Food chains in ecosystems exist in the form of food pyramids. Although a food chain might not always be a linear chain of progression and can alternatively be called a food web. However, according to certain defining characteristics, certain levels of production and consumption can be differentiated in a food chain. These are called trophic levels, which can be defined as the feeding levels in a food chain or web in an ecological community.
Fig: The Trophic Levels in a Food Chain
The only true producers who produce their own food from inorganic sources are the primary producers such as plants and algae, who utilize the energy of the Sun along with materials from the surrounding environment in a biochemical process called photosynthesis to produce the bio-energy required to power their biochemical processes. These represent the first trophic level – that of primary producers. Although certain bacteria are known to produce biochemical energy without the presence of sunlight, they represent an anomaly and most primary producers on earth utilize the energy provided by the Sun in photosynthesis to produce their energy requirements i.e. their food.
The rest of the food chain or web consists of consumers who consume other organic life-forms for their energy needs. The second trophic level is represented by primary consumers, who are organisms that consume primary producers for their food and energy needs. Herbivores can be classified as secondary producers, representing the second trophic level in an ecosystem.
The third broad category among the trophic levels in a food chain is secondary consumers, which are organisms that consume primary consumers such as carnivores such as snakes that eat primary consumers such as mice.
The fourth and the last trophic level is the last broad category of tertiary consumers, which are organisms that consume secondary consumers for their food and energy needs. An example that proceeds from the previous example is that of hawks, which can eat snakes, which in turn is a carnivore that preys on primary consumers.
The chain of consumption can keep progressing, however, these are the necessary categories of consumption that forms the substrate for an analysis of trophic levels at most ecosystems.
Having separated the various trophic levels, it cannot be said that there is always a clear separation between the various trophic levels in a given ecosystem. Many consumers can feed at multiple trophic levels. A prime example is humans themselves, who can be primary consumers while consuming plants, secondary consumers while consuming mutton and tertiary consumers while consuming salmon.
Also certain primary producers can also act as consumers as well. An example is insectivorous plants that photosynthesize and at the same time consume certain organisms such as insects as food. Thus instead of food chains in linear progression, most ecosystems form food webs in the literal sense consisting of dense networks of consumption and differentiation of roles forming ecological communities.
Going from one trophic level to a higher one in terms of consumption, it is found that just 10 per cent of the energy possessed at one level is available for consumption at the next level of consumption. The remainder of the energy is either utilized by the metabolism of organisms or is released to the environment as heat or waste (D. Wilkin & J. Brainard, 2015).
Thus one can observe a decrease in energy resources available the higher up the chain of consumption one travels in a food chain in a linear manner, resulting in a lower amount of species diversity at the specialized higher levels of food chains in an ecosystem. However, the incredible amount of species diversity at the lower levels of the food chain can add to the confusion over the adequate categorization and in proving a sense of structure to ecosystems.
Ecosystems almost always consist of food webs that are interlinked and differentiated, leading to great biodiversity and the resulting complexity.
Although food webs can exist in great biodiversity and complexity, they also represent hierarchies and organization of species in an ecosystem. Ecosystems can overlap and interact, and as such there is no distinct and definite characterization of ecosystems based on the spatial configurations of interactions.
However, ecosystems can be characterized by an in-situ fluid equilibrium existing among ecological communities of organisms of different species. The equilibrium in general is maintained in ecosystems although temporal heterogeneity can lead to the fluctuation of various variables within ecosystems.
Ecosystem processes result from the life-processes of the organisms in their interactions with each other as well as with the abiotic environment. These processes however generate ecosystem services that can provide useful utilities to humans. Studies of ecosystem services can bypass structural and behavioural studies of organisms at the various trophic levels of an ecosystem and go forward towards analyzing the transition of energy and matter through an ecosystem.
However both sets of activities and processes are not mutually exclusive and aspects can overlap in investigations. The interactions in the various trophic levels involve the transfer of energy and matter, but their analysis also utilizes documentary aspects of structure and behaviour in ecosystems.
Understanding ecosystem services
Various functions of ecosystems are provided to the environment as the result of the interaction of organisms in various trophic levels in food webs. Some of them include provision of nutrients, decomposition, nitrogen cycling, contributions to the hydrological cycle, soil functions, maintenance of biological equilibrium, etc. These in turn offer beneficial ecosystem services to humans such as food, medicinal applications, water purification, crop reproduction, and many more.
In fact, it can be safely said that a huge part of resource collection in human economic activity is dependant on ecosystem services in some part or another. As such, it becomes necessary to preserve the equilibrium of ecosystems by preserving the food webs that constitute the organization of various trophic levels in an ecosystem.
This would ensure that the transfer of energy and matter occurs undisturbed in the embedded structures and complex behavioural characteristics of organisms. For this an intimate understanding of ecological communities is necessary.
All ecological services are possible due to ecological communities of organisms interacting in consort to provide certain results that form part of the natural equilibrium that is a self-sustaining framework. These ecological communities are composed of interactions that are made up of ecological niches that constitute certain clearly appreciable roles that certain species perform in its interaction with its ecosystem, and act as the unit for analysis of the interactions that species have in constituting ecological communities.
The interactions in terms of ecological niches can be symbiotic or competitive. However, both can feature in food webs and trophic levels and exhibit an immense variety that contributes to the overall biodiversity.
This biodiversity, due to the food web and its arrangement according to various trophic levels, occurs as functional differentiation in a hierarchical mode of organization. However, the dense network of species interaction makes these hierarchies less visible, and instead what is usually observed are communities of interacting species.
Fig: Ecological Niches
All hierarchies are ordered according to certain values that serve to provide access to participants whose concomitant roles contribute to their sequential differentiation. In ecosystems the dominant values according to which hierarchies are differentiated is the food web, and trophic levels and ecological niches offer an easy tool with which to form genealogical associations of roles in ecological hierarchies.
Ecological niches thus offer a model according to which adjustments that organisms make to community living can be analyzed. While trophic levels can provide a basis for an triggering mechanism for roles to be hierarchically ordered, the finer aspects of the ecological roles of species are defined by the ecological niches they occupy.
These roles in turn shape ecosystem services and offer principles to better understand the formative processes and the complex web of interactions that constitute the structures, behaviours and relationships that constitute ecological communities.