Symbiotic Relationships {Living World

Symbiosis The word symbiosis literally means 'living

together,' but when we use the word symbiosis in biology, what we're really talking about is a close, long-term interaction between two different species.

Mutualism In many cases, both species benefit from the

interaction. This type of symbiosis is called mutualism.

An example of mutualism is the relationship between bullhorn acacia trees and certain species of ants. Each bullhorn acacia tree is home to a colony of stinging ants. The tree provides a home and food for the ants. The ants protect the tree from herbivores and remove competing vegetation, so the acacia gains a big advantage from the relationship.

Commensalism Commensalism is an association between two

different species where one species enjoys a benefit, and the other is not significantly affected.

Commensalism is sometimes hard to prove because in any symbiotic relationship, the likelihood that a very closely associated organism has no effect whatsoever on the other organism is pretty unlikely. But, there are a few examples where commensalism does appear to exist.

Commensalism Some biologists maintain that algae and barnacles

growing on turtles and whales have a commesalistic relationship with their hosts.

Others maintain that the presence of hitchhikers causes drag on the host as it moves through the water and therefore the host is being harmed, albeit slightly. In either case, it is unlikely that the fitness of the host is really affected by the hitchhikers, so commensalism is probably the best way to describe these relationships as well.

Commensalism Some biologists maintain that algae and barnacles

growing on turtles and whales have a commesalistic relationship with their hosts.

Others maintain that the presence of hitchhikers causes drag on the host as it moves through the water and therefore the host is being harmed, albeit slightly. In either case, it is unlikely that the fitness of the host is really affected by the hitchhikers, so commensalism is probably the best way to describe these relationships as well.

Amensalism Amensalism, association between organisms of

two different species in which one is inhibited or destroyed and the other is unaffected

There are basically two types of amensalism •  Competition: a larger or more powerful organism excludes

another organism from its source of shelter or food. •  Antibiosis: one organism secretes a chemical that kills the

other organism, while the one that secreted the chemical is unharmed.

Parasites Parasites are plants or animals that live on, or in, another organism (the host), getting their nutrients from that host. Sometimes the host is harmed by the parasite and sometimes the relationship is neutral, but the host never benefits from the arrangement. Ectoparasites are parasites that live outside the body. In animals, they live on the skin and can cause itching and rashes. Endoparasites are parasites that live inside the body. For instance, they may live in the blood system, muscles, liver, brain, or digestive systems of animals.

Parasites Parasites are typically the Cinderella species of

natural communities. They can play crucial roles in maintaining biodiversity and energy flow

through ecosystems. Yet they are often overlooked in studies of community organization and trophic structure.

Parasites are an important indicator of ecosystem health —

that is, the ability of the system to maintain: •  vigor (productivity) •  organization (biodiversity

and predictability) •  resilience (time to recovery

following a disturbance)

Parasites The researchers support their argument with

examples of systems where parasites have been shown to affect host population dynamics, interspecies competition, and ecosystem productivity.

They point out that host diversity is reflected in parasite diversity, and that it can sometimes be easier and cheaper to sample parasites than hosts.