Important Functions of an Ecosystem
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Important Functions of an Ecosystem
The components of an ecosystem are seen to function as a unit in the following aspects-
- Energy flow
- Nutrient cycling
- Ecological succession
Energy Flow-
Energy is a basic need for all metabolic activities.
Except for the deep-sea hydrothermal ecosystem, the sun is the only source of energy.
Trophic level interactions-
It deals with how the members of the ecosystem are connected in terms of nutrition
| Autotrophs | Green plants (producers) |
| heterotrophs | Herbivores (primary consumers) |
| heterotrophs | Carnivores (secondary consumers) |
| heterotrophs | Carnivores (tertiary consumers |
| heterotrophs | Top carnivores (quaternary consumers) |
- Energy flows through trophic levels and always flows from lower (producer) to higher trophic levels.
- The flow of energy is unidirectional.
- Some loss of energy in form of heat or some other form also occurs during its transfer. Therefore less energy is transferred to the next trophic level.
- So a food chain usually consists of 4-5 trophic levels.
- Three concepts are involved in trophic level interaction namely food chain, food web, and ecological pyramids.
- All organisms are arranged in a series in which food energy is transferred through repeated feeding.
- The amount of energy decreases at successive trophic levels.
- Herbivores consume plant matter and convert them into the animal matter. These herbivores are eaten by large carnivores.
- Energy flow is in the form of food.
- 10% law of Lindeman- according to it 90% part of obtained energy is utilized in various metabolic activities and heat and only 10% is transferred to the next trophic level.
Two main types of food chains are seen in nature.
Grazing Food Chain-
- Most of the food chains in nature are of this type.
- The food chain begins from green plants (producers)
- Consumers start the food chain by utilizing the plant or plant part as food
Terrestrial ecosystem
Grass-----> Rabbit-----> fox-----> lion
Aquatic ecosystem
phytoplankton---> zooplankton---> Small fish---> large fish
Detritus Food Chain-
- Starts from dead organic matter.
- Made up of decomposers mainly fungi and bacteria.
- Energy demands are fulfilled by detritus( degrading dead organic matter)
- Decomposers secrete digestive enzymes that break down dead and waste materials into simple, inorganic material which they subsequently absorb.
Eg. litter---> earthworm---> Chicken---> Hawk.
- In big ecosystems, food chains are linked together on different trophic levels to form a food web. The natural interconnection of the food chain is called the food web.
- More is the complexity of the food web more stable is the ecosystem
- A food web illustrates all possible transfers of energy and nutrients among the organisms, whereas a food chain traces only one pathway of the food.
- Transfer of energy is still unidirectional but many alternative pathways are available.
- Graphical representation of ecological parameters at different trophic levels in the ecosystem is called pyramids.
- Producers form the base of the pyramid and the top carnivore forms the tip.
- Horizontal bars in the pyramid represent specific trophic levels.
- The length of each bar represents either number, biomass, or energy of individuals at each trophic level.
Types of pyramids
1. Pyramid of numbers-upright
- The number of individuals is decreased from lower to higher trophic level
Eg. grassland ecosystem
- Grasses occupy the lowest trophic level
- The next trophic level includes primary consumer-herbivore eg. grasshopper
- Further levels include carnivore
Eg. rats then snake followed by hawks.
2. Pyramid of number-inverted
- The number of individuals increases from lower to higher trophic levels.
- Primary producers (tree) are less in number which represents the base of the pyramid.
- Herbivores eg. birds followed by parasites in next higher trophic levels
- Due to the difficulty in counting all the organisms in a particular trophic level, the pyramid of numbers does not completely define a trophic structure for an ecosystem.
- Pyramid of number shows the biotic potential of an ecosystem
- It represents the total amount of biomass(dry weight) of each trophic level of the ecosystem
- Pyramid of biomass shows standing crop of ecosystem
- Biomass is measured in gram/meter2
3. Upright pyramid-
In most ecosystems on land, the pyramid of biomass has a large base followed by smaller consecutive trophic levels.
- Biomass of producers is maximum
- Higher trophic levels have a very less amount of biomass.
Standing CROP-
Each trophic level has a certain mass of living material at a particular time called a standing crop.
- They represent the productivity of the ecosystem as well as the transfer of production in the ecosystem.
- It also follows the thermodynamics law, conversion of solar energy into chemical energy and heat energy.
- Therefore pyramid of energy is always upright.
- Each bar in the energy pyramid indicated the amount of energy present in each trophic level in a given time or annually per unit area.
- Example-an ecosystem receives 1000 calories of light energy in a day
Biomagnification-
- The tendency for pollutants to concentrate as they move from one trophic level to another.
- Few toxic substances present in the industrial wastewaters undergo biological magnification in the aquatic food chain.
- Cause- toxic substances accumulated by an organism are neither metabolized nor excreted, and thus pass to the next level
- Mercury and DDT are the most common examples.
- For biomagnification to occur the pollutants must be: long-lived, mobile, soluble in fats, and biologically active.
- Short-lived pollutants-break down
- Immobile pollutants- stay in one place
- If soluble in water- will be excreted by kidneys
- If a pollutant is not active biologically there is no need to worry.
- Fat-soluble pollutants are retained for a much longer time therefore in humans the concentration of pollutants is measured in milk produced by females since it consists of a large number of fats and is more susceptible to damage from toxins.
| Species A | Species B | Type of interaction |
| + | + | Mutualism |
| - | - | Competition |
| + | - | Predation |
| + | - | Parasitism |
| + | 0 | Commensalism |
| - | 0 | Amensalism |
- One species benefits other is harmed
-For prey and + for predator
Role of predators-
- They keep prey population under the control in the absence of predators prey species could achieve very high population density and can cause ecosystem instability.
- Transfer energy across trophic levels- they act as conduits for energy transfer
- Biological control methods are based on predation eg. ladybird and dragonflies are used to get rid of aphids and mosquitoes
- Maintain species diversity in a community by reducing the intensity of competition among prey species.
Defenses evolved by prey species
Animals-
Camouflage-some species of insects and frogs avoid being detected easily by predator via changing color
Eg. grasshopper, dead leaf butterfly, etc
Some are poisonous so avoided by predators
Some are distasteful eg. monarch butterfly, due to a chemical which it acquires in the caterpillar stage by feeding on a poisonous weed.
Plants-
Morphological defense-most common means of defense thorns eg. acacia, cactus
- Chemical defense- plants produce and store chemicals that make the herbivore sick, inhibit feeding or digestion, disrupt its reproduction or even kill it. Eg. Calotropis- contains cardiac glycosides
Other chemicals- nicotine, caffeine, quinine, opium, etc these act as defenses against grazers and browsers.
Both species are harmed in this interaction.
Gause’s competitive exclusion principle-
Two closely related species competing for the same resources cannot coexist and the competitively inferior one will be eliminated eventually.
Eg. the Abingdon tortoise in Galapagos island became extinct within a decade after the introduction of goats.
Competitive release-
A species whose distribution is restricted to a small geographical area because of the presence of a competitively superior
Species expand their distributional range all of a sudden when competing species are experimentally removed.
Eg. in Connell's field experiment on the sea coast of Scotland, the superior barnacle Balanus dominates the intertidal area and excludes the smaller barnacle chathamalus from that zone.
Resource partitioning-
If two species compete for the same resources they could avoid competition. By choosing a different time for feeding and
different foraging patterns etc. Eg. five closely related species of warblers living on the same tree avoided competition and co-exist.
One species is benefited and the other is harmed.
Special adaptations in parasites-
- Loss of unnecessary sense organ
- Presence of adhesive organs or suckers to cling on the host
- Loss of digestive system
- High reproductive capacity
- Anaerobic respiration
- Presence of resistant spores
- Complex life cycles, involving one or two intermediate hosts. Eg. human liver fluke depends on two intermediate host-snail and a fish
- All parasites harm the host; they may reduce the survival, growth, and reproduction of the host.
Types of parasites
Ectoparasites-
feed on the external surface
Eg. lice on human
Ticks on dog
Marine fishes with ectoparasites copepods
Cuscuta growing on hedge plant
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Endoparasites-
live inside the host body
Their life is more complex because of extreme specializations.
Brood parasitism-
the parasitic bird lays its eggs in the host and lets the host incubate them
Eg. cuckoo(koel) and the crow
COMMENSALISM-
One species benefits and the other is unaffected
Eg. orchid growing on another plant
Barnacles on the back of a whale
Cattle egret and grazing cattle
Sea anemone and clownfish
MUTUALISM-
Both species are benefitted.
Eg. lichens- algae + fungi
Mycorrhiza- association between fungi and roots of higher plants.
Plant pollinator relationship- fig and wasp, orchid and bees.
- The movement of nutrient elements through various components of an ecosystem is called nutrient cycling.
- Bio-living organism, geo- rocks, air, water
- The pathway by which chemical substances move through biotic and abiotic components of earth.
- Energy flow and nutrient circulation are the two important aspects of the ecosystem. They in turn affect the abundance of organisms, the metabolic rate at which they survive, and the complexity(stability) of the ecosystem.
- Energy flow enables various kinds of work and energy is ultimately lost as heat while nutrients are cycled again and again.
- 97% mass of our bodies is made by carbon, hydrogen, oxygen, nitrogen, and phosphorus.
Nutrient Cycling-
It describes how nutrients move from the environment to living organisms and then recycled back to the environment.
- Carbon and nitrogen cycles are the most important ones. Both these cycles make up an essential part of the overall soil nutrient cycle.
Types of nutrient cycles-
Perfect or imperfect cycle-
Based on the replacement period
Perfect- nutrients are replaced as fast as they are utilized eg. most gaseous cycle
Imperfect- some loss of nutrients takes place which becomes unavailable for cycling. Eg sedimentary cycles
Gaseous and sedimentary cycle-
based on the nature of the reservoir
Gaseous- reservoir exists in atmosphere or hydrosphere
They are more rapid and perfect.
Sedimentary- the reservoir is located in the earth’s crust
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Carbon Cycle-
- Carbon constitutes 49% of the dry weight of organisms.
- 71% carbon is found dissolved in oceans, the atmosphere contains only 1% of the total global carbon mainly in form of co2.
- Carbon cycling occurs through the atmosphere, ocean, and living and dead organisms.
- Carbon moves to green plants by photosynthesis and then to animals.
Phosphorus Cycle-
Phosphorus is a major constituent of biological membranes, nucleic acid, and cellular energy transfer systems.
It also takes part in the formation of shells, bones, and teeth
Reservoir -rocks
It enters into circulation by erosion and mining activities.
Succession-
It is a universal process in which composition and structure constantly change in response to change in environmental conditions.
- These changes finally lead to a community that is almost in equilibrium with the environment and is called the climax community.
- Both biotic and abiotic components are involved in successional changes and succession change occurs in both plants and animals.
- Pioneer community-first community to inhabit an area
- Climax community- last and stable community in an area
- Both biotic and abiotic components are involved in successional changes and succession change occurs in both plants and animals.
- Pioneer community-first community to inhabit an area
- Climax community- last and stable community in an area
Usually, mesophytes represent the climax community.
- Seral community-intermediate communities are called seral community
Characteristics of succession-
Increased productivity
- Increased diversity of organisms with increased niche
- Increased complexity of food web
- The shift of nutrients from the reservoir to general circulation
Types of succession-
- Primary succession
- Secondary succession
Primary succession
Succession where no living organisms ever existed.
Eg. newly cooled lava
Bare rock
Newly created pond
- Pioneer species are usually microbes, lichens, and mosses.
- Over hundreds of years, the pioneer species degrade the rock into soil that can support small grasses
- Grasses further modify the soil which is then colonized by plants
- The final stage of succession is the climax
Secondary succession-
The type of succession in which vegetation was present previously but was destroyed due to any cause, natural or artificial like fire, flood, sudden changes in climate, landslide, etc.
- It is faster when compared to primary succession as some soil is present
- The invading species depend on the condition of the soil, availability of water, etc.
- The abandoned farmland is first invaded by species of grasses that can survive in bare, sun-baked soil.
- Grasses soon form tall grasses and herbaceous plants also mice, rabbits, insects, and seed-eating birds are seen which all together dominate for several years
- Some trees come up in this area seeds of which may be carried by the wind, insects, etc.
- Finally, the abandoned farmland is dominated by trees and convert into a forest.
- It is important to note that several human activities like deforestation,
- Overgrazing, agriculture, etc or natural processes like a flood, drought, storms, etc can destroy a mature or intermediate community.
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