C.4.1 Populations & Communities

population

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

sample

a subset of a whole population or habitat used to estimate the values that might have been obtained if every individual or response was measured

random sampling

a method of choosing a sample from a population without any bias

sampling error

statistical errors that arise when a sample does not represent the whole population, i.e. it is the difference between the real values of the population and the values derived by using samples from the population.

stratified sampling

used in areas that contain two or more different habitat types; the technique takes into account the proportional area of different habitat types and samples each one accordingly

systematic sampling

used where the study area includes an environmental gradient; a transect is used to sample systematically along the environmental gradient

variation

a quantitative measure of the distribution (spread or clustering) of the values in a data set

range

the difference between the largest and smallest data values

standard deviation

the spread of a set of normally distributed data from the mean of the sample; it is a measure of the variability of a population from a sample. A small standard deviation indicates that the data are more reliable

normal distribution

a data-set distribution that is symmetrical about the mean, forming a bell shaped curve

carrying capacity

the maximum number of individuals of a species that can be supported by a given environment

negative feedback

feedback that tends to counteract any deviation from equiHbrium and promotes stability

density-dependent

factors that lower the birth rate or raise the death rate as a population grows

community

a group of different species living in an area

intraspecific competition

competition between individuals of the same species

interspecific competition

competition between individuals of different species

cooperation

the action or process of working together.

altruism

behaviour of an animal that benefits another at its own expense; biologists call a behaviour pattern altruistic if it increases the number of offspring produced by the recipient and decreases that of the altruist

mutualism

an interaction in which both species derive benefit; specific type of symbiotic relationship

parasitism

a relationship where one organism (the parasite) benefits at the expense of another (the host) from which it derives its food

pathogenicity

the capacity of a microbe to cause damage in a host resulting in disease

root nodule

small swelling on the root of plants that contain symbiotic nitrogen-fixing bacteria

symbiotic

a close and long-term biological interaction between two different species

mycorrhiza (mycorrhizae)

a fungus that grows in association with the roots of a plant in a symbiotic relationship

hypothesis

a provisional explanation of an observed phenomenon or event that can be investigated using the scientific method; when using a statistical test; states that there is a statistically significant difference between two variables

null hypothesis

there is no statistically significant difference between two variables

predator-prey relationship

the interrelationship of population sizes due to predation of one species (the predator) on another (the prey)

top-down control

changes to the food chain occur at the top trophic level and then impact on the trophic levels lower in the food chain

bottom-up control

changes to the food chain occur at the lowest trophic level (producers) and then impact on the trophic levels higher in the food chain

allelopathy

chemical inhibition of one plant (or other organism) by another, due to the release of chemicals (allelochemicals) that act as germination or growth inhibitors