Under different conditions, populations may grow, fail to grow, stop growing once they reach a certain density of individuals, or begin to shrink. Understanding how environmental conditions – including other populations – affect population growth is essential to putting all of the information in this unit together … and then adding human activity to the mix in the Chapter 6.

Why populations grow and decline

Why? Because all populations are affected by their physical environment, and all populations affect that physical environment. In fact, as we discussed in Chapter 3, the separation between “biotic” and “abiotic” factors is artificial, and can be misleading. On every level from a drop of water to the entire biosphere, organisms shape their environment as they gather and use energy and nutrients, and eliminate wastes. Understanding this reciprocal relationship is vital to appreciating the relationship between the still-growing global human population and the health of the biosphere.