Population Ecology: Size, Distribution, Growth, and Interactions
Population Characteristics
A population consists of individuals of a species that make up an ecosystem at any given time. Understanding population limitations is key for investigation.
Key Characteristics
- Size: Number of individuals.
- Density: Ratio of individuals to space occupied.
- Distribution: Spatial arrangement of individuals.
- Age Structure: Proportion of individuals in each age group.
Population Size
Census: Account of individuals in a population. Methods include:
- Counting by Scaring (Large Mammals): Teams scare animals from an area and count those leaving.
- Aerial Counting (Birds and Large Mammals): Photographs are taken and analyzed.
- Sampling (Large Areas or Numerous Individuals): A portion is counted to estimate the total.
Capture, Marking, and Recapture: Individuals are captured, marked, released, and then recaptured to estimate population size.
Population Distribution
Individuals in a population are arranged differently in their territory.
Distribution Patterns
- Grouped: Individuals cluster due to varying environmental conditions, aiding reproduction and defense but increasing competition.
- Random: Individuals are evenly spaced due to uniform environmental conditions and minimal competition.
- Uniform: Individuals maintain distance due to competition for resources.
Population Density
Population density is the ratio of the number of individuals to the space occupied at a given time. It reflects interactions and resource availability.
Age Structure
Age structure represents the proportion of individuals of each age in a population, often visualized using bar graphs or pyramids.
- Bar length indicates the number of individuals.
- The base represents births.
- Large differences between steps indicate reduced numbers in certain age groups.
Intraspecific Relationships
Intraspecific relationships are interactions between individuals of the same species.
Types of Interactions
- Cooperation/Mutualism: Predator defense, prey capture, reproduction, parental care. Forms include:
- Groups: Individuals with some independence but shared beneficial activities.
- Societies: Closely related individuals organized into castes with specific roles.
- Competition: Fights over resources (water, light, space).
- Cannibalism: Consumption of young in resource-scarce conditions.
Population Growth
Growth Patterns
- J-shaped Growth: Rapid population increase over a short period (exponential growth), limited by resources.
Carrying Capacity: Maximum number of individuals an environment can sustain.
- S-shaped Growth: Slow, steady population increase, stabilizing near carrying capacity.
Reproductive Strategies
- r-strategy: Fast reproduction, short lifespan, little parental care, favored in unstable environments.
- K-strategy: Slow reproduction, long lifespan, significant parental care, favored in stable environments.