20 public questions tagged with this topic.
Co-extinction occurs when the extinction of one species results in the extinction of another species that depends on it.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Alien Invasion Co-extinction Mass Extinction - Evil Quartet
The Passenger Pigeon became extinct mainly because of overexploitation by humans and is cited in NCERT as an example of this cause of biodiversity loss.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Alien Invasion Co-extinction Mass Extinction - Evil Quartet
The present extinction rate is estimated to be 100–1000 times higher than the natural extinction rate because of human activities.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Causes - Habitat Loss Overexploitation
Human activities have accelerated extinction rates to about 100–1000 times the natural background rate through habitat loss and fragmentation, overexploitation, alien species invasions, and co-extinctions.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Causes - Habitat Loss Overexploitation
The NCERT "Evil Quartet" consists of habitat loss and fragmentation, overexploitation, alien species invasions, and co-extinctions. Pollution is not included in this list.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Causes - Habitat Loss Overexploitation
NCERT cites the Passenger pigeon as an example of extinction caused by overexploitation by humans.
Ref: NCERT Class 12 Biology Chapter 13: Biodiversity and Conservation Loss of Biodiversity - Causes - Habitat Loss Overexploitation
cretaceous reflects key principle in quiz on geological time scale+pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, cretaceous aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why cretaceous fits helps integrate natural selection, environment.
Ref: USGS, Geological Time Scale, Eons and Eras.
Extinction of Trilobita finally occurred during end-Permian mass extinction about 252 million years ago, the most severe Phanerozoic crisis linked to Siberian Traps flood basalt volcanism, global warming, ocean anoxia, hypercapnia and acidification eliminating roughly 96 percent marine species. Trilobites already in decline after Late Devonian extinctions could not recover, disappearing with reef builders and many brachiopods. Triassic extinction affected crurotarsal archosaurs, Cretaceous extinction eliminated non-avian dinosaurs at 66 million years, Ordovician extinction reduced many marine taxa but trilobites survived, making Permian boundary terminal for the group.
Ref: NCBI Bookshelf, Mass Extinctions – Permian Trilobite Extinction; Campbell Biology, 12th ed., Chapter 25
“Over a long period of time” for colonization rates balanced by extinction rates. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Island biogeography explains species richness as a dynamic balance between immigration and extinction. Immigration generally declines as an island fills with species, whereas extinction rises as more species divide finite area and maintain smaller populations. The remaining alternatives—“Initially, then diverge”, “Only on large islands”, “Only on small islands”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Larger islands usually support more habitats and larger populations, lowering extinction risk; less isolated islands receive colonists more readily and may experience rescue effects. These mechanisms also apply to habitat fragments that function as ecological islands. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.
Ref: The Theory of Island Biogeography, MacArthur & Wilson, Ch. 2-4
“Common and frequent” for species turnover on islands is. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Island biogeography explains species richness as a dynamic balance between immigration and extinction. Immigration generally declines as an island fills with species, whereas extinction rises as more species divide finite area and maintain smaller populations. The remaining alternatives—“Rare and infrequent”, “Nonexistent”, “Always decreasing”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Larger islands usually support more habitats and larger populations, lowering extinction risk; less isolated islands receive colonists more readily and may experience rescue effects. These mechanisms also apply to habitat fragments that function as ecological islands. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.
Ref: The Theory of Island Biogeography, MacArthur & Wilson, Ch. 2-4
“Colonization and extinction rates” for according to island biogeography theory, species number depends on. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Larger islands usually support more habitats and larger populations, lowering extinction risk; less isolated islands receive colonists more readily and may experience rescue effects. These mechanisms also apply to habitat fragments that function as ecological islands. The remaining alternatives—“Birth rate and death rate”, “Immigration and speciation”, “Predation and competition”—refer to different states, processes, or scales and therefore do not express the same causal relationship. At equilibrium, species identities can continue to turn over even when richness is approximately stable. The model predicts a balance of rates, not an absence of colonization or extinction. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.
Ref: The Theory of Island Biogeography, MacArthur & Wilson, Ch. 2-4
Metapopulation persistence depends on a dynamic balance between local extinction and colonization. When a patch population disappears, dispersers from occupied patches can establish a new local population, a process called recolonization. If recolonization rates are sufficient relative to extinction rates, the species can persist regionally even though no particular patch is occupied continuously. In the classic Levins model, the fraction of occupied patches changes as colonization creates new occupancy and extinction removes it. Dispersal is the movement mechanism that makes recolonization possible, but recolonization is the demographic event that directly counterbalances extinction of an already empty patch. This differs from the rescue effect, in which immigrants reduce the probability that a still-occupied local population will go extinct. Speciation and aggregation do not restore occupancy on the relevant ecological timescale. Patch isolation, matrix hostility, propagule supply, and habitat quality all influence recolonization success. Conservation corridors can therefore support regional persistence by allowing colonists to reach vacant suitable habitat, even when local environmental fluctuations continue to cause extinctions.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 9
