Module 9S2 Changes in Populations

Lesson Summary

• A population can be described as r selected (J curve) or K selected (S curve). The terms are used in comparison to each other.
• K selected species live close to carrying capacity, have long life spans, are generally small in mass, reproduce later in life, and have small numbers of offspring, which they nurture.
• r selected species are growing close to their biotic potential, have short life spans, early reproductive ages, are generally small in mass, and have large numbers of offspring with large die-off.
• K and r selection are 2 extremes of a continuum – most species fit in between.
• Phenomena influenced by human activity such as climate change, over-harvesting, pollution, and introduction of invasive species into foreign environments can greatly affect populations.
• Age pyramids are useful tools for predicting future populations.
• Human populations were at carrying capacity for most of history. Technology has increased life expectancies and decreased infant mortality, causing the carrying capacity and population growth rates to increase exponentially.
• Due to reduced birth rates, most human populations are no longer growing exponentially, though a few are.
• The human carrying capacity will be influenced by growth rates, age structures, the state of the environment, and technological developments, but will likely be approximately 9 billion. 

Lesson Glossary

K-selected strategy: takes advantage of stable conditions; characterized by few offspring with much investment and nurturing to increase offspring survival

r-selected strategy: takes advantage of favorable conditions; characterized by early reproduction and high reproductive rate with little investment in offspring survival