If you're seeing this message, it means we're having trouble loading external resources on our website. Show If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Note how after 9 generations, the exponential curve (human population growth) outstrips food supply (arithmetic growth). Darwin used this information to help develop his theory of natural selection by assuming that this situation occurs for all living organisms, not just humans!! So, does it work? Consider that in a typical day, 35,000 humans starve to death around the world. Most in developing countries. What is the Current Population of the Earth? What is Current Net Reproductive Rate of Humans Worldwide? 0.013 x 6.2 B = 80,600,000 new people per year, or 80.6 million new humans each year!! That is the equivalent of 2.5 California's per year, or 1 new Germany per year. It is 1.6 million people per week (one New Mexico per week), or 221,000 people per day (one Charlotte, NC added per day!). An astounding growth rate, even though the net reproductive rate is actually quite small. But growth is not evenly distributed around the world. Certain countries are growing faster than others, while some are actually losing growth (deaths and emigration exceed births plus immigration - Albania is an example). Why the Increase in Human Population Growth Rates This Century? Due to decline in death rates, r for humans has risen nearly 6 fold!!! Some Representative Growth Rates for Countries Around the World
Net Reproductive Rates You can determine the population doubling times for the world and countries by dividing 69.3 by the growth rate. For example, if the world growth rate is 1.3%, then the time it takes to double the population is: 69.3/1.3 = 53 years Thus, if things don't change, the world population could rise to 12.4 Billion in the year 2055!! When I was born, the population was about 2 Billion in 1952. It is now 50 years later, and the population is 6.2 Billion. That is nearly a tripling!! Why? The world population growth rate was much higher in the past 50 years than it currently is. When I was born, the population growth rate was over 2% per year, and the doubling time was down to 42 years!! Why Do Growth Rates Differ Between Countries? What Can Be Done to Control Population Growth?
The Future - How Large Will the Population Become? 1. Have only 2 children per family. That way, population growth is reduced to essentially zero. What eventually happens to a population experiencing exponential growth?In exponential growth, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger. In nature, populations may grow exponentially for some period, but they will ultimately be limited by resource availability.
In what populations does exponential growth tend to occur?Exponential growth may occur in environments where there are few individuals and plentiful resources, but when the number of individuals gets large enough, resources will be depleted and the growth rate will slow down. Eventually, the growth rate will plateau or level off (Figure 19.5b).
Which processes influence the size of a population?Population growth is determined by rates of birth, death, immigration, and emigration.
What are the types of population growth?There are two main models used to describe how population size changes over time: exponential growth and logistic growth.
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