Module 8 Lesson 6 - 5
Lesson 6 — r and K-Selected Life Strategies
Lesson Summary
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A population can be described as r-selected (J-curve) or K-selected (S-curve). The terms are used to show comparisons.
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K-selected species live close to carrying capacity, have long life spans, are generally larger in mass, reproduce later in life, and have small numbers of offspring, which they nurture. Example: whales
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r-selected species are growing close to their biotic potential, have short life spans, have early reproductive ages, are generally small in mass, and have large numbers of offspring with high mortality. Example: insects
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K- and r-selection are two extremes of a continuum; most species fit within the continuum.
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Phenomena influenced by human activity such as climate change, over-harvesting, pollution, and introduction of invasive species can affect populations greatly.
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Age pyramids are useful tools for predicting future populations.
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Human populations were at carrying capacity for most of history. Technology has increased life expectancy and decreased infant mortality, causing the carrying capacity and population growth rates to increase exponentially.
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Due to reduced birth rates, most human populations no longer are growing exponentially although a few are.
- The human carrying capacity is influenced by growth rates, age structures, the state of the environment, and technological developments, but likely it will plateau at approximately 9 billion.
To describe changes in populations quantitatively requires several tools. Formulas for population size, density, growth rate, and per capita growth rate allow the collection of appropriate information to make informed decisions as wildlife managers, developers, politicians, academics, and concerned citizens. By itself, this data is not useful; we must compare it to the normal patterns of growth observed in various species.
Various species have evolved two distinct strategies of growth to maximize their reproductive potential and survivability (r-selection and K-selection). These patterns are indicated by specific growth curves (logistic K and exponential J). A given set of species characteristics indicates each strategy, and the course of a given population can be predicted by matching it with those characteristics.
Observed changes from the normal patterns are considered flags that indicate disruption from human activities, density-independent factors, or density-dependent factors. Human populations can be characterized by these same parameters; however, human populations tend to differ from others due to our tendency to change our own environments using technology. Debate and controversy about how human growth differs from the growth patterns of other species has led to differing predictions about future human population trends.