A Place in Which to Live

All creatures need a place in which to live. More specifically, they need a home. A home is a place that provides food, shelter, protection from enemies, and contact with others of its own kind.

We have already discussed the necessity of food. Some organisms live in or on food. Others may have to travel distances between their place of shelter and their food.

Consider, for example, bacteria which may live upon their diet, or plants that need exposure to sunlight, or migratory herds of antelope and caribou. Some flocks of birds daily or seasonally travel great distances to find forage.

There is some thought that the barren-land caribou seek out and travel long distances to bear their young in high windy areas where there are fewer swarms of biting flies to plague their newborn fawns. This, plus the abundance of new growth vegetation, is definitely an advantage to the caribou.

Migratory waterfowl tend to nest in areas rich in the type of food their young can eat, as well as where resident predators are few in number. Vernal ponds in the far North are filled with small crustacea and snails. These small organisms suffice to nourish the ducklings and goslings, for example, until they grow enough to eat abundant, but larger forms of plant life.

Barrenland Caribou

Canada Geese

Parasites living in other animals, in general, have found a satisfactory place in which to live. As long as the parasites do not over-tax the resources of their host, the parasite and host tend to get along with each other. It is a stupid parasite that kills its host.

Cowbird being fed by foster mother.

Heartworm in dog heart.

Fireworm (Dracunculus)

Origin of medical symbol.

A gut full!  One

is never alone.





The sign says it all!




In some cases the parasite and host are better off with each other than either would be living separate lives. Consider the bacteria and protozoa living in the rumen of cattle, sheep, goats, and deer. The parasites (commensals) digest food that the host cannot, and the host benefits by being able to digest the byproducts of the rumen inhabitants. It is also thought that certain bacteria living in the intestine of humans compete with and thus prevent disease producing bacteria from proliferating and causing disease. When antibiotics are used to prevent certain disease producing bacteria from damaging a person, it is common to prescribe milk products such as yogurt (lactic acid) producing bacteria to repopulate the intestine and prevent disease producing bacteria from living in the intestine.

Michelle Brooks and Wendy Garrett in the August 1, 2011 edition of Science blogs about how parasites and hosts "Share the Bounty."


A place in which to live includes a balance of competition between different species and between members of the same species. When people think of competition, they frequently think of the interspecies types. Examples are the competition between cattle and sheep for the same grasses, competition between wild geese and farmers for the same grain, and competition between cancer cells and normal cells for the same blood supply. There are hundreds of scientific research papers on interspecies competition.

Perhaps not as common are scientific or sociological papers on competition within the same species. We all know that larger active adults tend to consume more food than smaller adults. A large dog eats more than a smaller dog, etc. We all know stories of overgrazed pastures and woodlands.  Cattle, deer, and sheep, respectively, can literally eat themselves out of house and home.

Approximately 60 years ago, a scientist, Dr. Hans Selye, observed that organisms of the same species, but living in crowded conditions, tend to exhibit certain physiological and behavioral peculiarities. They tend to become more agitated, active, and aggressive.

These overcrowded organisms would increase in population to a point and then become what appears to be suicidal. Lemmings in Scandinavia are known to increase in number to a point that they blindly attempt to migrate elsewhere. They frequently drown in the ocean during the process. Squirrels in Appalachian parts of the United States would increase in number to a point that they would race by the thousands through the forest and destroy everything in their way. There are records of "crazy" squirrels ripping shingles off house roofs and tearing buildings apart.

Dr. Selye named this sort of phenomenon the "General Adaptation Syndrome." Many research scientists, under controlled laboratory conditions, have worked to demonstrate this phenomenon in various species.

An experiment that Dr. Robert Seabloom, I and several colleagues tried some years ago was to put a pair of meadow voles (Microtus pennsylvanicus) into a cage with surplus food, water, and nest material. Waste materials were regularly removed and not allowed to accumulate. At first the voles were healthy and reproduced. Eventually the cage became full of voles. Even under constant environmental controls, the voles became aggressive and started to kill each other. Reproduction rate declined because the animals were too crowded for successful mating, and the offspring of successful mating were frequently killed.

In some cages the numbers of voles per cage were reduced to 2 or 3 individuals, and then the process would start over again. In other cages the voles became extinct.

Much research was done to determine the cause of the hyperactivity of the crowded voles. In general, it was observed that the adrenal gland enlarged and kept adrenalin at an elevated level. Thus the voles were kept in a hyperactive state.

Richard Knox has written a paper recently released on NPR Health Blog for July 29, 2011.  The paper is called "Countdown to 7 Billion:  A Tale of Two Worlds."  He discusses centers of rapid human population growth, and points out that in a few decades India will have a higher human population than China. 

Another paper by David E. Bloom relates human population growth to food availability.  He points out that the capacity to produce food for humans is becoming less, while the human population increases.

Felicity Barringer wrote a AAG Smart Brief in August 22, 2011 called "What Drives Cities' Runaway Growth?"  She describes the increasing populations of cities at the expense of rural areas.

The population of humans is increasing at an accelerated rate. The amount of food available now and for the immediate future is insufficient.  Human aggression is rampant. I canít help but wonder if the human race, too, is experiencing the beginning of its own "General Adaptation Syndrome?" Perhaps we are destroying our own "place in which to live"?