Interspecific Relationships
and Niche

Background

Interspecific interactions are interactions among organisms of different species. Typically, these interactions are classified based on whether they are beneficial to one or both of the species involved or whether they are detrimental to one of the species involved. An organism’s niche is its functional role within the community, including its activities and relationships, its “address,” its “job” or function within the community, and how it relates to other organisms. The niche of each species is a little different to avoid competition. Different species, even closely-related ones, will have different food preferences, seasonality, daily feeding rhythms, and location within the habitat. For some species of katydids within the same genus, the difference may be as subtle as a preference for perching on the top vs the middle of a stem on a grass plant.

Types of Relationships

Symbiosis

Any relationship that involves two (or more) species living together and interacting. This is a general term which includes predation, parasitism, commensalism, mutualism, etc., but often is used to mean mutualism.

Predation

When a larger animal eats other, smaller animals. Lions may eat antelope, and wolves may eat deer. Spiders, like this orbweaver, capture and eat insects such as the cricket she’s eating.

Commensalism

A relationship between two species that is beneficial to one but of neutral benefit to the other. Cattle egrets follow cattle to feed on the insects stirred up by the grazing cattle.

Mutualism

A relationship between two species where both benefit. The yucca moth both pollinates and feeds on the yucca plant; acacia ants live in the thorns of, defend, and are fed by the acacia tree in which they live; and trees can’t get along without mycorrhizae living in/on their roots and absorbing food for them. Many plants and their pollinators have evolved mutualistic relationships. Butterfly-weed provides food for and is pollinated by butterflies like pipevine swallowtails.

Parasitism

When a smaller organism feeds on a larger, weakening or killing it. This is a relationship where one organism benefits and the other is harmed. Often the host is not killed outright. Because a parasite lives in/on the body of its host and needs the host to remain alive, it is usually advantageous for the parasite to not kill its host. Humans and domestic animals are occasionally infected with or bothered by tapeworms, roundworms, mosquitoes and/or leeches.

Parasitoid

A parasite that eventually causes the death of its host. By the time the parasitoid undergoes metamorphosis, all of the host’s innards have been eaten. Often, insect larvae that are parasitoids of other insects eat the host’s tissues, timing things such that just as they’re ready to pupate, they have eaten up the whole insides of their host, and it dies. Braconid wasps do this to tomato hornworms, and this hornworm, covered with cocoons of pupating braconids, probably has almost no body parts left inside. If you see a caterpillar like this on your tomato plants, leave it alone. The wasps will eventually hatch, mate, and lay eggs in any other tomato hornworms they can find – a good means of biological control.