Evolutionary Rescue: What It Is And How It Affects The Preservation Of Species
Climate change and anthropization take their toll on ecosystems and, therefore, experts estimate that 150 to 200 species of living beings become extinct every 24 hours. Habitats are not going through their best moment either, as it is also estimated that a total of 13.7 million hectares of forest are cut down per year around the world, the equivalent of the area occupied by Greece.
All these data show us a reality that is hard to recognize: the Earth is approaching a point of no return. Will nature be able to keep up with the changes introduced by humans? Do living beings have sufficient evolutionary strategies to cope with the dizzying pace of environmental variation? This question and many others try to be answered by evolutionary rescue theory We explain it to you below.
Human beings are in the sixth mass extinction (Holocene extinction), since the extinction rate of species today is 100 to 1,000 times the natural average in evolution. Unfortunately, these data have been supported by scientific evidence on multiple occasions.
According to the International Union for Conservation of Nature (IUCN) more than 32,000 taxa of living beings are in danger, that is: one in every eight species of birds, one in every four mammals, almost half of the amphibians and 70% of the plants. In summary, 27% of all species assessed by humans are in some threatened category.
This raises the following question for conservation professionals: Do living beings have tools to face the growing threat that is human action? How have some species survived other extinction events? The theory of evolutionary rescue tries to partially cover these answers, at least on paper.
Theoretical foundation of the theory of evolutionary rescue
In the face of climatic variation, Populations of living beings have three tools to endure over time:
Although in the short term dispersion phenomena may be the solution, Physical space is finite and the new territories explored are usually already occupied by other living beings For this reason, the persistence of species in a changing environment largely depends on their ability to evolve adaptively, that is, to specialize in new environmental variants before disappearing.
The theory of evolutionary rescue is based on this last point. In other words, proposes that living beings can recover from environmental pressures through advantageous genetic modification instead of placing all their “hopes” on gene flow, the migration of individuals or dispersal.
“Typical evolution” proposes that living beings evolve slowly, but we are no longer in a typical situation. Thus, a new concept of “contemporary evolution” is explored, or what is the same, that living beings can evolve more quickly in a short time to persist in the environment despite the rapid changes that occur in it.
Factors to take into account
Various factors play a key role in evolutionary rescue theory. We present them briefly in the following lines.
1. Demographic factors
Theoretical postulations stipulate that the size of the population evaluated is an essential factor to know whether evolutionary rescue can occur or not. In the populations There is a value called “minimum viable population” (MVP), the lower limit that allows a species to survive in nature When taxa are below this value, extinction becomes much more plausible due to stochastic or random processes, such as genetic drift.
Thus, the longer a population is below the MVP, the less likely it will be that an evolutionary rescue will occur. Furthermore, the faster the population decreases, the more the viability of this theory is reduced: The species must be given “time” to generate a viable adaptation before it is evoked into extinction
2. Genetic factors
The genetic variability of a species, the rate of mutations it presents and its rate of dispersion are also key for an evolutionary rescue phenomenon to take place in it.
Naturally, The greater the genetic variability of a population, the more likely rescue will be, since natural selection can act on a greater number of traits. In this way, the most suitable for that moment will be favored and, ideally, the least prepared will disappear and the population will fluctuate to the most effective change: adaptive evolution will occur.
The mutation rate should also promote evolutionary rescues, since non-deleterious or beneficial mutations are another way to acquire genetic variability in species. Unfortunately, in animals this phenomenon is usually quite slow.
3. Extrinsic factors
Clearly, the probability of a successful evolutionary rescue also depends on the environment If the speed of change in the environment is faster than the rate of generational turnover of the population, things become enormously complicated. In the same way, interactions with other living beings play an essential role: both intra- and interspecific competitions can increase or reduce the probabilities of evolutionary rescue.
A practical approach
So far we have told you part of the theory, but ideally any postulation should be based, at least in part, on practical observations. Unfortunately, proving the theory of evolutionary rescue is tremendously complex, even more so when we take into account that Genetic tests and population follow-ups are required and must be maintained for decades
A very clear example (although not entirely valid due to its anthropogenic nature) is resistance to antibiotics by various groups of bacteria. Bacteria mutate at a much faster rate than evolutionarily expected, since drugs unintentionally select the most resistant and viable individuals on a continuous basis. The same happens with some species of insects and the application of insecticides on crops.
Another ideal case could be that of rabbits, since viral myxomatosis reduced their populations in some areas of Europe and Australia by up to 99% during the 20th century This caused the long-term selection of those individuals with mutations resistant to infection (up to 3 effective genetic variations have been identified). This fact has prevented, at least in part, the complete disappearance of the species, since the immunoresistant are those who have offspring and last over time.
Although the data previously presented seem promising, we must emphasize that, for every striking case, there are many others in which species have disappeared due to viruses and pandemics without being able to do anything. This is the example of the chytrid fungus in amphibians, which has caused the decline of 500 amphibian species and the complete extinction of almost 100 of them in just 50 years. Of course, in no case are we facing a miraculous adaptive mechanism.
Another issue to resolve is to perform the real distinction between evolutionary rescue and normal adaptation rates Differentiating both terms is complex, to say the least, since a lot of empirical evidence and factors are required to be taken into account for each species analyzed.
Summary
Perhaps these terms may sound a little confusing for the reader, but if we want you to leave with one idea before finishing, this is the following: evolutionary rescue is not an act carried out by human beings nor a measure of conservation, but a hypothetical situation in which living beings can cope with environmental pressures thanks to rapid adaptive evolution
Testing this concept empirically presents titanic logistical complexity, as it requires very long-term population monitoring, genetic analyzes and many other parameters. In any case, we cannot trust nature itself to fix the disaster that we have created: if anyone can reverse this situation, at least in part, it is man.
