4 6.4 Chapter 6 Summary
Learning Objectives
- Predict the effect of biotic and abiotic factors on population growth
- Predict the impact of changes in growth rate (r) and carrying capacity (K) on a population curve
- Identify specific areas on a population model graph as having a general r value that is positive, negative, or zero.
- Determine under what conditions a population growth model allows a deviation from carrying capacity.
- Explain why the logistic growth model is so resilient and stable around K
- Explain what circumstances in the real world would lead to a change in K.
- Discuss the influence of social policies and scientific advances on human population growth.
6.1 Exponential and Logistic Population Growth
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Populations with unlimited resources grow exponentially, with an accelerating growth rate.
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When resources become limiting, populations follow a logistic growth curve. The population of a species will level off at the carrying capacity of its environment.
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The carrying capacity is determined by the amount of resources available to support a given number of individuals in a population.
6.2 Density Dependence Leads to Logistic Growth
- Populations are regulated by a variety of density-dependent and density-independent factors.
- Density dependent factors are often biotic and depend on population density. Examples include competition, predation, and disease.
- Density-independent factors are often abiotic and affect populations regardless of density. Examples include weather, pollution, and natural disasters.
- These factors can also interact to impact populations. For instance, a dense population hit by a harsh winter may recover faster than a sparse one due to more remaining individuals.
- Exponential growth assumes unlimited resources and is density-independent. In small populations, resources are abundant → high birth, low death rates → which leads to rapid growth.
- Logistic growth accounts for resource limitations, making it density-dependent. In large populations, resources are scarce → low birth, high death rates → which leads to slowed or negative growth.
- Populations stabilize at carrying capacity, where resource use is maximized without over exploitation.
6.3 Human Population Growth
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The world’s human population is growing at an exponential rate.
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Humans have increased the world’s carrying capacity through migration, agriculture, medical advances, and communication.
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The age structure of a population allows us to predict population growth.
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Unchecked human population growth could have dire long-term effects on our environment.
Practice Questions
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