Multi-site PVA
I. Introduction to multi-site PVA
A. How many sites to rare species occupy?
B. What is a metapopulation?
II. How to approach multi-sites PVAs
A. Prerequisites
1. First, determine if
there is one main ‘source’ or ‘mainland’ population
2. If so, then just worry
about that one population
3. If not, then consider
the relative movement rates and population correlations
B. Data needs
1. Site specific population data
2. Something about movement
between sites
3. Something about correlation of
fates
- Assume no
negative correlation.
- If
positive, then
reduces
insurance created by metapopulation
III. Count-based multi-site PVA
A. Usually the most useful, as there is the greatest available
data
B. Need:
- mean, variance, and covariance
of
population growth rates for local populations
- movement probabilities
C. If lots of movement, treat as a single population
D. If populations are totally independent of one
another, then:
1. Pglobal = P1 * P2*...Pn
2. Can test the importance
of
saving an additional site
E. For correlated populations or with limited
dispersal,
project a matrix
V. Demographic PVA
A. Needs
- demographic rates for each local population
- class-specific estimates of movement
B. Models are enlarged versions of basic, population specific
matrix models
VI. Patch occupancy and PVA
A. Needs
- Assume modest movement
- Patch occupancy collected over a sequence of years
B. Classic metapopulation model by Levins
-dp/dt =
m*p*(1-p) – e*p
-Equilibrium p is dependent on a balance between
colonization and extinction
-Patches are occupied as long as m>e
-There are always unoccupied patches, and these are
important to the maintenance of the population
C. The Incidence Function model
Mi = βSi
Si = ∑pj exp(-αdij) Aj
dij is the distance between patch i and patch j
Solve with logistic regression