humans, destruction of their habitat, and predation by introduced species to the island they lived on.
COEVOLUTION AND MUTUALISM With mutualism, there is an ecological interaction between at least two organism types that is beneficial to both species. Mutualism is actually the most common interaction between two species. It happens in all types of organisms, including flowering plants and pollinators, the dispersal of plants by animals, and the interaction between mycorrhizal organisms and vascular plants. The relationship increases the fitness of both species, which is different from interspecies competition, which decreases the fitness of both species. It is also different from parasitism and exploitation, which decreases the fitness of one species. There are differences between mutualism, cooperation, and symbiosis. Cooperation increases the fitness of the organisms that share the same species; symbiosis is a broader term that can include commensal relationships, mutualistic relationships, and parasitic relationships. Mutualism is a factor in the growth of about 48 percent of land plants because of mycorrhizal relationships. Mycorrhiza are fungi that provide phosphate and nitrogen to the plant in exchange for carbohydrates. Many mutualistic relationships are called service-resource relationships. This is what happens with flowers and pollinating species, cleaning symbiosis, and zoochory. In cleaning symbiosis, one species gets rid of pests on certain species in exchange for the nutrients that come from the pests. In zoochory, there is the dispersal of seeds by animals, which is similar to pollination. A miscellaneous category is the protection by ants of aphids. The ants live off the sugar on the aphids and give predator defense for the aphids. A service-service relationship is what happens between clownfish and sea anemones. The fish will drive off predators and the anemone s have tentacles that also protect the fish from predators. These relationships are not common. The other aspect of this is that the fish secrete ammonia that is used by the sea anemone for food. These types of mutualistic relationships exist everywhere on earth. This is true of plants and their pollinators in different parts of the world. When conditions get harsh, the relationships break down. When one species reaches a critically low level or suffers a major insult to a significant degree, a critical point is reached and both organisms collapse, with the potential to
168
