Grasslands: Life histories Flashcards
Define a population
A group of species that breeds with each other
What is a useful characteristic of a population and why?
Age distribution because it is very sensitive to ecological influence
How is age distribution described?
Using a life table which tabulates mortality by age. Data is used to investigate causes of changes e.g. mortality could show predation
How is survivorship calculated?
Number surviving / total number born (per year)
What is suggested by a survivorship curve?
Population strategies
How many types of survivorship curve are there?
3
Describe a Type I survivorship curve
Most individuals die late in life. They have few offspring and invest much time and effort into them.
Describe a Type II survivorship curve
Individuals die at a uniform rate
Describe a Type III survivorship curve
Most individuals die at a young age. They have many offspring and invest little time and effort into them.
How is age-specific mortality calculated?
Number of dying / number surviving
Give five life history events that affect population growth
Maturity, inter-birth interval, generation time, age at death, litter size
What does population in a given year depend on?
The population and growth rate of the year before
What type of growth is seen in a population that breeds seasonally?
Geometric growth
What type of growth is seen in a population that breeds continuously?
Exponential growth
Which type of population growth is faster?
Exponential
When are growth rate models applicable?
When a new species is introduced/reintroduced into an empty niche
What is a limitation of growth rate models?
They continue to predict growth after a population has reached a maximum
What results in a maximum population?
Limited resources
What is a more applicable growth model and why?
Logistic growth because it is more generalised
What does logistic growth use?
Uses carrying capacity, as the population approaches the maximum, the rate of increase reaches zero
Name three density dependant mechanisms
Crowding, parasitism, competition for resources
When do density dependant mechanisms take effect?
After a lag period
