Carrying Capacity and Density Dependence Flashcards
What are density independent and dependent factors that limit population growth rates?
Density Independent Limitation
weather and environmental stress
natural disasters
Density Dependent Limitation
- lack of food/nutrients/water
- lack of space/light
- disease/parasites
- predation
Give an example of weather and environmental stress on population (finches)
- drought led to high mortality of finches
- rain led to high rates of finch population growth as more plants grow so more seeds for finches
Give an example of disease on a population (virus, phytoplankton)
Disease -Density Dependent Limitation
- viruses regulate phytoplankton populations by lytic methods
- viruses can rapidly spread through a phytoplankton population when the population is at high density
- mortality rate per capita is therefore higher at high phytoplankton population density
Give an example of predation - negative density dependence on population
Lynx and Hare
- increased negative effects at high density
What is density dependent regulation and examples? (carrying capacity, K)
Density Dependent Regulation
Results in the stabilisation of a population size
How can you identify density dependence?
by experimentally manipulating density
- e.g yield (biomass of crop) as a function of planting density (number of plants/pot)
Natural variation in density over time or across space
- density increase causes increase in mortality
What are ricker diagrams?
Ricker Diagrams= show model of pop size of current time step as a fraction of pop size of next time step
What is the ‘Allee’ effect? (nonlinearites at LOW densities)
Allee Effect
correlation between population size or density and the mean individual fitness (often measured as per capita population growth rate) of a population or species.
at LOW DENSITIES, there are NON LINEARITIES - why?
- mate limitation at low densities
- cannot find a mate, might have to travel too far
- inbreeding depression (higher mortality rate)
- Cooperative strategies that rely on high population densities:
- anti-predator behaviour (grouping together) e.g schooling in fish
- predators that hunt in packs
→ unstable equilibrium point at low densities
Strong Allee effect:
- at high pop densities
- when the population density or size hits a number below this threshold, the population will be destined for extinction without any further aid.
- A strong Allee effect is often easier to demonstrate empirically using time series data, as one can pinpoint the population size or density at which per capita growth rate becomes negative
Weak Allee Effect
- possess a reduced per capita growth rate (directly related to individual fitness of the population) at lower population density or size.
- the population will always exhibit a positive per capita growth rate.
What is intraspecific competition and the types? (nonlinearites at HIGH densities, scramble, )
Intraspecific Competition
Individuals of the same species often require similar resources leading to fewer resources per capita at high density
Types:
Scramble Competition
Competing individuals do not interact with one another directly. Instead individuals respond to the level of resource, which as been depressed by the presence and activity of other individuals
e.g Gypsy moth-scramble competition
Content Competition
refers to a situation where available resources, such as food and mates, are utilized only by one or a few individuals, thus preventing development or reproduction of other individuals.
Individuals interact directly with each other, and one individual will prevent another form exploiting the resources within a portion of the habitat
e.g great tit territories in Wytham Woods