitat patches
List of benefits to corridors
increase immigration and emigration, stem inbreeding
depression, lower extinction rates, lessen demographic
stochasticity, and generate higher population
densities
What is the Drift Fence Hypothesis
at corridors function as drift fences, ‘‘intercepting’’ organisms as they disperse through matrix habitat and redirecting them into habitat patches attached to the corridor
Evidence against drift fence hyopthesis
Townsend and Levy 2005 compared pollen flow to plots with corridor ‘wings’ and those without. No sig diff
Who created the millennium goals
Convention for biological diversity
What are the root causes of biodiversity loss the 2020 conservation targets address
Habitat destruction and fragmentation (e.g. stop deforestation)
Climate change (e.g. agreement on reduced emissions and carbon capture and storage)
Over-exploitation (e.g. sustainable fisheries)
Invasive species (e.g. control invasive species to prevent extinction of endemic species)
Pollution (e.g. significant decrease pollution levels
In 2018, how much of the world is protected
3.6% MPA Sala et al 2018
Why do scientists disagree on how much of the land is protected
Because protected areas still under intense human pressure and sala et al 2018argue that only strongly or fully protected areas actually succeed in protecting biodiversity
Example of when a PA has not been effective
Kruger to the Canyons Biosphere Reserve has experienced deforestation
What determines a species ability to shift range
Degree of habitat fragmentation Species dispersal ability Presence of competitors, parasites and predators
Why are static protected areas still effective during changing climates
They are the first to be colonised by range expanding species
They help retain conracting species in the landscape
How much has the global climate warmed during the 20th century
0.8 C
Who recommended the use of ecological networks and corridors
Hopkins et al 2007
What did hopkins et al 2007 recommend
ecological networks to improve connectivity between habitat patches by habitat expansion, and establishing physical linkages such as corridors and habitat “stepping stones”, and improving the permeability of the matrix to species movement.
How many butterfly species have decline in Britain since 1970
34/46
How does range shift differ between generalist and specialist butterflies
Specilaist sedentary butterflies = range cintracting
Mobile generalists = range expanding
What are the 3 purposes of corriodors
- routes and habitats for organisms responding to climate change
- Allow movement of
individuals, some species
move using major pathways - Increasing the movement of individuals among otherwise isolated populations
– Rescue from stochastic local
extinction
– Maintain genetic diversity
What is connectivity
measure of how a landscape facilitates or impedes the movement of individuals between habitat patches
What are the two ways connectivity can be described
functional and structural
What is structural connectivity
structural connectivity of the landscape is the degree to which habitat patches are physically linked
What is functional connectivity
depends on a species dispersal ability
the size and spatial arrangement of habitat patches
the nature
of land cover and land use in the intervening matrix.
ie what may be functionally connected for one species wont be for another
In terms of edge effects, what is a disadvantage to corridors
Have a high edge effects
May at as a sink attracting species into high edge proportion areas which may increase their mortality and predation risk (evidence needed)
For edge averse species,
corridor width needs to be
such that some portion of the corridor represents core
habitat
Described Haddad (1999) evidence that corridors work
He studied the variegated fritillary and found that their movement between adjacent patches increased with corridors
Why may corridors increase population size of isolated populations
They provide a rescue effect against stochastic extinction
Why might their be higher densities in connected patches than unconnected (evidence)
Greater effective area caused by corridor e.g bird biodivesity in small connected vs small isolated (schmiegelow et al 1997)
What is the benefit of a wrap shaped corridor rather than linear
Buffering core populations may be more efficient than increasing connectivity among numerous vulnerable populations aiding in the rescue effect
Disadvantages of corridors, other than edge effect
can increase incidence of biotically dispersed parasites
may act as a sink when high quality patches are nearby
increase invasion by exotic species
Why are large scale and continental scale corridors important
To support population connectivity, gene flow, range responses to climate change, or dispersal / home range movements of large-area species
