Mutualism Notes

Symbiosis - Mutualism Essentially means living together - species in close interaction with each other. May be face to face or closer, where an organisms lives within an organism. For example a cleaner fish and its host is face-to-face, whilst the nitrogen-fixing bacteria in the root nodules in legumes is an example of an interaction where one organism is living within another. There can be more than 2 participants. Frequently there is evidence of co-evolution in symbiotic relationships and these relationships may either be exploitative or co-operative. Mutualism is an example of cooperative whilst parasitism is exploitative. It is thought that co-operative interactions evolved from exploitative ones, where the benefits to both partners outweighs the cost to either partners. Mutualism - both benefit Commensalism - commensals benefit at no cost to the host Parasites - parasites benefit, the host does not. Sometimes the distinctions are more difficult to draw on. Mutualism Extremely widespread in nature. Thought they evolved from parasitism or commensalisms. The benefits may be in terms of growth, survival and reproduction, a favourable growth environment, services (protection from predation or herbivory), seed dispersal and pollination and cleaning. Definitions Obligate something has to happen. Both partners dependant on each other to survive. Facultative - not necessary but beneficial. Partners are not dependant on each other for survival but they both benefit Can be partnerships where one is dependant on other, which is in turn not dependant on the other. This is an unequal mutualistic relationship. Most common partnerships are between two parties. These are the most common and are usually surface to surface. There is another kind, like legumes, where one species lives within another but within extracellular spaces. Interactions where one exists within the cells of another organism. Ants and acacias Ants are provided with food from extra-floral nectaries (sugar) and Beltian bodies (protein) and shelter from the acacia trees and in turn provide protection for the trees from herbivores such as invertebrates and megaherbivores. Ants will also attack and clear away any plant material around the tree, reducing competition. Many different species of ants and acacias. Studies investigating herbivory levels on top leaves and bottom leaves against time on trees with ants and without ants show that the levels of herbivory on ant trees are progressively lower than on non-ant trees. Leaf longevity on ant trees, non-ant 

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