Unit 4 Populations and Ecosystems

Populations and Ecosystems

Population = All the organisms of one species in a habitat at one time

Community = All the organisms of all species in a habitat at one time

Ecosystem = A self supporting unit where all organisms interact with biotic and abiotic factors

Niche = The role of a species in its environment

The study of the inter-relationships between organisms and their environment is called ecology. The layer of land, air and water that surrounds the Earth is called the biosphere. An ecosystem is more or less a self contained functional unit made up of all the living (biotic) features and non living (abiotic) features in a specific area. Within each ecosystem are groups of different organisms called a community, which live and interact in a particular place at the same time. A group of interbreeding organisms occupying the same place at the same time is called a population, and the place where they live is known as a habitat.

Investigating Populations

Random Sampling

• Eliminates bias - more representative sample
• When a species occurs in groups - large number of smaller quadrats
• More species = more quadrats
• Larger species = large quadrats

Systematic Sampling

• Shows transition of species distribution along transect
• Line transect - any organism over which line passes is recorded
• Belt transect - shows density of species

Measuring Abundance

• Abundance = number of individuals of a species within a given space.
• Frequency = likelihood of a particular species occurring in a quadrat (gives idea on general distribution but not on density). Number of samples a species is recorded in.
• Percentage Cover = estimate of the area of which a plant species covers…