Those who know the land depend on certain constants. One constant we all recognize is that nature is cyclic. The sun comes up in the east and goes down in the west. Seasons come and go in the same order every year and this progression brings with it certain weather patterns.
Animals and plants behave accordingly. There is a time to be born and a time to die - times of activity and times of rest - lean times and times of plenty.
Vegetative succession - from old fields to shrubs to forest, for example - repeats itself every time a fire or tornado occurs. And once a cycle is complete, it starts over again.
Another constant is that while all these cycles constantly repeat themselves, some changes are occurring that seldom or never do - at least not for thousands or millions of years. For example, we are not likely to ever see dinosaurs again. The passenger pigeon, once more abundant than blackbirds are today, probably won't be back either. Human influence causes some of these changes, but not others.
In recent years, we have seen many changes in the Southeastern U.S., with regard to wildlife distribution patterns. A notable example is the coyote. Now widely found in the Southeast, many people alive today - including myself - can remember when they were only found in the Western U.S.
Without prompting from man, they began to expand their range eastward along the northern half of the country.
When they reached New England, their range limits moved southward along the coast, then westward again along the southern half of the U.S. They arrived in Tennessee in the late 1960s/early 1970s.
Human interference didn't directly prompt this range expansion (except for - as rumor has it - a few possibly stocked by fox hunters). But indirectly, humans probably assisted the project more than we realize, by the way we changed our use of the land. Coyotes are animals which like open land, and we continually opened up the forest. And since coyotes area so adaptable, they moved in close to cities, mating our dogs while their populations were low, then eating them - along with the cats - when there were enough of their own kind.
That same land use change has caused blackbird populations to explode. They love our big grain fields, both the grain in summer and fall, and grubs and weed seed in winter.
When I was a boy, English sparrows were abundant everywhere, and European starlings were seldom seen. We imported the sparrow many years ago, and then brought the starling later - about 1834.
Now starlings are everywhere and sparrows are a rarity.
They both occupy a niche in association with people, feeding on our crumbs and nesting in our buildings.
The starling, being dominant, has elbowed the sparrow out - nearly out of existence.
The pigeon lives around people, too, but their larger size and different nesting behavior makes co-existence with starlings possible. Monk parakeets, another exotic species released through the pet trade, have also fared well in association with people.
Openings have caused the reduction of woodland birds too (we call them neo-tropical migrants, because they spend winters in the tropics). The loss and fragmentation of large sections of woodland habitat is partly the reason.
Another reason is perhaps more subtle. The brown-headed cowbird is thriving. Preferring to nest in woodland edges (more abundant because of forest fragmentation), it lays its eggs in nests made by neo-tropical migrants. The stronger cowbird nestlings bully their way to the food, resulting in starving the other nestlings, or even pushing them out of the nest.
Beavers came back to prominence in the Southeast, probably due to our poor management of the river systems. The first beaver in West Tennessee in recent years (that I know about) was killed in the Obion River bottom in the early 1960s. Now they are all over the place.
Deer and turkeys, non-existent in West Tennessee when I was a boy, are now everywhere, thanks to a calculated relocation effort by the state wildlife agency.
Groundhogs, once only found in West Tennessee along the Mississippi River now have expanded all across the state. Skunks, once rarely found in West Tennessee, now can be smelled on any roadway in the state. Groundhogs and skunks probably expanded as we continued to open up the forest.
Several species have, in the last few years, expanded northward from the deep Southeast. Cattle egrets moved north along the Mississippi River, and are now as far north as southern Illinois. Even more recently, fire ants and armadillos are marching northward. They are now half way up into Tennessee (all across the state from east to west), and it will be interesting to see how far north they will come.
The reasons for all these range expansions are not yet known - maybe never will be. But, when you think you have things all figured out, be careful. Nature will change before your eyes!