To understand and appreciate ecology at the community and ecosystem levels, you must first have a good grasp on ecology at the population level, often called population ecology. Population ecology is the level of ecology that focuses on characteristics of whole populations rather than attributes of individual organisms. In fact, most of the aspects of populations that ecologists look at cannot even be measured using individual organisms. 

These aspects include

• Growth rates
   
• Population size
   
• Survivorship probabilities
   
• Age structures
   
• Distributions
   

If you are saying to yourself "cool words, but…huh?" don’t fret. We will explore each of these population characteristics in turn and hopefully help you see why each of them is relevant to your life.

Population Growth

Let’s start with one of the most important and foundational characteristics of a population: growth. Before we begin, let us clarify what we mean by the term "growth." Now would be a good time to put on your "time to think about familiar concepts in new ways" hat. In ecology, growth does not just mean an increase in size or numbers, which is usually the way we think about it in daily life. Growth in ecology means a change in numbers, either positive or negative. This means that when a population is increasing in numbers, ecologists say it has positive growth. When it is decreasing in numbers, they say it has negative growth. If a population is not increasing or decreasing in numbers, which is pretty rare, then there is no growth, or zero growth. This new way of thinking about growth will help you understand the next intimately related concept of growth rate. Ooh. We can't wait.

Brain Snack

Ever heard of Thomas Malthus? He made the argument in the late 18th century that exponential population growth was not a sustainable phenomenon.  Read more here.