Avoid the Optimal
All sensible species avoid living on the edge. But as the world’s temperature goes up a few degrees in the course of the present century, many will be pushed over.
We humans, if I am to judge from the thermostat settings, prefer room temperatures up in the mid-70s [24°C]. All species have an environmental temperature that they prefer–but it is always less than the optimal temperature for making a living and raising offspring. Why is “cool it” so important?
All species have a range of temperatures in which they can live. Near the edges, they get into trouble. Population numbers fall as raising offspring becomes difficult. This band of acceptable environmental temperatures is broad for species in the temperate zones of the world. Tropical species can afford to specialize in a narrower temperature range because they are not often exposed to anything else.
But possible and desirable temperatures are different. You’d expect, recalling whatever you’ve learned from economics or evolution, that a species would prefer to live in a band of temperatures that straddles the peak of the curve, the optimal temperature for gaining weight and producing offspring. However, put the animal in the optimal temperature and it will soon seek out cooler places. The entire band of desirable temperatures is cooler than the peak of the species’ fitness curve.
That curve, you see, isn’t bell-shaped but skewed, dropping steeply as it gets hotter than the optimum. Several degrees beyond the optimum gets into scary territory. The species may not be avoiding the optimum so much as staying well away from the drop-off cliff.
So some species may be better off with a small temperature rise–they will be nearer their optimum– but in big trouble as the temperature rises further. Evolution could adapt a species to a warmer world but it takes time. A few million years ago, the world was warmer but it was a very slow warming. It didn’t jump up to the new temperature in only one century.
Speed matters.