Conservation biology aims to improve the protection of biodiversity—that is, all the species, genetic diversity, and ecosystems on Earth. By this definition, the process of documenting life on Earth requires us to consider biodiversity on three different levels (Figure 3.1):
- Species diversity: The full variety of species, from single-celled organisms like bacteria to larger multicellular organisms like animals and everything in between.
- Genetic diversity: The full range of variability in genetic material within a species. This variation can occur spatially as differences between populations or as differences between individuals of the same population.
- Ecosystem diversity: The full variety of ecosystems—i.e., assemblages of species and the physical environments in which they live.
The relationship between species, genetic, and ecosystem diversities is complex and interdependent. That is, a species cannot exist without genetic diversity or ecosystem diversity, and vice versa. For that reason, it is virtually impossible to affect one aspect of diversity without affecting the other. We can therefore think of species, genetic, and ecosystem diversities simply as different ways to measure the variety of life.