Population Ecology

One of the first concepts taught in ecology is that of the ecological hierarchy. Organisms of the same species are grouped into populations; different species are grouped into communities, which interact with nonliving components to make up the ecosystem. Dynamic interactions take place between members of the same species as well as between species. While most of ecology is focused on the ecosystem level, much can be learned from the dynamics at the population level. 

The most important concept of population ecology is the size of the population. Changes in population size are due to births, deaths, immigration, and emigration. This is easy for students to understand if they can remember the difference betweem immigration and emigration. I help them by relating the first letters: Immigration is movement Into the population and Emigration is Exiting the population. If births and immigration exceed deaths and emigration, the population will grow. 

The capacity of a population to grow is known as its biotic potential. Some species have a high intrinsic rate of increase (r). These species are known as r-selected species.  Characteristics of r-selected species include early and frequent reproduction with many offspring, short life spans, and little parental care of offspring. Bacteria, most invertebrates, and annual plants are examples of r-selected species whose populations can grow quickly. 

Population growth, however, is limited by environmental resources. By adding environmental resistance to the biotic potential of an organism, we are able to obtain the carrying capacity (K) of an environment for a population. Species are known as K-selected if they reproduce later in their life cycle, have fewer offspring, longer generations, and more parental care of offspring. My ecology students apply their understanding of r- and K-selected species by graphing population data for several unknown species. I give them information about the unknown species and they must match the species to its graph. This approach not only applies ecological concepts, but mathematical concepts as well. 

In learning about population dynamics, students gain a deeper understanding of the reproductive strategies that produce evolutionary advantages for various species. Try some of the lessons below to help your students learn these concepts. 

Population Ecology Lesson Plans:

Analyze Population Dynamics Within an Ecosystem  

Students discuss the various ways in which natural populations maintain equilibrium and relate this equilibrium to the resource limits of an ecosystem. They construct and/or interpret graphs of population dynamics. Students explore the technologies used to study biotic and abiotic components of ecosystems.

How Do Populations Grow?  

Students examine how populations grow and how invasive species can affect the balance of ecosystems. They simulate the growth of lily pads, analyze and record the data, and simulate the results of an invasive species on an ecosystem.

Population Limiting Factors

Students examine how limiting factors regulate population growth. They evaluate historical data from the wildlife management of the deer of the Kaibab Plateau in Arizona and then assess why nature requires flexible and interactive management planning.