Biological magnification is most commonly a problem with compounds that are toxic, slow to degrade, and can accumulate in organisms' bodies such as DDT and methylmercury. For example, consider methylmercury. Methylmercury breaks down into less toxic forms very slowly over time and it is excreted from organisms' bodies relatively slowly. Though aquatic plankton may only absorb relatively small or trace amounts of methylmercury over their life spans, they are likely unable to excrete the chemical at the rate that they absorb it into their bodies. Small fish that feed on the plankton must eat large amounts of plankton to survive—in doing so, they are exposed to all of the methylmercury that has accumulated in the bodies of the plankton. They, too, are unable to excrete this methylmercury at the rate they absorb it. When larger fish feed on the small fish, these larger fish are exposed to and absorb the methylmercury contained in the small fish. They are likely unable to excrete the majority of this methylmercury at the rate that they continue consuming mercury found in the small fish. This process continues upwards through the trophic levels, until organisms at high trophic levels, such as birds of prey (or humans!) are exposed to high levels of methylmercury that have been concentrated/magnified up through the trophic levels.

Dominant species are more numerous than their competitors in an ecological community. They can be said to define their communities, and they exert influence over the other species within their communities. For example: mangroves are generally the dominant species in tropical tidal swamps.

Critically, dominant species are different from keystone species. Despite their often relatively low total biomass, keystone species have a large impact on the distribution and abundance of species around them. Sea otters are a good example of a keystone species: even though otters have relatively low total biomass, they are crucial to many marine ecosystems because they prey on sea urchins. If otters are removed from a habitat, sea urchins will eat or destroy large portions of the habitat's kelp, which can threaten species at all trophic levels. 

Because energy transfer between trophic levels is only about 10% efficient, it takes several organisms at a lower trophic level to support one organism at a higher trophic level. If each fish (lower level organism) has 10 toxin molecules in its body, and each eagle (higher level organism) eats 10 fish, the eagle now has 100 toxin molecules in its body. Molecules stored in an organism accumulate at higher trophic levels; this accumulation is known as biological magnification.

Heterotrophs obtain their organic materials by feeding on other organic organisms. Scavengers are an examples of heterotrophs. Autotrophs are self-feeders in that they do not consume organic material but rather create their own organic material from inorganic substances.  

The cascade model, or top-down model, states that there is a unidirectional influence from higher to lower trophic levels. This model follows the idea that predation controls community organization. Predators limit the number of herbivores, and herbivores limit plants, and plants limit the amount of nutrients available in the soil. 

The energetic hypothesis states that the length of a food chain is limited by the inefficiency of energy transfer along the chain. Only ten percent of energy stored in organic matter at each trophic level is actually converted to organic matter at the next trophic level. This keeps trophic structures in check and limits the abundance of predatory organisms at the top of the trophic structure.  

Autotrophs are the producers of the biosphere in that they turn inorganic materials into organic material. Plants are an example of autotrophs. Heterotrophs feed on autotrophs and other heterotrophs. Animals are an example of heterotrophs.

Heterotrophs are the consumers of the biosphere in that they do not produce organic material but rather consume other organisms. Animals are an example of heterotrophs. Autotrophs produce their own organic material from inorganic materials. Plants are an example of autotrophs.

Animals are a type of heterotrophs. Heterotrophs are unable to make their own organic materials and so they must consume other organic materials in the form of autotrophs and other heterotrophs.

Heterotrophs get energy from organic molecules. They are unable to fix carbon dioxide from the atmosphere into organic molecules, nor do they make oxygen as a byproduct of metabolism. They can consume autotrophs and heterotrophs (organic molecules) to get energy and carbon.