Species interactions — EST 2 Biology Revision Notes & Topical Questions

A community contains all populations living and interacting in one area. A species' ecological niche includes its role, habitat, resource use and relationships with other organisms.

Species richness counts the species present, while species evenness considers their relative abundances. Greater diversity often gives a community more alternative pathways and greater stability.

Competition occurs when organisms require the same limited resource, such as food, water, space or mates. It can occur within a species or between different species.

Both competitors are negatively affected because each gains fewer resources. Strong competition may reduce population growth or force species to divide resources by occupying different niches.

In predation, a predator gains food while the prey is harmed. Predator and prey numbers can regulate one another and produce linked population cycles.

Prey adaptations include camouflage, warning coloration, mimicry, spines, toxins and rapid escape. Predators may evolve improved senses, speed or hunting strategies in response.

In parasitism, the parasite benefits while the host is harmed. A parasite may obtain food, shelter or a place to reproduce and normally avoids killing the host immediately.

In commensalism, one species benefits while the other is neither helped nor harmed, such as an organism using another for transport or shelter without damaging it.

In mutualism, both partners benefit. Pollinators obtain food while transferring pollen, and animals may gain fruit while dispersing the plant's seeds.

Interactions occur within complete ecosystems, so changes in resources, climate or other species can strengthen or weaken a relationship and alter both populations.

Parasitism one organism benefits while its host is harmed; a tick feeding on a mammal is an example. Commensalism: one benefits while the other has no clear benefit or harm; a cattle egret may catch insects disturbed by grazing cattle.

Mutualism both partners benefit. A bird that eats ticks gains food while the large mammal has parasites removed. In each example, state the effect on both organisms to identify the interaction correctly.

To predict the effect of removing a predator, first identify its prey. The prey may increase; if it feeds heavily on producers, producer biomass may then decrease. Real food webs contain several feeding links, so the size of each effect depends on other available food and predators.

Check Why might two similar species coexist in one habitat? Answer: They may partition their niches by using resources at different times or in different locations, reducing direct competition.