Module 9S2 Changes in Populations

Big Picture

 As a biologist employed by National Parks Canada, you might be required to collect data on population changes of different species within the park. Why? What are the applications of this kind of information? Ecological communities are so complex – often there are several species at the same trophic level, or some species occupying two levels in intricate food webs. Every level of the food chain controls the populations of those levels above and below it, limiting the prey available to levels above it, and limiting the amount of predation on levels below it. The result is a complex interdependence that is difficult for us to comprehend. This is why communities are so fragile and easily disrupted – often unintentionally – by human activities. One seemingly isolated human action has a domino-like effect throughout the community. 

To prevent disruption, or perhaps to determine the effect of a disruption, we need to quantify populations – the size of them, and the factors that lead to changes in them. We can use this information to predict the consequences that our actions hold for other species. We need to be able to use simple mathematical formulas to describe the quantitative changes taking place.  Similarly we need to know the normal growth patterns of different populations in order to know whether something abnormal is going on. Different species have evolved different strategies of growth rates to maximize their survivability and reproductive success. Understanding these strategies is key to managing populations. Lastly, we need to view our own species as a population and quantitatively describe the patterns of human growth and how these patterns are likely to affect other members of the community.

Essential Question

• How do you measure, interpret, and analyze the changes in a population over time?