IB Environmental systems and societies 2.1C Ecological Niche and Population Interactions Key Definitions

Biomass is the total mass of living organisms in a given area or volume.

Competition occurs when two or more organisms require the same limited resource, resulting in a negative effect on all participants’ growth, survival, or reproduction.

If two species compete for exactly the same limited resources, one will always be the better competitor, so the two cannot occupy the same niche indefinitely. The weaker competitor is eliminated from that niche.

Disease is a biological interaction in which a pathogen (virus, bacterium, fungus, or protozoan) infects a host organism, causing harm or death.

An ecological niche is the unique set of abiotic and biotic conditions and resources that a species requires to survive, grow, and reproduce.

Herbivory is an interaction in which an animal (the herbivore) feeds on a plant or algal species (producer) for energy and nutrients.

Mutualism is a symbiotic relationship between two different species in which both organisms benefit from the interaction.

Parasitism is a symbiotic relationship where one organism (the parasite) benefits by living on or within another organism (the host) and obtaining nutrients from it, usually without immediately killing the host.

Predation is an interaction in which one organism (the predator) kills and consumes another organism (the prey) for food.

Selective pressure refers to any environmental factor (natural or human-made) that influences which traits are favorable for survival and reproduction in a population.