8.3 Effect of Density on Populations

What is population ecology?

• The study of how the number, density, and distribution of a specific species' population change over time, and how they interact with their environment and other species

• It explores how biotic and abiotic factors influence density

What is a population?

A group of individuals of a single species living in the same general area

What is density?

The number of individuals per unit area or volume.

• It's a measure of how concentrated a population is within a given space and is a dynamic characteristic that changes with births, deaths, immigration, and emigration.

What is dispersion?

The pattern of spacing among individuals within the boundaries of the population

What does dispersion help scientists do?

Analyzing these patterns helps ecologists understand how a species interacts with its environment and other organisms, revealing information about resource availability, social behaviors, and competition. 

What are sampling techniques?

• Methods for estimating population size and density by studying a representative subset of a population instead of the entire population.

• They can be used to estimate densities and total population sizes.

How can population density be estimated?

Extrapolation from small samples or an index of population size.

What is extrapolation?

A predictive technique that uses historical and current population data to estimate unknown values outside the range of the original data.

What is a quadrat?

A marked-off, standard-sized area, often a square or rectangular frame, used to sample a small portion of a habitat to estimate the abundance, density, and distribution of plants or slow-moving animals.

How do additions occur in populations?

Through birth and immigration, the influx of new individuals from other areas.

How does removal occur in populations?

Through death and emigration, the movement of individuals out of a population.

What are patterns of dispersion?

Spatial arrangement of individuals within a population, describing how they are spread out in their environment.

What are the three patterns of dispersion?

1. Clumped dispersion

2. Uniform dispersion

3. Random dispersion

What is a clumped dispersion?

• Individuals aggregate in patches.

• It is the most common pattern in nature

• Occurs from factors such as resource distribution, advantages of social behavior, and limited seed dispersal in plants.

What is uniform dispersion?

• Individuals are evenly distributed

• Can be influenced by territoriality, the defense of a bounded space against other individuals

What is random dispersion?

• The position of each individual is independent of other individuals

• It occurs in the absence of strong attractions of strong attractions or repulsions