The Diversity of Life

Learning Outcomes

  • Explain 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.

If you were asked to categorize the living things on earth, how would you do so? Most likely, you would sort things into three groups: animals, plants, and microorganisms: these are the most visible divisions of life.

Biological diversity is the variety of life on earth. This includes all the different plants, animals, and microorganisms; the genes they contain; and the ecosystems they form on land and in water. Biological diversity is constantly changing. It is increased by new genetic variation and reduced by extinction and habitat degradation.

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. Click for a larger image.

Video Review

Watch this discussion about biodiversity:

Scale of Biodiversity

Diversity may be measured at different scales. These are three indices used by ecologists:

  • Alpha diversity refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa within the ecosystem (usually species).
  • Beta diversity is species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecosystems.
  • Gamma diversity is a measurement of the overall diversity for different ecosystems within a region.

Benefits of Biodiversity

Biodiversity provides us with all of our food. It also provides for many medicines and industrial products, and it has great potential for developing new and improved products for the future. Perhaps most importantly, biological diversity provides and maintains a wide array of ecological “services.” These include provision of clean air and water, soil, food and shelter. The quality—and the continuation— of our life and our economy is dependent on these “services.”

Australia’s Biological Diversity

The echidna is a small brown spiney animal. Its spines all face away from the animal’s head, and it has a narrow beak.

Figure 3. The short-beaked echidna is endemic to Australia. This animal—along with the platypus and three other species of  echidnas—is one of the five surviving species of egg-laying mammals.

The long isolation of Australia over much of the last 50 million years and its northward movement have led to the evolution of a distinct biota. Significant features of Australia’s biological diversity include:

  • A high percentage of endemic species (that is, they occur nowhere else):
    • over 80% of flowering plants
    • over 80% of land mammals
    • 88% of reptiles
    • 45% of birds
    • 92% of frogs
  • Wildlife groups of great richness. Australia has an exceptional diversity of lizards in the arid zone, many ground orchids, and a total invertebrate fauna estimated at 200,000 species with more than 4,000 different species of ants alone. Marsupials and monotremes collectively account for about 56% of native terrestrial mammals in Australia.
  • Wildlife of major evolutionary importance. For example, Australia has 12 of the 19 known families of primitive flowering plants, two of which occur nowhere else. Some species, such as the Queensland lungfish and peripatus, have remained relatively unchanged for hundreds of millions of years.

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