C4.1 - Populations and Communities

Population

interacting groups of organisms of the same species living in an area

Population

Members of a population normally interbreed with each other and do NOT interbreed with individuals in populations of other species

Random sampling

Taking samples without any bias in order to estimate the size of a population

Random sampling

Any part of the population has equal chance of being included in the sample

Sampling error

The difference between a sample statistic (the estimated population size) and the equivalent value for the whole population (the true size of the population)

Quadrat sampling

Repeatedly placing a quadrat frame at random positions in a habitat and recording the number of organisms present each time

Quadrat sampling

Suitable for plants and other sessile organisms

Carrying capacity

The maximum size of a population that an environment can support

Competition

The struggle between organisms to survive in a habitat with limited resource(s)

Carrying capacity

Often determined by the limitation of one resource (or a small number of resources), therefore impacting population size

Negative feedback control

Allows for the overall population to remain relative stable over time (with fluctuations)

Density-independent factors

Have the same effect however large the size of a population

Density-dependent factors

Have an increasing effect as the population becomes larger

Density-dependent factors

Are the basis for negative feedback mechanisms because they reduce larger populations and allow smaller populations to increase

Competition

Example(s) of a density-dependent factor

Predation

Example(s) of a density-dependent factor

Predation

Becomes more intense if a population of prey becomes more dense (and easier to find)

Infectious disease, parasitism and prey infestation

Example(s) of a density-dependent factor

Sigmoid population growth curve

Displays the population change over a given period of time

Predation

One consumer species killing and eating another consumer species

Pathogenicity

One species living inside another species and causing a disease in the host

Community

All of the interacting organisms in an ecosystem

Community

A group of populations living together in an area and interacting with each other

Ecosystem

A community of organisms and their abiotic environment

Intraspecific relationship

A relationship that exists between individuals of the same species

Example of competition

Light availability in plants

Example of competition

Using nectar to attract pollinators

Example of cooperation

Communal roosting in animals

Example of cooperation

Hunting in groups

Interspecific relationship

Relationships between species in a community

Herbivory

Primary consumers feeding on producers (which may or may not be killed)

Interspecific competition

Two or more species using the same resource, with the amount taken by one species reducing the amount available to the other species

Example of herbivory

Aphids feeding on phloem sap from plants

Example of predation

Starfish eating oysters

Example of interspecific competition

Ivy climbing up oak trees and competing for light

Example of parasitism

Ticks living on deer

Mutualism

Interspecific: close associations between species where both species benefit from the relationship

Species

Organisms that can breed with each other and produce fertile offspring

Species of asexually reproducing organisms

Organisms with highly similar genomes

Reproductive isolation

Cannot breed with each other to produce fertile offspring