Population Ecology
Ecology
The study of the interactions of organisms with their physical &
biological environments
& how these determine the distribution & make up of populations
within an ecosystem
Population ecology
Concerned with fluctuations in population size & factors (both social &
physical) that regulate populations
Important terms
Biosphere
- The part of earth where living organisms are found
Ecosystem
- Made up of groups of different species that interact with each other
& the environment
Organism
- Individual form of life,
- Such as bacterium, protest, fungus, plant, or animal
- Composed of a single cell or a complex of cells that are capable of
growing & reproducing
Community
- Group of different species that inhabit & interact in a particular
area
Species
- Group of closely related organisms that are very similar to each
other, are usually capable of interbreeding & producing fertile
offspring
Individual
- Single organism capable of independent existence
Population
- Group of organisms of the same species that occupy the same area
& can breed freely with each other
,Demographics
Statistics of a population
Such as: population size; age distribution; growth rate; etc.
What affects the population size?
Population size
Total number of individuals in a population
Dynamic Population Parameters:
1. Natality – birth rate ↑
2. Mortality – death rate ↓
3. Immigration – individuals that move into a population & stay
↑
4. Emigration – individuals that leave a population & do not return ↓
Humans:
Birth rate is the number of births per 1000 people in a year
Death rate is the number of deaths per 1000 people per year
How do these parameters affect population size?
Population size will therefore…
Grow when birth & immigration exceed death & emigration
Decline when death & emigration exceed birth & immigration
Remain stable when birth & immigration = death & emigration
,Closed Population
No immigration or emigration
Only parameters affecting population size will be births or deaths
E.g. fish in a small pond
How is population growth regulated?
Exponential Growth
Population size will increase rapidly
Occurs when:
- No shortage of food (constant food supply)
- No shortage of resources
- No predators
- Therefore, they will reproduce, & the number of individuals will
increase rapidly
Environmental Resistance
Total number of factors that stop a population from reproducing at its
maximum rate
As numbers increase, more demands are made on the available
resources, which builds up to environmental resistance
This causes:
- Decrease in birth rate / immigration rate
- Increase in death rate / emigration rate
Carrying capacity
The population density that the
environment can support
Eventually a balance is reached & the
population is maintained (balanced)
at a particular size or number
The population fluctuates around the
carrying capacity until the
environment changes again
, Population size fluctuates seasonally & annually - depending on
resources available
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