Global ecology refers to large-scale interactions between the earth’s ecosystems, atmosphere, landscapes, and seascapes. Landscape ecology refers to the spatial orientation and patterns within specific landscapes or seascapes. Ecosystem ecology observes the interactions, both biotic and abiotic, within a given landscape area. Community ecology is like ecosystem ecology, but applies to communities of organisms. It observes the spatial distribution, abundance, relationships, and interactions between organisms of different species in a given ecosystem. Population ecology refers to the spatial distribution, abundance, relationships, and interactions within the same species in a given community. Organismal ecology studies each organism’s behavior, anatomy, evolution, adaptation, and relative fitness in a given environment. 

Variable limiting refers to when an environmental variable that is lacking. If light is lacking, the algae will not grow and reproduce; the environmental variable, light, is limiting the algae’s success. The variable optimum is when the variables are perfectly balanced. Variable inhibiting refers to when when an environmental variable is in abundance, to the point where it is harmful. If there is too much light, the algae will no longer continue growing and reproducing, but will begin too die off.  In this situation, light is variable inhibiting. 

An ecological niche is the sum of a species’ use of its environment, including both biotic and abiotic factors. Resource partitioning is the differentiation of niches; it is impossible for two species to have the same niche and use the same resources. Resource partitioning allows for differentiation of niches between similar species so they can coexist. A fundamental niche is described in forest B, where moss 2 grows both above and below the shrubbery. It is the niche that could be potentially occupied by a species. The realized niche is the term that refers to the area of moss 2 in forest A. The realized niche is the portion of the fundamental niche that an organism actually occupies. We know that moss 2 can potentially occupy areas above and below shrubbery, but in forest A, it only occupies the area below the shrubbery (its realized niche). 

The term “abiotic” refers to the nonliving components of the environment; therefore, a rock would be characterized as an abiotic part of the environment.

Human activities can have negative impacts on the proper functioning of ecosystems and environments. One human activity that has a direct impact on marine environments is overfishing, which may critically change the delicate balance of the ecosystem.

A community includes populations of different species. The study of a community looks at interactions between species, such as competition, symbiotic relationships, or predation. 

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.

Negative feedback inhibition prevents populations from continually increasing in size. Without these such factors, population sizes would not be controlled. For example, perch feed on and find shelter in kelp. Where there are too many perch, there is not enough kelp to sustain them all (for food and shelter), and the fish population decreases in size. When there are less perch, there is enough kelp for them to feed on and hide in. Because conditions are favorable, the perch numbers increase. This negative feedback inhibition is density dependent and controls population size dynamics. 

K-selection is density dependent selection, while r-selection is density independent selection; the two are opposites. While all the answer choices are related, only one displays the same (opposite) relationship: semelparous and iteroparous.  Semelparous refers to the “one shot” reproductive trend, producing many offspring only once during an organism's lifetime. Iteroparous refers to organisms that breed multiple times, producing few offspring each time. For semelparous organisms, survival is low and the environment is generally unpredictable. For iteroparous organisms, survival rates are high and the environment is stable and dependable.  

The logistic growth model shows that population size levels off as it approaches its carrying capacity. In this situation, as the population increases and resources are used, the population approaches its carrying capacity, which is the maximum population size that the environment can support. The exponential growth model is unrealistic, as it shows a population’s growth when resources are abundant, but this there is no environment where resources are always in abundance. Survivorship curves show the life patterns of species; rather than comparing the relationship between resources and population size, these types of graphs compare age and population size.