Ecology Theory: Interactions of Organisms in their Environment

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In the original Greek, “oikos” means “house.” So, ecology is “the study of the house,” the place where you live, or the environment which technically includes all those factors, both non-living and living, that affect an organism. Ecology then is the study of the interactions of organisms in their environment, which includes both the living (biotic) and physical (abiotic) factors of the environment. It’s also the science that formulates and tests hypotheses about the environment. Ecology studies the relationships, identification, and analysis of problems common to all areas. Ecology studies the population and the community, evaluates cause and effects of the responses of populations and communities to environmental change.

Populations are defined as an assemblage of individuals of a single species that live in the same place at the same time. Also, biologists add an additional condition: the individuals in a population must interact with each other to the point of being able to interbreed. Population is important to understanding many important ecological and evolutionary phenomena. Ecologists can use information from population ecology to predict the success of a given species or assemblage of species. One attribute of populations observed in nature is their dispersion, or the way in which individuals are distributed in a given area. Typically, biologists refer to three types of dispersion: clustered (aggregated), regular (evenly spaced), and random (irregularly spaced). Populations showing a clustered pattern are common in nature and are found among many different types of organisms.

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Clustered dispersion patterns are often due to environmental heterogeneity. Regular dispersion patterns are relatively rare in nature and occur when a resource is scarce. A good example of regular spacing occurs in animals that exhibit territoriality, a phenomenon in which animals establish an area for themselves and fight off all other individuals seeking to invade that area.

Regular dispersion patterns can also be observed in plants. Random patterns can be found in a variety of organisms, such as trout in a lake or maple trees in a forest. Regardless of the organism, the number of births almost always has the potential to be greater than the number of deaths. In other words, populations of all species have the capacity to grow. This property is of crucial importance to the success of all species. However, not all species will increase under all circumstances, but they can given appropriate conditions. There are two models of population growth: the exponential model and the logistic model. One of the most basic models of population biology is the exponential growth equation, which is: dN/dt = rmaxN. This equation states that in a growing population, the rate of change in population size is determined by the maximal intrinsic rate of increase (rmax) multiplied by the number of individuals in that population (N). If a population grows very quickly, we call that an exponential increase, and its growth curve has a J-shaped curve.

A population cannot continue to grow indefinitely because this equation contains an additional term called the carrying capacity (K), which is not fixed but is constantly affected by many factors, both biotic (living) and abiotic (non-living). The logistic population growth predicts that populations will grow rapidly at first. However, as the number of individuals in the population (N) approaches the carrying capacity (K), the population growth rate eventually slows to zero, and the population stabilizes at K. The result is a sigmoidal or S-shaped curve, which is often divided into three phases: the first is called the lag phase (the period of slow growth that occurs when population numbers are low).

The second is the log phase, which occurs when growth rate accelerates and becomes relatively rapid. The third is the saturation phase, during which population growth decelerates as N approaches K. All species have a well-defined life history that involves a beginning of life, a juvenile and reproductive phase, and death. There are two important parameters of a population: survivorship (how long one lives) and fecundity (how many offspring one produces). Survivorship is the number still living at the beginning of each age interval. The number of deaths determines the death rate during a given period of time divided by the number still living at the beginning of the time period.


A community is an assemblage of populations that interact with one another, and the effects that they have on each other often greatly influence their ability to survive and reproduce. Because they are assemblages of different species, communities have properties that make them unique from individual organisms and populations. Some communities simply blend gradually into others and are called open communities. Forest communities are like that, as different plant types blend together.

Conversely, closed communities have more definite borders; few organisms pass from one community to another. In these types of communities, fewer organisms move in and out, so they are more isolated in terms of energy and nutrients. Despite the fact that communities can sometimes be difficult to define, ecologists have been able to identify a lot of attributes by which communities can be described and analyzed.

These include species composition, which is the most fundamental attribute of a community. It’s simply a list of species of which the community is comprised. Communities vary tremendously in their composition. Frequency is a measure of how often we find a species in a community. Distribution, or how species are arranged in a community. Diversity is a measure of the variation in a community and has two components. The first is richness, which is the number of species in the community. The second component is called evenness, which is the degree to which the different species are represented in a community. Stability is the concept of the ability of a community to handle disturbance or to resist being disturbed. It also can refer to the resilience of a community (that is, its ability to recover quickly from a disturbance). Certain communities can be called “fragile”, which is used to refer to communities that have low stability when faced with human disturbance.

The competition involves a struggle for limited resources. Exploitative competition is the use of the same resources in which one competitor has greater access than the other to the resources. Interference competition is actual fighting over resources. Intraspecific competition is between members of the same species and interspecific competition is between different species. The competition exclusion principle is that no two species can occupy the same niche at the same time. Because the niche of an organism (the way in which it interacts with its environment) is often dependent on how it fares in competition with its neighbors, both kinds of competition are important in the structure of the community.


A biome is defined as a large, distinct, and recognizable association of life. More precisely, a biome is a particular array of plants and animals within a geographic area brought about by distinctive climatic conditions. Plant associations more than those of animals, not only usually identify biomes more because the first is far more obvious, but also because it determines the second. Ecologists recognize about a dozen major biomes, each one formed under a certain prevailing climate and has a characteristic type of plant and animal life. Some examples of biomes include grasslands, deserts, and deciduous forests. Biomes may be subdivided into communities.


For this paper, I read a lot of books and did a lot of research on the internet. I learned a lot about ecology, populations, communities, and biomes. It’s very hard to write about this subject in only five pages. My first draft was eight pages long, so I cut out a lot of details. However, I spent a lot of time and energy doing this paper, and I really enjoyed it. I hope it will be the same for you. Science.

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Ecology Theory: Interactions of Organisms in their Environment. (2019, Mar 02). Retrieved from

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