TOPIC 11-Metapopulations

Question 1

WHAT structure do landscapes have

Answer 1

Landscapes have spatial structure
– Habitat occurs in patches ->may be occupied by
local sub-populations

Question 2

why might we need a new model for a species based on spatial use/structure

Answer 2

nfrequently cross open fields
Discontinuous set of small
Populations linked via limited
dispersal -> metapopulation
Need to build new model

Question 3

define pop

Answer 3

Group of interacting individuals of same
species inhabiting a given area (defined spatial
boundaries)

Question 4

define meta pop

Answer 4

Group of local sub-populations, occurring in
patches; linked by limited dispersal
• Driven by colonization & extinction
dynamics

Question 5

4 conditions for strict definition of metapop

Answer 5

1. Spatial heterogeneity: suitable habitat occurs in discrete patches
   that are occupied by local breeding populations
2. Dispersal (colonization/isolation): habitat patches must not be
   too isolated to prevent colonization or re-colonization following
   local extinction
3. Extinction: all local populations must have a risk of extinction
   (must be sufficiently small)
4. Dynamics: local populations not synchronized (not acting as one
   large population; occurs if dispersal between patches too high)

Question 6

what is a key feature of meta pops

Answer 6

limited dispersal

Question 7

when is it not a meta pop?

Answer 7

Dispersal too high or low à not a metapopulation
– If individuals move too infrequently between patches, populations act
independently
– If movement is too high, local populations function as large population
(dynamics synchronized)q

Question 8

what level of dispersal does a meta pop have

Answer 8

Intermediate levels of dispersal: metapopulation
– Dynamics governed by extinction & colonization
– Shifting mosaic of occupied & unoccupied patches

Question 9

Levins Metapopulation Model

Answer 9

dp/dt = mp(1-p) - epp: proportion of patches occupied/colonized
Models changes in patch occupancy over time depending on
rates of colonization & local population extinction
change in patch occupancy = colonization - extinction

Question 10

what is ep in levins model

Answer 10

Extinction rate across metapopulation (ep):
e = rate of extinction per occupied patch
p = proportion of patches occupied

Question 11

what does levins model assume

Answer 11

Assumes all occupied patches have equal extinction risk

Question 12

How will the extinction rate (ep) vary with patch occupancy?

Answer 12

linear exponential

higher ep is the higher patch occ is

Question 13

what is mp(1-p) in levins model

Answer 13

Colonization rate across metapopulation = mp(1-p)
m = per patch migration (colonization) rate
p = proportion of patches occupied
**Migrants can only colonize empty patches (1-p); multiply mp by (1-p)

Question 14

colonization rate relationship w patch occupancy? why?

Answer 14

parabola from 0-1
Low patch occupancy:
Lots of empty patches, but...
limited by few potential colonizers
High patch occupancy:
Lots of potential colonizers, but...
few patches left that can be colonized

Question 15

What does the intersection point represent for colonization and extinction graphs?

Answer 15

ntersection point:
Equilibrium patch occupancy (P’)
• Where colonization = extinction
• dp/dt = 0
• Can calculate P’
set dp/dt=0 & rearranging Levins model

Question 16

how to calculate p in levins model

Answer 16

P’ = 1 - e/mWhen e > m; P’ < 0 (metapopulation cannot persist)
Where e < m; P’ > 0 (metapopulation will persist at some positive patch occupancy rate)

Question 17

look at graphs of effects of raising or lowing e

Answer 17

ok

Question 18

Assumptions of Levins model

Answer 18

Assumptions of Levins model
Does not consider patch size or degree of isolation
Assumes all local populations produce migrants at same rate
– Large patches likely produce more migrants
Assumes colonization rates constant among patches
– Isolated patches less likely to be colonized
Assumes risk of extinction is constant among patches
– Small patches (with small populations) more
vulnerable to extinctions

Question 19

what models consider patch size or degree of isolation

Answer 19

Considered in other metapopulation models:

Mainland-island models (similar to theory of island biogeography)

Question 20

all patches equally likely to exchange migrants assumption - ex

Answer 20

Assumptions of the Levins model
All patches equally likely to exchange migrants
Relaxed in spatially explicit metapopulation models
Stepping-stone metapopulation models
Ricklefs, Ecology Fig. 17.2
© W.H. Freeman
A Southern Spotted Owl metapopulation