Table of Contents
What are Trophic levels?
Trophic levels are positions of an organism in a nutritive series or food chain of an ecosystem in ecology. These levels are simply the position, a group of organisms with similar feeding habits occupies in a food chain.
A food chain is a linear hierarchy that transfers food energy when an organism feeds on another. In a food chain, organisms are grouped into nutritional levels and food energy is transferred amongst these levels.
Trophic levels can be shown in a succession to portray food energy flow among organisms and their feeding relationship with one another. In a trophic pyramid, the flow of energy or the biomass in an ecosystem is represented. Every food chain and tropic pyramid starts with the primary producers at trophic level 1.
The next trophic level comprises organisms that feed on the primary producers. The succession continues as the next trophic levels comprise organisms that feed on the group before them. This succession can occur in a one-way chain as a food chain or in a more complex feeding relationship known as a food web. A food web is made up of many food chains that are interconnected. The majority of the ecosystems have a food web rather than a direct food chain.
The organisms of the nutritive series or food chain are grouped into trophic levels based on feeding behavior. Green plants are the organisms in the first and lowest trophic level as producers. These plants are consumed by organisms in the second trophic level which are herbivores (plant eaters).
At the third trophic level are primary carnivores who are meat eaters and consume herbivores (organisms in the second trophic level). The secondary carnivores are the organisms at the fourth trophic level that eat the primary carnivores.
However, this grouping is not defined as many organisms eat on several trophic levels. For instance, some organisms are omnivores and feed on herbivorous organisms and plants. Also, some herbivorous organisms consume animal matter occasionally.
Furthermore, some organisms known as decomposers or transformers belong to a separate trophic level as they break down dead organisms and waste materials. Bacteria and fungi are examples of such organisms that break down organic waste and remains into nutrients that are in turn used by the producers (plants).
Trophic levels definition in biology
Trophic levels can be defined in biology as the feeding positions of organisms in a food web of a particular ecosystem. These levels can be seen as food chain levels or the position of the organism in the food chain.
What is a trophic level in biology?
The trophic level of an organism is simply the position an organism occupies in a food web. Since a food chain or food web is a series of organisms eating other organisms and in turn, get eaten, the trophic level of an organism is literally the number of steps it is, counting from the start of the food chain.
However, a food web starts in a sequence with plants as primary consumers at trophic level 1, then moves to herbivores at level 2, followed by carnivores at level 3 or higher, and usually finishes with apex predators level 4 or 5. Though, an ecological community with higher biodiversity will form more complex and intricate paths. A trophic level can be represented by numbers.
Different trophic levels
- Level 1: Primary producers which comprise plants and algae that make their own food.
- Level 2: Primary consumers that comprise herbivorous animals that eat plants.
- Level 3: Secondary consumers that comprise carnivorous animals that eat herbivorous animals.
- Level 4: Tertiary consumers that comprise carnivorous animals that eat other carnivorous animals. This level also comprises omnivorous animals that eat other carnivorous animals and plants.
- Level 5: Apex predators have no predators and top their food web.
- Level 6: Decomposers or detritivores that comprise organisms that feed on dead animal and plant matter. They convert this matter into energy and nutrients for plants to use for growth. Detritivores occupy the last trophic level and make up the last part of the food chain. They recycle organic waste from other trophic levels and are very important for a functioning ecosystem. Examples of such organisms are bacteria, fungi, earthworms, etc.
The highest energy concentration is in the first trophic level, the base, and the lowest trophic level in the ecosystem. This energy is transferred to several other organisms in the successive 3 or 4 trophic levels. Organisms can be in a specific trophic level based on their size, eating habits, or function. However, one can find difficulties placing organisms with complex behaviors. Nevertheless, trophic levels are of two basic categories:
The autotrophs in an ecosystem are those organisms that can produce organic matter from inorganic matter. They manufacture their own food and do not feed on other organisms. This is why they are usually referred to as primary producers in the ecosystem. They manufacture their own food by using water, light energy, and carbon dioxide. Also, some use chemical energy to manufacture their own food instead of using solar energy. Because autotrophs are primary producers, they occupy the first trophic level and are the base of the food chain. Autotrophs vary widely and can be found on terrestrial or aquatic ecosystems. Examples of autotrophs are algae, plants, cyanobacteria, seaweeds, and phytoplanktons.
Furthermore, autotrophs are divided based on how they produce their food into two types:
Photoautotrophs are organisms that manufacture their own food via photosynthesis with light energy from the sun. The energy gotten from the sun is used to manufacture food from water and carbon dioxide. These organisms possess chlorophyll that enables them to capture light energy from the sun. The majority of photoautotrophs have chloroplast and membrane-bound nucleus. Hence, they are eukaryotic organisms.
Additionally, there are several prokaryotes, which include several bacteria that carry out photosynthesis. Examples of photoautotrophs are algae, euglena, higher plants, and bacteria (e.g cyanobacteria: the only type of bacteria that can produce oxygen during photosynthesis).
Contrary to photoautotrophs, chemotrophs do not manufacture their food in the presence of sunlight, rather they get their energy from molecules around their environment. These organisms do not need energy from sunlight. Chemotrophs, however, are grouped into two types: chemoorganotrophs and chemolithotrophs. Chemoorganotrophs are those organisms that use organic molecules as their source of energy. Whereas chemolithotrophs use inorganic molecules as their source of energy.
Chemolithotrophs are also called lithotrophs. Examples of such organisms include several bacteria like nitrifying bacteria and the bacteria seen in tubeworms of deep-sea levels. Chemolithotrophs do not have access to sunlight. Hence, they rely on inorganic matter. These organisms live in habitats with no sunlight and have sufficient inorganic material for biosynthesis.
Biosynthesis is the oxidation of inorganic matter. In this process, Chemolithotrophs take in electron donors that are then oxidized. These donors are oxidized to manufacture energy. The electron donors could be iron, hydrogen sulfide, elemental sulfur, etc.
Take the oxidation of hydrogen sulfide, for example. Its oxidation produces electrons that are transported for oxidative phosphorylation via the electron transport chain. This eventually produces chemical energy in form of ATP energy. The ATP energy is then used in biosynthesis. This energy is used to fix carbon for the production of organic compounds.
Heterotrophs are organisms that don’t manufacture their own food and obtain organic matter directly by consumption. These organisms hunt or gather food from other organisms since they cannot make their own food like the autotrophs. They get energy from organic compounds and thereby have to ingest or consume organic compounds. Hence, they are called consumers. Therefore, heterotrophs can be grouped further into:
- Primary consumers: are plant-eating organisms referred to as herbivores.
- Secondary consumers: organisms that feed on the primary consumers
- Tertiary consumers: are organisms that feed on the secondary consumers
- Reducers: are organisms that feed on dead organic matters referred to as decomposers or detritivores
Since heterotrophs depend on autotrophs, they occupy the upper levels of the food web. They vary and consist of various animals, mammals, and bacteria. Examples of heterotrophs are humans, ants, plasmodium species, snakes, cows, tigers, sheep, sharks, snails, mosquitoes, elephants, bears, etc. Heterotrophs survive by eating other organisms and this is achieved differently in various animal types. The main type of heterotrophic nutrition are:
- Parasitic nutrition
- Saprotrophic nutrition
- Holozoic nutrition
- Parasitic nutrition: Some heterotrophs obtain food through a parasitic mode of nutrition. This is a type of nutrition where one organism depends totally on another organism called the host. In this type of nutrition, there is a harmful relationship between the two organisms. Such a relationship is called parasitism. The organism that depends and benefits from the other is referred to as the parasite while the organism that is being harmed and depended on for nutrition is the host. This mode of nutrition causes harm and can lead to the death of the host. Plants and animals could be parasites. Examples of organisms exhibiting this mode of nutrition are tapeworm, ticks, mosquitoes, malaria parasites, mycelium, bed bugs, nematodes, dodder, mistletoe, etc.
- Saprotrophic nutrition: Some heterotrophs feed via a saprotrophic mode of nutrition. This is a type of nutrition that involves the consumption of food material from decaying organic matter. Heterotrophs that get their food from dead and decaying organic matter are referred to as saprophytes or saprotrophs. Such organisms include bacteria, water mold, and fungi.
- Holozoic nutrition: Most heterotrophs obtain their food through the holozoic mode of nutrition. This type of nutrition involves the ingestion of food matter. These organisms eat solid food matter from plants or animals which are then digested within the organism and transported to various cells in the organism. Examples of heterotrophs that exhibit a holozoic mode of nutrition are humans, single-celled organisms (like the amoeba), birds, mammals, etc. Furthermore, holozoic heterotrophs are divided into herbivores, carnivores, and omnivores.
Trophic Level examples
- Trophic Level 1: Primary producers
- Trophic Level 2: Primary consumers
- Trophic Level 3: Secondary consumers
- Trophic level 4: Tertiary consumers
- Trophic level 5: Apex predators
- Trophic level 6: Decomposers
Trophic Level 1: Primary producers
Examples of organisms in the Trophic level 1 are primary producers. A food chain starts with primary producers consisting of plants and algae. Autotrophs or primary producers produce biomass from inorganic substances. The characteristic of an organism to be able to occupy level 1 is its ability to manufacture its own food.
Plants and algae are at this trophic level because they manufacture their own food through a process of photosynthesis. In photosynthesis, carbon dioxide, light energy, and water are utilized to make an energy-rich carbohydrate such as glucose, and oxygen is released as a by-product. The glucose produced is then stored as energy within the plant and oxygen is released into the atmosphere.
Photosynthesis can be simplified in this equation:
6CO2 + 12H2O + energy= C6H12O6 + 6O2 + 6H2O
i.e Carbon dioxide + water + energy= Glucose + oxygen + water
Structurally, producers like algae and plants have chloroplasts which are light-harvesting cellular structures. There are photosynthetic pigments called chlorophyll inside the chloroplasts that absorb light energy. However, organisms in the trophic level 1 of a terrestrial ecosystem comprise vascular plants such as ferns, trees, gymnosperms, and angiosperms. In a marine ecosystem, organisms like seaweed, phytoplankton, and algae occupy trophic level 1. Also, some autotrophs produce food without photosynthesis. They are called chemoautotrophs and such examples are the bacteria seen in tubeworms of deep-sea levels and the bacteria living in the active volcanoes that use sulfur instead of carbon dioxide, to produce their own food. Chemoautotrophs also occupy the first trophic level in the ecosystem.
Trophic Level 2: Primary consumers
Examples of organisms occupying this trophic level are organisms that feed on primary producers. They are called primary consumers and occupy trophic level 2. This trophic level is the next level after trophic level 1. Such animals are called herbivores and their anatomical and physiological system is adapted to an only plant-based diet. As herbivorous animals, they eat algae, plants, shrubs, trees, and other primary producers.
Structurally, they have mouthparts designed for rasping and grinding plant matter. For instance, is the possession of wide flat teeth for grinding bark of trees and foliage. Furthermore, herbivorous animals possess gut flora which is made up of cellulose digesting bacteria or protozoans that aids the digestion of cellulosic matter.
Animals like cattle, sheep, elephants, mice, horses, goats, rabbits, deer, etc are all examples of animals in this trophic level 2. These animals can be divided into two groups: browsers and grazers. The browser’s diet consists of at least 90% of tree twigs or leaves. Whereas a grazer diet will consist of at least 90% of grasses. Examples of browsers are goats and deers. Cow, rabbits, and sheep are examples of grazers.
Furthermore, some organisms feed on other parts of a plant like their fruits, nectar, or wood. Such organisms are also primary consumers. Typical examples are frugivores like monkeys, birds, and bats that feed on fruits. Another example is xylophages like termites and beetles that feed on wood. Also are organisms like insects, bats, birds, and spiders that feed on the nectar of a plant.
Additionally, in the marine ecosystems are tiny crustaceans and zooplankton that feed on phytoplankton (photosynthesizing algae). Many fish types and turtles in the water eat algae and seagrass. Some echinoderms like sea urchins are primary consumers in kelp forests that feed on lots of giant kelp every day. Also, a mouse that eats seeds and fruits of a plant is a primary consumer in a desert ecosystem.
Trophic Level 3: Secondary consumers
Secondary consumers are the organisms on the trophic level 3. These organisms feed on the primary consumers. Since they fed on herbivorous animals they are called carnivorous animals. They are predators and occupy the trophic level 3 of a food chain or an ecological pyramid. Secondary consumers at this trophic level three could include carnivores and omnivores. They get some of their nutrients from the tissue of herbivorous animals.
Also, there are carnivorous plants that feed on herbivorous insects (insectivores). Carnivores are adapted anatomically and physiologically for a meat-based diet. Since they are predators and prey consumption could involve pursuit or ambush, these animals usually have advanced senses for hearing, vision, touch, or smell.
Also, they could adopt mimicry or camouflage to avoid being seen by potential prey. Animals of such feeding behavior have sharp claws, fangs, and strong jaws to grip and cut up their prey. Similarly, preys eventually adopted counter-adaptations and defense strategies against predation. Examples of such defense mechanisms are alarm calls, thanatosis, mimicry, warning coloration, spines, chemicals, and camouflage. Examples of such predator-prey relationships are lion and zebra, spiders and flies, fox and rabbit, and bear and fish.
Secondary consumers occupy trophic level 3 and are usually small animals (frogs, weasels, and snakes), fish, and some bird types like eagles. However, some larger apex predators like eagles and lions may eat herbivores, and can also occupy the second trophic level of an ecosystem. Moreso, all species that consume zooplankton in an aquatic ecosystem are secondary consumers. Jellyfish, sardines, crabs, lobsters, whales, sharks, etc occupy the trophic level 3 of a marine ecosystem. Sea otters are secondary consumers in the kelp forest that hunt sea urchins. In a desert ecosystem, a snake may be a secondary consumer when it eats a mouse.
Trophic level 4: Tertiary consumers
Organisms that feed on the secondary consumers are referred to as tertiary consumers. These organisms occupy trophic level 4 and get energy from other carnivores. However, they can also be preyed upon and organisms that feed on tertiary consumers are called quaternary consumers. The tertiary consumers and the quaternary consumers can respectively occupy trophic level-4 and 5.
A typical example of a tertiary consumer is the Owl. Even though owls feed off mice and other herbivores, they can also feed on stoats which are secondary consumers. Also, in turn, owls can be hunted by hawks and eagles. Hence, they are not apex predators. Another example is an eagle or owl feeding on snakes in the desert ecosystem.
Trophic level 5: Apex predators
Some organisms top the food chain and don’t have predators. Such organisms are called apex predators. There may be more levels of consumers before the food chain reaches apex predators. Hence, depending on the food web in the ecosystem, apex predators can occupy the trophic level-4, 5, or 6. Usually, they don’t have natural enemies except for humans.
These top predators are very important in the ecosystem. This is because, via predation, they help control populations of lower trophic levels. For instance, grazing herbivores can overpopulate when apex predators are absent in an ecosystem. Hence, the overpopulation of herbivores can cause intense browsing and grazing pressure on the plants in the ecosystem. This can result in fewer available plant resources causing other organisms like insects and small mammals that depend on the plants to suffer population decline. Thus, affecting all trophic levels within an ecosystem. This can lead to an ecosystem collapse and this defect is called a top-down trophic cascade.
Apex predators are highly efficient hunters and often have specific adaptions. These adaptations are sharp teeth, sharp claws, stealth, speed, and agility. Sometimes, these top predators work in groups which enhances the success of their hunting abilities. Moreso, not all apex predators are brutal hunters. The whale shark for example is a large filter feeder that eats only small fish and plankton. But it is an apex predator in its ecosystem because it has no natural predators.
However, there are many apex predators and common examples in the terrestrial ecosystem include wolves, eagles, lions, cheetahs, and jaguars. In grassland ecosystems, lions are seen as apex predators. Also, mountain lions and bobcats are seen as apex predators in the desert. In the marine ecosystem, examples of apex predators are tuna, sharks, dolphins, whale sharks, and killer whales.
Trophic level 6: Decomposers
Some organisms feed on dead plants and animal matter from other trophic levels. Such organisms are decomposers and occupy the last of the trophic level. Examples of these decomposers are detritivores that feed on dead animals and plant matter. Contrary to other consumers that consume their food and digest it, these organisms feed on nutrients at the molecular level.
Detritivores are organisms that are specifically fragmented to consume their food. They depend on the available nutrient in their simplest form like substrate gotten from dead or decaying organisms or matter that has already been digested. Examples of such organisms are millipedes, worms, woodlice, dung flies, and slugs. Others may include bacteria and fungi. Detritivores act on the remains after the process of decomposition. They scavenge for detritus or decomposing organic matter. Also, there are scavengers that eat non-living remains of plants and animals. An example is a vulture that eats dead animals and the dung beetles that feed on animal feces.
Also, some parasites do not necessarily kill their host and feed on available organic materials. Such parasites can also be included in this group of detrivores. Fungi are the most common decomposers and are usually the first instigators of decomposition. This is because they possess enzymes and other compounds that break down biomolecules of dead organisms. Bacteria too have enzymes that separate organic compounds into simpler forms.
The presence of decomposers in the ecosystem is crucial. This is because they break down the organic matter of deceased organisms and return part of it to earth as a geochemical component. Decomposers complete the food chain and turn organic wastes into inorganic matter such as nutrient-rich soil. They literally complete the life cycle by giving back nutrients to the ocean or soil for autotrophs to use. Hence, starting a whole new sequence of food chains.
Trophic levels of a food chain
Food chains consist of 3 or 4 trophic levels. A typical sequence may be:
Plant —-> herbivorous organism —-> carnivorous animal —-> top carnivorous animal
Plant —-> herbivore —-> parasite of the herbivore —-> parasite of the parasite
Many organisms eat more than one species, and a huge number of animal species at different stages of their life cycle feed on different foods. Moreso, many organisms eat both plants and animals. Therefore, feeding at more than one trophic level in a food chain. Eventually, food chains connect into highly complex food webs. Thus, a simple food web can show a complicated network of trophic feeding relationships.
Biologically, not all predators have an exclusive meat diet. Some also feed on meat and plants. Such predators or consumers are called omnivores. An omnivorous organism may get their nutrient from algae, fungi, bacteria, plants, and animals. Hence, such organisms feed on more than one trophic level. Examples of omnivorous animals are pigs, gorillas, hedgehogs, skunks, opossums, rodents, most bears, mice, raccoons, orangutans, squirrels, sloths, chimpanzees, and humans.
Humans for instance consume many types of foods. They can eat vegetables and fruits (plant), animal products like eggs, meat, and milk. Also, humans eat mushrooms which is a fungus, and eat algae, in edible seaweeds like sea lettuce and nori which are used to wrap sushi rolls. Bears too for instance eat berries, mushrooms, and animals like deer and salmon. Also, carnivorous plants like Venus flytrap and pitcher plants are capable of predation. They prey on insects as another means to obtain nutrients aside from photosynthesis.
As a result of such omnivorous feeding habits, there is more than one food chain or trophic level for most organisms in the ecosystems. This is because most organisms feed on more than one kind of food and can be eaten by more than one type of predator. However, a food web of an ecosystem sets out and shows the complicated network of intersecting and overlapping food chains.
Usually, decomposers are left off in the food webs. But if they are included, they mark the end of the food chain in an ecosystem. Therefore a food chain starts with primary producers at trophic level 1 and ends with decomposers and decay. Nevertheless, decomposers are regarded to occupy their own separate trophic level since they recycle nutrients that are reused by primary producers.
Trophic level in food web
Food webs contain all the food chains in an ecosystem. It connects many different food chains and trophic levels. Each living organism in a habitat is part of multiple food chains. Hence, all of the interconnected and overlapping food chains in the ecosystem form a food web. However, it can consist of food chains that are very short or long and complicated.
An example of a short food chain is the grass in a forest that produces its own food through photosynthesis and gets eaten by a rabbit. A fox later feeds on the rabbit. The fox body when dead is broken down by worms and mushrooms. These decomposers then return the organic matter to the soil to provides nutrients for plants like the grass. This short food chain is a part of the food web in the forest.
Another example of a food chain in the same ecosystem might include different organisms completely. A caterpillar, for example, may feed on the leaves of a tree in the forest. Then, a sparrow (bird) may later eat the caterpillar. The sparrow may in turn be preyed on by a snake and an eagle as an apex predator may eat the snake. Also, a vulture may eat the body of the dead eagle. Whereas, the bacteria in the soil may decompose the remains.
In a marine ecosystem, algae and plankton as primary producers may be eaten by tiny shrimp. These tiny shrimp called krill are then preyed upon by the blue whale. The blue whale is the largest animal on earth and feeds on thousands of tons of krill in a day. An apex predator, orcas (killer whales) then prey on blue whales. Detritivores such as worms break down the bodies of the whales that sink to the seafloor. Nutrients are then released by the decaying flesh. This provides chemicals for primary producers like the algae and plankton to start a new sequence of food chains.
Normally, food webs are defined by their biomass. The energy in living organisms is biomass and it reduces with each trophic level. Primary producers in a food web convert the energy from the sun into biomass. Thereby, there is always more biomass in lower trophic levels than in higher trophic levels.
Biomass in trophic levels
The trophic structure of an ecosystem is controlled mainly by the biomass of primary producers. The trophic structure is the partitioning of biomass between various trophic levels. Primary producers affect the transfer efficiency across different trophic levels. This is because they are the essential providers of nutrient input and energy. Aside from the primary producers, the predators are another important factor. This is because their consumption suppresses lower trophic levels. These predators help primary producers by preying on herbivores. Hence, limiting and controlling excessive herbivory. Predators are therefore biological control of lower trophic levels. They also promote primary productivity by intraspecific competition.
The energy in living organisms (biomass) reduces with each trophic level. Primary producers in a food web convert the energy from the sun into biomass. Thereby, there is always more biomass in lower trophic levels than in higher trophic levels. This means the biomass in trophic level 1 will be more than the biomass in trophic level 2 and so on. Since biomass decreases with each trophic level, for a food web to be healthy, there are always more plants or autotrophs than herbivores. Then, more herbivores than carnivores. The ecosystem cannot promote a large number of omnivores without promoting an even larger number of herbivores and autotrophs. The trophic structure of a healthy food web should consist of:
- An abundance of autotrophs
- Many herbivores
- Relatively few carnivores
- Few omnivores
This will eventually bring balance and help the ecosystem in the maintenance and recycling of biomass. Ecosystem biomass is dependent on how balanced and connected its food web is because every link in a food web is connected to at least two others. Thus, all or some of the links in the food web are stressed or weakened once one link is threatened. Hence, the biomass of the ecosystem declines.
Furthermore, biomass in an ecological or trophic pyramid is usually lost gradually from the bottom up. The base trophic level that includes the producers has the greatest amount of biomass. Since the consumers rely on producers, the amount of biomass of the producers is a limiting factor to the biomass of consumers. Hence, it is common to find a biomass pyramid in an ecosystem where the 1st trophic level is the widest whereas the topmost trophic level is the narrowest. This simply shows that the distribution of biomass in an ecosystem implicates ecosystem stability. However, an ecosystem in the case of an inverted pyramid could fail when there are more consumers than primary producers. This results in a trophic cascade.
A top-down trophic cascade is an adverse effect that resulted from the reduction or removal of a trophic level (species) in an ecosystem. The ecological interaction of species in an ecosystem keeps the ecosystem balanced. Predation is an important factor in the ecosystem as it helps maintain balance. This is why top predators are very important in the ecosystem. Through predation, animals help control populations of lower trophic levels.
For instance, grazing herbivores can overpopulate when predators are absent in an ecosystem. Hence, the overpopulation of herbivores can cause intense browsing and grazing pressure on the plants in the ecosystem. This can result in fewer available plant resources causing other organisms like insects and small mammals that depend on the plants to suffer population decline. Thus, affecting all trophic levels within an ecosystem. This can lead to an ecosystem collapse called a top-down trophic cascade.
The ecosystem cannot promote a large number of omnivores without promoting an even larger number of herbivores and autotrophs. Hence, a trophic cascade occurs when keystone species like plants or apex predators are removed from the habitat or ecosystem.
For instance, losing plant life due to disease, drought or anthropogenic activities can result in a decline in the population of herbivores. Also, the loss of biomass or species on the 2nd or 3rd trophic level can cause an imbalance in a food web. For instance, if a salmon run (river where salmon swim) is diverted by an earthquake or landslide. This will eventually cause loss of species as salmon are taken out of the river. Animals like bears, for instance, that feed on salmon will be forced to feed heavily on another species like ants.
The ant population eventually shrinks. Ants being scavengers and detrivores break down fewer nutrients in the soil due to their lessened population. Hence, the soil won’t be able to promote many autotrophs. Thereby biomass is lost and a trophic cascade occurs. Also, the insect and smaller fish that salmon prey on gets overpopulated. Since salmon isn’t present to keep their population in check, aquatic insects may destroy plant communities. As a result, fewer plants survive and there is a subsequent loss of biomass energy which would have been utilized by other species in the ecosystem.
Even on higher trophic levels, a loss of organisms like carnivores can disrupt a food chain and lead to a top-down tropic cascade. For instance, sea urchins are the primary consumers of kelp in kelp forests. These sea urchins are preyed upon by sea otters. Once the population of the sea otters reduces, urchins will destroy the kelp forest. Hence, leading to a decrease in primary producers and biomass drops. The entire kelp forest eventually disappears and such areas are referred to as urchin barrens.
A real-life example of a trophic cascade happened in 1986. The officials in Venezuela dammed the Caroni River and created an enormous lake. A lot of hilltops were turned into islands in this lake. As a result of the degradation of their habitats to tiny islands, many terrestrial predators experienced food scarcity. Thus, animals like leaf-cutter ants, howler monkeys, and iguanas flourished. Eventually, these ants became so much that they destroyed the rainforest. They killed all the trees and plants and the food web surrounding the Caroni River was destroyed.
Trophic pyramid (Trophic level pyramid)
Generally, each trophic level interacts with the one below it by taking some of the energy it consumes. One can say each trophic level is supported by the next lower trophic level. The food chain can be shown in a diagram to illustrate the amount of energy that is transferred from one feeding level to the next. This diagram is called an energy pyramid, ecological pyramid, or trophic pyramid.
It can also be viewed as a biomass pyramid since the energy transferred between levels can also be thought of as the transfer of biomass. Therefore, the efficiency at which biomass or energy is transferred from one trophic level to another is known as ecological efficiency. However, energy is utilized as it is transferred between trophic levels. At each trophic level, consumers convert only 10% of the chemical energy in their food to their own body tissue. They convert the 10% of the energy consumed into biomass and the rest is lost as heat. Hence, the food chain barely extends above 5 or 6 levels. As a result of this gradual loss of energy, the biomass at each trophic level is viewed as a pyramid.
The trophic pyramid, however, shows the progression of food energy. A trophic pyramid can be defined as a structure of interaction that shows the manner in which food energy is passed along the food chain from one trophic level to the next. It is a pyramid-shaped graphical representation that is comprised of animals and plants in a certain ecosystem. The pyramid comprises different trophic levels and is shaped similar to a pyramid to indicate the diminishing amount of biomass and energy as the trophic level goes up.
The base of the pyramid contains primary producers (autotrophs) and all the other organisms in the pyramid are consumers (heterotrophs). The consumers at each trophic level are consumed by organisms at the trophic level above and feed on the organisms from the level below. Since most of the food energy that enters a trophic level is lost as heat, the higher the trophic level on the pyramid, the lower the amount of available energy. As organisms expend energy for metabolic processes, food energy is lost as heat.
Generally, the organisms that make up the base level of the pyramid would vary from ecosystem to ecosystem. Multicellular plants would generally form the base of the pyramid in terrestrial habitat. Whereas in freshwater lakes, algae, and multicellular plants form the first trophic level. The trophic structure of the ocean is built on plankton. Zooplanktons act as consumers of phytoplankton and as food for a wide range of marine animals.
However, several freshwater streams have detritus instead of living plants as their energy base. These detritus is made up of plant parts and leaves from the surrounding terrestrial habitat that falls into the water. The detritus is broken down by microorganisms. These microorganism-rich detritus are eaten by aquatic invertebrates, which are in turn eaten by vertebrates.
Habitats surrounding hydrothermal vents on the ocean floor are the most unusual biological habitats. The biological habitats around these vents are so different from those in the rest of the ocean. These vents are a result of volcanic activities that creates cracks in the seafloor. Chemoautotrophic bacteria survive in the warm sulfur-rich water that surrounds these cracks. The bacteria utilize the reduced sulfur as an energy source to fix carbon dioxide.
Hence, contrary to other ecosystems, the energy that forms the base of this deep-sea habitat comes from chemosynthesis instead of photosynthesis. Thus, the deep-sea community is supported by geothermal energy instead of solar energy. Some species around these vents eventually feed on these bacteria. Though some other species have formed mutualistic relationships with the sulfur bacteria. They harbor the chemoautotrophic bacteria within their bodies and benefit from nutrition directly from the bacteria.
Bioaccumulation in trophic levels
As biomass declines as you move up through the trophic levels, some toxic chemicals increase with each trophic level in the food web. These chemicals are usually stored in the fat of animals. Bioaccumulation usually occurs within a trophic level.
For example, once a herbivorous organism feed on plants that are covered in pesticides, it stores the pesticide in its body fat. Once a carnivorous organism eats many of these herbivores, it bioaccumulates the pesticide chemicals that are stored in its prey. This increase in the concentration of the toxic compound in the organism tissue due to absorption from the environment and food is called bioaccumulation.
Even in an aquatic ecosystem, bioaccumulation can happen too. Runoffs from urban areas or farms that enter water bodies can contain pollutants. Producers like bacteria, algae, and seagrass can absorb minute amounts of pollutants from urban runoffs. These producers can get eaten by primary consumers like fishes and sea turtles. As they feed on them, they utilize the energy and nutrients provided by the plants but store the pollutant chemical in their fatty tissue. Predators that occupy the 3rd trophic level like tuna and sharks then eat the fish. When it reaches the trophic level that humans consume these tuna or sharks, a remarkable amount of bioaccumulated toxins will be stored.
A good example of the bioaccumulation process along trophic levels is mercury contamination. Through industrial emissions and rain, methylmercury can get into freshwater habitats. This methylmercury can be taken up by phytoplankton and bacteria. Once small fishes feed on the phytoplankton and bacteria, they accumulate mercury.
As the food chain gradually moves across the trophic level, the small fishes are eaten by larger fishes. These larger fishes can become food for other animals and humans. Thereby as the methylmercury concentration increases up the food web, it can reach dangerous levels for both the fish and the animals that consume the fish. Consuming these larger fishes from time to time can lead to the build-up of large concentrations of this heavy metal in the tissue of animals and humans.
Some fishes like swordfish, sharks, and tuna normally have bioaccumulated levels of mercury. Thereby the federal government and some states have issued advisories against consuming too much of certain types of fish. Also, oysters in the harbor of the United States’ New York City are unsafe to eat because the oysters, a filter feeder bioaccumulate the pollutants in the harbor.
Organisms can be affected adversely when they bioaccumulate harmful substances. Thereby, distorting the ecosystem by reducing the population of predators that control prey populations. This can also lead to an increase in the number of extinct animals and loss of biodiversity. The loss of biomass brings imbalance to the ecosystem. Ecosystem biomass is dependent on how balanced and connected its food web is because every link in a food web is connected to at least two others. Thus, all or some of the links in the food web are stressed or weakened once one link is threatened to cause a decline in the biomass of the ecosystem.
Bioaccumulation of some toxins can cause mutations in animals and humans. For example, is the thinning of eggshells of predatory birds caused by bioaccumulation of DDT in the 1940s and 1950s. Eagles as apex predators had high amounts of DDT in their bodies. They bioaccumulated the DDT from the fish and small mammals they fed on. The birds with high amounts of DDT in their bodies started laying eggs with extremely thin shells. These thin shells would usually break before the baby birds were ready to hatch. Hence, the bioaccumulation of these DDT was the major reason for the decline of the bald eagle. The bald eagle was an apex predator that preys mainly on fish and small rodents. However, the use of DDT was banned and the food webs it affected have recovered in most parts of the country.