Scientists sound the alarm of next mass extinction

Scientists warn we are on the brink of the next major mass extinction event

Scientists warn we are on the brink of the next major mass extinction event

 

Biologists (yet again) sound the alarm in this latest article via Stanford News Service, warning that 16 to 33 percent of vertebrates are now endangered. Larger animals such as elephants, rhinos and polar bears face the highest decline rates, which follows in the pattern of past extinction events. The loss of such creatures would mean devastating trickle-down effects on the human population and other species.

[P]revious experiments conducted in Kenya have isolated patches of land from megafauna such as zebras, giraffes and elephants, and observed how an ecosystem reacts to the removal of its largest species. Rather quickly, these areas become overwhelmed with rodents. Grass and shrubs increase and the rate of soil compaction decreases. Seeds and shelter become more easily available, and the risk of predation drops.Consequently, the number of rodents doubles — and so does the abundance of the disease-carrying ectoparasites that they harbor.

“Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission,” said Dirzo, who is also a senior fellow at the Stanford Woods Institute for the Environment. “Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle.”

Vertebrates aren’t the only species on a troubling path of defaunation. Over the last 35 years, while the human population has doubled, invertebrate numbers have plummeted by 45 percent.

Past mass extinctions were driven by planetary transformations or catastrophes, but the extinction we face today can be attributed to man-made causes.

This is far from the first time that scientists have cautioned us of the next looming mass extinction. Last month, The Week delivered a similar warning that we could be headed the way of the dinosaurs if we don’t address these crises immediately. In February, NPR concluded the mass extinction is already underway.

In the words of Neil deGrasse Tyson:

We just can’t seem to break our addiction to the kinds of fuel that will bring back a climate last seen by the dinosaurs, a climate that will drown our coastal cities and wreak havoc on the environment and our ability to feed ourselves. All the while, the glorious sun pours immaculate, free energy down upon us, more than we will ever need. Why can’t we summon the ingenuity and courage of the generations that came before us? The dinosaurs never saw that asteroid coming. What’s our excuse?

Source:  dailykos.com

Evolution demographic schedule

Does Age Bring Death? Not For All Species:

Evolution

Evolution

Humans have a pretty straightforward view of aging: They’re born, they mature, they gradually become weaker and lose fertility, and eventually, they die.

But in nature, aging is far more diverse, new research finds. In fact, some animals are actually less likely to die the older they get — at least up to a point.

Understanding mortality

Evolutionary theorists working in the 1950s through 1970s explained the familiar pattern of increasing mortality with age as a trade-off between reproduction and survival. If an organism only has a certain number of resources, it has to decide whether to allocate them to creating offspring (searching for mates, wooing them and mating) or to surviving for another year.

“The question is how do you balance that,” Jones sad. “If you put everything into survival, you don’t reproduce very much or at all. If you put all your energy into reproduction, then you will have a low survival.”

No matter how healthy and resource-rich you are, there is always a slight chance that you’ll die. You could be hit by a bus, struck by lightning, or end up in the path of a rockslide. For this reason, Jones said, evolution favors those who reproduce early, before anything bad can befall them. Thus, genetic mutations that favor early reproduction, even at the expense of an organism’s later life, will be preserved.

Still, a few studies had revealed that some species don’t age as classical theory suggests, Jones said. Jellylike animals called hydras (Hydra magnipapillata) have low mortality rates that are constant throughout their lives. Hydra die so infrequently in laboratory conditions that researchers estimate it would take 1,400 years for 95 percent of a population to die of natural causes.

The desert tortoise (Gopherus agassizii) actually becomes less likely to die with age. The tortoises aren’t immortal, of course — they do still die. But their mortality rate in youth is actually higher than their mortality rate in old age. If they make it past their younger years, they’re likely to keep trucking until as old as 80 years of age.

A hydra, a small animal with constant mortality.

The diversity of aging

Most people who study aging focus on just a few species. Jones and his colleagues wanted a broader view, so they drew from across the tree of life, comparing aging patterns in 11 mammals, 12 other vertebrates (animals with backbones), 10 invertebrates, 12 plants and a green alga. They picked species for which there was good quality data on the life trajectory.

“We were restricting ourselves to the datasets which followed enough individuals that you had good pictures over the whole life course, which we defined as following 95 percent of the individuals until death,” Jones said.

The results highlighted the diversity between organisms, Jones said. “Mortality can go up [with age], it can stay constant, or it could go down,” he said. “And the same for fertility.”

At 102, the age at which 95 percent of humans are dead, a Japanese woman has 20 times the risk of mortality than the average for adult humans over the life span. In comparison, a white mangrove tree at the same so-called “terminal age” (123 years, for mangroves) is less than half as likely to die than the average adult of its species.

The Southern fulmar (Fulmarus glacialoides), a seabird, becomes more likely to die with age. But it also becomes more fertile as it grows older. Hydras have constant fertility rates their entire lives. And many animals other than humans have life spans that continue past their reproductive years, including killer whales (Orcinus orca), mynah birds (Leucopsar rothschildi) and nematode worms (Caenorhabditis elegans).

The diversity of mortality and aging is independent of life span, Jones added. It’s not only long-lived creatures like the desert tortoise that show declining or constant mortality with age. The collared flycatcher (Ficedula albicollis), a migratory black-and-white bird, lives only about five years, maximum — at that age, 95 percent of collared flycatchers are dead. But the flycatcher’s mortality is fairly constant throughout adulthood, not rising with age.

Challenging theory

The findings challenge the assumptions of classical theory, suggesting the old ideas need a tweak, Jones said.

“In order to make sense of what we’re seeing, theoreticians need to figure out why it is that we’re seeing these patterns and make sense of it,” he said.

It’s likely that body size plays a role, he said. Organisms that grow with age without stopping at a certain size, like some trees, may be less vulnerable in old age to environmental fluctuations or other threats. Fish that outgrow all of their predators are likely to make it to a ripe old age, for example.

Jones and his colleagues plan to study wider populations of species and to get a sense of the reasons behind the varying life spans. For example, does it matter whether a plant is a tree or a shrub? Do certain environments promote longevity?

“There’s good evidence that a lot of these plants that live a very long time tend to live in arid regions,” Jones said. “Aridity might have some kind of effect.”