EEB365: Final Notes Module 2 and 3
Lecture 1: Topic 1. From Population to Metapopulation
How can we tell that a species/population is at risk? What processes increase or decrease the risk?
Harvesting species sustainable
Key Conservation Strategies
Captive breeding with reintroduction
Elimination of harmful exotic predators or competitors
Reduction or elimination of harvesting Removing disease agents
Restoration of natural environmental conditions
A population is a group of coexisting, interacting individuals of the same species at a given location and time
Population: All coexisting individuals of the same species living in the same area at the same time
N = Birth + Immigration Death Emigration
Historically, most population models assumed panmixus: all animals within a population equally likely to mate
There are barriers to panmixus, like Spatial structure, road/traffic, clumped distributions of animals, and sub-populations located in
Fragmentaion: N (population size) is a function of Demographic (random fluctuations in age structure and birth death rates),
Environment. For a population to persist ,its colonization rate must be equal or larger to its extinction rate. Dispersal of the animal
The extinction vortex:
Things acting to lower the effective population (Ne) size:
Environmental variation and catastrophic events or:
1. Habitat destruction
2. Environmental degradation
3. Habitat fragmentation
4. Over harvesting
5. Effects of exotic species
These create changes cause:
1. Demographic variation
2. Population which is more subdivided by fragmentation,
3. Inbreeding depression,
4. Genetic drift and less of an ability to adapt
5. ALL lowering effective population size.
What can be done to counteract the risk factors?
Increase birth and immigration
Decrease death and emigration
Several populations act as metapopulations. A metapopulation is a population made up of discrete local (sub)-populations, each
with its own probability of extinction (i.e., unique set of fecundity and survival values), which are connected by migration.
Subpopulations that go extinct, can become re-established through migration from existing subpopulations.
When should metapopulations exist?
1. Suitable habitat occurs in discrete patches
2. Demes have substantial risk of extinction
3. Dispersal among patches sufficient for recolonization
4. Dynamics of demes asynchronous, environmental and demographic variation
Demes contained in discrete patches
1 Patches undefined: Shape, content, size
Distance between patches undefined
Extinction and immigration rates constant across all patches
Different Metapopulation Models
Remember however that a model can be at most 2 of 3 things:
Levins (1970) Metatpopulation Model: Levins was the first to model dynamics of local populations vs. overall population. He
coined the term metapopulation. He looked at the distribution of sub-populations (demes) among patches and patch occupancy.
Patch occupancy depends on rates of extinction and recolonization (dispersal).
Levins (Classic) Metapopulation Model the patch areas are undefined and are assumed equal. The distance between patches is
irrelevant. In visual model dashed circles: subpopulations gone extinct due to lack of migration; Filled circles: occupied patches;
Arrows indicate migration.
Assumptions of Levins model
A metapopulation is made up of discrete local (sub)populations
Habitat patches are equal in area, isolation and quality
Local populations have independent (uncorrelated) population dynamics (demographic independence)
Migration occurs among local populations and is so low that it does not affect local dynamics (except to rescue local
populations that have gone extinct)
Math for Levins Model
dP / dt = cP(1 - P) eP
1. P = fraction of currently occupied patches
2. ^P = equilibrium fraction of occupied patches
3. e = probability of extant local population going extinct
4. c = colonization rate per empty patch and extant local population
Metapopulation persists if e/c<1 because probability of the population going extinct is smaller then the colonization rate.
P (occupied patches) increases with increasing patch area, due to decreasing extinction
P(occupied patches) increases with decreasing distance among patches due to increasing colonization
Refinements to Levins Model
1. Populations are structured into local (breeding) populations (i.e., subpopulations)
2. Migration occurs among local populations
3. Subpopulation reestablishment in an area occurs following extinction because of migration.
Island Biogeography vs. Metapopulation: both emphasize balance between extinction and immigration rates. The differences in
Island Biogeography: the patches are defined; there is a mainland and island structure. The area, and distance between the main
land and the island is taken into account. In metapopulation the Patch areas undefined (i.e., assumed equal) , and the area, and
distance between populations is irrelevant
There are modifications made to Metapopulation Theory which are take into account:
1. The Effects of patch size and density
2. Rescue effect recolonization
3. Size of demes (sup-populations)
4. Location of the patches occur and also the territory it is in
5. Stochasticity (environmental changes and variation)
The new models therefore do not assume, equal area, quality, or isolation of habitat patches. The relaxation of these assumptions
have led to the identification of three other types of metapopulations:
3. Non-equilibrium metapopulations Most
populations 2 When Patch Area Differs: Mainland-Island Metapopulation Model
When Patch Quality Differs: Source-Sink Metapopulation Model
the green circle is high quality habitat (source), while the white are poor quality habitat sinks
Fragmentation reduces Metapopulation Viability because it reduces patch and population sizes, thereby increasing extinction
rates. It also increases inter-patch distance, reduces migration rates between patches, reducing the likelihood of local populations
sustaining one another
When Isolation Changes: Nonequilibrium Metapopulation Model: White, dashed circles: declining subpopulations; unfilled,
dashed circles: extinct subpopulations; arrows indicate migration and are thin to indicate very low migration
Dispersal abilities of animals determine metapopulation boundaries, and point out key connections in the landscape
Importance of Dispersal between Populations
1.In non-equilibrium dispersal distance is low as well as the variance in patch size (a determinant of population persistence).
2. In the Classic Levins dispersal distance is at a medium level and patch size variance is low
3. For mainland the variance in patch size is high and the dispersal distance is at a medium level
4. In Patchy populations the dispersal distance is high and the variance in patch size is low.
Metapopulations and dispersal: The probability of dispersal between habitats is high when dispersal distance is low. It is species
dependant however, because some species can disperse better then others.
Barriers and cut off source sink patch and cause extirpation of a species
After fragmentation of patches dispersal distance is increased.
How Fragmentation and Area Effect Reduce Metapopulation Viability
1.Reduces patch and population sizes, thereby increasing extinction rates of subpopulations
2.Increases inter-patch distance, reduces migration rates between patches, reducing the likelihood of local populations
sustaining one another
What a metapopulation is NOT: migration is so high that populations exhibit demographic panmixia!
What is spatial synchrony? It refers to synchronized changes in abundance (or other time-varying characteristics) of
3 geographically disjunctive populations. Generally, populations located near each other tend to be more synchronous than those
located farther apart, and the patterns of variation in spatial synchrony with distance differ between species.
Synchrony among spatially separated populations can be caused by:
1) Migration, or dispersal, of individuals among population is liable to cause population synchrony
2) Synchronous stochastic effects; correlated environmental disturbances (Moran effect)
3) Trophic (eg. predation) interactions with other species that are either themselves synchronized or mobile
Metapopulation Theory and Owl Conservation
Use spatially explicit models and explored habitat geometry on population viability
They Incorporated: Distance between patches related to juvenile dispersal distances, and Patch sizes in terms of nu