EE31 Flashcards
what is a metapopulation?
a group of spatially separated populations of the same species which interact at some level by immigration and emigration (patchy population)
what
did Carl Huffaker’s experiment show ?
predator prey co-existence can be facilitated by spatial structure and the rescue effect
what is wrong with Nicholson bailey models describing the dynamics of coupled host-parasite / predator-prey systems?
model is not stable - tiny deviations from equilibrium mean populations crash
could not explain non-extinction population stability
what is the context of Huffakers experiment in terms of the mites involved? should the populations persist?
predatory mite is voracious predator of the citrus mite that eats from oranges . Organes are firstly infested with citrus mite then predatory mite follows. Predatory eats citrus mites (they die) then predatory mite dies of starvation. However, in the wild both species persist and do not go extinct. Huffaker’s experiments show this is because spatiall aggregation can be stabilising
what was the method to Huffaker’s experiments/
1)fields of oranges and rubber balls
20dispersal distances between oranges adjusted using rubber balls
3)patch quality adjusted by covering portions of oranges
4)sticks added to the oranges to manipulate the mites’ natural dispersal mechanisms
what is the rescue effect?
ability of a habitat being rescuable by immigration (recolonisation )
although single orange=unstable the whole system= stable
where is extinction in Huffaker’s experiments? in individual patches?
yes. extinction occurs in individual patches
what stabilises nicholson-bailey (predator-prey) type interactions ?
spatial structure (aggregations)
metapopulations
what is the result summanry of Huffaker’s experiments? (3)
Clear demonstration that predator-prey coexistence can be facilitated by spatial structure
You see prolonged cycles overall (total population)
Extinction and colonization play a key role here in dynamics and persistence
what did the field mole in Tvärminne archipelago case study show?
Spatial aspect important
repeated immigration emigration extinction
Independent dynamics but emmigration links the populations
Cannot treat this as one population!
where are the field moles?
Tvärminne archipelago
What does the larch budmoth case study show?
- outbreaks in waves/immigration
- evidence for cycles go back to tree rings in Roman times
The Larch budmoth: defoliates trees throughout the European alps
Parasitoids of the budmoth
What are Levin’s model assumptions? (5)
- infinite number of patches
- patches are equivalent
- patches are equally connected
- colonisation is not affected by distance
- patches are in a binary state 1 or 0 (no consideration of local population dynamics or pop abundance)
What was levin interested in?
exploring effect of occupied/empty patches (binary state- open or occupied only)
he looked at the balance between local system extinction and colonisation.
what is levin’s model?
dP/Dt = cp(1-p) - ep
c=colonisation rate
p=occupancy
e=extinction rate
dp/dt=rate of change of fraction of patches occupied
what is p when dp/dt= 0 (equilibrium patch occupancy state)?
p=1-e/c
if e>c then p
metapopulation goes extinct
if e
p>0 so the metapopulation survives even though over time each patch will eventually go extinct
what happens to c if some habitat patches are removed? effect on pop?
c is reduced, pop more likely to go extinct
what happens to c if wildlife corridors are added e.g hedges? EFFECT ON POP?
c is increased. population persistence is more likely
what 2 things did lenvins model shows wrt proportionality?
1) extinction is proportional to occupancy
2) colonisation is proportional to p*(1-p)
what is p(t)?
the fraction of patched currently occupied at time (t) by the species of interest.
Lenvins model flaw= not all patches are equal and equally connected, give an example
Skipper butterfly
Hesperia comma (skipper butterfly)
-only lives in certain grassland
-only lays eggs on certain size of certain grass species
what is the effect of patch size and remoteness?
Small patches go extinct more frequently
Remote patches colonized less readily
what is the link between good quality patch(source) , migration and bad quality (sink)
such a system CAN BE EVOLUTIONARY STABLE
source;most competitive,good quality
sink: less competitive individuals here, bad quality
note: it is better for competitive individual to move back to the bad quality patch (the sink) than to not breed at all
example of source sink dynamic? would the population survive in isolation?
Cakile edentula
annual plant on seashores in Martinque Bay, Nova Scotia
by the shore -Seed production high
Mortality low
Net disperser of
seeds
landward-Seed production low Mortality high Net receiver of
seeds
Population stable here, although it would not survive in isolation
Back to the moles, explain their population dynamics wrt emigration and patches
small populations can “rescue” large
emigration increases before extinction
Patches not equal but metapopulation roughly follow Levins model
are source-sink patch quality dynamics the only ones?
No. There are many other configurations besides one source and one sink.
Patch-quality effects are more than just source-sink dynamics
are within patch dynamics important?
yes.The Levins model is only a “patch occupancy” model Each patch is either inhabited or not No population dynamics within patches Clearly dynamics do occur within patches The Huffaker experiments made this clear Within-patch dynamics can be important!
YOU COULD ADD Lotka-Volterra dynamics
Problems with metapopulation models:
Patch occupancy or within-patch dynamics model?
Patches homogeneous in terms of size and quality? Or heterogeneous?
Patches homogeneous in terms of remoteness? Or is there spatial structure?
What is the Glanville fritillary an example of?
a well studied system with much complexity. It is a butterfly population. Also gene for dispersal propensity shows another limitation in that ecologists often forget genetics
what is the Glanville fritillary
Butterfly metapopulation, Aland islands, Finland
Has two host plants: the plantain, Plantago lanceolata and the speedwell, Veronica spicata
as patch size increased in glanville fritillary what happened to extinction probability?
extinction probabilty declined
What does the habitat mapping of the glanville fritillary show wrt patches?
some areas have many nearby patches
Some have few, distant patches
Also, some patches are larger/better than others
what is the purist definition of metapopulations?
1) chance of extinction and recolonization on each oatch
2) dynamics of populations shouldn’t be too related (synchrony)
3) dynamics of pops shouldn’t be completetly independednt
what to geneticists think needs to be considered? more
inbreeding- increases extinction risk
why do we need a metapopulation perspective?
if a population as a whole functions as a metapopulation then the rates of subpopulation extinction and colonization may be of importance.
