6.1. Basic concepts of ecology


ecosistema-ribera51An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system. These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows. As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can come in any size but usually encompass specific, limited spaces (although some scientists say that the entire planet is an ecosystem).

Energy, water, nitrogen and soil minerals are other essential abiotic components of an ecosystem. The energy that flows through ecosystems is obtained primarily from the sun. It generally enters the system through photosynthesis, a process that also captures carbon from the atmosphere. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.

Ecosystems are controlled both by external and internal factors. External factors such as climate, the parent material which forms the soil and topography, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem. Other external factors include time and potential biota. Ecosystems are dynamic entities—invariably, they are subject to periodic disturbances and are in the process of recovering from some past disturbance.

Biodiversity affects ecosystem function, as do the processes of disturbance and succession. Ecosystems provide a variety of goods and services upon which people depend; the principles of ecosystem management suggest that rather than managing individual species, natural resources should be managed at the level of the ecosystem itself. Classifying ecosystems into ecologically homogeneous units is an important step towards effective ecosystem management, but there is no single, agreed-upon way to do this.

According with the definition of Tansley in 1935, an Ecosystems is a biotic community (or biocoenosis) along with its physical environment (or biotope). In ecological studies, biocoenosis is the emphasis on relationships between species in an area. These relationships are an additional consideration to the interaction of each species with the its physical environment.

biocoenosis (biocoenosebiocenosebiotic communitybiological communityecological community), coined by Karl Möbius in 1877, describes the interacting organisms living together in a habitat (biotope). Biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. Biotope is almost synonymous with the term habitat, which is more commonly used in English-speaking countries. However, in some countries these two terms are distinguished: the subject of a habitat is a species or a population, the subject of a biotope is a biological community.

The ecosystems have two different kinds of components, abiotic (non-living) and biotic (alive) components.

Abiotic Components

16-02a-abiotic-biotic-ecosystem-componentsAbiotic components are such physical and chemical factors of an ecosystem as light, temperature, atmosphere gases(nitrogen, oxygen, carbon dioxide are the most important), water, wind, soil. These specific abiotic factors represent the geological, geographical, hydrological and climatological features of a particular ecosystem. Separately:

  • Water, which is at the same time an essential element to life and a milieu
  • Air, which provides oxygen, nitrogen, and carbon dioxide to living species and allows the dissemination of pollen and spores
  • Soil, at the same time source of nutriment and physical support. The salinity, nitrogen and phosphorus content, ability to retain water, and density are all influential.
  • Temperature, which should not exceed certain extremes, even if tolerance to heat is significant for some species
  • Light, which provides energy to the ecosystem through photosynthesis
  • Natural disasters can also be considered abiotic. According to the intermediate disturbance hypothesis, a moderate amount of disturbance does good to increase the biodiversity.

Biotic Components

The living organisms are the biotic components of an ecosystem. In ecosystems, living things are classified after the way they get their food. Biotic Components include the following:

  • Autotrophs produce their own organic nutrients for themselves and other members of the community; therefore, they are called the producers. There are basically two kinds of autotrophs, “chemoautotrophs and photoautogrophs. “
  • Chemautotrophs are bacteria that obtain energy by oxidizing inorganic compounds such as ammonia, nitrites, and sulfides , and they use this energy to synthesize carbohydrates.
  • Photoautotrophs are photosynthesizers such as algae and green plants that produce most of the organic nutrients for the biosphere.
  • Heterotrophs, as consumers that are unable to produce, are constantly looking for source of organic nutrients from elsewhere. Herbivores like giraffe are animals that graze directly on plants or algae. Carnivores as wolf feed on other animals; birds that feed on insects are carnivores, and so are hawks that feed on birds. Omnivores are animals that feed both on plants and animals, as human.
  • Detritivores – organisms that rely on detritus, the decomposing particles of organic matter, for food. Earthworms and some beetles, termites, and maggots are all terrestrial detritivores.
  • Nonphotosynthetic bacteria and fungi, including mushrooms, are decomposers that carry out decomposition, the breakdown of dead organic matter, including animal waste. Decomposers perform a very valuable service by releasing inorganic substances that are taken up by plants once more


BIOOOBiodiversity (an abbreviation of “biological diversity”) describes the diversity of life from genes to ecosystems and spans every level of biological organization. The term has several interpretations, and there are many ways to index, measure, characterize, and represent its complex organization. Biodiversity includes species diversity,ecosystem diversity, genetic diversity and the complex processes operating at and among these respective levels. Biodiversity plays an important role inecological health as much as it does for human health. Preventing species extinctions is one way to preserve biodiversity, but factors such as genetic diversity and migration routes are equally important and are threatened on global scales. Conservation priorities and management techniques require different approaches and considerations to address the full ecological scope of biodiversity. Populations and species migration, for example, are sensitive indicators of ecosystem services that sustain and contribute natural capital toward the well-being of humanity. An understanding of biodiversity has practical application for ecosystem-based conservation planners as they make ecologically responsible decisions in management recommendations to consultant firms, governments, and industry. The protected areas have been established under the protected area network across the world for conservation of biodiversity.


ullal2A habitat is an area with specific environmental conditions in which an organism lives and reproduces. Many species of plant and animal have very specific environmental requirements. This means that these organisms are only found in areas that meet these requirements.

Habitats have many features or factors that are important to the organisms living there. Conveniently, we can divide habitat factors into two major groupings, physical factors and biotic factors.

In terrestrial habitats some important physical factors are elevation, steepness, slope direction, soil type, and water availability. Elevation affects air temperature and rainfall—higher elevations are cooler and moister than lower ones. The steepness of a slope will affect the kind of soil that can form there and the amount of water that can soak into the ground after it rains. Slope aspect (the direction a slope faces) is particularly important. In the northern hemisphere, south-facing slopes get more sun, are warmer and dryer, and thus support different vegetation than north-facing slopes. In aquatic habitats such characteristics as pH, salinity, dissolved oxygen concentration, temperature, and flow rate are important physical factors.

Biotic factors include all the other species that occur in the habitat. For an herbivore such as the desert bighorn sheep many of the grass, shrub, and herb species of the desert mountains constitutes its food source. Trees and shrubs form both hiding cover from predators and thermal the dead trees in which their holes are found but also the other birds (e.g., Pileated woodpeckers) that make the holes in the first place.

Finally, physical and biotic factors may interact to determine the quality of the habitat for a given organism. For example, the nutritional quality of plants available as food for herbivores, such as deer, is determined in large part by the quality of the soils present.



Perhaps the simplest, most general definition of the ecological niche is an organism’s “ecological position in the world” (Vandermeer 1972). Even though this may seem straightforward, determining what constitutes an organism’s position in the greater scheme of things is not a trivial pursuit. In fact, the concept of niche is a notoriously difficult one for beginning (and even advanced) students of ecology. Some of the difficulties arise because the word niche has a common meaning to the layperson but a very specific meaning to the ecologist.

A plant’s or animal’s niche, or more correctly, ecological niche, is a way of life that is unique to that species. Niche and habitat are not the same. While many species may share a habitat, this is not true of a niche. Each plant and animal species is a member of a community. The niche describes the species’ role or function within this community.

For example, the red fox’s habitat might include forest edges, meadows and the bank of a river. The niche of the red fox is that of a predator which feeds on the small mammals, amphibians, insects, and fruit found in this habitat. Red foxes are active at night. They provides blood for blackflies and mosquitoes, and are host to numerous diseases. The scraps, or carrion, left behind after a fox’s meal provide food for many small scavengers and decomposers. This then is the ecological niche of the red fox. Only the red fox occupies this niche in the meadow-forest edge communities. In other plant communities different species of animal may occupy a similar niche to that of the red fox. For example, in the grassland communities of western Canada and the United States, the coyote occupies a similar niche (to that of the red fox.)

f31-07_feeding_niches_f_cThe ecological niche includes both the animal’s or plant’s physical habitat and how it has adapted to life in that habitat. In examining its adaptive strategy, ecologists consider how the plant or animal obtains its energy in order to live. Each organism has made many adaptations to its habitat. The first adaptation concerns where in the habitat the animal or plant has chosen to live.


istock_population-t3v211population is all the organisms of the same group or species who live in the same geographical area and are capable of interbreeding. In ecology the population of a certain species in a certain area is estimated using the Lincoln Index. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals from other areas. Normally breeding is substantially more common within the area than across the border.


In ecology, a community is an assemblage or associations of populations of two or more different species occupying the same geographical area. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, “the fish community of Lake Ontario before industrialization”.

ecological_levelsCommunity ecologists study the interactions between species in communities on many spatial and temporal scales, including the distribution, structure, abundance, demography, andinteractions between coexisting populations. The primary focus of community ecology is on the interactions between populations as determined by specific genotypic and phenotypic characteristics. Community ecology has its origin in European plant sociology. Modern community ecology examines patterns such as variation in species richness, equitability, productivityand food web structure (see community structure); it also examines processes such as predator-prey population dynamics, succession, and community assembly.


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