Scientists are proud of our technical terms. But we often fail to clearly define them when promoting an idea for public discourse. “Biodiversity” is just one of those terms that ranks near the top of my list of those that we need to explain and promote.
Understanding biodiversity underlies our reasons for promoting better stewardship of our natural world. So, channeling my wonderful English teachers, the term has two parts: the root term diversity and the prefix bio. Bio is easy enough to understand. Diversity simply references a measure of variety—how many kinds of things we are discussing.
At its basic level, biodiversity refers to how many kinds of organisms occupy a given place and is typically used to qualify diversity—greater numbers of kinds of organisms (species) are usually better. The number of species (referred to as species richness) is, however, only part of our understanding of biodiversity. An equally important element, equitability, refers to the degree to which the total number of individual organisms in a place are distributed among species.
Two communities may have the same number and group of species (the same five species of plants, for example), but the distribution may be quite different. If we only consider species richness, we might conclude that biodiversity is the same. But what if both communities also have the same total number of individuals and that these numbers are not shared equally among species?
My friend, Janet Wright, used the following example in her ecology classes. Two fruit salads contain apples, melons, pears, grapes, and bananas, so richness is the same. Each salad also has the same total number of pieces of fruit (say 20). Janet’s salad has the same number of pieces of each type of fruit (4 each) while mine has 16 pieces of bananas (I like them!) and one each of the remaining types of fruit. This difference in equitability leads to a very different conclusion about biodiversity for these two salads.
In nature, this does happen when an invasive species dominates a community. A wetland that I recently restored was overwhelmed by torpedograss, an aggressive invasive plant that depresses the growth of native species. It was hard to find individuals of native plants within the thick cover of torpedograss. Once the torpedograss was treated, the native plants quickly recovered. Species richness was basically the same before and after, but equitability shifted for the better. Biodiversity is greatest when both richness and equitability are high.
So now you know a bit more about the 50-cent term called biodiversity. Numbers of species (species richness) are important, but so too is a balance (equitability) within the number of individuals present. Natural ecosystems work best this way and invasive species and humans tend to upset this balance.
Hope to see you in our great outdoors!