Community interactions are classified by whether they help, harm, or have no effect on the species involved. Diversity and trophic structure characterize biological communities. Di... Community interactions are classified by whether they help, harm, or have no effect on the species involved. Diversity and trophic structure characterize biological communities. Disturbance influences species diversity and composition. Biogeographic factors affect community diversity. A biological community is an assemblage of populations of various species living close enough for potential interaction. Ecologists call relationships between species in a community interspecific interactions. Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0). Interspecific competition (–/– interaction) occurs when different species compete for a resource in short supply. Strong competition can lead to competitive exclusion, local elimination of a competing species. The competitive exclusion principle (Gause’s principle) states that two species competing for the same limiting resources cannot coexist in the same place. The total of a species’ use of biotic and abiotic resources is called the species’ ecological niche. An ecological niche can also be thought of as an organism’s ecological role—it’s job in the environment. Ecologically similar species can coexist in a community if there are one or more significant differences in their niches. Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community. Reduce competition through microhabitats. As a result of competition, a species’ fundamental niche may differ from its realized niche. Even though the Chthamalus species can live anywhere (fundamental niche), with competition only live higher (realized niche). Character displacement (niche shift) is a tendency for characteristics to be more different in populations of two species that live together than in two species separated by geography populations. Examples include two species of finches that live on two different islands in the Galápagos Islands. Predation (+/– interaction) refers to interaction where one species, the predator, kills and eats the other, the prey. Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison. Prey display various defensive adaptations. Behavioral defenses include hiding, fleeing, forming herds or schools, self-defense, and alarm calls. Animals also have morphological and physiological defense adaptations. Cryptic coloration, or camouflage, makes prey difficult to spot. Animals with effective chemical defense often exhibit bright warning coloration, called aposematic coloration. Some prey species may gain significant protection by mimicking the appearance of another species. Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga. Symbiosis is a relationship where two or more species live in direct and intimate contact with one another. Parasitism (+/–), mutualism (+/+), and commensalism (+/0) are types of symbiotic relationships. Community structure encompasses species diversity and feeding relationships. Trophic structure is the feeding relationships between organisms in a community. Certain species exert strong control on a community’s structure. Read more