We can call plants producers as a result. A primary consumer is a plant-eating animal, and a secondary consumer eats these primary consumers. This food chain is a flow of energy in the form of nutrients from one to another. There will be more primary producers and consumers than secondary consumers, since less energy is available as one progresses through the food chain. Populations are groups of individuals of the same species that occupy a given area at the same time.
Animal populations change over time as the results of births, deaths, and dispersals.
The population size that a particular environment can support is the carrying capacity . In contrast, populations that are r -selected produce many young quickly, with few survivors, as in most of the invertebrates. But eventually, there is a limiting resource, like food, water, or space, and the population grows in a sigmoid or s-shaped curve, as in logistic growth. Thinking about a niche includes thinking about the surroundings of the organism, its habitat . We will see many examples, especially with roundworms and flatworms.