54

key concepts

54.1

Populations Show Dynamic Variation in Size over Space and Time

54.2

Population Growth Describes the Change in Population Size over Time

54.3

Life History Is the Lifetime Pattern of Growth, Reproduction, and Survival

54.4

Population Biology Can Be Used in Conserving and Managing Populations

Earth’s Human Carrying Capacity

In 1798 Thomas Robert Malthus, in his Essay on the Principle of Population, pointed out that the human population was growing exponentially but its food supply was not, and argued that at some point, famine and death would be the ultimate fate of the human race. Malthus could not have anticipated the technological innovations over the next 200 years that would greatly enhance our food production and health care. Today, however, the size of the human population is once again a serious concern as we confront the effects of our contributions to climate change, pollution, habitat destruction, and species extinctions.

For thousands of years, Earth’s capacity to support human populations was low because of the relative inefficiency with which we could obtain food and water. The development of social systems and communication, the domestication of plants and animals, ever-increasing crop and livestock yields due to ongoing technological advances, and our increasing proficiency at managing diseases all contributed to unprecedented growth of the human population. It took more than 200,000 years for the human population to reach 1 billion people, which happened in the early nineteenth century. Today, a mere 200 years later, the planet is home to roughly 7.4 billion human beings.

Many believe that human populations will (if they have not already) reach some maximum size (known as the population’s carrying capacity) above which continued population growth is unsustainable. Food production is critical to human population growth and currently uses large amounts of land, water, fertilizers, and energy. Housing and quality health care require advances in infrastructure and drug production, and these too are highly energy-intensive. In addition, if Earth’s ecosystems continue to be degraded, human populations may experience a general breakdown of Earth’s life support systems.

Luckily, population growth rate has slowed from its high after World War II, but with a base of 7.4 billion, even minimal population growth rate means millions more individuals each year. As you will see later in the chapter, population biologists have used census data and standard population growth models to predict human population sizes into the future.

What is the human population growth projected to be in the next century, and how will that affect population size?

www.life11e.com/mc54.1