When ecologists look at an ecosystem, initially they may think in terms of biodiversity - i.e. what species and how many species are there in the area.
They may focus on their favorite kingdom and/or class of organisms, such as plants, birds, mammals, or fish. Or, they may focus on many kingdoms if they are interested in the interactions of these organisms.
Generally, the more diverse the species are in a given system, the more complex a system it is. However, this simple statement is not always true.
In this module, we focus on the plant kingdom.
We looked at a section along the San Juan River. We counted the number of plant species. We measured and compiled the foliar (above-ground green parts) coverage of each species. And we repeated this method for five different sites.
We then moved on to the dry mesa area above Bluff Road between Shiprock and Hogback and did the same thing for an additional five sites.
Some sites had more species than others. Some sites had more foliar coverage by one species than the others. Counting the number of species (species richness) is a good beginning but not enough. Recording the number of individuals of each species found is as important.
One square kilometer of land may contain two species of plants, one individual in one species and 99 individuals in the other.
Another one square kilometer of land may also contain these species but contain fifty individuals of each. Both have exactly same number of species (species richness) and same number of individuals, but the two lands are drastically different in terms of favoring species.
Additional data, the number of individuals per each species is called ABUNDANCE. Abundance will improve our understanding.
The first site had a very uneven split of the two species. The second site had an equal number of individuals of each species. The "even - ess" or "uneven - ess" of species is called SPECIES EVENNESS.
When the relative abundance is extremely "low", one of species is rare in a given area. When the relative abundance is "high", individuals across species are evenly represented.
For our purposes we did not count individuals. We measured foliar coverage. Coverage is how much area is occupied by a species of plants. Abundances used in this module were estimated from the foliar coverage.