By Luke Strotz, University of Kansas
Although they say "it is impossible to be certain of anything other than death and taxes", a little financial deception can keep you from paying the tax officer. But no amount of deceit will stop the inevitability of death. Death is the inevitable end point of life.
And this applies equally to species as to individuals. Estimates suggest that 99.99 percent of all species that have ever lived are now extinct. All species that exist today-including human beings-will invariably die out at some point.
Paleontologists like me know that there are key moments in the history of the earth when the extinction figures are high. For example, researchers have identified the Big Five mass extinctions: the five times in the past half a billion years or so, when more than three-quarters of the species were extinct in the short term. Unfortunately, we now also get a good idea of what extinction looks like, with the rapid increase in extinction rates in the past century.
But which factors make a species more or less vulnerable to extinction? The rate of extinction varies between different groups of animals and in the course of time, so clearly not all species are equally susceptible. Scientists have done an excellent job of documenting the extinction, but determining the processes that cause extinction has become somewhat more difficult.
Who is more vulnerable to extinction?
If we look at modern examples, some tipping points that lead to the extinction of a species become clear. Reduced population sizes is so & # 39; n factor. As the number of individuals of a species decreases, this can lead to reduced genetic diversity and a greater susceptibility to random catastrophic events. If the remaining population of a species is small enough, a single forest fire or even random variations in sex ratios can eventually lead to extinction.
Outbreaks that have occurred in the recent past receive a lot of attention – for example the dodo, thylacine or passenger pigeon. But the vast majority of extinctions occurred well before the appearance of people. The fossil record is thus the primary source of data about extinction.
When paleontologists consider fossils in the context of what we know about environments in the past, a clearer picture of what causes the extinction of species begins to appear. To date, the likelihood of extinction of a species has been associated with a large number of factors.
We are certain that changes in temperature are an important element. Almost every major rise or fall in world temperatures in earth history has resulted in the extinction of a strip of different organisms.
The size of the geographical area that a species occupies is also crucial. Species that are widely distributed will die less quickly than animal species that occupy a small area or whose habitat is incoherent.
There are also random phenomena that cause extinction. The meteorite responsible for the extinction of about 75 percent of life at the end of the chalk, including the non-avian dinosaurs, is perhaps the best example of this. This random aspect with extinction is the reason why some have argued that survive the happiest is perhaps a better metaphor for the history of life then Surviving the strongest.
Recently my colleagues and I have identified a physiological component for extinction. We found that the representative metabolic rate for both fossil and living mollusk species strongly predicts the likelihood of extinction. Metabolism rate is defined as the average rate of absorption and allocation of energy by individuals of that type. Mollusc species with higher metabolic rates will die out earlier than those with lower speeds.
Returning to the metaphor of survival of the fittest / luckiest & # 39 ;, this result suggests that & # 39; survival of the most lazy & # 39; can sometimes apply. Higher metabolic rates correlate with higher mortality rates for individuals in both mammals and fruit flies, so metabolism can represent an important control of mortality at multiple biological levels. Because the metabolic rate is linked to a constellation of characteristics, including growth rate, time to maturity, maximum life span and maximum population size, it seems likely that the nature of one or all of these characteristics plays a role in how vulnerable a species is with extinction. .
Many more extinction unknowns
As much as scientists know about extermination drivers, there is still a lot that we do not know.
For example, some of the species will die out regardless of an important ecological or biological upheaval. This is called the background extinction frequency. Because paleontologists tend to focus on mass extinctions, background extinction rates are poorly defined. How much, or how little, this rate fluctuates is not well understood. And in total, most extinctions probably fall into this category.
Another problem is determining how important changing biological interactions are when explaining extinction. For example, extinction of a species can occur when the abundance of a predator or a competitor increases, or when a crucial prey species is extinct. The fossil record, however, seldom catches such information.
Even the number of extinct species can be a mystery. We know very little about the current or previous biodiversity of micro-organisms, such as bacteria or archaea, let alone dying patterns for these groups.
Perhaps the biggest mistake we could make when it comes to assessing and declaring extinction, is adopting a one-size-fits-all approach. The vulnerability of a species to extinction varies over time and different biological groups react differently to changes in the environment. Although major changes in the global climate have led to extinction in some biological groups, the same events have ultimately led to the appearance of many new species in others.
So how vulnerable a kind of extinction is as a result of human activities or the associated climate change, sometimes remains an open question. It is clear that the current rate of extinction far exceeds everything that background level could be called, and that it is on track to be the sixth mass extinction. The question of how vulnerable each species – including ours – can be to extinction, is therefore a science that wants to respond quickly if we want to have a chance to preserve future biodiversity.
Luke Strotz, postdoctoral researcher in the paleontology of invertebrates, University of Kansas
This article was originally published on The conversation. Read the original article.
In short: a paleontologist discusses what makes some species more vulnerable to extinction.
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