Every life form has an optimum temperature range at which it will flourish. When temperature varies from that optimum, it causes stress. Each life form has come up with ways of coping with temperature variation.
Most plants don’t have the option of moving to more comfortable surroundings, but some primitive single celled algae actually are mobile. They photosynthesize and are plants, but they can move up and down in the water column to find more comfortable light and temperature levels. Plants like the grass and trees in your yard depend on evaporative cooling. Tiny pores called stoma on the underside of their leaves allow air into and out of the plant. When it’s too hot, the plants open their stoma to allow more water to evaporate out of the leaf, thus cooling the plant. That works fine as long as the all-important water is available. When it becomes too scarce (like now) plants resort to more extreme measures in order to survive. Dormancy is a sort of suspended animation that many plants use to get through normal periods of harsh conditions like winter. It can also be used by some to stay alive through summer heat stress, as well. The living, upper portions of perennial plants may cut life processes to a minimum to attempt to ride out a heat wave. Corn, an annual grass, can’t afford to stop entirely and risk not making any seed, the plant’s only means of surviving into the next year. Instead, it curls its leaves to reduce air flow from its stoma and preserve moisture. Other grasses may let their leaves entirely die, but hold onto life in their perennial root stocks. Even trees may drop their leaves and go into early dormancy to get through extreme heat or insect outbreaks.
Animals are more mobile and move to cooler areas if they can. It may be seeking shade like a herd of cows under a tree or it may involve shifting periods of activity to cooler times of the day. Others head underground to escape the heat, just as we used to play in our basement where it was cooler on hot days before air conditioning. Warm-blooded creatures, like birds and mammals, also depend on evaporative cooling. Some mammals do it by sweating and allowing the drying moisture to cool their skin. Others that can’t sweat may pant, moving larger volumes of air into and out of the body, where it evaporates moisture in the mouth and lungs and helps to cool the animal. That, of course, leads to a need to drink more water at the same time water resources may become harder to find.
Cold-blooded creatures like insects, fish, amphibians and reptiles depend on mobility to maintain optimum body temperatures. Warmer bodies lead to increased metabolism and a greater need for oxygen, too. Iowa’s excessively algae-laden waters are good at kicking out lots of extra oxygen on hot summer days, but algae have a dark side, as well. At night, these plants begin to use oxygen more like animals. Oxygen levels during heavy algae blooms can fluctuate from supersaturated in the daytime to fish-killing low levels at night. Not only that, but Iowa lakes tend to stratify in hot weather. Deeper, cooler water that fish might seek for comfort can’t mix effectively with more oxygenated surface water. Deep areas can completely run out of oxygen by late summer, leaving fish stranded in the shallower, hotter, high-stress water. It’s little wonder that fish may go off feeding when they’re just plain uncomfortable
Think about all our wild neighbors as you hide from the heat in front of a fan or in your air-conditioned home or workplace. It wasn’t so long ago that we humans had to cope with summer heat, just like other living things still must. Be sure to drink extra water if you must be out in the heat!
(Steve Lekwa is a former director of Story County Conservation.)