The earth's habitats and ecosystems are dispersed based on air circulation, rainfall, and topography. For example, when looking at the globe, we may notice that the world's major grasslands are always leeward of major mountain ranges, or that tropical rain forests are located around the equator. Why do grasslands fall on the leeward side of mountain ranges, and tropical rainforests at the equator? As the air travels up the mountain, it condenses and precipitation occurs. Once the air reaches the leeward side, it is dry, resulting in the grasslands and plains. Tropical rainforests are located at the equator, an area that gets constant sunlight and rainfall regardless of the earth's tilt. The dispersion of the earth's habitats and ecosystems is very dependent on such environmental factors.

Though all of these statements are true, the fact that species can occupy different trophic levels depending on what they're eating is not a consequence of the fact that only 10% of all stored energy can ascend from one trophic level to the next. These facts are related, but one does not cause the other.

Food chains only have four or five trophic levels at maximum because the food chain is rapidly depleted of stored energy after each trophic level increase. Logically, producers always have the most biomass of any trophic level because they must produce all of the energy that will sustain the trophic levels above them. Finally, it makes sense that fluctuating population sizes threaten the stability of longer food chains because if even one trophic level suffers a population decrease, then all of the trophic levels above it are potentially jeopardized.

The earth's habitats and ecosystems are dispersed based on air circulation, rainfall, and topography. For example, when looking at the globe, we may notice that the world's major grasslands are always leeward of major mountain ranges, or that tropical rain forests are located around the equator. Why do grasslands fall on the leeward side of mountain ranges, and tropical rainforests at the equator? As the air travels up the mountain, it condenses and precipitation occurs. Once the air reaches the leeward side, it is dry, resulting in the grasslands and plains. Tropical rainforests are located at the equator, an area that gets constant sunlight and rainfall regardless of the earth's tilt. The dispersion of the earth's habitats and ecosystems is very dependent on such environmental factors.

Though all of these statements are true, the fact that species can occupy different trophic levels depending on what they're eating is not a consequence of the fact that only 10% of all stored energy can ascend from one trophic level to the next. These facts are related, but one does not cause the other.

Food chains only have four or five trophic levels at maximum because the food chain is rapidly depleted of stored energy after each trophic level increase. Logically, producers always have the most biomass of any trophic level because they must produce all of the energy that will sustain the trophic levels above them. Finally, it makes sense that fluctuating population sizes threaten the stability of longer food chains because if even one trophic level suffers a population decrease, then all of the trophic levels above it are potentially jeopardized.

Disease is a biotic factor, while the other choices are abiotic factors. Density-dependent factors are biotic in nature, and may involve things such as mating, food, competition, and disease. Density dependent factors will affect different populations differently depending on how many organisms are present in a given area. In the case of disease, consider that the flu will spread more easily in a densely-populated city than it will in a loosely-populated desert.

The other answer options will affect a population the same, regardless of density, because they affect large areas with the same magnitude.

Disease is a biotic factor, while the other choices are abiotic factors. Density-dependent factors are biotic in nature, and may involve things such as mating, food, competition, and disease. Density dependent factors will affect different populations differently depending on how many organisms are present in a given area. In the case of disease, consider that the flu will spread more easily in a densely-populated city than it will in a loosely-populated desert.

The other answer options will affect a population the same, regardless of density, because they affect large areas with the same magnitude.

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.

Competitive exclusion is when an inferior competitor is eliminated. In the moss example, the moss that is able to use resources more efficiently and reproduce quicker will beat out the less competitive moss. An ecological niche is the sum of a species’ use of the biotic and abiotic resources in its environment. Resource partitioning is the differentiation of niches that allows similar species to coexist in a community. If one of the mosses could adapt to use different resources, the two species could coexist together. Character displacement has to do with speciation. It refers to the tendency for character traits to diverge more in sympatric populations rather than allopatric populations.

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.

Competitive exclusion is when an inferior competitor is eliminated. In the moss example, the moss that is able to use resources more efficiently and reproduce quicker will beat out the less competitive moss. An ecological niche is the sum of a species’ use of the biotic and abiotic resources in its environment. Resource partitioning is the differentiation of niches that allows similar species to coexist in a community. If one of the mosses could adapt to use different resources, the two species could coexist together. Character displacement has to do with speciation. It refers to the tendency for character traits to diverge more in sympatric populations rather than allopatric populations.