Humans have played a significant role in reshaping the Earth's biodiversity. From habitat destruction to direct hunting, many species have been pushed to extinction due to anthropogenic activities. Understanding these causes is essential in this era of the sixth mass extinction.
1. Causes of Anthropogenic Species Extinctions
Human-induced changes to the environment have resulted in the decline or outright extinction of numerous species. Delving deeper into these causes:
Habitat Destruction
Deforestation
- Vast areas of forests, especially tropical rainforests, are being cleared at alarming rates for agriculture, urbanisation, and infrastructure.
- This not only removes the direct habitats of numerous species but also fragments the remaining habitats, making them less viable for many species.
- Examples: Amazon rainforest in Brazil, Bornean forests in Indonesia.
The Namanve forest area that was cleared for an industrial park.
Image courtesy of Davidwandeka
Deforestation in the state of Rondônia in western Brazil.
Image courtesy of NASA
Wetland Draining
- Wetlands, essential for various amphibians, birds, and aquatic species, are drained for purposes ranging from agriculture to construction.
- They play crucial roles in water purification and flood control.
- Examples: Florida Everglades in the USA, Mesopotamian Marshes in Iraq.
Pollution
Water Pollution
- Industrial waste, untreated sewage, and agricultural run-offs lead to eutrophication in freshwater bodies, affecting aquatic life.
- Oil spills in oceans have catastrophic impacts on marine ecosystems.
Air Pollution
- Industrial and vehicular emissions contribute to acid rain. This acidic precipitation harms freshwater systems and soils, affecting plants and the broader ecosystem.
Land Pollution
- Improper waste disposal, especially non-biodegradable waste, contaminates soil and groundwater.
- Use of pesticides and fertilisers in agriculture contaminates soils, affecting plants and soil-dwelling organisms.
Water pollution due to domestic garbage at RK Beach in Visakhapatnam
Image courtesy of Adityamadhav83
Overexploitation
Overhunting and Overfishing
- Unsustainable hunting and fishing practices lead to a sharp decline in many species.
- Examples: The passenger pigeon, once numbering in the billions, was hunted to extinction in the 20th century.
Pet Trade and Medicine
- Many species, especially reptiles, birds, and some mammals, are captured and sold, often illegally.
- Rhino populations are threatened due to poaching for their horns, believed to have medicinal properties in some cultures.
Introduced Species
Invasiveness
- Non-native species introduced to new environments can outcompete, prey on, or bring diseases to native species.
- Without natural predators, these invasive species thrive, altering native ecosystems.
- Examples: Cane toads in Australia, grey squirrels in the UK.
Cane Toad - Bufo marinus
Image courtesy of CSIRO
Grey squirrel (Sciurus carolinensis)
Image courtesy of Charles J. Sharp
Climate Change
Temperature and Weather Patterns
- Changes in global temperature and unpredictable weather patterns directly affect habitats and food availability for various species.
Melting Ice Caps
- Polar species, like polar bears and penguins, face habitat losses due to melting ice caps.
Globalisation
Spread of Diseases and Pests
- Increased movement of goods and people can introduce diseases or pests, which might decimate local species not adapted to these new threats.
2. Case Studies: Extinct Species
North Island Giant Moas
- Scientific Name: Dinornis novaezealandiae
- Location: Formerly native to North Island, New Zealand.
- Characteristics: These flightless birds, without any natural predators, could weigh up to 250 kg and reach heights of 3.6 meters.
- Reasons for Extinction:
- Overhunting: The Māori, upon their arrival, hunted them primarily for food.
- Habitat Destruction: Forest clearances for agriculture and settlements further diminished their habitats.
Image courtesy of Takver
Caribbean Monk Seals
- Scientific Name: Neomonachus tropicalis
- Location: Once found throughout the Caribbean Sea.
- Characteristics: These medium-sized seals had a diet mainly of fish and crustaceans, making them vital for maintaining a balance in their marine ecosystem.
- Reasons for Extinction:
- Overhunting: Hunted extensively by European settlers for their oil-rich blubber, meat, and hides.
- Habitat Degradation: Coastal development and pollution decreased suitable habitats.
- Reduced Prey Availability: Overfishing and pollution reduced their primary food sources.
Image courtesy of Henry Wood Elliott
FAQ
Global trade and transportation have made the movement of goods and people faster and more widespread than ever. While this has economic and social benefits, it also poses environmental threats. Non-native species can be transported, either intentionally or accidentally, to new regions via trade and transportation. When these introduced species find the new environment suitable and lack natural predators, they can become invasive, threatening local biodiversity. Additionally, the global movement can introduce pathogens that might devastate local species populations, as they lack immunity against these foreign diseases.
Agriculture and farming, especially when practised unsustainably, can be significant contributors to species extinction. For starters, large swathes of natural habitats are often cleared to make way for farmland, leading to habitat destruction. Moreover, the use of pesticides, herbicides, and fertilisers can introduce harmful chemicals into the environment, affecting non-target species and polluting waterways. Overgrazing by livestock can degrade land and reduce its suitability for native species. Furthermore, intensive farming can lead to soil erosion, reducing the quality of habitats for many terrestrial species.
The term "sixth" mass extinction recognises that Earth has witnessed five major mass extinctions in its history, where a significant portion of life was wiped out in a relatively short geological timespan. These occurred at the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous periods. The causes ranged from volcanic eruptions, asteroid impacts, to sudden climate changes. The current mass extinction, driven primarily by human activities, is resulting in a rapid loss of species at rates comparable to or even exceeding those of the past. Hence, it's often referred to as the "sixth" to denote its severity and significance in Earth's history.
Apex predators play a crucial role in maintaining the health and balance of ecosystems. They regulate the populations of herbivores and smaller predators, ensuring that they don't overexploit resources. When apex predators are removed, often due to human activities like hunting or habitat destruction, it can lead to a trophic cascade. This is where the balance between predators and prey at different levels of the food chain is disrupted. Overpopulation of herbivores, for instance, can result in overgrazing, leading to habitat degradation. Such imbalances can cause a decline in overall biodiversity as species interactions are thrown off-kilter and certain species dominate at the expense of others.
Urbanisation, the transformation of areas from rural to urban, often involves land conversion and results in significant habitat destruction. As cities and towns expand, forests, wetlands, and grasslands can be replaced by buildings, roads, and other infrastructure. This directly destroys the habitats of numerous species, causing immediate displacement. Furthermore, urban areas can fragment the remaining habitats, making them less viable for the species that used to reside there. Urban areas can also increase pollution due to higher densities of vehicles and industries. This pollution affects nearby habitats, further exacerbating the negative impacts on biodiversity.
Practice Questions
Habitat destruction is one of the significant anthropogenic causes of species extinctions. For instance, deforestation in New Zealand played a critical role in the decline of the North Island Giant Moa, as vast areas of its habitat were cleared for agriculture and settlements. Another crucial cause is overexploitation, where species are unsustainably hunted, fished, or harvested. The Caribbean Monk Seal, once found throughout the Caribbean Sea, faced extinction largely due to overhunting by European settlers who sought their oil-rich blubber, meat, and hides. These activities drastically reduced their numbers leading to their eventual extinction.
Introduced or invasive species pose a significant threat to native biodiversity because they can outcompete, prey upon, or bring diseases to native species. Often, these invasive species flourish in new environments as they lack natural predators, allowing them to quickly dominate and alter native ecosystems. An example of this is the introduction of the grey squirrel in the UK. Originally from North America, the grey squirrel outcompeted the native red squirrel for food and introduced a disease called squirrelpox, which is lethal to red squirrels. This led to a decline in red squirrel populations in areas where the grey squirrel became established.
