Populations dynamics and rates of spread Flashcards
(21 cards)
Two factors that impact probability of invasion
- Number of attempted introductions
- Total number of colonizers
Why are smaller populations more vulnerable to extinction?
- Bad luck (demographic stochasticity)
- small gene pool
- population is spread too thin - hard to mate
- vulnerable to disturbance
Propagule pressure two types
- Propagule size
- Propagule number
Propagule size
of individuals released
Propagule number
of release events
Propagule pressure hypothesis
As propagule pressure increases, so does risk of invasion
Colonization pressure
number of species released into an ecosystem
Colonization pressure hypothesis
As colonization pressure increases so does the risk of invasion
Three types of dispersal
- Neighbourhood diffusion
- Jump dispersal
- Stratified diffusion
neighbourhood diffusion characteristics
- Through a homogenous environment
- Move equally in all directions
- Disperse as the populations grows
Jump dispersal characteristics
- Rapid and long distance
- Often through heterogeneous environments (across oceans, ponds etc.)
Stratified diffusion characteristics
Short distance expansion combined with long distance jumps
Three expansion types
- Linear
- Biphasic
- Exponential
Linear range expansion
This range expansion time is characterized by an initial time lag followed by establishment and constant growth rate
Bi-phasic range expansion
This range expansion type is characterized by an initial time lag followed by “jumps” and establishment of organisms.
Exponential range expansion
This range expansion type is characterized by an initial establishment phase followed by constant bump ups and production of satellite colonies.
Why does a lag phase in establishment happen?
1 - Limits on detection - “perceived” lag phase
2 - Period of genetic readjustment
3 - Allee effects (birth rate impact by population density)
4 - Lagging introduction of mutualists
Three assumptions of the Fisher-Skellam model
- Every individual moves at random
- Individuals move through a homogenous environment
- Birth and death rate do not vary within the population
Rate of spread equation
Vf = 2 SQRT(rD)
Why does the Fisher Squellam model constantly overestimate rate of spread?
- D calculations don’t take currents, wind etc. into account
- Organisms may spread far but not be able to establish due to being spread too thin
