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Disease and it’s effect on population balance

In nature there is a balance between the populations of all living organisms in an ecosystem. Balance is not static but dynamic and it is constantly shifting away from the balance point, only to be brought back through some correcting element.Some of these population shifts can be so small and slow that they are not easily perceive, others are large and happen so quickly that we are amazed to see them take place. These shifts in a population’s balance are not abnormal but are part of the natural cycle of life.Many of the biological changes in our recent history are due to both intentional and unintentional human manipulation of balanced ecosystems. Once humans stopped being hunter-gathers and developed a settled agrarian life they began to alter their local ecosystems through farming and animal husbandry activities. By doing this we removed organisms and controlled environmental conditions that were not conducive to growing the plant and animal products we wanted.These activities narrowed the ability of the ecosystem to respond to change and thus allowed for uncontrolled expansion of populations of organisms that thrived in the systems we modified. Modern transportation systems are so rapid that pathological organisms can move from one part of the globe to another and start affecting our crops and animals before we are even aware of them. History provides us with many examples of this in plants, animals and the humans.Within living memory there are several examples for plants. One such slow motion change was the Dutch elm disease. The Elm is a tree whose stately form and cooling shade have been extolled in song and verse for centuries. Scientists believe the fungus that causes Dutch elm disease originated in the Himalayas. It traveled to Europe from the Dutch East Indies in the late1800’s. In the 1930’s, the disease spread to North America on wooden crates made with infected elm wood and began killing elm trees.A second introduction of the disease into North America occurred in 1945 starting in Sorel, Quebec. It destroyed over half the elm trees remaining from the first infection in eastern Canada and the US. By 1976, only 34 million elm trees were left and now (2008) over half of these are gone. In England new strains of the fungi have appeared and 17 million of that country’s remaining 23 million elm trees have been killed.Another plant that was heavily impacted by a transplanted disease was the potato. It was affected by a blight, which caused the Irish potato famine. In 1845, the fungus Phytophthora infestans arrived accidentally in Ireland from North America. A slight climate variation at that time brought warm wet weather, which the blight thrived on. Much of the Irish potato crop was made up of only two species and these rotted in the fields. More than a million Irish citizens, about one of every nine, died of starvation or disease in the Great Potato Famine of the 1840s. This famine resulted in a mass Irish emigration to America.One plant plague that I can relate to is the chestnut blight which has killed all but a very few of the Native American chestnut trees. The chestnut blight is another fungal disease, Cryphonectria parasitica. It was accidentally introduced to the United States around 1900-1908, either in imported chestnut lumber or imported chestnut trees and by 1940 the American chestnut had been made virtually extinct by this disease.The American chestnut was once the most important tree in America’s forests throughout much of the eastern United States but has been driven to the brink of extinction. It is estimated that before the 1900’s one out of four trees in the eastern US were American chestnut, for a total of some 3.5 billion trees. The number of surviving mature trees can now be counted in the dozens due to the blight. You can still find this tree in New England but you have to know where and what to look for.In our domested animals we have problems like hoof and mouth and mad cow disease. The proliferation of which is due to intensive selective breeding, unregulated transportation of animals and overcrowding.Humanity as a species is faced with these same problems as its numbers have expanded and overcrowding has increased. The black death (Pasteurella pestis) killed two thirds of the population of Europe in the middle ages not to mention tens of millions in the Near East and Asia.Cholera, yellow fever, small pox, measles (ask any American indian) have killed tens of millions and now Lyme disease and S.A.R.S. are spreading. If a microbe like Ebola was transmittable by air or a virus like the 1918 flu were to come along through mutation, which the flu does every year, we would have a very big problem.The 6.7 billion humans we how have on the planet are about three plus billion too many for the planet’s resources to sustain. For humanity it is not a matter of if but when.

Think Global – Act Local!


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