Classify interactions and calculate population changes from supplied numbers.
Method and worked examples
A niche describes how an organism uses resources and interacts with its environment, including feeding relationships and conditions it tolerates. A habitat is where it lives. Competition occurs when organisms use a limiting shared resource and can occur within or between species. Predation benefits the predator and harms the prey. Mutualism benefits both participants; parasitism benefits one and harms its host.
Population change equals births plus immigration minus deaths and emigration over the same interval. A population can fluctuate as resources, enemies and conditions change. A keystone species has an ecological effect disproportionately large relative to its abundance. Removing it can cause large food-web or habitat changes. A correlation between two populations describes an association; it does not alone show every cause of the pattern.
Example 1
A population starts at 100, with 20 births, 5 immigrants, 12 deaths and 3 emigrants. Find its final size.
Net change =20+5−12−3=10. Final size =110.
Example 2
A pollinator gains nectar and the plant gains pollen transfer. Classify the interaction.
It is mutualism in the stated situation because both participants benefit.
Watch out:Habitat describes location; niche includes resource use, environmental tolerances and interactions.
Niches, interactions and population change | Year 11 Biology | Ascent Arcade