Interactions Between Species

TL;DR: The limited amount of energy available at each level of the community web gives rise to competition between species with overlapping requirements and this competition constitutes an alternative direction of relationships in the community often described in the terms of trophic levels.

Abstract: Other plants and animals constitute an important part of the environment for all living organisms. Any species is a part of a web constituted by species which exploit each other or compete for vital resources. The persistence of a species in a habitat must consequently be understood from its position in the biotic community to which it belongs. All heterotrophic organisms provide for the energy and nutrients which are needed for maintenance and growth by assimilating and oxidizing organic molecules. This is frequently done by eating another organism; such relationships are called prey-predator relationships if the “victim” is smaller or of about the same size as the “profiteer” and host-parasite relationships if the victim is larger than the profiteer and the former is often not killed by the latter. This fundamental relationship of energy transfer from primary producers of organic matter (plants) through herbivores and detritivores to different levels of carnivores constitutes one dimension of a community often described in terms of food chains. The limited amount of energy available at each level of the community web gives rise to competition between species with overlapping requirements and this competition constitutes an alternative direction of relationships in the community often described in the terms of trophic levels.