Reading: The Diversity of Life

A photo collage of a tiger, a lizard, mushrooms, a fish, an ant, trees, a parrot, pine needles, and a flower.

Figure 1. Life on earth is incredibly diverse.

How many species exist? We don’t really know for sure. But all those species together, from the smallest bacteria, the deadliest protist, the most bizarre fungi, the prettiest plant, and the biggest mammal, compile the diversity of life, or biodiversity.

What Is Biodiversity?

Biodiversity refers to the variety of life and its processes, including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur. Scientists have identified about 1.9 million species alive today. They are divided into the six kingdoms of life shown in Figure 2. Scientists are still discovering new species. Thus, they do not know for sure how many species really exist today. Most estimates range from 5 to 30 million species.

Three pie charts showing the diversity of life. The first shows the known species of organisms. The total equals roughly one million eight hundred thousand species. Animals take up approximately 72 percent of the chart, plants 17, fungi 6, protists 4, and eubacteria 1. The second chart shows the know species of animals. The total equals roughly on millions three hundred fifteen thousand and three hundred seventy eight. Invertebrates total one million two hundred fifty-six thousand and eight hundred eighty (about 95 percent) and vertebrates total fifty-eight thousand and four hundred ninety-eight (about 5 percent). Invertebrates include insects, arachnids, nematode worms, annelid worms, mollusks, flatworms, cnidarians, sponges, echinoderms, and crustaceans. Vertebrates include fish, amphibians, reptiles, birds, and mammals. The third chart shows the known species of plants. The total equals about 287,655 species. Flowering plants dicots equal about 68.5 percent, flowering plants monocots equal 21, mosses 5, ferns 5, and conifers .5.

Figure 2. Known life on earth

Cogs and Wheels

To save every cog and wheel is the first precaution of intelligent tinkering.

—Aldo Leopold, Round River: from the Journals of Aldo Leopold, 1953

What are the “cogs” and “wheels” of life?

Although the concept of biodiversity did not become a vital component of biology and political science until nearly 40 years after Aldo Leopold’s death in 1948, Leopold – often considered the father of modern ecology – would have likely found the term an appropriate description of his “cogs and wheels.” Literally, biodiversity is the many different kinds (diversity) of life (bio-). Biologists, however, always alert to levels of organization, have identified three measures of life’s variation. Species diversity best fits the literal translation: the number of different species in a particular ecosystem or on Earth. A second measure recognizes variation within a species: differences among individuals or populations make up genetic diversity. Finally, as Leopold clearly understood, the “cogs and wheels” include not only life but also the land, sea, and air that support life. Ecosystem diversity describes the many types of functional units formed by living communities interacting with their environments. Although all three levels of diversity are important, the term biodiversity usually refers to species diversity.

Video Review

Watch this discussion about biodiversity:


Watch this video to answer the questions below:

  1. Define biodiversity.
  2. What factors help a region survive?
  3. What is genetic biodiversity? Why is it important?
  4. What is species diversity? Why is it important?
  5. What is ecosystem diversity? Why is it important?
  6. What is meant by interdependent?