Biodiversity pro manual10/27/2022 ![]() But site A is relatively overrun by rabbits with low numbers of the other species, whereas site B has a pretty even distribution of species, so it is considered to have greater evenness compared to site A. For example, these two sites have the same richness, or alpha diversity, as they both have seven species. As well as recording diversity, scientists often refer to species evenness, meaning how many individuals of each type are present. So to summarize the three kinds of biodiversity, we can look at them this way, alpha, beta, and gamma. In this example, there is a gamma diversity of 12. ![]() Finally, gamma diversity is the number of different species in all sites combined. Sites B and C have two common species between them, or a beta diversity value of eight. Sites A and C also have three species in common, leaving eight unique ones. This means that there is a beta diversity between site A and site B of six. Counting the remaining species, we find that there are six. So if we compare site A with site B, we see three species in common between the two. But by comparing between sites, we can determine what is called the beta diversity, the sum of species unique to each area. A second site, site B, has five species, and a third, site C, has seven. For example, at this site there are seven different species, so the alpha score is seven. Alpha diversity refers simply to the number of species in an area and is often referred to as species richness. In 1972, the ecologist Robert Whittaker described three major kinds of biodiversity, alpha, beta, and gamma. But while measuring diversity at a single site is incredibly useful, comparing sites over a greater area can give us an even larger scale indication of diversity. The asymptote of this type of curve represents an estimate of the number of species supported by an environment. For example, in this data set, when four quadrats were investigated, it was found that there were 10 unique species. If the cumulative number of species found in a quadrat are plotted against the number of quadrats sampled, a curve will emerge. In order to then estimate the total number of species in an area, species accumulation curves are used. After cataloging the species and individuals found in this small section, the process is repeated, placing more quadrats at random, or alternatively, at set positions along a line through the environment, referred to as a transect. Trying to count everything in an entire ecosystem would be impossible, so scientists use a tool called the quadrat, which is a frame of fixed size placed randomly in the environment in which to do the counting. What is a convenient way to count species? ![]() This means figuring out how many different species are living together in a particular space. To protect biodiversity, scientists must be able to measure it. The word evokes the splendor of a great forest, or the teeming richness of the ocean, and is simply defined as the variety of organisms in an ecosystem of interest. ![]()
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