Populaiton Growth Flashcards
What is population ecology
Using numbers to assess how populations change in space and time
How well is pop doing?
Influences and effects of the environment on pop dynamics
Density independent forces
Reduce/increase the population by same proportions regardless of pop density
Often abiotic e.g. floods, fires
Density dependent forces
Forces that alter depending on population density
Often biotic e.g. competition
Explain mark recapture
Capture sample of animals
Mark/tag them in some way and re-release
Come back at a later time and capture random sample again
Compare proportion marked to proportion unmarked
(Total marked first time x total captured second time)/ marked animals recaptured
Cormack-sieber-jolly method = open popualtions
- recapture multiple times
- accounts for births, deaths and emigration
Schnaebel method
- closed populations
Closed population.
Animals contained within a space e.g. island
Describe a life table
Used for closed pops
Uses population census data (capture recapture every year)
Age/stage dependent info needed
Provides age/stage specific mortality/survivorship data
- often as prop of surviving decreases fecundity increases up to a point
Type I survivorship curve
High survival when young, more likely to die when old e.g. humans
Type II survivorship curve
Relatively constant death rate throughout life e.g. Carl’s, many reptiles
Type III survivorship curve
Large numbers of offspring die before maturity, but there is then a high rate of survival post maturity e.g. plants, oysters, sea urchins
The limitations on calculating population growth
- most dont grow up constrained so simple model doesnt fit
- often populations have a carrying capacity
- sigmoid or logistic curve can describe growth to a carrying capacity
Exponential growth in natural systems
- there are very few examples, normally constrained
- can show exponential growth if they are well below the environmental constraints
E.g. recovering population, invading population, human race (until recently)
Population growth rate equation.
Births - deaths = growth rate
Per capita, per time unit
