The variation among living organisms is re­ferred to as biological diversity or biodiversity, but the concept includes much more than simply the number of different species (called species diversity). It also takes into account ge­netic diversity, the genetic variety within a species— that is, the different populations that make up a particular species. Biological diver­sity also encompasses ecosystem diversity, the vari­ety of interactions among living things in natural communities. For example, a forest community, with its trees, shrubs, vines, herbs, insect, worms, vertebrate animals, fungi, bacteria, and other mi­croorganisms, has greater ecosystem diversity than does a cornfield (Figure 16-3). Ecosystem diversity also means the variety of ecosystems found on Earth: the forests, prairies, deserts, coral reefs, lakes.