MEVE 014: Unit 07 - Extinction of Biodiversity

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 UNIT 7: EXTINCTION OF BIODIVERSITY

7.0 Introduction

Extinction is a natural process, but in recent centuries, the rate and scale of species extinction have accelerated alarmingly due to human activities. Biodiversity extinction not only signifies the permanent loss of unique life forms but also disrupts ecosystems, threatens human well-being, and accelerates global environmental crises. Understanding extinction—its types, causes, rates, and implications—is crucial for conservation strategies and biodiversity management.

7.1 Objectives

After studying this unit, you will be able to:

  • Understand the concept and types of biodiversity extinction.
  • Learn about the IUCN Red List categories.
  • Examine the phenomenon of the Sixth Mass Extinction.
  • Analyze extinction rates in different environments.
  • Understand the concept of vulnerability to extinction.
  • Explore the implications of biodiversity loss on ecosystems and human society.

7.2 Types of Extinctions

Extinction can be categorized in several ways:

  • Local Extinction: A species disappears from a particular geographical area but exists elsewhere.
  • Ecological Extinction: Species become so rare that they no longer play a significant role in ecosystem functioning.
  • Biological (Global) Extinction: The complete disappearance of a species from the Earth.
  • Mass Extinction: A rapid and widespread decrease in the diversity of life forms, usually caused by catastrophic global events.
  • Background Extinction: The standard rate of extinction in Earth's history before human influence.

7.3 IUCN Threatened Categories

The International Union for Conservation of Nature (IUCN) provides a global framework for assessing the conservation status of species. The key categories include:

  • Extinct (EX) – No known individuals remaining.
  • Extinct in the Wild (EW) – Only survives in cultivation or captivity.
  • Critically Endangered (CR) – Extremely high risk of extinction in the immediate future.
  • Endangered (EN) – Very high risk of extinction in the near future.
  • Vulnerable (VU) – High risk of extinction in the medium term.
  • Near Threatened (NT) – Close to qualifying for a threatened category.
  • Least Concern (LC) – Low risk of extinction.
  • Data Deficient (DD) – Inadequate information to assess risk.

7.4 Sixth Extinction/Biological Crisis

The Earth has witnessed five major mass extinctions in its history. The Sixth Mass Extinction, however, is unique as it is human-induced. Key features include:

  • Driven by habitat destruction, climate change, pollution, overexploitation, and invasive species.
  • Occurring at rates 100 to 1,000 times faster than natural background rates.
  • Affecting both terrestrial and marine ecosystems.
  • Threatening the survival of millions of species, including large mammals, amphibians, and pollinators.

This biological crisis is not only an environmental concern but a humanitarian one, affecting ecosystem services and human livelihoods.

7.5 Rate of Extinction

Estimating extinction rates is complex, but current findings indicate alarming trends:

  • Natural Background Rate: Approximately 1 species per million per year.
  • Current Rate: Estimated at 100–1,000 times the background rate.

7.5.1 Extinction Rate in Aquatic Environments

  • Marine species face threats from ocean acidification, pollution, overfishing, and coral bleaching.
  • Coral reefs are declining globally, endangering marine biodiversity hotspots.
  • Freshwater species are among the most threatened due to damming, water extraction, and contamination.

7.5.2 Extinction Rate in Terrestrial Environments

  • Forest clearing, urbanization, and agriculture are leading causes of habitat loss.
  • Amphibians, reptiles, and large mammals are highly vulnerable.
  • Mountain, grassland, and tropical forest ecosystems are experiencing rapid declines in species.

7.5.3 Extinction Rate in Island Environments

  • Islands harbor many endemic species with limited ranges.
  • Invasive species, habitat loss, and hunting have caused disproportionate extinction on islands.
  • Over 50% of known extinctions since 1500 have occurred on islands.

7.6 Local Extinctions

Local extinctions, while not global, can significantly disrupt ecosystem function:

  • Lead to trophic cascades (e.g., disappearance of apex predators).
  • Reduce genetic diversity and adaptability of metapopulations.
  • Affect ecological services like pollination and seed dispersal.
  • Serve as early warning indicators of broader environmental problems.

7.7 Vulnerability to Extinction

Species are not equally vulnerable. Factors increasing extinction risk include:

  • Restricted geographic range (e.g., endemics).
  • Small population size or low reproductive rate.
  • Specialized habitat or diet requirements.
  • Low genetic diversity.
  • Sensitivity to environmental changes.
  • Human exploitation (e.g., hunting, trade).
  • Poor dispersal ability.
  • Dependence on mutualistic relationships.

Examples:

  • The Dodo (extinct due to hunting and invasive species).
  • Amphibians (vulnerable to diseases and pollution).
  • Tigers (vulnerable due to poaching and habitat fragmentation).

7.8 Let Us Sum Up

  • Biodiversity extinction includes local, global, ecological, and mass extinctions.
  • The IUCN Red List is a key tool for identifying species at risk.
  • The current Sixth Mass Extinction is primarily human-driven.
  • Extinction rates vary across aquatic, terrestrial, and island ecosystems.
  • Many species are vulnerable due to biological, ecological, and anthropogenic factors.
  • Preventing extinctions requires urgent, science-based conservation action.

7.9 Keywords

  • Extinction – The permanent loss of a species.
  • IUCN Red List – Global inventory for species' extinction risk.
  • Sixth Mass Extinction – Ongoing human-caused biodiversity crisis.
  • Endemic Species – Species confined to a particular region.
  • Local Extinction – Disappearance of a species from a specific area.
  • Vulnerability – Degree of susceptibility to extinction.

 

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