Students tend to group animals by size and actions. This type of classification scheme is based on prior knowledge that the students have gained outside of the classroom. Some misconceptions about the construction food chains were also found in Gallegos research. In addition, some students believe that members of a food chain are only grouped together in predator-prey pairs, and most students have yet to grasp the concept of a producer and its place in the food chain. Organisms higher in a food web feed on some organisms lower in the food web.
Available energy decreases as one progresses up a food web.
The numbers of individuals in the populations of any species decreases with each step up the trophic levels, because the available energy decreases while the body size generally increases as one progresses up a food web. Traits appear as a result of random processes. Traits are properties of individuals and vary within a population. Natural selection influences the increasing or decreasing prevalence of traits in a population Populations exist in a state of dynamic equilibrium, fluctuating in numbers around an average population size. Biotic and abiotic factors in an ecosystem are limited and affect the carrying capacity for any given species.