Ecosystem
An ecosystem is a community of plants, animals and smaller organisms that live, feed, reproduce and interact in the same area or environment. Some ecosystems are very large. For example, many bird species nests in one place and feed in a completely different area. On the other hand, some ecosystems may be physically small, such as you would find in a meadow at the edge of a forest, or in a coral reef in the ocean. How does everything fit together in a forest ecosystem versus a meadow ecosystem? While some species may be found naturally in both areas, the species that live in the forest ecosystem are usually very different from those that inhabit the meadow, even though the two environments are right next to each other. In other words, if we protect existing natural habitats, we will help to maintain biodiversity (biodiversity is the variety of life in all its forms, levels and combinations). Unfortunately, natural habitats and their ecosystems are more and more endangered because of the damaging environmental effects of growing human populations everywhere.
The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic, components to the non-living, or abiotic, components. Energy transformations and biogeochemical cycling are the main processes that comprise the field of ecosystem ecology. As we learned earlier, ecology generally is defined as the interactions of organisms with one another and with the environment in which they occur. We can study ecology at the level of the individual, the population, the community, and the ecosystem.
Studies of individuals are concerned mostly about physiology, reproduction, development or behavior, and studies of populations usually focus on the habitat and resource needs of individual species, their group behaviours, population growth, and what limits their abundance or causes extinction. Studies of communities examine how populations of many species interact with one another, such as predators and their prey, or competitors that share common needs or resources.
In ecosystem ecology we put all of this together and, insofar as we can, we try to understand how the system operates as a whole. This means that, rather than worrying mainly about particular species, we try to focus on major functional aspects of the system. These functional aspects include such things as the amount of energy that is produced by photosynthesis, how energy or materials flow along the many steps in a food chain, or what controls the rate of decomposition of materials or the rate at which nutrients are recycled in the system.
Aspects of ecosystem are:
- Actors (species)
- Relations between actors (network)
- Performance (health)
- Dynamics (evolution)
- Strategies and behaviour of actors (roles).
Components of an Ecosystem
You are already familiar with the parts of an ecosystem. You have learned about climate and soils from past lectures. From this course and from general knowledge, you have a basic understanding of the diversity of plants and animals, and how plants and animals and microbes obtain water, nutrients, and food. We can clarify the parts of an ecosystem by listing them under the headings "abiotic" and "biotic".
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Abiotic
Components
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Biotic
Components
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Sunlight
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Primary producers
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Temperature
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Herbivores
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Precipitation
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Carnivores
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Water or moisture
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Omnivores
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Soil or water chemistry (e.g., P, NH4 +) etc.
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Detritivores etc.
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All of these vary over space or time
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By and large, this set of environmental factors is important almost everywhere, in all ecosystems. Usually, biological communities include the "functional groupings" shown above. A functional group is a biological category composed of organisms that perform mostly the same kind of function in the system; for example, all the photosynthetic plants or primary producers form a functional group. Membership in the functional group does not depend very much on who the actual players (species) happen to be, only on what function they perform in the ecosystem.
Processes of Ecosystems
This figure with the plants, zebra, lion, and so forth illustrates the two main ideas about how ecosystems function: ecosystems have energy flows and ecosystems cycle materials. These two processes are linked, but they are not quite the same (see Figure).
Energy enters the biological system as light energy, or photons, is transformed into chemical energy in organic molecules by cellular processes including photosynthesis and respiration, and ultimately is converted to heat energy.
This energy is dissipated, meaning it is lost to the system as heat; once it is lost it cannot be recycled. Without the continued input of solar energy, biological systems would quickly shut down. Thus, the earth is an open system with respect to energy. Elements such as carbon, nitrogen, or phosphorus enter living organisms in a variety of ways. Plants obtain elements from the surrounding atmosphere, water, or soils. Animals may also obtain elements directly from the physical environment, but usually they obtain these mainly as a consequence of consuming other organisms. These materials are transformed biochemically within the bodies of organisms, but sooner or later, due to excretion or decomposition, they are returned to an inorganic state. Often bacteria complete this process, through the process called decomposition or mineralization (see previous lecture on microbes).
During decomposition these materials are not destroyed or lost, so the earth is a closed system with respect to elements (with the exception of a meteorite entering the system now and then). The elements are cycled endlessly between their biotic and abiotic states within ecosystems. Those elements whose supply tends to limit biological activity are called nutrients.
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