Study Guide

Animal Evolution and Diversity In the Real World

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  • Health

    More Rodents, Please

    We sometimes hear about nasty diseases for which we don't have cures, like Lyme disease and the Hantavirus. There are lots of ways to tackle these problems, but one lies a bit outside the usual medical arena.

    Some diseases are spread through contact with animal carriers. A tick with Lyme disease bites a mouse and the mouse gets infected. The Lyme disease causing bacteria gets into new ticks when they bite an infected animal. Eventually, an infected tick bites a human and the human gets Lyme disease.

    We haven't yet found a way to get rid of Lyme disease once a person is infected. Getting rid of infected ticks or mice is hard, as is keeping them away from people. There might be another way.

    Studies are showing that loses in biodiversity correlate with increased spread of certain diseases. When there are lots of different kinds of animals, the ones that are good carriers are less prominent. In the Lyme disease case, ticks have more chance of biting hosts that can't carry the disease if there are plenty of other kinds of animals around besides mice.

    The Hantavirus is another example. This virus is spread between small mammal species, but doesn't affect all related species. When there are a variety of animals around, there seems to be a lower incidence of the disease. When there are lots of other kinds of animals around, infected animals just may not come in contact with as many animals of their species and so can't spread the disease as fast.

    In this case, more rodents, at least more kinds of rodent, is a good thing for our health.

  • Agriculture

    Where Did They Go?

    Bees are in need of their own Sherlock Holmes. Since 2006, beekeepers have been reporting the disappearance of most or all adult bees in hives, a phenomenon called Bee Colony Collapse Disorder. The queen bee and young bees are still there. There are no dead bee bodies and no adult bees at all. Perhaps they need Fox Mulder instead. It's like the bees were abducted.

    No one is quite sure this is happening. Bee colonies sometimes lose a lot of bees over the winter, but not like this.

    There are a few possible culprits and no single one seems to be the sole issue. Mites and internal fungi are common in colonies that collapse, but are also found in healthy colonies. One theory is that the problem is when the total number of these reaches a certain level.

    Bees are also affected by stress. Yes, it even afflicts insects. Nectar and pollen availability and quality are a problem. Managed bees are also affected by beekeepers moving the hive around or the hive getting too crowded. Makes us crazy, too.

    Pesticides may be an issue, though no one pesticide alone seems to be the culprit. It could be an issue of how pesticides are used or a combination of pesticides.

    The going theory is that it is a few of these factors together that are behind the collapse. Scientists are still hard at work figuring this out.

    There are lots of theories, but one big problem for humans. Many plants, including important agricultural crops, depend on bees for reproduction. Per the USDA, "about one mouthful in three of our diet directly or indirectly benefits from honey bee pollination." Yikes.

    How are bees and our crops connected? Honeybees coevolved with flowering plants. This means that the bees evolved over time to use the resources provided by flowering plants, while the plants were evolving over time to depend upon bees. Bees pick up pollen and nectar provided by flowers. They use nectar to make honey and eat some of the pollen as food. Some of the pollen, however, is spread between flowers as the bees forage. This pollinates the flowers, creating a whole new batch of flowers, which means for us a whole new batch of fruits and vegetables. The bees and flowers need each other and we need them.

  • Environment

    You Are What You Eat

    To be more specific, you are what you eat eats. There is a whole web of intertwined plants and animals and bacteria and fungi tied to each carrot and each burger. There probably aren't six degrees of separation between bacon and Kevin Bacon.

    How much life is there? There is a lovely, big word for this. Biodiversity is a term that describes the number and kinds of life forms that exist in a given place and time. A place that has great biodiversity has many life forms and many different kinds of life.

    All life is part of larger systems that are interdependent. Whoa. We are not getting metaphysical here. We are getting physical. One basic law of physics is that matter is neither created nor destroyed. What we eat today becomes part of something else later. It all comes back around. Nutrients are cycled through the ecosystem, though all the kingdoms of life. Biodiversity is a crucial part of this recycling process.

    Our food supply—what we grow and catch and raise—depends on the diversity of organisms that support natural systems. It isn't just sun, water, and air that grow our crops, but also earthworms, nematodes, and insects. Organisms in the soil break down nutrients for plants and ensure the quality of soil. These organisms in turn depend upon others. Without these, the whole system starts to fall apart and so does our food supply.

    We are part of this system and we are also great at manipulating it, though not always to our long-term benefit. Modern agricultural techniques provide one example. Earthworms are necessary for soil health, but are harmed by frequent tilling and some chemicals used to control plant and animal pests. We need a diversity of creatures in the soil and the trick is to maintain this while still controlling pests.

    The food we catch is also equally dependent on biodiversity. For instance, the fish and seafood we eat depend upon a healthy aquatic ecosystem. There are plenty of things in rivers, lakes and the ocean that we don't eat. However, those other animals are also part of the nutrient cycling and prey-predator balance that keeps the whole thing healthy for the ones we do eat.

    So, the next time you bite into a carrot, give earthworms a little shout out.

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