Every living thing in an ecosystem is part of various food chains.
Every food chain is one available path that energy and nutrients may catch as they turn through the ecosystem.
All of the interlinked and overlapping food chains in an ecosystem compose a food web. It is also known as a consumer-resource system.
1. What Is a Food Web?
A Food Web comprises all the food chains in one ecosystem in other words we can say that our own food web is made up of multiple food chains.
Food Chains and Food Webs explain the feeding relationship among the different species.
2. Why Food Webs Are Important?
Food webs are limited representations of actual ecological interactions as well as an ecosystem as they essentially aggregate several species into trophic species.
They are functional moieties of species that have the ditto predators and prey in a food web.
Charles Elton developed the concept of food cycles, food size, and food chains in his classical book “Animal Ecology“, Elton’s food cycle was replaced by a food web.
Ecologists utilize these simplified food webs in quantitative models of trophic dynamics.
By using these models they can test and measure generalized patterns in the structure of actual food web networks.
3. 6 Different Types of Food Webs
There are different types of Food Webs:
- Source Web– One or more nodes, all of their predators, entire the food these predators eat, and so on.
- Sink Web– One or more nodes, all of their prey, entire the food these prey eat, and so on.
- Community Web– A group of nodes and entire connections of who eats whom.
- Paleo Ecological Web– A web that redevelops ecosystems from the fossil record.
- Energy Flow Web– Quantified energy flows between nodes along with a link between a consumer and a resource.
- Functional Web– Functional webs have many compartments, which are subgroups in the bigger network where there are different strengths and densities of interaction food webs. Functional Food Web explains the significance of each population in regulating the integrity of an association is reflected in its effect on the growth rates of other animals or populations.
4. What Are Trophic Levels?
In the food web, the grouping of organisms into different levels. These feeding groups are called Trophic Levels.
These levels are further divided into three Levels -Producers (First Trophic level), Consumers (Second Trophic level), and Decomposers (Last Trophic level).
4.1. Producers (First Trophic Level)
Producers build up the first Trophic level. These are also known as autotrophs because they can make their food and do not depend upon any other organism for nutrition.
Autotrophs use a process, namely photosynthesis to make food (a nutrient called glucose) in the presence of sunlight, water, and carbon dioxide.
Those algae are autotrophs, whose biggest forms are known as seaweed.
Some kinds of bacteria are also autotrophs. That means they produce their food.
A food web example, bacteria living in active volcanoes do not use carbon dioxide but use sulfur to make their food. This process is known as chemosynthesis.
4.2. Consumers (Second Tropic Level)
The next trophic level consists of animals that eat producers. Such organisms are called Consumers.
Consumers can be carnivores (those animals that eat other animals) or omnivores (those animals that eat both animals as well as plants). Omnivores, such as humans, consume many kinds of foods.
Humans eat plants, such as fruits and vegetables, and also eat animals or animal products, such as milk, eggs, and meat.
We eat fungi for example, mushroom is edible fungi. We also eat algae, in edible sea lettuce (in the form of salad), and seaweeds such as nori (used to wrap sushi rolls).
Just like us, bears are also omnivores. They eat mushrooms and berries, as well as eat salmon and deer-like animals.
4.2.1. Primary Consumers
Primary consumers are herbivores in nature. Herbivores eat only algae, plants, and other producers. They are at the second trophic level.
Mice, deer, and even elephants are herbivores in a grassland ecosystem. They eat shrubs, grasses, and trees.
A mouse that eats fruits and seeds is a primary consumer in a desert ecosystem.
White-tailed deer, intermediate species such as grasshopper, and some other organisms are other examples of primary consumers.
In an ocean ecosystem, many kinds of turtles and fishes are herbivores that eat seagrass and algae only.
In kelp forests, seaweeds consider giant kelp and provide food and shelter for an entire ecosystem.
In kelp forests, sea urchins are known as powerful primary consumers. Every day these small herbivores eat dozens of pounds of giant kelp.
4.2.2. Secondary Consumers
Secondary consumers eat herbivore animals. They are at the third trophic level. For example, Frogs eating Insects.
Sea otters are also secondary consumers in the kelp forest, those hunt sea urchins. Other examples of secondary consumers are spiders and seals etc.
4.2.3. Tertiary Consumers
Those consumers that eat the primary and secondary consumers are called tertiary consumers. They are at the fourth trophic level.
Bird Predators like owl or eagle that consume snakes in the desert ecosystem is known as tertiary consumer. Other animals like lion and vultures are also tertiary consumers.
There may be more other levels of consumers before a chain eventually reaches its top predator (top predators also known as apex predators), and eat other consumers.
Such consumers may be at the fourth or fifth level. Except for humans, they have no natural enemies. In the grassland ecosystem, lions are apex predators.
Fish such as the great white shark are apex predators, in the ocean. In the desert, mountain lions and bobcats are top predators.
4.3. Decomposers And Detritivores (Last Tropic Level)
Decomposers and Detritivores make up the final part of food chains. Detritivores are those organisms that eat nonliving animals and plant remains.
Depend upon dead organic material. For example, dung beetles eat animals’ faeces, and scavengers like vultures eat dead animals.
Decomposers, like bacteria and fungi, are the complete food chain. They convert organic wastes, like decaying plants, into inorganic materials.
They complete the life cycle, returning nutrients to the ocean or soil for use by autotrophs. This starts a completely whole new series of food chains.
5. Role of Food Chains in Food Web
The food chain shows how energy and nutrients move by an ecosystem.
The food chain refers to the order of the events in an ecosystem and the food chain also explains who eats who.
Food webs join many different food chains and many various trophic levels. Food webs can support food chains that are long and complicated or may be very short.
- For example, in the forest, grass produces its food by the process called photosynthesis. A rabbit eats green grass and a fox eats the rabbit.
- When the fox dies, mushrooms and worms like decomposers break down its body and return it to the soil where it gives nutrients to plants, like grass.
- This short food chain is one of the parts of the forest’s food web. Other food chains in this same ecosystem might involve entirely different organisms.
- Caterpillars eat the leaves of the tree. A bird such as a pigeon may eat the caterpillar.
- A snake then preys on the pigeon and plays the role of bird predator. The eagles are apex predators and prey on the snake.
- Another bird such as the vulture consumes the dead material of the eagle. Eventually, bacteria present in the soil decompose the remains.
Plankton and algae are the main primary producers in marine ecosystem ecology. Tiny shrimp that are marine primary consumers such as krill eat producers (plankton).
The blue whales, the largest living organisms on Earth, prey species diversity of krill every day in thousands of tons.
Apex predators such as orcas prey species of blue whales. As the body of whales sinks to the seafloor, worms like detritivores break down the material.
The nutrients that are released by the decaying flesh give chemicals for plankton and algae to begin a new series of food chains.
6. Role of Biomass in Energy Flow Webs
Food webs represent energy flow via trophic linkages. Energy flow is directional. Includes consumption, production, assimilation, non-assimilation losses, and respiration.
In a very normal sense, the flow of energy can be explained as the sum of metabolic production and respiration. Food webs are explained by their biomass. It is the energy in living organisms or different organisms.
In a food web, autotrophs are producers with the help of the sun’s energy transferred into biomass. Biomass reduces with each level.
The biomass in lower trophic levels is always more than in higher ones. Because the biomass reduces with each level, there are more autotrophs compared to the herbivores in a healthy food web.
There are always more herbivores than carnivores. One of the healthy food webs has a considerable amount of autotrophs, many herbivores, and a few omnivores and carnivores. This balance helps to maintain the ecosystem and recycle biomass.
In a food web, every link is connected to at least two others. The biomass of an ecosystem only depends on how connected and balanced its food web is.
When in the food web one link is threatened, then some or all links are stressed or weakened. The ecosystem’s biomass declines.
Plant life depends upon the herbivore population, the loss of plant life generally shows the decline in the herbivore population.
Plant life can decline due to disease, drought, and human activities. Forests are cut down to give lumber for construction and grasslands are paved for parking lots and shopping malls.
The loss of biomass on the second or third level can also keep a food web out of balance.
Think what may happen when a salmon run is diverted. Salmon runs can be diverted by earthquakes and landslides, as well as the construction of levees and dams.
Biomass decreases as salmon are cut out of the rivers. Omnivores like bears are unable, to eat salmon then they are forced more heavily on other food sources, like ants.
The area’s ant population shrink. Ant is usually detritivore and scavenger, so only certain nutrients are broken down in the soil. Like many autotrophs, the soil is unable to support so biomass is lost.
On higher trophic levels, the loss of organisms, such as carnivores, can disrupt a food chain. Sea urchins are the primary consumers of kelp in kelp forests.
Sea otters prey on urchins that are secondary consumers. If the population of sea otters shrinks due to hunting or disease, Urchins devastate the kelp forest.
6.2. The Effect
Biomass plummets, if lacking in the producer’s community structure. The whole kelp forest disappears. These areas are called Urchin barrens. Human activity can decrease the number of predators.
In 1986, Venezuela dammed the Caroni River, creating a huge lake that is twice the size of Rhode Island. Hundreds of hilltops are converted into islands in this lake. Many terrestrial predators were not able to find enough food.
Therefore, prey animals like monkeys, howlers, iguanas, and leaf-cutter ants flourished. The ants became so diverse that they destroyed the rainforest, killing all the plants and other trees. The food web surrounding the Caroni River was demolished.
7. Energy Flow Across Ecosystems
Research has approved that primary producers fix carbon at comparable rates across ecosystems.
Once carbon has been popularized into a system as an applicable energy source, the mechanism that governs the energy flow to higher trophic levels varies across ecosystems.
In terrestrial ecosystems and aquatic ecosystems, patterns have been identified that can feature this variation and have been classified into two pathways of control: top-down control and bottom-up control.
Top-down control involves mechanisms that are related to consumption by consumers. These control the rate of energy transfer from one to the other.
Bottom-up control involves mechanisms that are related to resource availability and quality, which control primary productivity and energy flow and biomass to higher trophic levels.
7.1. Terrestrial And Aquatic Ecosystems
There is a great deal of variation in the amount of energy transferred within each type of ecosystem.
Generally, the energy flow is a function of primary productivity with water availability, temperature, and light availability.
For example, among aquatic ecosystems, higher production rates generally occur in large rivers and shallow lakes than in clear headwater streams and deep lakes.
Among terrestrial ecosystems, swamps, marshes, and tropical rain forests have the higher production rates, whereas alpine and tundra ecosystems have the lowest.
8. Energy Pyramid
The Energy Pyramid is sometimes referred to as a trophic or ecological pyramid. It is a graphical representation of different organisms in an ecosystem.
An energy pyramid is very useful in quantifying the energy transfer from one organism to another in a food chain.
At the bottom of the pyramid, the food energy is higher but reduces as you move up through the trophic levels.
As energy flows through the different levels, some energy is usually dissipated as heat at each level, about 10% of the total energy is transferred during the flow of energy through many levels.
8.1. Examples Of Energy Pyramid
There are several examples of energy pyramids that can help better understand the concept:
- An earthworm breaks down dead organic material in the soil that the plants, sitting one level up the pyramid, used to produce their food along with the light from the sun during photosynthesis.
- The herbivores are the next level up in the pyramid and use stored energy in plants by feeding relationships with the plants. Then energy contained in the faecal from the herbivores is recycled back into that system where it is broken down by the earthworms.
- Mice in the forest ecosystem, eat the fruits and seeds, and flowers for energy, and energy is transferred from these products to mice.
- An eagle sits at the next level of the energy pyramid and eats the mice, absorbing the energy they have stored. Adult eagles have no predators. That means they found the topmost level of their energy pyramid.
- Grasshoppers eat only grass for their energy and give their energy to frogs.
- The energy is then transferred from grasshopper to frogs and then to frogs in the next level up in the pyramid, and frogs give their energy to the snakes in the next level up in the pyramid.
When you move up the trophic levels biomass declines. However, some kinds of materials, especially toxic chemicals, grow with each trophic level in the food web. This chemical energy is generally collected in the fat of animals.
When a herbivore eats an autotroph or a plant that is covered in pesticides, those pesticides are stored in the fat of animals.
When a carnivore eats many of these herbivores, it absorbs the pesticide chemicals stored in its prey. This process is known as Bioaccumulation.
Bioaccumulation also happens in aquatic ecosystems. Runoff from urban areas can be full of pollutants.
The smallest producers such as bacteria, algae, and seagrass absorb a minute amount of these pollutants. Because of bioaccumulation, organisms in certain polluted ecosystems are unsafe to feed and not allowed to be harvested.
This article explains everything about Food Chains and Food Webs. You can read more about it in the article Energy Flows Through an Ecosystem by National Geographic.
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