Figure 20-1 presents simple diagrams of some possible interactions between and among species. This figure illustrates competition, which may be direct or indirect . The combined interactions between individuals of species may have consequences at the population level. A resource is any factor whose increase enhances population growth. Resources are consumed.
Consumers utilize the resources.
Temperature, salinity, humidity, altitude, and other conditions are not resources. For many years this was the concept accepted by most ecologists. Currently, ecologists believe that it is frequently possible that more than one resource can be limiting and the Law of the Minimum has been modified to take that into account. These are the most common types of consumers. Keep in mind that not only are these two-species interactions occurring in a community, but many other interactions are occurring among the various other species of organisms.