Single-Species Populations IV: Metapopulations and Other Spatially-Structured Populations Flashcards
The spatial ecology of individual small, extinction-prone populations is often
patchy, but not isolated.
In individual small, extinction-prone populations, population persistence and dynamics depend on
the capacity of individuals to move and disperse between connected patches.
On a landscape scale, population persistence can be explained by
- rates of movement
- colonisation
- extinction
- interactions between these three variables
Under logistic growth
- r declines with density
- reflects the ability of density-dependence to regulate an exponentially growing population abouts its environmental carrying capacity
r
per capita growth rate
Fragmented habitats often display
- small populations undergoing breeding depression
- extinction prone because of the vulnerability of their local population to stochastic events
On landscape fragmentation, local population patches are
reduced in area and coupled with high extinction rates and disintegration of social structures
From what do high extinction rates arise?
- environmental and demographic stochasticity
- drift
- high heterozygosity
- alee effects
Describe recolonisation in an open system
Nt+1 = Nt + Births - Deaths + Immigrants – Emigrants.
What are the amoung-population processes
Immigration and emigration
Describe the amoung-population processes
- critical to fragmented population persistence
- dispersal ability relative to fragmentation determines population structure and survival
In a spatial context, fragmented landscapes sometimes form
metapopulations – populations of populations.
A non-equilibrium metapopulation is when
extinction is higher than colonisation, leading to an inevitable, albeit slow, population decline
What does metapopulation formation allow?
- species persistence in the landscape as a balance of rates of local extinction and colonisation events between patches
- patches ‘blink’ on off, with colonisation and extinction respectively
- only some of the patches are occupied during any one time slice.
Give an example of a non-equilibrium metapopulation
- Meliteaea cinxia, the Glanville Fritillary, found in Åland, Finland
- studied by Hanski, broadly considered the godfather of metapopulation biology
Describe Hanski
pioneered the study of dynamic spatial distribution of populations
Describe the formalisation and modelling of metapopulations
- Levins
- rate of change of occupied patches = c - e.
- dp/dt = cp(1-p) – ep
c
colonisation
e
extinction
p
patch
stable equilibrium of occupied p fraction occurs when
- c = e
- when the differential = 0
- pˆ = 1- e/c
Describe Levins analysis
- higher the rate of colonisation and lower the rate of extinction, the greater the proportion of patches that would be occupied
- coser habitat patches ease dispersal and have a higher colonisation rate
- smaller populations more vulnerable to stochastic extinction
Describe a phenomenon that increases the chance of landscape-level extinction
correlated population dynamics that mirror each other across fragments
Describe how colonisation rates have been maximised
ensuring the geographical closeness and connection of patches
Describe uncorrelated population dynamics
- decrease the probability of simultaneous local extinction
- leads to global extinction, across patches
- allow for the dispersal events that allow recolonisation of locally extinct patches
Which metapopulations are the most unstable?
correlated metapopulations
Give an example of spatial conservation to minimise e rates
- habitat management to increase habitat area and resources (to allow for a corresponding increase in carrying capacity)
- reducing population variations ensuring heterogeneity of patches
- differential management to allow optimisation to different stochastic events reduces population synchrony, maintaining the likelihood of dispersal events to avoid landscape-level extinction
Describe how p-hat has been maximised
conservation of empty habitat patches to prepare for potential future colonisation
What are metapopulations?
populations of just less than average connectivity and variance in patch size
What are non-equilibrium populations?
when patches are highly isolated and the variance in size is mostly small
How is population connectivity measured
dispersal distance relative to inner-patch distance
What are island-mainland (or core-satellite) populations
highly isolated but with high patch size variance
What are patchy panmictic populations?
connectivity is slightly better than in metapopulations, but patch size variance is slightly larger
What are dissected populations?
connectivity is high but patch size is still variable
Each different fragmented population structure has
different implications for their practical conservation strategies.
Describe and give an example of a patchy population
- organisms display high mobility and therefore dispersal is high
- extinction rate is much less than the colonisation rate
- Holly leafminer (Phytomyza ilicis)
Describe and give an example of island-mainland dynamics
- Edith’s checkerspot (Euphydras Editha)
- mainland extinction rate is always = 0
- island population, in a spatial sense, can be deemed immortal
Describe source-sink dynamics
- source is the net exporter of individuals
- does not receive immigrants, but provides a lot of emigrants
- persistence of the sink can only be explained by its high immigration from the source, otherwise its population would decline towards extinction
- cannot support a barrier being inplaced
Describe a sink populations
always exhibits a mortality greater than its natality
Give an example of source-sink dynamics
- seed-plant (Cakile edentyka), Sea Ricket populations that live close to the tidelines and require a constant input of seeds near the high watermark
- beach source and dune sink
