Ecology

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Ecology

Ecology is the study of the relationships of organisms with their living and nonliving environment. Ecologists are interested in questions involving the natural environment and, increasingly, are concerned about human-related environmental degradation. The study of ecology is fundamentally important in the design of systems of resource use and management that will sustain humans, other species, and natural ecosystems.

Ecology is concerned with the relationships of organisms with their biological and nonliving environment. These relationships can be complex, reciprocal interactions; put another way, organisms are influenced by their environment, but they also cause environmental change, and are components of the environment of other organisms. Thus, ecology involves many relationships between different organisms, as well as between the organisms and the environments in which they live.

Ecology is also be considered to be the study of the factors that influence the numbers and distribution of organisms. Although mostly a biological subject, ecology also draws upon other sciences, including chemistry, physics, geology, mathematics, computer science, and others. Often, ecologists must also deal with socioeconomic issues, because of the rapidly

increasing importance of human impacts on the environment.

The biological focus of ecology is reflected by the majority of the time spent by ecologists in studies of organisms. Examples of common themes of ecological research are the physical and physiological adaptations of organisms to their environment, patterns of the distribution of organisms in space, and how these are influenced by environmental factors, and changes in the numbers of organisms over time and the environmental influences on these dynamics.

An individual is a particular, distinct organism, with a unique complement of genetic information encoded in their genetic material (deoxyribonucleic acid or DNA). The physical and physiological attributes of individuals are a function of their genetically defined capabilities (genotype) and environmental influences that affect the actual expression of the genetic capabilities (phenotype). Individuals are the units that are selected for (or against) during evolution.

A population is a collection of individuals of the same species that are interbreeding, or exchanging genetic information. Evolution refers to changes over time in the genetic information of a population. Evolution can occur randomly, or given circumstances can favor advantageous phenotypes or select against less well-adapted genotypes.

An ecological community is an aggregation of populations that are interacting physically, chemically, and behaviorally in the same place. Strictly speaking, a community consists of all plant, animal, and microbial populations occurring together on a site. Often, however, ecologists study functional “communities” of similar organisms, for example, bird or plant communities.

A broader aspect of ecology is known as the ecological landscape; an aggregation of communities on a larger area of terrain. Sometimes, ecological units are classified on the basis of their structural similarity, even though their actual species may differ among widely displaced locations. A biome is such a unit. Examples of a biome include alpine and arctic tundra, boreal forest, deciduous forest, prairie, desert, and tropical rainforest.

The biosphere is the integration of all life on Earth, and is spatially defined by the occurrence of living organisms. The biosphere is the only place in the universe known to naturally support life.

Less than 1% of the solar energy reaching Earth’s surface is absorbed by green plants or algae and used in photosynthesis. However, this fixed solar energy is the energetic basis of the structure and function of ecosystems. The total fixation of energy by plants is known as gross primary production. Some of that fixed energy is used by plants to support their own metabolic demands, or respiration. The quantity of energy that is left over is known as net primary production. If the net primary production has a positive value, then plant biomass accumulates over time, and is available to support the energy requirements of plant eaters (herbivores), which are themselves available as food to support to meat eaters (carnivores). Any plant or animal biomass that is not directly consumed eventually dies, and is consumed by decomposers, the most important of which are microorganisms such as bacteria and fungi. The complex of ecological relationships among all of the plants, animals, and decomposers is known as a food web.

Compared with the potential biological “demand,” the environment has a limited ability to “supply” the requirements of life. As a result, the rates of critical ecological processes, such as productivity, are constrained by so-called limiting factors, which are present in the least supply relative to the biological demand. A limiting environmental factor can be physical or chemical in nature, and the factors act singly, but sequentially. For example, if a typical unproductive lake is fertilized with nitrate, there would be no ecological response. However, if that same lake is fertilized with phosphate, there would be a great increase in the productivity of single-celled algae. If the lake is then fertilized with nitrate, there would be a further increase of productivity, because the ecological requirement for phosphate, the primary limiting factor, had previously been satiated.

This example illustrates the strong influence that the environment has on rates of processes such as productivity, and on overall ecological development. The most complex, productive, and highly developed ecosystems occur in relatively benign environments, where climate and the supplies of nutrients and water

KEY TERMS

Genotype— The genetic information encoded within the DNA of an organism (or a population, or a species). Not all of the information of the genotype is expressed in the phenotype.

Interdisciplinary— A field of investigation that draws upon knowledge from many disciplines.

Phenotype— The actual morphological, physiological, and behavioral expression of the genetic information of an individual, as influenced by its environment.

Population biology— Study of changes in the abundance of organisms over time, and of the causes of those changes.

are least limiting to organisms and their processes. Tropical forests and coral reefs are the best examples of well-developed, natural ecosystems of this sort. In contrast, environmentally stressed ecosystems are severely constrained by one or more of these factors. For example, deserts are limited by the availability of water, and tundra by a cold climate.

In a theoretical environment with an unlimited availability of the requirements of life, organisms can maximize the growth of their individual biomass and of their populations. Conditions of unlimited resources might occur (at least temporarily), perhaps, in situations that are sunny and well supplied with water and nutrients. Population growth in an unlimited environment is exponential, meaning that the number of individuals doubles during a fixed time interval. This is an enormous rate of growth, and it would never be sustainable under real-world ecological conditions. Before long, environmental conditions would become limiting, and organisms would begin to interfere with each other through an ecological process known as competition. In general, the more similar the ecological requirements of individuals or species, the more intense the competition they experience. Therefore, competition among similar-sized individuals of the same species can be very intense, while individuals of different sized species (such as trees and moss) will compete hardly at all.

Competition is an important ecological process, because it limits the growth rates of individuals and populations, and influences the kinds of species that can occur together in ecological communities. These ecological traits are also profoundly influenced by other interactions among organisms, such as herbivory, predation, and disease.