Natural Selection Image Map

We can know how safe our environment is if we monitor it: measure the amount of toxins and other pollutants in our air, water, and soil. This works, but we have to know which specific chemicals to monitor. This is not always possible. Sometimes, we rely on biological monitors. Ever hear of canaries in the coal mines? Canaries can act as an early warning signal. They would die from toxic chemicals at much lower concentrations than would humans. More recently, frogs are attracting attention as sentinels. For example, male frog sexual development is impaired by a weed killer (atrazine) at 1/30th of the level thought to be safe for people. In the past decade, 200 frog species have declined and 20 are thought to have become extinct.

But some things are obvious, right? You don't have to be the class whiz to know that we probably ought to clean up dirty air, dirty water, radioactive wastes, and other such obvious sources of environmental hazards. Nor is there much debate over such ecology-damaging events as soil erosion and chopping down forests and jungle. A little common sense can help us know when we are not protecting the environment.

Below, we will remind you of some things that may not be so obvious.

Fertilizer run-off

Fertilizer that runs off into ponds and lakes creates an environmental problem. Do you know why? If you look at ponds and lakes that drain heavily fertilized farm fields, what do you suppose you would see? You would see that the water was greenish (like pea soup) or brown, that there was much plant growth in it. If you looked at water samples under the microscope, you would see many single-celled animals and a wide range of insects and other invertebrates.  These organisms fix the nitrogen from the fertilizer.  However, most plants cannot use this nitrogen and excess nitrogen in the environment limits species diversity.  See our water quality lesson on nitrates.  Many fertilizers also contain toxic chemicals than can cause accumulate in the environment.  

The whole Florida Everglades has a fertilizer run-off problem. Here a technician conducts studies on how to deal with the problem.  Click here for more.

Antibiotic Resistance

Technician smearing bacterial sample on culture medium to test
for sensitivity to antibiotics

How do we know if a given bacterium has developed resistance to an antibiotic? The original technique was to collect a sample of the bacterium. For example, if you have a sore throat, the doctor might swab the back of your throat and send that swab to a laboratory. A laboratory technician would gently rub the swab on some growth medium in a round glass dish and place little disks containing antibiotic on top of the growth medium.  When the glass dish is placed in a warm oven for a day or so, the bacteria will grow all over the growth medium, EXCEPT near the disks that contain antibiotic that kills the bacteria. There will be a clear zone, a halo, around each disk that has the kind of antibiotic in it that prevents bacterial growth. In recent years, this technique is showing that more and more kinds of antibiotics have lost their effectiveness.




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