We all live in a beautiful world surrounded by a number of organisms. If you go to a forest, you will find a variety of plants and animals, right?. You can see that the plant life ranges from small herbs to large trees and in the same way animal life varies from tiny insects to large mammals.
Just check the status of most of the forests now. Have you noticed what is happening these days? As you see around the world, the number of species is decreasing day by day and deforestation is at its peak.
Can you tell me what is the main reason for biodiversity loss? As you know, the larger the number of species, the more sustainable the ecosystem is. Therefore, species diversity is important for sustaining life on the Earth. The species diversity varies in different geographical locations. The tropics have higher biodiversity and it goes decreasing as we move towards the poles.
The biodiversity loss affects the health of an ecosystem. Each species adds value to the planet’s wealth. There are various reasons due to which loss of biodiversity occurs. One of the main reasons is human activities like deforestation and urbanisation. Let’s discuss more about loss of biodiversity in this article, so that we can work together to make our ecosystem sustainable.
Table of contents
Earth is a unique planet as it supports life and possesses a vast diversity amongst the organisms that exist on it. Biodiversity is defined as the variety and variability amongst life forms at all levels of biological organisation, i.e, organism, species, population, community, and ecosystem.
Species diversity is described as the different types of species present in an ecosystem. The species diversity is measured in terms of species richness. Western Ghats are said to have greater species diversity compared to that of the Eastern Ghats in amphibian species.
Species diversity has two major constituents as follows:
It is considered normally as the number of species present in an area at that particular time.The example of species diversity includes 1000 different varieties of mangoes found in India.
Species richness = Number of species/Area
It is considered as the relative abundance of each species in communities. It is said to have high evenness if the number of individuals within a species is reasonably stable throughout communities, while it is said to have poor evenness if the number of individuals fluctuates from species to species. When there is a lot of evenness, there is a lot of specific variability.
For a healthy and balanced ecosystem, diverse existence of species is required. All species in an ecosystem are dependent on one another, either directly or indirectly. It is therefore critical to maintain high species diversity in order to create a more efficient, productive, and sustainable environment. Some of the importance of species diversity are as follows:
Fig: A stable community - Forest ecosystem
A stable community is defined as the one in which the size of the populations of almost all species remain relatively constant over time. Ecologists consider that communities with more species are more stable in general than communities with fewer species.
Fig: Community stability
A stable community has the following characteristics:
A plant community is a collection of plant species within a designated geographical unit, which forms a relatively uniform patch. As per ecologists, a stable community should not allow too much variation in productivity from year to year. This was proved by David Tilman.
Fig: David Tilman
David Tilman performed long-term ecosystem experiments using outdoor plots in algal and grassland ecosystems. He created outdoor plots with different numbers of species and found that plots with more species showed less year to year variation in total biomass. He also found that increased diversity contributed to higher productivity.
Fig: Outdoor plots on grassland ecosystem
By the outdoor plot experiment David Tilman concluded that ‘‘stability of a community depends on its species richness’’.
Fig: Observations of David Tilman
For example, the Western Ghats of India are one of the world's biodiversity hotspots. The indigenous frog species of the Western Ghats are noted for their rich and unusual diversity.
Fig: Frog species in Western Ghats
Stanford ecologist Paul Ehrlich used an analogy called the ‘rivet popper hypothesis’ to provide a right perspective about the stable ecosystem. The aeroplane, in his analogy, is the ecosystem, and rivets are the animals.
Fig: Paul Ehrlich
This hypothesis explains the effect of decrease in biodiversity on the ecosystem in comparison with an aeroplane. In this hypothesis, the ecosystem represents an aeroplane, rivets represent species of the ecosystem and wing rivets represent the key species of the ecosystem.
According to this hypothesis, in an aeroplane, all parts are joined together using thousands of rivets. Similarly in the ecosystem all components are joined together by thousands of species.
If every passenger travelling in an aeroplane starts pulling out a rivet to take home, it may not affect the safety of the flight initially. But as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Similarly in an ecosystem (aeroplane), all components are joined together by thousands of species (rivets). Loss or extinction of species from the ecosystem initially will not create any threat to the existing species.
Removal of rivets of a crucial part like wings will pose a serious threat to the safety of flight. The same way, extinction of key species (rivets on the wings), which are performing a major function in that ecosystem, will become a threat to the safety of other species.
Fig: Rivet popper hypothesis
For example, removing a predator like tiger from an ecosystem will result in the increase in the number of the prey species like deer, rabbits etc. This will result in the competition among the herbivores for the same food (plants and plant products) and finally they will starve to death, once their number increases drastically.
Fig: Interspecific competition among rabbits and deers
Keystone species are those species that have a very vital and pivotal role in the functioning and stability of the whole ecosystem. The starfish Pisaster ochraceus is a keystone species in the rocky marine intertidal communities of North America's northwest coast. The predatory starfish feeds on the mussel Mytilus californianus, preserving much of the local species diversity within particular communities.
There has been a reduction in biodiversity since people began to alter the environment. Although many new species are found on a regular basis, many others are lost due to a variety of factors. Each species adds value to the planet’s wealth. If the producers are present in a great amount, it means a larger number of varieties of crops exist. All life forms benefit from increased species diversity because it maintains natural sustainability. Ecosystems that are healthy are better able to resist and recover from a variety of disasters. Due to human actions, the planet's biological wealth has been fast declining.
Around 4,000 years ago, humanity ventured into an uncharted territory: the Pacific Islands. They rowed from one island to the next for thousands of years, stepping on coastlines never seen by humans before. As a result of deforestation, the massive colonisation brought a new period in human history, with the extinction of thousands of bird species. More than 2,000 species of native birds have been wiped out as a result of humans colonising the tropical Pacific Islands.
Fig: Colonisation lead to extinction of bird species
IUCN is an international organisation that works on nature conservation and sustainable use of natural resources. The Red Data Book is referred to as the public document that records the information about all rare and endangered species of plants, animals, and fungi existing within the boundary of a state or territory. It can be considered as a catalogue of species facing the risk of extinction. This book also contains the records of local subspecies that are native to a particular region.
The Red List only contains the names of the endangered species whereas the Red Data Book contains all the information about the species that are on the verge of extinction. It contains information about the threatened species, extinct species, vulnerable species and endangered species. This comprehensive document is used for the conservation of biological species. According to the IUCN Red List of 2004, 784 species became extinct in the last 500 years. It includes 338 vertebrates, 359 invertebrates and 87 plants.
Fig: The IUCN Red List of 2004
Extinct species are referred to as those species whose individuals are not alive anywhere in the world. This results in the disappearance of species. This is also known as extinction. There have been 27 species extinctions in the previous few years. Extinction rates do not appear to be random among species; some groups, such as amphibians, appear to be more prone to extinction. This is due to the fact that the amphibians live in both terrestrial and aquatic habitats. If either habitat faces a threat, it affects the population. There are nearly as many threatened amphibian species as there are threatened bird and mammal species combined. More than 15,500 species are on the verge of extinction around the planet. Currently, extinction threatens 12 percent of all bird species, 23% of all mammal species, 32% of all amphibian species, and 31% of all gymnosperm species on the planet.
Fig: Extinction of species
The dodo (Raphus cucullatus) of Mauritius, quagga (Equus quagga quagga) of Africa, thylacine (Thylacinus cynocephalus) of Australia, Steller's Sea Cow (Hydrodamalis gigas) of Russia, and three tiger subspecies (Bali, Javan, and Caspian) are only a few examples of recent extinctions.
Fig: Examples of recently extinct species
Mass extinctions are described as the large-scale loss of species. The extinction of not one, not two, not a hundred, but nearly half of all species on the Earth in a short period of time is referred to as a mass extinction.
There were five episodes of mass extinctions that happened in the last 450 million years ago (mya). The sixth extinction is different from these five extinctions. These are as follows:
Fig: The five episodes of mass extinctions
This mass extinction occurred around 440 mya. According to the scientists, there were two main phases to this extinction: a glacial event and a heating event. As per the theory carbon dioxide (CO2) was extracted from the air by abundant plant life, triggering global cooling and glacier formation. As a result, the sea level dropped and it reduced habitat. Later, global warming occured and the sea level began to rise again. The increasing temperature made it impossible for creatures that had evolved to the cooler climate to survive. The majority of the fauna at that time was marine, 85% of life was destroyed due to their inability to adjust to climate changes.
Fig: Ordovician-silurian extinction
This extinction occurred around 365 mya. During this extinction period, around 75% of life died off. Two theories suggest the late Devonian extinction. According to the first theory, terrestrial plants developed deep roots, released a large amount of nutrients into the waters, which algae used as nutrition. As a result, algal blooms occur in the oceans which absorb large amounts of oxygen (O2). This suffocated many marine animals. According to another theory, another phase of global cooling occurred, resulting in glaciation and a drop in sea level, resulting in habitat loss.
Fig: Late devonian extinction
This extinction took place around 250 mya. The Permian - Triassic extinction was the deadliest in history, with 95% of marine species and 70% of terrestrial life destroyed. According to the scientists, volcanic activity occurred in Siberia. This puts a large amount of carbon dioxide and greenhouse gases into the atmosphere. Methane and other greenhouse gases were produced by bacteria that thrive on CO2. Large amounts of these gases increase the temperature of the Earth and interact with the water on the surface. It produced oceans and acidic rain. As a result, an extremely dangerous environment is produced which makes it hard for life to survive.
Fig: Permian-triassic extinction
This extinction occurred around 200 mya. According to some scientists, volcanic eruptions sprayed massive amounts of CO2 into the sky that trapped heat and acidified the waters, resulting in this global extinction. Some scientists believe that the extinction was caused by an asteroid or comet strike. During this extinction, about 80% of life was lost.
Fig: Triassic-jurassic extinction
This extinction occurred around 60 mya. This extinction wiped out 60 - 76% of life from the Earth along with dinosaurs. According to the widespread opinion, an asteroid fell in Mexico and killed the dinosaurs. Massive amounts of debris would have been thrown into the atmosphere, causing global temperatures to drop. Local fires, earthquakes, tsunamis, and acid rains may have been caused by the impact.
Fig: Mass extinction of dinosaurs
This extinction has been occurring since around 11,000 years ago and is still ongoing. Human activities, as well as changes in marine temperature, contribute to the phenomenon. Over 500 species are on the verge of extinction at the moment.
This is the sixth extinction which is different from the last five extinctions. The difference occurs in the rate of extinction. The current rate of extinction of species is predicted to be 100 to 1,000 times quicker than in pre-human eras, and this is due to human activities. According to ecologists, if current trends continue, over half of all species on the planet will be extinct within the next 100 years.
There are four major causes of biodiversity losses which are known as the evil quartet. The term ‘evil quartet’ refers to the four key factors that have contributed to the rapid loss of species. These four causes are listed below:
Fig: The evil quartet
Forests contribute to the health of the planet's flora and fauna as well as the environment. The forests are currently being removed, and the species that live there are rapidly becoming extinct. For example, rain forests once covered more than 14 percent of the Earth's land surface but today only cover about 6% of the surface.
Destruction of natural habitat is the primary cause of loss of biodiversity. Natural habitats which protect natural flora and fauna are being converted into human settlements, agricultural fields, grazing grounds, mines, reservoirs and dams. Loss of habitat deprives animal life of shelter and food and declines their reproductive capacity resulting in loss of many species.
Fig: Habitat loss
The Amazonian rainforest is a tropical rainforest in Brazil that covers most of the Amazon basin of South America. An example of habitat loss is that occurred in the Amazon rainforest. The Amazon rainforest is vast, known as the ‘lungs of the Earth,’ and is home to millions of species. It is being cut and cleared for soybean cultivation or conversion to grasslands for beef cattle grazing. Moreover, habitat loss due to pollution leads to death of plants and animals. The death of aquatic life is caused by polluted water.
Fig: Amazonian rain forest
Fragmentation is described as the phenomenon in which a large habitat is broken into smaller fragments because of human activities. Due to fragmentation of habitat predators get separated from the prey. As a result, prey competes for their resources. Fragmentation badly affects mammals and birds which require large territories and other animals with migratory habits, leading to decline of their population. Deforestation has a negative impact on several migratory animals, resulting in population decrease.
Fig: Fragmentation of habitat
Humans depend on nature for their basic needs, such as food, shelter, medicines and clothing. When 'need' transforms into 'greed,' natural resources are over-exploited. The over-exploitation of nature by human activities has resulted in the extinction of many species in the last 500 years. Examples include passenger pigeon (Ectopistes migratorius), Steller’s sea cows (Hydrodamalis gigas) etc.
Steller’s sea cow was found in the sub-Arctic waters of the Northern Pacific Ocean. Its length is about 9 - 10 m and weight is more than 10 metric tonnes. It became extinct because it was over hunted for meat. The steller’s sea cow was discovered in the year of 1741 and became extinct in the year of 1768.
Fig: Steller’s sea cow
The passenger pigeon was the most common bird in North America. Human hunting drove them to extinction in the year of 1914.
Fig: Passenger pigeon
Now-a-days, humans over harvest many marine fishes. As a result, the commercially important marine fishes become endangered.
Fig: Overharvesting of marine fishes
Alien species is a type of species that is introduced outside its natural past or present distribution. When foreign species are introduced, whether accidentally or on purpose, some of them become invasive and cause the decline or extinction of native species.
Fig: Invasion of alien species
Some of the examples of alien species invasion are as follows:
The most striking feature of Lake Victoria’s fish community was its amazingly diverse community of cichlids (Cichlidae). In the 1950s, to boost the fishing industry, Nile perch were introduced to Lake Victoria. But the cichlids were their prey. The introduction generated an economic boom, but it also drove hundreds of species of native cichlids to near-extinction.
Fig: Nile perch
It is considered as one of the worst invasive species with a high concern in India. It competes for space and resources with native plants, and it also disrupts the soil's nitrogen cycle. The negative aspects of Lantana occur when it invades into the agricultural landscapes, forests and wastelands. Here, the Lantana causes deterioration of biodiversity and it harms the commercial crops as well. For wild herbivores, this invasion has resulted in a lack of native feeding plants. If these plants are consumed by animals, this will cause allergies. Excessive Lantana consumption has resulted in diarrhoea, liver failure, and even death in certain animals.
It is a weed that has spread throughout agricultural areas and grasslands. It inhibits the development of agricultural crops. Herbivores and humans are both poisoned by it. This weed came to India as a contaminant along with the imported wheat.
Fig: Carrot grass (Parthenium)
It is another type of weed whose invasion causes complete depletion of dissolved oxygen, which is essential for aquatic life. By stagnating water in ditches and shallow areas, water hyacinth provides ideal hatching conditions for mosquitoes and other disease-carrying insects. The plants have also been found to carry viruses that infect a variety of crops. This plant was introduced in India by Lady Hastings, the wife of the First British Governor-General, as an ornamental plant.
Fig: Water hyacinth
African catfish introduced for aquaculture recently in India from Bangladesh poses a threat to native catfish and other fishes.
Fig: African catfish
When a species goes extinct, the plant and animal species that it is connected with go extinct as well and this is known as co-extinction. For example, when a host fish species goes extinct, its parasite relationship goes extinct with it. Another example is mutualism between coevolved plants and pollinators, in which the loss of one causes the extinction of the other.
In addition to the evil quartet, biodiversity loss occurs due to the following reasons too:
Nature and man- made disturbances like forest fires, tree fall, locust attacks etc., adversely affect the communities and result in loss of biodiversity.
GIF: Massive forest fire
Use of synthetic compounds, oil spills and release of radiation degrade the ecosystem. Many species are sensitive to this pollution. For example, the population of fish eating birds has declined due to the excessive use of pesticides in the crop fields. The nutrient enrichment also leads to loss of biodiversity.
Fig: Effects of pollution on ecosystem
Intensive agriculture is based on a few high yielding varieties. This reduces biodiversity. It also increases the vulnerability of crop plants to sudden attack by pathogens and pests. For example, The Amazonian rainforest is being cut and cleared for soybean cultivation or conversion to grasslands for beef cattle grazing.
Some effects of biodiversity loss are listed below:
Q1. Match column I with column II and find the correct option:
A. Fragmentation of large habitats
B. Species turn invasive and cause extinction of indigenous species
C. Mutual extinction
a. A - 1, B - 2, C - 3, D - 4
b. A - 4, B - 3, C - 2, D - 1
c. A - 4, B - 1, C - 3, D - 2
d. A - 4, B - 1, C - 2, D - 3
Solution: Fragmentation is described as the phenomenon in which a large habitat is broken into smaller fragments because of human activities. Due to fragmentation of habitat predators get separated from prey. As a result, prey competes for their resources. The most striking feature of Lake Victoria’s fish community was its amazingly diverse community of cichlids. In the 1950s, to boost the fishing industry, Nile perch were introduced to Lake Victoria. But the cichlids were the prey of the Nile perch. This introduction generated an economic boom, but it also drove hundreds of species of native cichlids to near-extinction. When a species goes extinct, the plant and animal species that it is connected with go extinct as well and this is known as co-extinction. For example, when a host fish species goes extinct, its parasite relationship goes extinct with it. Steller’s sea cow was found in the sub-Arctic waters of the Northern Pacific Ocean. Its length is about 9 - 10 m and weight is more than 10 metric tonnes. It became extinct because it was over hunted for meat. Hence, the correct option is d.
Q2. The term ‘the evil quartet’ represents ______________.
A. four major causes of forest loss
B. four major causes of population explosion
C. four major causes of air pollution
D. four major causes of biodiversity losses
Solution: There are four major causes of biodiversity losses. The term ‘evil quartet’ refers to the four key factors that have contributed to the rapid loss of species. These four causes are listed below:
Hence, the correct option is d.
Q3. Which of the following mass extinction is anthropogenic?
Q4. What is co-extinction?
Answer: When a species goes extinct, the plant and animal species that it is connected with go extinct as well and this is known as co-extinction. For example, when a host fish species goes extinct, its parasite relationship goes extinct with it. Another example is mutualism between coevolved plants and pollinators, in which the loss of one causes the extinction of the other.
Q1. What is the main cause that affects the biodiversity lost the most?
Answer: The habitat loss and fragmentation affects the biodiversity loss the most. This is because human activities destroy the number of species of plants and animals. In return to this, the species associated with that also get affected.
Q2. How does biodiversity loss affect the ecosystem?
Answer: The biodiversity loss results in the decline in the genetic variability, number and variety of species, and the biological communities in a particular area. This leads to a breakdown in the functioning of the ecosystem. Biodiversity loss has a significant impact on human and animal health too. The number of diseases also increases in the local population.
Q3. How does overpopulation affect biodiversity?
Answer: Increasing population growth creates pressure on the environment to convert wild habitat into urban areas. This leads to over exploitation of resources and due to which they ultimately get extinct. Humans depend on nature for their basic needs, such as food, shelter, medicines and clothing. When 'need' transforms into 'greed,' natural resources are over-exploited.
Q4. List some of the factors that contribute to biodiversity loss?
Answer: The factors that contribute to the biodiversity loss are listed below:
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