EE Lecture 31: Metapopulations Flashcards
define metapopn
a set of spatially isolated popns linked to one another by dispersal
what are metapopns characterized by
repeated extinctions and colonizations
why are the popns of some species prone to extinction
1) the patchiness of their habitat makes dispersal between pops difficult
2) enviro condns often chnage in an unpredictable and rapid manner
outline conclusions of Huffakers experiments
although the individual popns may be prone to extinction, the collection of popns (the metapopns) persists because it includes popns that are going extinct and new popns that are established by colonization
RANDOM EXTINCTIONS AND COLONIZATIONS
represent popn eqtn for metapopns - Levins model
dp/dt = cp (1 - p) - ep
p - proportion of habitat patches occupied at time t
c-colonization
e-extinction
what is the rescue effect of metapopns
extinction occurs in individual patches but then these patches are rescued by immigration - recolonization - so the whole metapopn persists even though no patch is stable
why does a metapopn persist even though no patch is stable
because of the recolonization rescue effect, where if a popn goes extinct - the patches will get recolonized by immigration
for a metapopn to persist for a long time, what must the e/c ratio be
less than 1
give an example of a metapopn in nature
voles in Tvarminne archipelago.
the larch budmoth, Zeiraphera diniana
repeated immigration
emigration and extinction cant treat as one popn
what is Levins model
dp/dt = cp (1 - p) - ep
what is the eqbm patch occupancy rate for Levins metapopn model
p = 1 - e/c
according to Levins model, when would the metapopn go extinct
when e > c
what does Levins model assume
- infinite patches equally connected
- all patches have equal chance of receiving colonists, so spatial arrangements of patches doesnt matter
- all patches have an equal chance of extinction
- once a patch is colonized, its popn increases to its carrying capactiy more rapidly than the rates at which extinction and colonization occur
what is habitat fragmentation
anthropogenic effects converting large tracts of habitat into a set of spatially isolated habitat frgments causing a species to have a metapopn structure when it didnt have one before
why is huffakers experiment not realisticq
all patches equally and equally connected - not true in reality
habitat patch area and distance from other patches related to the probability of patch being occupied in a given year
what did Carl Huffaker experiment on
oranges to determine metapopns
citrus mite and predatory mite
took oranges in isolation -changed distances between them by separation with plastic balls - patch quality adjusted by covering parts of oranges
each field was a separate universe
RESULT:
cpredator prey coexistance can be facilitated by spatial structure
you see prolonged cycles
extinction and colonization play a key role in dynamics and persistance
give an example of how metapopns might exist in nature
n.alaska - group of lakes, sometimes connected to one another by temporary streams that form after the snow melts or after periods of heavy rainfall
what are the 2 important features of metapopns to consider
- isolation by distance
2. the effect of patch area - small patches harder to colonize
in metapopns what is a good quality patch called
which individuals here
good quality patch - source
most competitive individuals here
in metapopns whats a bad quality patch called
which individuals here
sink
less competitive individuals here
which patch will have the most competitive individuals
a source
which is better - less comp individuals to not breed at all, or to go to the sink
to go to the sink
