Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
Trophic Levels in an Ecosystem – Species Composition Role and Importance
The characteristic structure of an ecosystem is obtained by the systematic physical organization of the abiotic and biotic components of that particular ecosystem. The two main structural features of any ecosystem are its species composition and stratification.
Species Composition of an Ecosystem
The species composition varies with ecosystems. For example, in a tropical rainforest large number of species are found but in a desert ecosystem, the number of species is small.
Stratification of an Ecosystem
The species distribution vertically varies with ecosystems. For example, in a forest ecosystem tall trees occupy in the top vertical strata but shrubs and herbs are occupied in the lower strata. An ecosystem can be represented by depicting the producers-consumer relationship in the given ecosystem. This is also called the ‘Trophic structure’ of an ecosystem where each animal population forms various trophic levels. The producers (green plants) always form the first trophic level. Herbivores which feed on the producers, are at the second trophic level followed by the secondary consumers, tertiary consumers, and so on. The trophic structure of an ecosystem can be described in terms of its total amount of nutrients or the amount of living material. The amount of nutrients in the soil at any given time is referred to as a ‘Standing state’ whereas the amount of living material is referred to as a ‘Standing crop’.
The functional attributes of an ecosystem help to keep its component parts running together. By definition, all ecosystems cycle matter and use energy, and the processes define the fundamental ecosystem functions as well. Energetic processes in an ecosystem are normally described by speaking of trophic levels that define the position of organisms according to their level of feeding in comparison to the original energy taken in by primary producers. Always the energy doesn’t cycle and ecosystems need a continuous inflow of high-quality energy in order to maintain their function and structure.
For this reason, ecosystems are “open systems” needing a net inflow of energy to continue over time without the sun, our biosphere would shortly run out of energy! Energy inputs to ecosystems and drives the flow of matter within organisms and their environment in a process called biogeochemical cycling. Our biosphere gives a good example of the process, as it exchanges matter with and interacts with the lithosphere, atmosphere, and hydrosphere, driving the Earth’s biogeochemical cycles of nitrogen, phosphorus, sulfur, carbon, and other elements.
An ecosystem process is dynamicm, undergoing strong seasonal cycles responding to changes in the solar irradiation; causing fluctuations in the primary productivity; varying the inflow of energy from photosynthesis and carbon dioxide fixation into organic materials during the year; driving remarkable annual diversity in the carbon cycle, which is the biggest of all global biogeochemical cycles. The fixed organic carbon in plants becomes then food for decomposers and consumers, who degrade this carbon into forms with less energy, and finally release this photosynthesis-fixed carbon back into carbon dioxide in our atmosphere, creating the global carbon cycle.
Nitrogen biogeochemical cycling also uses energy, because bacteria fix the nitrogen gas from the atmosphere in reactive forms useful to living organisms with energy from organic materials or from the sun and from plants. Ecosystems cycle sulfur, phosphorus, and other elements as well. Because biogeochemical cycles are determined by the transfer of matter between the environment and its organisms, they are good examples of ecosystem-level processes.
Biological Diversity and Maintenance of Stability
The numerical strength and biomass of organisms affect the functioning of the ecosystem. In ecosystems, the biotic communities usually contain a few common species represented by a large number of individuals or by a large biomass and a comparatively large number of individual species occurring in small numbers. Under stress conditions, the number of rare species is usually reduced, and only a few species may survive and their frequency of occurrence may be very high. As a rule, the total number of species in any ecosystem is reduced under the conditions of extreme stress as found in arctic, antarctic, and desert regions, and so on. A system is considered stable in the ecological sense if its structure and functions remain more or less the same from year to year. A system with high species diversity and low dominance is less productive but stable. On the other hand, a system with a community with low species diversity and high dominance is more productive but unstable.
Trophic Level of an Ecosystem
The trophic level of an organism is the position it occurs in a food chain. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps of an organism from the start of the chain is a measure of its trophic level. Food chains start at trophic level 1 with primary producers such as plants, move to herbivores at level 2, predators at level 3, and typically finish with carnivores or apex predators at level 4 or 5. The path along the chain can form either a one-way flow or a food “web”. Ecological communities with’ higher biodiversity form more complex trophic paths.
The three basic ways in which organisms get food are as producers, consumers, and decomposers.
Producers are typically plants or algae. Plants and algae do not usually eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using photosynthesis. For this reason, they are called primary producers. In this way, it takes energy from the sun that usually powers the base of the food chain. An exception occurs in deep-sea hydrothermal ecosystems, where there is no sunlight. Here primary producers manufacture food through a process called chemosynthesis.
Consumers are species that cannot manufacture their own food and need to consume other organisms. Animals that eat primary producers (like plants) are called herbivores. Animals that eat other animals are called carnivores, and animals that eat both plants and other animals are called omnivores.
Decomposers break down plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as bacteria and fungi (mushrooms), feed on waste and dead matter, converting it into inorganic chemicals that can be recycled as mineral nutrients for plants to use again.
Trophic levels can be represented by numbers, starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.
- First trophic level, T1: Plants and algae make their own food and are called primary producers.
- Second trophic level, T2: Herbivores eat plants and are called primary consumers.
- Third trophic level, T3: Carnivores that eat herbivores are called secondary consumers.
- Fourth trophic level, T4: Carnivores that eat other carnivores are called tertiary consumers.
- Fifth trophic level, T5: Apex predators that have no predators are at the top of the food chain.
Formation of Typical Ecosystem
Ecosystem can be found in any place of the earth where life exists. For example, Freshwater ecosystems, Forest ecosystems, Desert ecosystems, Marine ecosystems, etc. There are five general categories of aquatic ecosystems:
- Marine pelagic – areas within the water mass of oceans with water of high salinity.
- Marine benthic – areas on the ocean floor with water of high salinity.
- Estuaries – bodies of oceanic water near the mouths of freshwater rivers with the intermediate salinity.
- Freshwater lotic (streams and rivers) – with flowing water of low salinity.
- Freshwater lentic (ponds and lakes) – nonflowing water of low salinity. Here we are discussing a typical aquatic ecosystem.