Biologist warns of Earth's 6th mass extinction event which may hurt human health

Harold Mandel's picture
Planet Earth
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The planet Earth is not actually in very good health. On a daily basis hunting, fishing, pollution, wars and natural disasters undermine the ecological environment of the planet. Those who wish to live in denial of the potential catastrophe on the planet which could result from this state of affairs appear to think those who are concerned about the health of the planet are left wing radical fanatics who are out of touch with the realities of the needs of day to day existence as they attempt to somehow undermine progress. This is far from the truth. In fact the planet may be facing a new mass extinction which may dramatically harm human health.

A global wave of loss of biodiversity is happening now

We are existing amidst a global wave of loss of biodiversity reported the journal Science. There are total destruction of species and populations occurring alongside critical declines in local species abundance. The impact of people on animal biodiversity is now being viewed as an under-recognized form of global environmental change.

Ever since 1500 322 species of terrestrial vertebrates have become extinct. Populations of the remaining species have demonstrated a 25 percent average decline in abundance. There has also been a crisis among invertebrates. Monitoring of invertebrate populations shows that 67 percent of monitored populations show a 45 percent mean abundance decline. Scientists think such declines in animals will cascade onto ecosystem functioning and ultimately human well-being.

Defaunation is a pervasive component of the planet’s sixth mass extinction

Scientists see defaunation as being both a pervasive component of the planet’s sixth mass extinction and also a primary driver of global ecological change. Defaunation is defined as a process in an ecosystem during which top predators and herbivores are declining because of anthropogenic pressures.

A Stanford University biologist has warned of the early stages of Earth's 6th mass extinction event reports the Stanford News Service in a discussion of this research. Stanford Biology Professor Rodolfo Dirzo and his colleagues have warned that defaunation could have harmful downstream effects on the health of people. The are 3.5 billion years of evolutionary trial and error behind the planet's current biodiversity. This biodiversity may now be reaching a tipping point.

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The present die-off is associated with human activity

An international team of scientists has warned that the loss and decline of animals is contributing to what appears to be the early days of the planet Earth's sixth mass biological extinction event. Previous extinctions on Earth have been driven by natural planetary transformations or by catastrophic asteroid strikes. The present die-off is viewed as being associated to human activity. This is a situation that Dirzo has designated as an era of "Anthropocene defaunation."

The largest animals, which are described as megafauna which includes elephants, rhinoceroses, polar bears and many other species worldwide, are being confronted with the highest rate of decline. This trend matches previous extinction events. There are lower population growth rates among larger animals who tend to produce fewer offspring. These larger animals need larger habitats to maintain viable populations. Because of their size and meat mass they are easier and more attractive hunting targets for people.

Even though these species actually represent a relatively low percentage of all the animals at risk, their loss would have trickle-down effects which could undermine the stability of other species and, in some cases, even human health. Consider herein previous experiments in Kenya where it was observed how an ecosystem reacts to the removal of its largest species such as zebras, giraffes and elephants. It has been observed these areas become quickly overwhelmed with rodents.

Risk of disease transmission increases with defaunation

As the number of rodents doubles so does the abundance of the disease-carrying ectoparasites which they are found to harbor. Dirzo says where human density is high you see high rates of defaunation, high incidence of rodents, and therefore high levels of pathogens. This increases the risks of disease transmission. This can become a vicious circle.

There has been a similar disturbing trend in invertebrate defaunation. While the human population has doubled in the past 35 years the number of invertebrate animals such as beetles, butterflies, spiders and worms has fallen by 45 percent. As is being seen with larger animals the loss is driven primarily by the loss of habitat and global climate disruption. This could result in trickle-up effects in our everyday lives.

Consider that insects pollinate about 75 percent of the world's food crops. This is an estimated 10 percent of the economic value of the entire world's food supply. Insects also play a very important role in nutrient cycling and decomposing organic materials which helps to ensure ecosystem productivity. The value of pest control by native predators is enormous.

As Dirzo points out increasing awareness of the ongoing mass extinction and its associated consequences should help to spark initiatives for change. Defaunation is emerging as a critical phenomenon with clearing consequences to the planet and to the wellbeing of the human species. If we ignore this problem mankind may pay a critical price. The time to act on preserving the ecosystem is now.

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