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The species that propagate slowly, become extinct sooner

18.10.2002


The animals and plants of our planet are becoming extinct under the pressure of civilization. The scientists have counted that one species vanishes from Earth every hour. The mammoth, passenger pigeon, gare-fowl, Steller`s sea cow - these are the most well-known of extinct species, but hundreds of species are next in turn. Can the scientists forecast what species is the first in this succession and what species is not under the threat of complete extinction? If the answer is known, the effort and funds intended for the preservation of natural resources could be distributed correctly. Leonard Polishchuk, Ph. D. (Biology), research assistant of the Chair of General Ecology, Faculty of Biology, Lomonosov Moscow State University, has found a mathematical index of animal vulnerability.



It is common knowledge that the species of large animals that propagate themselves slowly and produce scarce posterity extinct earlier than others. Therefore, Leonard Polishchuk was looking for the characteristic of extinction risk among common demographic and ecological parameters. The researcher analyzed several parameters for 90 species mammal inhabiting the territory of the former USSR: life interval, quantity of litter, body weight of a sexually mature female, annual prolificacy and the number of posterity that each specific animal species produces within the entire lifetime. Applying the logistic regression method, he compared the above parameters to the probability of these species` registration in the Red Book. The most appropriate characteristic has appeared to be natural annual prolificacy, i.e. the number of daughters born by a female within a year.

The leaders of this index have turned out to be the rodents: common shrew (11.4), rabbit (10.5), Pallas` pika and steppe mouse-hare (8.8 è 7.9), field mouse (7.7), Alpine hare and European hare (5.0 è 4.4) - these species are well-known for their vitality.
About one third of all investigated species is characterized by the index exceeding 2.9. Almost all the species registered in the Red Book are grouped closer to the end of the list - their production/mortality ratio is lower than the above value. The list is ended by the walrus (0.17), bison (0.20), and the sea-otter (0.25), which were on the verge of extinction in the 19th century.



This index coincides with the probability of species` extinction; on top of that, it has a distinct biological meaning and is mathematically valid. From the ecological point of view, this value is the measure of the species` capability for reproduction, the high rate of quantity restoration being a prerequisite to successful survival of animal in adverse conditions. Mathematically, the probability of the species` registration in the Red Book (L) is in the negative dependence on the annual prolificacy, this dependence is described by the equation: L=1 / [1 + exp.(-1.52 + 2.10 B)].

Another important outcome of Polishchuk`s research is that he has proved that the risk of extinction is proportional to the range of quantity fluctuation. It seems that it should be the other way round, if the species quantity goes down, the probability of complete extinction should go up. However, it has turned out differently, and the researcher`s explanation is as follows: "The point is that extensive quantity fluctuations are normally inherent to the species capable of quick reproduction. Consequently, these species have lower probability of becoming extinct and less chances of registration in the Red Book. Therefore, the rate of population increase influences both the quantity variability (in a positive way), and the probability of extinction (in a negative way). For example, hares and rabbits are the species famous for high rises and drastic falls of their quantity, but they have never been recorded in the Red Book, on the contrary, these species are flourishing. Everywhere, should the climate be suitable, the rabbits are the usual inhabitants of cities and the countryside, while the hares are the traditional target of hunting ".

The above research of the Russian scientist has caused an extensive feedback in Russia and around the world. So far, the conservancy practice has lacked an unbiased index of the necessity to take nature-conservative measures for a certain species, the animals and plants were recorded in the Red Books based on the specialists` expert judgements. Now the environment protection priorities can be computed. The most important result is that the funds can be distributed in proportion to the calculated coefficients. Let us consider the following example. According to the 2002-2010 Russian Federal Target Program, the right to priority financing was assigned to two Russian animals - the tiger (USD 16.7 million) and the polar bear (USD 13.7 million). All existing polar bear females give birth annually to 0.3 daughters in the average, and the tiger females - to 0.4. Evidently, with such reproduction level these two species are doomed to extinction, and the funding for nature-conservative measures have been allocated and distributed between them quite reasonably, i.e. almost equally. However, what can be done about the other twenty rare species which also have low reproduction capabilities, but the share of them all taken together makes about 20 times less funding? Will the Russian desman, wild ass and mountain sheep survive? Will the wild ass and goral be preserved? What about the Far-East leopards, the quantity of which counts about 20? The proposed concept is to help distribute reasonably the funds allocated for nature protection.

Elena Krasnova | Informnauka

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