Populations

- individuals of a species that interact with one another with in given area at a particular time
- Population ecology—study of births, deaths, dynamics forces which regulate the number of individuals in a population
- Populations are patchy in space and dynamic over time
• Population distribution
- Clumped-social patterns or source distribution
- Random
- Spaced-competing individuals
- Births increase and deaths decrease population size
- Life histories determine population growth rates
- Measures of population abundance
• Population density—number of individuals per unit area/volume
• Population size—total number of individuals in the population
• Estimating population size—density X total area occupied by population
- Population abundance varies on several spatial scales
• Geographic range-region in which a species is found
• within the range, species restricted to specific environments or habitats
• Habitat patches-“islands” of suitable habitat separated by areas of unsuitable habitat
- Population distribution
• patterns in age structure
• Type 1 —low mortality early in life, high mortality late in life
• Type 2 —Constant mortality throughout life
• Type 3 —Higher mortality early in life, low mortality late in life
- Population growth models
• “birth-death” BD model
- change in population size depends on # of births and deaths over a given time
- Estimating changes in population size
• Per capita= “Per individual”
• Per capita birth rate (b) —number of offspring an average individual produces
• Per capita death rate (d) -average individual's chance of dying
• Per capita growth rate (r)=(b-d)
- average individual's contribution to total population growth rate
- Life histories
• timetable of individual organism's life
- Life span
- age at maturity
- parity-number of reproductive events
- fecundity-number of offspring per event
• timetable is modified by environment
- individual organisms require resources (materials and energy) and physical conditions they can tolerate
- rate at which an organism can acquire resources increases with availability of the resources
• resource (use up/consumed)
• conditions (experience, not consumed)
- Principle of allocation-once an organism has acquired a unit of some resource, it can be used for only one function at a time
• functions—maintenance, foraging, growth, defence, reproduction
• schedule of organism's growth, development, reproduction and survival
• Parental investment-amount of time and energy given to an offspring by its parents
• Longevity (life expectancy)-life span of organism