When ecologists study populations they ask certain

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When ecologists study populations, they ask certain questions: How large is the pop- ulation and how is it changing? How do populations interact? Can we control changes in a population? Before addressing these questions, let’s start with a bit of history. See How We Grow Growth of the human population. What is the estimated size of the worldwide human population today? Watch how that number changes over the next few days. The Study of Populations Has Been One of Ecology’s Major Tasks Ecology inherited concerns about populations. In 1798,Thomas Malthus, a British cler- gyman and economist, published An Essay on the Principle of Population . His major thesis was an observation: Humanity has an innate and almost unlimited ability to pro- create, but a limited ability to produce food.Thus, human populations tend to grow and outstrip their ability to feed themselves, which inevitably leads to problems. His rather pessimistic prediction was that if human population growth were left unchecked, the result would be pestilence, war, and famine. If a person’s worth can be measured by the amount of controversy his works gener- ate,Thomas Malthus was one of the greatest writers of all times. His essays were instant- ly controversial because he challenged head-on the prevalent view of his day that humanity was moving inexorably toward social perfection, becoming a Utopian state in which all would be fully provided.Heaven on Earth was just a matter of time and continued progress. No, said Malthus, humanity is moving inexorably toward misery—misery that can only grow and continue indefinitely.The Establishment did not take his challenge lightly.
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15-2 How Do Ecologists Study Populations? 495 Figure 15-5 Modern farms are large, expensive to operate, and highly efficient.They have been described as food factories. 1 Why rates and not absolute numbers? Rates work well in calculations and make comparisons between populations easier. Rates are always expressed over an appropriate time interval, as in “births per year.” Nor do they do so today. Two hundred years after publication, his works continue to be widely quoted, to challenge established policies, and to spark controversy. Cer- tainly, he underestimated humanity’s ability to grow food (Figure 15-5). But his overall thesis—that our ability to procreate is nearly unlimited while our ability to produce food sooner or later will meet its limits—concerns some policy makers today. More important to our story, his concerns went beyond the populations of humans. He observed, “Through the animal and vegetable kingdoms, nature has scattered the seeds of life abroad with the most profuse and liberal hand. She has been comparatively sparing in the room and nourishment necessary to rear them.” In this and other passages, he focused attention on populations of animals and plants. Malthus’s works were well known to Darwin.Remember that,nearly half a century after the essay’s first publication,
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