Species Relationships: Can't We All Just Get Along?

From mutualism to predation, these are ways that species interact in nature.

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Male brown bear eating fat rich salmon skin. Photo: nps.gov.

Ecology is all about learning how the pieces of an ecosystem fit together.  That includes how the species interact with their environment and with each other.  Species interactions range between those that are mutually beneficial (mutualism) and those in which one species consumes the other to survive (predation.)

A relationship that is mutually beneficial to both species is called mutualism.  Take for example the crocodile bird and the Nile crocodile.

 You might expect the crocodile to simply eat any bird that dared to perch near its mouth.  But in this case, the crocodile bird cleans the croc's teeth and mouth, removing leeches and other organisms that might harm the reptile over time.  The bird gets a free meal, and the crocodile gets clean teeth.  

Another good example of mutualism is the relationship between a cow and the bacteria in its stomach.  Cows eat plants and other grasses, but they can't digest the plant fiber called cellulose that makes up the cell walls of their food.  The bacteria that thrive in a cow's stomach release a special chemical that breaks down cellulose enough for the cows to digest it.  In return, the bacteria get a moist, protected, nutrient-rich environment in which to grow.  

It's win-win for everyone involved.  That's mutualism.

Another type of special relationship is called commensalism, in which one species benefits while the other is neither helped nor harmed.

 Cattle egrets and cattle are a good example of commensalism. These birds live in and around where the cattle graze, and they benefit from the assistance the cows give by stirring up insects for the birds to eat.  The cattle, on the other hand, are completely unaffected by the presence of the birds.

 In commensalism, one species - such as a mite - might use another species -such as a fly - for transportation, without really affecting the health of the host species.  

On the other end of the species interaction spectrum, are the interactions in which one species benefits while the other is harmed.  Parasitism is one such type of species interaction. In a parasitic relationship, one organism (the parasite) survives by feeding off of the other (the host.)  

Head lice are parasites that live off of their mammalian hosts.  Their presence alone does not kill their host, but it could be enough to lead to a harmful infection.  Another interesting example of a parasite is the case of the cowbirds that remove other birds' eggs from their nests and leave their own in its place.  The other bird will unknowingly incubate and raise the cowbird chick instead of its own young.  The cowbird species benefits while the host bird species is harmed.   

Most parasites do not kill their host, but their presence may weaken or impair the growth of the host to the extent that opens the door for illness or predation.

Speaking of predation, that is yet another type of species interaction and it is one in which one species (the predator) lives by consuming another species (the prey.)  Lions and zebras; dolphins and fish; and snakes and frogs are all good examples of predatory relationships.

Finally, there are plenty of instances in nature where two species interact with one another but are neither benefited nor harmed by the interaction.  A tarantula and a cactus both live within the desert ecosystem, but their interactions are indirect and neither species is benefited nor harmed when they do get together.

Of course, the general premise of the study of ecology is that health and well-being of one species affects the health and well-being of any other species within its ecosystem.  So the theory of true neutralism is more difficult to prove when you think of it in that respect.  

What do you think?  Is it possible for two species to co-exist without affecting one another?