Arkansas Forest Resources Center: University of Arkansas
PDF is sophisticated, but good for "Extends" students in middle school. Challenging. Useful graphs and charts. Quotes from PDF are given below as examples.
"A universal characteristic of living things is that sexually mature individuals have the ability to produce ≥1 offspring. Thus, natural populations have the ability to grow.
Sizes of populations fluctuate in terrestrial, as well as aquatic, environments. The capacity for population growth, even among vertebrates, is enormous, a fact that is sometimes clearly demonstrated when species are introduced to new regions having suitable habitat.
Ever since humans began to understand the consequences of the rapid increase in its numbers, human population growth has been a cause for economic and ecological concern. These concerns led to the development of mathematical techniques to predict the growth of populations and to intensive study of natural and laboratory populations to learn about mechanisms of population growth and regulation."