Biodiversity loss pushing Earth towards sixth mass extinction

As per a review by Stamford researchers published in Science magazine, the danger is decline of biodiversity lurking near us which may lead to an era of ‘Anthropocene defaunation’.

Scientists in the review are warning that the persistent loss and decline of biodiversity is leading humanity to early days of the planet’s sixth mass biological extinction event.

As per the Science magazine review

• Since 1500 AD, more than 320 terrestrial vertebrates have become extinct.
• Populations of the remaining species which were in abundance previously, now show a 25 per cent average decline.
• The previous extinctions have been driven by natural planetary transformations or catastrophic asteroid strikes, the current extinction can be associated with human activity, leading to an era of ‘Anthropocene defaunation’. The loss is driven primarily by loss of habitat and global climate disruption.
• Across vertebrates, 16-33 per cent of all species are estimated to be globally threatened or endangered.
• Large animals which are described as megafauna and including elephants, rhinoceroses, polar bears and countless other species worldwide are facing the highest rate of decline. This decline trend matches previous extinction events.
• The population of rodents is increasing leading to the abundance of the disease-causing ectoparasites.
• Where human density is high, there are high rates of defaunation, high incidence of rodents and thus high levels of pathogens, which increases the risks of disease transmission.
• The scientists also detailed a troubling trend in invertebrate defaunation.
• Human population has doubled in the past 35 years; in the same period, the number of invertebrate animals such as beetles, butterflies, spiders and worms has decreased by 45 per cent.
• As with larger animals, the loss is driven primarily by loss of habitat and global climate disruption, and could have trickle-up effects in our everyday lives.
• Reducing rates of habitat change and over exploitation would help but these approaches need to be tailored to individual regions and situations.
• We tend to think about extinction as loss of a species from the face of Earth but there is a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well.

What is Biodiversity?

Biodiversity means the variability of life in all its forms i.e. the diversity of species, of genetic variations within one species, and of ecosystem.

It has great importance on human society but hard to overstate.

40 per cent of the global economy is based on the biological products and processes.

Large proportion of world population living in areas of low agricultural productivity , depend heavily on the genetic diversity of the environment.

Latitudinal Diversity Gradient

Terrestrial biodiversity is highest at low latitudes near the equator. The main reason is due to warm climate and high primary productivity.

The increase in species richness or biodiversity that occurs from the poles to the equator (tropics) is referred as Latitudinal Diversity Gradient.

Marine biodiversity is highest along coasts in the Western Pacific as the sea surface temperature is highest. It is also high at mid-latitudinal band in all the oceans.

Note- Terrestrial biodiversity is upto 25 times greater than ocean diversity.

What is the concept of Mass Extinction?

Biodiversity in current form is the result of 3.5 billion years of evolution.

As per current scientific theory, the origin of life or biopoiesis started around 3900 million years ago (MYA).

The earliest known life on Earth existed between 3900- 3500 MYA during the Eoarchean Era (during this period sufficient crust solidified)

Approximately 600 MYA, all life was in the form of archaea, bacteria, protozoans and similar single-celled organisms.

Around 542 million years ago, Cambarian explosion occurred. During this period phylum of multicellular organisms first appeared. Afterwards, there was dramatic rise in the species of both vertebrates and invertebrates.

This rise of diversity was marked by the periodic, massive losses of diversity is classified as mass extinction events.

Since life began on Earth, 5 major mass extinctions have led to large and sudden drops in biodiversity.

1. Ordovician- Silurian extinction event- This was the first mass extinction of biodiversity which took happened 450-440 MYA.
2. Late Devonian extinction- Occurred 375-360 MYA.
3. Permian-Triassic extinction- Occurred 251 MYA. It is called Earth’s largest extinction. This extinction event ended the primacy of mammal-like reptiles on land. After this event vertebrates took 30 million years
4. Triassiac-Jurassic extinction- Occurred 200 MYA. This extinction period eliminated most of the non-dinosaurian archosaurs, most therapsids and most of the large amphibians.
5. Cretaceous-Paleogene extinction- Occurred 65.5 MYA. Major non-avian dinosauurs became extinct during that time. Mammals and birds emerged.

There were several other minor events of extinction also such as the Carboniferous rainforest collapse (359.2 MYA) which led to great loss of plant and animal life. 

The fossil fuel that we are using today, was the result of this Carboniferous rainforest collapse.