Ecology: the Biology of Interactions. 3.02. Components of Ecosystems

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3.01. Ecosystems and Biogeocenoses

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.03. Examples of Ecosystems

3.02. Ecosystem Components What components can an ecosystem be divided into? On the one hand, we can use the same subdivisions as in a biogeocenosis: biocenosis (phytocenosis + zoocenosis + microcenosis) + geocenosis (edaphotope + climatotope). This classification focuses on the origin of individual components. If we are more interested in the functioning of the ecosystem, we can identify the following components within it: 1) inorganic substances used in the biological cycle (e.g., H2O, CO2, NH4+, etc.); 2) organic matter outside of organisms (detritus); 3) environment (air, water, substrate); 4) producers (organisms that synthesize organic matter from inorganic matter); 5) consumers (organisms whose main role is to convert organic matter from one form to another); 6) decomposers (organisms whose main role is to break down organic matter into inorganic matter). Thus, living organisms are divided into three functional groups—producers, consumers, and decomposers. These groups correspond to three types of processes that can occur with organic matter: its creation, transformation, and decomposition. Although this division seems quite common, it is not easy to clearly distinguish these groups. To do this, we need to consider the ecological roles that different organisms can perform. A number of terms are used to characterize the feeding habits of organisms and their ecological roles. By feeding habits, all living organisms are divided into autotrophs and heterotrophs. Autotrophs (Greek autos - self, trophe - food, feeding) are capable of synthesizing organic substances from inorganic substances themselves, using external energy sources. Heterotrophs (Greek heteros - other and trophe) feed on other organisms or their remains and obtain energy from "foreign" organic matter. Mixotrophs (Greek mixis - mixing and trophe) are sometimes distinguished as a separate group—organisms that combine auto- and heterotrophic nutrition. These include some bacteria and algae. However, since these organisms are still capable of synthesizing organic matter, mixotrophs can be considered a subset of autotrophs. The two main types of autotrophic nutrition are photosynthesis and chemosynthesis. Photosynthesis (Greek photos - light and synthesis - combination) is the formation of organic substances from inorganic substances using light energy. During photosynthesis, light energy is converted into the energy of chemical bonds of glucose, synthesized from inorganic substances (CO2 and H2O). Chemosynthesis (Greek chemeia - chemistry and synthesis) is the formation of organic substances from CO2 at the expense of the energy of oxidation of inorganic substances. For example, sulfur bacteria oxidize hydrogen sulfide to form sulfur or sulfuric acid, nitrifying bacteria oxidize ammonia, etc. As oxidants, chemosynthetic bacteria can use oxygen and some other inorganic substances. Organisms capable of photosynthesis can be called phototrophs, and chemosynthetic organisms can be called chemotrophs. By the nature of obtaining food, organisms can be divided into two groups. Osmotrophs (Greek osmos - pressure and trophe) are organisms that absorb nutrients in dissolved form through the surface of their body. Various bacteria, as well as plants and fungi, feed this way. Phagotrophs (Greek phagos - devourer, and trophe) are organisms that consume food in the form of particles. This feeding method is characteristic of a very diverse group of organisms—animals. Using the terms provided, it is easy to see the difference in feeding habits characteristic of multicellular eukaryotic organisms (Table 3.2.1). However, when it comes to unicellular and colonial eukaryotes, their classification based on such a simple principle is impossible. Table 3.2.1. Main life forms of multicellular eukaryotes and their representatives.

Type of nutrition

Autotrophs

Heterotrophs

Osmotrophs

Plants

Mushrooms

Phagotrophs

—

Animals

Having understood the feeding habits, let's move on to the ecological roles of organisms. There are three of them. Producers (Latin producentis - one who produces) produce organic matter from inorganic matter. Naturally, this role is performed by autotrophs—plants and cyanobacteria capable of photosynthesis, as well as chemosynthetic bacteria. Although this group of organisms is distinguished based on the ability of its representatives to synthesize organic substances, one should not forget that any organism in this group also transforms organic matter (for example, when building its own body) and decomposes it (extracting energy from it). The main role of consumers (Latin consume - I consume) is the transformation of organic matter. In contrast, decomposers (Latin reducere - to return) perform the function of breaking down organic substances into inorganic ones. However, the line between consumers and decomposers is not easy to draw. Every heterotroph (both a tiger and honey mushrooms on a rotten stump) both creates its own organic matter and "burns" part of the organic matter obtained from food. Perhaps there is no fundamental difference between consumers and decomposers? From the perspective of what they spend the obtained organic matter on, generally no. But from the perspective of obtaining it, yes. Some organisms consume others, while others utilize organic reserves. Therefore, it is more correct to consider phagotrophs (animals) as consumers, and osmotrophs (fungi and heterotrophic bacteria) as decomposers.

3.01. Ecosystems and Biogeocenoses

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.03. Examples of Ecosystems