Population Ecology Flashcards
What is population ecology?
The study of change in population size and composition and identifying factors that underpin that change
What are the three main principle of population ecology?
Density
Dispersion
Demography
What is a population?
A group of interbreeding individuals belonging to a particular species and sharing a common geographic area
What are the three main methods of estimating population size?
Sampling random sub-populations
Using an indicator of numbers present
Mark-recapture
Outline the process of mark-recapture
Capture, mark and release C1 animals
Repeat capture getting C2 animals of which CM are already marked
Estimate population size from N = C1 x C2 / CM
What assumptions do we make in mark recapture?
All individuals have equal probability of being recaptured
Marking has no effect
Marked animals mix back into the population
There is no change in population size between marking and recapture
What are the three types of dispersion?
Random
Clumped
Uniform
Clumped dispersions occur when?
Resources are not evenly distributed
Protection from predators is required
Animals live in social groups
At breeding sites
Uniform dispersion occurs when?
There is direct interaction between individuals
Territoriality is involved
What is demography?
The study of change in a population’s vital statistics over time
What are the two most important influences on demographics?
Age structure as different ages have different mortality and fecundity rates
Sex ratio as in sexual species the population growth is usually dependent upon the number of females
How can demographics be presented?
Age pyramids
Life tables
Survivorship curves
Reproductive rates
How can individuals be aged?
Some can be classed purely on appearance e.g. Gulls
Some require more invasive procedures e.g. Growth rings in scales and otoliths in fish
What are the variables to consider in life history?
How many reproductive episodes?
When to start reproducing?
How many offspring?
What is semelparity?
A single reproductive episode in which all energy is expent on reproduction
What is iteroparity?
When an organism has many reproductive episodes
Give an example of a semelparitic organism
Pacific salmon
Agave plant
How to decide when to start reproducing?
Reproduction is costly and may be particularly costly for young animals as they are less experienced and have more to lose. If survivsl rates are good and fecundity increases with age then they normally delay first reproduction
How many offspring per clutch?
This is dependent on the amount of investment in each individual offspring
What is population growth limited by?
Limited resources
Predation
Disease
What us per capita growth rate over time given by?
R= per capita birth rate - per capita death rate
If r>0 population is growing
If r =0 population is stable
If r <0 population is shrinking
What is the carrying capacity?
The limit of population determined by the environment
What is the logistic growth model?
At anytime there is room for K-N individuals therefor thr percentage capacity = K-N/K.
Thus for a more realistic growth model we use dN/dT=rN(K-N/K)
What are the limitations of the logistic growth model?
It does not incorporate:
Causes of density dependence
Density independent factors
Allele effects when the population is at low levels they sometimes cause further decline
Time algs before the negative effects of high population size are incurred
