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Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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MIMICRY AND MUTUALISM

Not all species interactions are antagonistic.  Often advantages are gained from such interactions.

I.  Mimicry occurs when species evolve similar shapes and/or coloration, making them more difficult to tell apart.

A.  Sometimes species attempt to fool potential predators by making themselves look like something they are not.
        Examples:

Many butterflies have large eye-shaped spots on their wings, which may make predators think they are a larger animal.

Other butterflies have evolved false eyes and antennae on their rear wings, to confuse potential predators as to which way they will flee.

Many tropical butterflies look like dead leaves when their wings are folded up.

Caterpillars of some moths and butterflies look like bird droppings.

B.  Mullerian mimicry

Mullerian mimics represent groups of species which share a similar defense against predation or attack, and have adopted similar coloration patterns.

Examples:  bees and wasps, many highly colored tropical butterflies.

In general, species will only evolve bright colors if they have strong defense mechanisms, and use those colors as a warning.

C.  Batesian mimicry

Batesian mimics adopt the coloration of a Mullerian mimic, but are cheaters, as they do not share the defense strategy.

Examples:  Serphid flies which look like bees; Viceroy butterflies which look like Monarch butterflies (although recent research suggests these two butterflies may actually be Mullerian mimics)

II.  Mutualisms

Mutualistic interactions occur when the species involved all directly benefit from the relationship.  Mutualisms can be classified based on how tightly the interacting species are tied together.

A.  Symbiotic mutualisms occur when the species always live together and require each other to survive.

Examples:

Lichens, which are the symbiotic relationship between an algae and a fungus.  The algae provides the fungus with food (sugar), while the fungus provides the algae with nutrients and a place to live.

Corals and Zooxanthellae.  Coral polyps (the individual animals which make up coral reefs) are carnivorous animals related to jellyfish.  These animals allow certain species of algae to live in their bodies.  The corals provide the algae with nutrients, while the algae provide the corals with extra food.

Plants and Mycorrhizae.  Mycorrhizae are soil fungi which live in or on the roots of plants (including trees, shrubs, grasses).  The mycorrhizae provide the plants with phosphorus, while the plants provide the mycorrhizae with extra food.

Plants and Nitrogen-fixing bacteria.  Nitrogen-fixing bacteria require energy and an oxygen-poor environment to function.  Some plants (for instance, alders trees, bean plants) make root nodules (which exclude oxygen) for these bacteria to live in and provide the bacteria with food.  The bacteria provide the plant with ammonia.

B.  Non-symbiotic mutualisms occur when the two species are not always living together, and can live on their own (though not as well as they would together).  Examples:

Figs and fig wasps.  Figs are pollinated when a specialized wasp lays its eggs in a fig flower.  Each species of fig has a special wasp which provides this service.  The wasp is provided with a nutrient-rich environment for its larvae, while the fig gets pollinated.

Ants and acacias.  Acacia trees in the tropics often have hollow thorns which aggressive ant colonies live in.  The acacia tree also feeds the ants by providing them with oil bodies on the margins of their leaves.  In return, the ants will weed out competing plants, and will attack herbivores who try to eat the acacia.

Oak trees, Truffles, and Pigs.  The truffle mushroom is a mycorrhizal symbiont with oak trees.  As the truffle never emerges above the ground, there is no direct way for their spores to be moved.  Truffles have evolved a chemical which is very close to pig sex pheromones.  When pigs smell this, they get distracted, and begin rooting around to try and locate its source.  In the process, the truffle is found, eaten, and spores scattered around.  The pig is provided with a cheap thrill
 

C.  Facultative mutualisms occur when large groups of species loosely interact in a positive way.  Examples:

Pollination in flowering plants:  animal gets food, plant gets pollinated

Seed dispersal:  again, animal is provided with food, while the plant seeds get moved around.

This can be easily seen with berries and fruits which have indigestible seeds (blackberries, raspberries) which are eaten and then deposited elsewhere by the animal.

Another example are many wildflower seeds which have oil bodies on their surface.  Ants will collect these seeds, bring them back to their nests where the oil bodies are eaten, and the seed 'thrown out' on the ant hill, when it germinates.

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Created 2 September 2011, Last Update 02 September 2011

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