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BILD 3 - Lecture 27

BILD 3 - Lecture 27 - How competition coefficients can lead...

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How competition coefficients can lead to a stable equilibrium Why should competition between members of different species be less than that between members of the same species? This might happen if the two species utilize different resources. It might also happen if members of the two species have a mutualistic interaction — that is, if they live together for mutual benefit. Another possibility is that the two species can protect each other from diseases that are specific to each species. This might happen if coexistence reduces the population density of each species and thus reduces the likelihood that the diseases will spread in each species. In the course of evolution, carrying capacities and competition coefficients will change over time, leading to very complex interactions among the individuals of different species. These interactions are all characterized by strong frequency-dependence — that is, they depend on the relative numbers of the different species involved. Rainforests may have as many as 600 different species of tree and shrub in a one-hectare plot, 100 meters by 100 meters. There are thousands more species of epiphytes and fungi. Why should there be so many different species? Here are three reasons: 1) Different ecological niches provided by the physical environment. Some tree species grow tall, and need lots of sunlight to do so. Others thrive in the deep shade of the forest floor. They grow slowly because there is little light, but they are adapted to survival under these conditions. 2) Mutualistic interactions with fungi or with other tree species. Many plants in the rainforest associate with fungi called mycorrhiza that can either benefit or harm them. In some cases the fungi are widespread, but in others, particularly orchids, the fungi are specialized. A fungus-orchid interaction can maintain both species.
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