Causes of Biodiversity Losses Questions in English

(A) The most significant cause of biodiversity loss and the extinction of species is $Habitat \text{ } loss \text{ } and \text{ } fragmentation$.
As human populations increase, the demand for land grows, leading to the destruction of natural habitats such as tropical rainforests.
When large habitats are broken into smaller fragments, species that require large territories or those that are migratory are severely affected, leading to population decline and eventual extinction.

(D) Biodiversity loss is primarily driven by human activities that negatively impact ecosystems. The four major causes,often referred to as the 'Evil Quartet',are:
$1$. Habitat loss and fragmentation: This is the most significant cause,where natural habitats are destroyed or broken into smaller pieces.
$2$. Over-exploitation: Humans over-harvest species for food,medicine,or trade,leading to population decline.
$3$. Alien species invasion: The introduction of non-native species can outcompete or prey upon native species,causing their extinction.
$4$. Co-extinction: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct.
Since all four factors listed $(i, ii, iii, iv)$ are recognized as primary causes of biodiversity loss,the correct option is $(D)$.

(B) The tree species in question is the Calvaria major (tambalacoque) tree.
It was found that the tree species failed to reproduce because of the extinction of the Dodo bird,which was native to Mauritius.
The Dodo bird played a crucial role in the germination of the seeds of this tree by passing them through its digestive tract,which helped in breaking the hard seed coat.
Following the extinction of the Dodo in the $17^{th}$ century due to over-exploitation by humans,the tree species also faced the threat of extinction.

(C) Tropical rain forests are located in the equatorial regions where the annual rainfall exceeds $140\, cm$.
They are also called jungles and cover one-twelfth of the Earth's surface but contain more than half of the Earth's flora and fauna,meaning they are extremely rich in biodiversity.
Therefore,the Reason provided is factually incorrect because these forests are actually very rich in biodiversity,not poor.
Nowadays,these forests are disappearing rapidly due to excessive deforestation for domestic purposes like fuel,furniture,accommodation,clothing,resin,gum,etc.

(D) The introduction of non-native or exotic species into a new ecosystem often leads to the decline or extinction of indigenous species. This phenomenon is known as $Alien$ $species$ $invasion$. $Clarias$ $gariepinus$ (African catfish) is an invasive species that was illegally introduced into Indian water bodies,including the river Yamuna,where it competes with and preys upon native fish species,leading to a significant decline in their population.

(N/A) Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land,air,and water. Biodiversity around the world is declining at a very fast pace. The following are the major causes for the loss of biodiversity around the world:
$1$. Habitat loss and fragmentation: Habitats of various organisms are altered or destroyed by uncontrolled and unsustainable human activities such as deforestation,slash-and-burn agriculture,mining,and urbanization. This results in the breaking up of the habitat into small pieces,which affects the movement of migratory animals and decreases the genetic exchange between populations,leading to a decline in species.
$2$. Over-exploitation: Due to over-hunting and over-exploitation of various plants and animals by humans,many species have become endangered or extinct (such as the tiger and the passenger pigeon).
$3$. Alien species invasions: Accidental or intentional introduction of non-native species into a habitat has also led to the decline or extinction of indigenous species. For example,the Nile perch introduced in Lake Victoria in Kenya led to the extinction of more than $200$ species of native fish in the lake.
$4$. Co-extinction: In a native habitat,one species is connected to the other in an intricate network. The extinction of one species causes the extinction of other species,which is associated with it in an obligatory way. For example,the extinction of the host will cause the extinction of its parasites.

(D) The Earth's biological wealth is declining rapidly due to various human activities.
$(i)$ The colonization of tropical Pacific islands by humans has led to the extinction of more than $200$ species of native birds.
(ii) According to the $IUCN$ Red List $(2004)$ documents, $784$ species have become extinct in the last $500$ years, including $338$ vertebrates, $359$ invertebrates, and $87$ plant species.
(iii) Recent examples of extinct species include the Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller's Sea Cow (Russia), and three subspecies of tiger (Bali, Javan, and Caspian). The last twenty years have witnessed the disappearance of $27$ species.
(iv) Currently, more than $15,500$ species worldwide are facing the threat of extinction. Approximately $12\%$ of all bird species, $23\%$ of all mammal species, $32\%$ of all amphibian species, and $31\%$ of all gymnosperm species in the world face the threat of extinction.

(N/A) The world is currently facing accelerated species extinction,primarily due to four major causes,collectively known as 'The Evil Quartet':
$(a)$ Habitat loss and fragmentation: $(i)$ Tropical rainforests,which once covered more than $14\%$ of the Earth's land surface,now cover no more than $6\%$. $(ii)$ The Amazon rainforest,often called the 'lungs of the planet',is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle. $(iii)$ Pollution and degradation of habitats also threaten the survival of many species. $(iv)$ When large habitats are broken into small fragments due to human activities,mammals and birds requiring large territories are badly affected,leading to population declines.
$(b)$ Over-exploitation: Humans have always depended on nature for food and shelter,but when 'need' turns to 'greed',it leads to over-exploitation. $(i)$ Many species extinctions in the last $500$ years (e.g.,Steller's sea cow,passenger pigeon) were due to over-exploitation by humans. $(ii)$ Currently,many marine fish populations around the world are being over-harvested,endangering the continued existence of some commercially important species.
$(c)$ Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose,some of them turn invasive and cause decline or extinction of indigenous species. $(i)$ The Nile perch introduced into Lake Victoria in east Africa led to the extinction of an ecologically unique assemblage of more than $200$ species of cichlid fish. $(ii)$ Invasive weed species like carrot grass $(Parthenium)$,$Lantana$,and water hyacinth $(Eichhornia)$ cause environmental damage and pose a threat to our native species. $(iii)$ The illegal introduction of the African catfish $Clarias$ $gariepinus$ for aquaculture is posing a threat to the indigenous catfishes in our rivers.
$(d)$ Co-extinctions: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct. For example,when a host fish species becomes extinct,its unique assemblage of parasites also meets the same fate. Another example is the case of a co-evolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

(N/A) Habitat is the natural environment where an organism lives,providing essential resources for food,reproduction,and survival. Habitat loss occurs due to deforestation,agricultural expansion,urbanization,and environmental pollution. When a habitat is destroyed,organisms lose their shelter and food sources,which increases predation risks and reduces reproductive success. This cumulative stress leads to a decline in population size,eventually driving species toward extinction.

(D) Mass extinctions in the past were caused by various natural geological and climatic events. These include:
$(i)$ Volcanic eruptions,which release massive amounts of gases and ash,altering the atmosphere.
$(ii)$ Earthquakes and tectonic shifts.
$(iii)$ Extremes of temperatures,leading to rapid climate change.
$(iv)$ Glaciations,which drastically reduce habitable areas.
$(v)$ Continental drift,which alters ocean currents and global climate patterns.
Therefore,all these factors have contributed to mass extinctions throughout Earth's history.

(D) Tigers play a crucial role as apex predators in the food chain,which helps in maintaining the stability of the ecosystem.
As carnivores,they keep a check on the uncontrolled growth of herbivore populations.
They remove sick and old animals from the population,ensuring the health of the prey species.
Tigers serve as an indicator species for the health of the jungle ecosystem.
Protecting tigers essentially means protecting the entire forest habitat,as they require large areas to hunt and maintain the balance of the food chain.

(B) The figures $A$ and $B$ represent $Lantana$ $camara$ and $Eichhornia$ $crassipes$ (water hyacinth),respectively. Both of these are well-known examples of invasive alien species that have caused significant environmental damage and pose a threat to our native biodiversity.

(B) The species extinction occurring at present is primarily driven by anthropogenic (human-induced) activities such as habitat destruction,overexploitation,and pollution.
In contrast,the earlier mass extinctions that occurred in Earth's history were caused by natural phenomena such as volcanic eruptions,asteroid impacts,or major climatic shifts.
Furthermore,the current rate of extinction is estimated to be $100$ to $1000$ times faster than the natural background rate of extinction.

(B) Habitat loss and fragmentation is the most important cause driving animals and plants to extinction.
The most dramatic examples of habitat loss come from tropical rain forests.
Once covering more than $14$ percent of the earth's land surface,these rain forests now cover no more than $6$ percent.
They are being destroyed fast.
By the time you finish reading this chapter,$1000$ more hectares of rain forest would have been lost.
The Amazon rain forest (it is so huge that it is called the 'lungs of the planet') harbouring probably millions of species is being cut and cleared for cultivating soybeans or for conversion to grasslands for raising beef cattle.

(N/A) When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct.
For example:
$(i)$ When a fish species that serves as a host for a specific parasite becomes extinct,the parasite species that are uniquely dependent on that host fish will also face extinction.
$(ii)$ Insects can be polyphagous (feeding on more than one plant species) or monophagous (feeding on only one particular plant species).
The monophagous insect species are highly vulnerable and may become extinct if the specific plant species upon which they feed becomes extinct.

(B) species is categorized as threatened based on several criteria,primarily focusing on the risk of extinction:
$(i)$ Population decline: The number of individuals of the species is decreasing at an alarming rate.
$(ii)$ Habitat loss and fragmentation: The natural environment required for survival is being destroyed or broken into smaller,isolated patches.
$(iii)$ Predation and competition pressure: Increased pressure from predators or invasive species.
$(iv)$ Introduction of alien species: Non-native species outcompeting or preying on the native species.

(C) $\Rightarrow$ Amphibians are uniquely vulnerable because they occupy a dual life strategy.
$\Rightarrow$ While they live in terrestrial habitats,they are strictly dependent on aquatic habitats for their sexual reproduction and larval development.
$\Rightarrow$ Consequently,habitat loss or degradation in either the terrestrial or aquatic environment directly threatens their survival and reproductive success,making them more susceptible to extinction than groups that rely on a single type of habitat.

(N/A) Apart from anthropogenic (human-induced) activities,the loss of biodiversity is primarily driven by natural causes. Two major natural causes are:
$1$. Natural Calamities: Events such as volcanic eruptions,earthquakes,floods,and forest fires can cause sudden and massive destruction of habitats,leading to the loss of species.
$2$. Climate Change: Long-term shifts in temperature and weather patterns,such as ice ages or prolonged droughts,can alter ecosystems significantly,making it difficult for certain species to survive and adapt,eventually leading to their extinction.

(N/A) An endangered species is a species that is facing a very high risk of extinction in the wild in the near future if conservation measures are not promptly taken.
Example of an endangered animal species: Red panda $(Ailurus \text{ } fulgens)$.
Example of an endangered plant species: $Drosera \text{ } indica$ (Sundew).

(N/A) Co-extinction refers to the process where the extinction of one species leads to the inevitable extinction of another species that is obligatorily associated with it.
$1$. Parasite-Host Example: When a host fish species becomes extinct,its unique assemblage of parasites also meets the same fate because they cannot survive without their specific host.
$2$. Plant-Pollinator Example: In cases of coevolved plant-pollinator mutualism,the extinction of the plant species leads to the extinction of the pollinator,and vice versa,as they depend entirely on each other for survival and reproduction.

(N/A) Alien species invasion is one of the major causes of biodiversity loss. When alien species are introduced intentionally or unintentionally into a new habitat,they often become invasive due to the absence of their natural predators or competitors in the new environment.
$1$. Competition for Resources: Invasive species often outcompete native species for limited resources such as food,water,space,and sunlight.
$2$. Predation: Alien species may act as predators to native species that have not evolved defense mechanisms against them,leading to a rapid decline in native populations.
$3$. Disruption of Ecosystem Processes: They can alter the physical environment,nutrient cycling,or fire regimes,making the habitat unsuitable for native species.
$4$. Example: The introduction of the Nile Perch into Lake Victoria in East Africa led to the extinction of more than $200$ species of native cichlid fish.

(N/A) The history of life on Earth,as revealed by fossil records,shows that large-scale loss of species has occurred previously,even before the appearance of humans.
During the long period of over $3$ billion years since the origin and diversification of life,there have been five episodes of mass extinction.
The 'Sixth Extinction' currently in progress is distinct from previous episodes.
- The primary difference lies in the rate of extinction; current rates are estimated to be $100$ to $1,000$ times faster than in pre-human times,and human activities are directly responsible for this acceleration.
Ecologists warn that if current trends persist,nearly half of all species on Earth could be wiped out within the next $100$ years.
Historical evidence,such as the colonization of tropical Pacific Islands by humans,led to the extinction of more than $2,000$ species of native birds.
The $IUCN$ Red List $(2004)$ documents the extinction of $784$ species,with $27$ species disappearing in the last twenty years alone.

(N/A) Human activities have accelerated the rate of species extinction from the Earth. The four main causes,collectively known as the 'Evil Quartet',are responsible for the loss of biodiversity:
$(A)$ Habitat loss and fragmentation: This is the most significant cause driving the extinction of both plant and animal species. For example,due to habitat loss,the Earth's land surface covered by tropical rainforests has shrunk from $14 \%$ to only $6 \%$ in recent years. The Amazon rainforest,often called the 'lungs of the planet',is being cleared for soybean cultivation or converted into grasslands for cattle ranching. Additionally,habitat degradation due to pollution threatens many species. When large habitats are fragmented into smaller pieces by human activities,mammals and birds requiring large territories,as well as migratory animals,are severely affected,leading to population declines.
$(B)$ Over-exploitation: Humans have always depended on nature for food and shelter. However,when human needs turn into greed,it leads to the over-exploitation of natural resources. Many species have become extinct in the last $500$ years due to over-exploitation,such as the Steller's sea cow and the passenger pigeon. Currently,many marine fish populations are being over-harvested,threatening the survival of commercially important species.
$(C)$ Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose,some of them turn invasive and cause the decline or extinction of indigenous species. For example,the Nile perch introduced into Lake Victoria in East Africa led to the extinction of an ecologically unique assemblage of more than $200$ species of cichlid fish in the lake.
$(D)$ Co-extinctions: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct. For example,when a host fish species becomes extinct,its unique assemblage of parasites also meets the same fate.

(D) Water hyacinth $(Eichhornia \text{ } crassipes)$ was introduced in India primarily because of its beautiful flowers and unique shape of leaves.
However, it later became a problematic invasive weed because it propagates vegetatively at a phenomenal rate and spreads all over the water body in a short period of time, making it difficult to eliminate.

(A) Parthenium hysterophorus,commonly known as carrot grass or congress grass,was introduced into India accidentally as a contaminant in imported wheat shipments. It has since become a widespread invasive weed across the country.

(D) When an alien species is introduced into a new habitat,it often becomes invasive because it lacks its natural predators and competitors that would normally keep its population in check in its native environment. This release from natural enemies allows the species to proliferate rapidly and outcompete native species for resources. Additionally,favorable environmental conditions,such as soil fertility or climate,can further facilitate this rapid expansion. Therefore,all the given factors contribute to the invasive nature of alien species.

(A) According to the $IUCN$ Red List $(2004)$ documents,the recent extinction of species is a major concern for global biodiversity.
Specifically,the data indicates that $12 \%$ of all bird species and $32 \%$ of all amphibian species currently face the threat of extinction.
Therefore,$X = 12 \%$ and $Y = 32 \%$.

(A) According to the fossil record and evolutionary history,there have been $5$ major mass extinction events in the history of life on Earth since the origin of life approximately $3.5$ to $3.8$ billion years ago. These events are known as the 'Big Five' mass extinctions. Therefore,the correct answer is $5$ times.

(D) The loss of biodiversity is primarily attributed to four major causes,which are collectively known as the '$Evil Quartet$'.
$1$. $Habitat$ loss and fragmentation: This is the most important cause driving animals and plants to extinction.
$2$. Over-exploitation: Humans have always depended on nature for food and shelter,but when '$need$' turns to '$greed$',it leads to over-exploitation.
$3$. Alien species invasions: When alien species are introduced unintentionally or deliberately,some of them turn invasive and cause the decline or extinction of indigenous species.
$4$. Co-extinctions: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct.

(A) The Caspian tiger $(Panthera \text{ tigris virgata})$ is an extinct subspecies of tiger that was once found in the region around the Caspian Sea. It is a classic example of a species that has gone extinct due to human activities and habitat loss.

(C) The term 'The Evil Quartet' is used to describe the four major causes of biodiversity loss.
These four causes are:
$1$. Habitat loss and fragmentation.
$2$. Over-exploitation.
$3$. Alien species invasions.
$4$. Co-extinctions.
Therefore,option $C$ is the correct answer.

(C) Overexploitation refers to the excessive harvesting of a species for human needs,which leads to its extinction. The $Steller's$ sea cow and the Passenger Pigeon are classic examples of species that went extinct due to overexploitation by humans. The Thylacine (Tasmanian wolf) also went extinct due to human hunting. However,in the context of $NCERT$,the Passenger Pigeon is a primary example cited for extinction due to overexploitation.

(B) The introduction of the Nile perch,an alien predator fish,into Lake Victoria in East Africa led to the extinction of more than $200$ species of cichlid fish in the lake. This is a classic example of biodiversity loss due to the invasion of alien species.

(A) Lake Victoria in East Africa is famous for its high biodiversity of $Cichlid$ fish.
When the $Nile \text{ } Perch$ (an alien predator fish) was introduced into Lake Victoria, it led to the extinction of more than $200$ species of $Cichlid$ fish, which were endemic to the lake.
Therefore, $Cichlid$ is the correct answer as it represents the group of endemic fish species that were native to Lake Victoria.

(B) Co-extinction is a phenomenon where the extinction of one species leads to the extinction of another species that is obligatorily associated with it.
For example,when a host fish species becomes extinct,its unique assemblage of parasites also meets the same fate.
Another example is the co-evolved plant-pollinator mutualism,where the extinction of one inevitably leads to the extinction of the other.

(B) The introduction of the Nile Perch, an alien predator fish, into Lake Victoria in East Africa led to the extinction of an ecologically unique assemblage of more than $200$ species of Cichlid fish in the lake.
Therefore, $X = \text{Cichlid}$ and $Y = 200$.

(C) Eichhornia crassipes,commonly known as water hyacinth,is an invasive aquatic weed.
It was introduced in India for its beautiful flowers but became a major environmental problem as it grows rapidly in water bodies,causing an imbalance in the aquatic ecosystem.
Parthenium and Lantana are also invasive weeds,but they are terrestrial,not aquatic.

(A) The introduction of the Nile Perch $(Lates \text{ niloticus})$ into Lake Victoria in East Africa caused the extinction of an ecologically unique assemblage of more than $200$ species of Cichlid fish in the lake. This is a classic example of biodiversity loss due to the introduction of alien species.

(C) The correct matches for the extinct species and their regions are as follows:
$(a)$ Dodo was native to Mauritius.
$(b)$ Quagga was native to Africa.
$(c)$ Thylacine was native to Australia.
$(d)$ Steller's sea cow was native to Russia.
Therefore, the correct matching is $a-3, b-1, c-4, d-2$.

(B) $Eichhornia crassipes$,commonly known as Water Hyacinth,is an invasive aquatic weed.
It was introduced in India for its beautiful flowers but became a major problem because it grows at an alarming rate in water bodies.
It drains oxygen from the water,which leads to the death of fishes and other aquatic organisms.
Due to its rapid spread and the destruction it causes to aquatic ecosystems in West Bengal,it is famously referred to as the 'Terror of Bengal'.

(C) $Eichhornia$ $crassipes$ (Water Hyacinth) was introduced in India for its beautiful flowers and leaves for ornamentation. However, it grew uncontrollably in water bodies, causing an imbalance in the ecosystem and becoming a troublesome weed, often referred to as the 'Terror of Bengal'.

(A) The introduction of high-yielding varieties (HYVs) has led to a significant reduction in genetic diversity. Farmers often replace traditional,locally adapted landraces with a few genetically uniform high-yielding varieties to maximize production. This practice creates a monoculture,making crops more susceptible to diseases and pests,and results in the loss of valuable genetic traits present in traditional varieties.

(D) An introduced,alien,exotic,non-indigenous,or non-native species is a species living outside its native distributional range,which has arrived there by human activity,either deliberate or accidental.
These terms are synonyms used to describe organisms that have been transported by humans to a new geographic region where they do not naturally occur.
Therefore,all four terms ($I, II, III,$ and $IV$) are correct synonyms for exotic species.

(C) Exotic species become invasive when they are introduced into a new environment where they lack their natural predators. In their native habitat,natural predators keep their population in check. In the absence of these predators in the new environment,the species faces no biological control,allowing its population to grow exponentially and spread rapidly.

(D) Exotic species are those that are introduced into a new environment from their native range. $Parthenium$ (carrot grass),$Lantana$ $camara$,and $Eichhornia$ $crassipes$ (water hyacinth) are all well-known examples of invasive exotic species in India that have caused significant damage to native biodiversity. Therefore,all the given options are correct.

(B) Taxa whose numbers have been reduced to a critical level or whose habitats have been so drastically reduced that they are deemed to be in immediate danger of extinction are called endangered species.
These species require immediate conservation efforts and proper care to prevent them from becoming extinct.
Examples include the lion-tailed macaque,crocodile,musk deer,and rhinoceros.

(C) The four major causes of biodiversity loss,often referred to as the 'Evil Quartet',are habitat loss and fragmentation,over-exploitation,alien species invasion,and co-extinction. These factors significantly contribute to the decline of species worldwide.

(D) species that is facing an extremely high risk of extinction in the wild in the immediate future is classified as $Critically \text{ } Endangered$.