LE 8: Population Dynamics Flashcards
When are exponential growth models observed and used?
Observed when:
- resources ≠ limit growth
- individuals can reproduce lots of offspring (r-selected)
- population density ≠ limit growth
Used for:
- estimate population size by using the equation
When are logistic growth models observed and its graphical behavior?
Observed when:
- resources limit growth
- individuals produce few offspring (k-selected)
- population density limits growth
Graph:
- early growth is exponential
- inflection point = fastest growth before it slows
- carrying capacity = growth falls to zero; carrying capacity is proportional to food supply
What is density independent growth?
- occurs in species that do not increase or decrease (≠ change reproductive rate) with respect to density (not affected by being at high density)
- affected by changes in abiotic factors or resources
What is density dependent growth?
Population density affects the lifespan, survivability, or other aspects about individuals within a population and its size.
- low population = positive density
- high population = negative density; decreases fecundity and lifespan (≠ enough resources)
What are some examples of positive density and negative density affecting populations, in relation to density dependent growth?
Positive density:
- plants that are in larger populations make more seeds
- bees are attracted to larger populations helping to pollinate and reproduce the plants
Negative density:
- plants self-thin when there is a high population, resulting in smaller sizes; ≠ use sunlight to make energy to reproduce
What is the Allee effect?
Lack of positive dependence when the population size is is low
Occurs when:
- difficult to find mates
- uneven sex ratio
- inbreeding
- low genetic diversity = lower fitness
- predation risk
Strong Allee effect when there is negative growth and weak Allee effect when there is stagnant growth.
What is cycling and the different types?
There are fluctuations around the carrying capacity.
Types:
- stable: even fluctuations
- small fluctuations that dampen
- little to no fluctuations
What are the characteristics of stable fluctuations on cycling?
- population overshoots capacity and dies off
- more stable = increase in fecundity
- time delay when t > 0 resulting in equation where r x torque
- no time delay results in regular change in population size
How does energy storage and availability affects population cycling?
the more energy that is stored, allows for reproduction
- some species can afford to overshoot carrying capacity because they can store energy even when food is low, allowing for more cycling
- abiotic factors causes populations to cycle
- limited food = less overshooting = less cycling
What are the variations in age structure?
fecundity curves changes in magnitude due to its life history each year
- high fecundity one year affects population size the next
- when young individuals replace the old, the population is growing
- when there are more elderly dying and not enough children replacing, the population has a negative growth
What is a meta population and its relation to population dynamics?
a group of spatially separated populations of the same species that interact at some level
- subpopulations make up a meta population
the smaller the population, the more likely extinction is to occur
- sheer probability
- lack of genetic diversity that helps with fitness
What is the rescue effect?
