by S. KUZMIN, Cand. Sc. (Biology), Institute of Evolutionary Morphology and Ecology of Animals, Russian Academy of Sciences
Salamanders, newts, frogs, and toads are the representatives of amphibians most familiar to people. However, non-specialists know very little about them. To some extent, this can be explained by latter's hiding way of life, and also by relative rarity in human settlements. To add to this, most of amphibian species are tropical dwellers. Russia is poor in amphibians: only six species of tailed amphibians and 21 of tailless ones are living here. Some of these species were formed in the long passed geological periods, sometimes as a result of natural catastrophes or major climatic changes and today they have rather restricted geographical ranges. So, as is supposed, in the Middle Volga area (the district of modem Kazan city) the psychrophilous species of the taiga complex, Siberian newt (Salamandrella keyserlingii),expanded its range during the cold periods, whereas at warmer times the expansions of the common treefrog (Hyla arborea) took place.
Northern species: crested newt (Triturus cristatus), common toad (Bufo bufo) and grass froa (Rana temporarig) among them, in the past were distributing far to the south, beyond the Kama River. Then, when the forest cutting started, their ranges shifted northwards. Along with the development of agriculture in the Bulgar Kingdom (a feudal state in the Middle Volga area in the 10-14th centuries) and later on the southern species preferring open areas, such as the red-bellied toad (Bombina bombina) and the green toad (Bufo viridis)were widening their geographical ranges northwards.
So, man unwillingly intervened into the amphibians' life. As a result of all these influences, part of amphibian species is now on the verge of extinction. To organize their protection, some of them were included in the Russia's Red Data Book. Eastern spadefoot (Pelobates syriacus), Caucasian parsley frog (Pelodytes caucasicus) are among them. Such species as the Karelins'newt (Triturus karelini) and the Caucasian toad (Bufo verrucosissimus) also need protection - although being numerous as yet, they are very vulnerable.
It must be taken into consideration, that amphibians' number varies drastically in this or that year. Sometimes this fluctuation makes 20-30 times. Commonly it is related to climatic changes: e.g., during severe droughts in Central Russia most of the amphibians' breeding ponds dry up which leads to death of spawn and tadpoles of grass frog (Rana temporaria). Strong frosts and snowless winters lead to overfreezing of adults, bringing about sharp decrease of their number in
the years to come. Then, in favorable conditions, the number of these animals rapidly restores and even increases.
At the same time, recent data evidence that together with permanent fluctuations of the amphibian number, the latter gradually decreases in many regions of Russia. This is just the case with the Volga area, some sites in the Baikal and Siberian regions, in the lower Don, in the Northern Caucasus, in many large cities and their surroundings: Moscow, St. Petersburg, Novosibirsk, Voronezh, Nizhni Novgorod, etc. Evidently, this is the "tip of the iceberg": real proportions of this process must be larger, when we take into account the fact of relative rarity of amphibian studies. However, scientists indicate natural causes for amphibians' decline (pond overgrowing, long-term droughts, frosts, etc.) not so often, as those proceeding from different forms of human activity.
At present, the main threat for amphibians is the destruction of their habitat: bush and forest cutting, swamp drainage, destroying of small ponds in the process of agricultural amelioration. Changes in the hydrology and microclimate gradually lead to the population disappearance. This is just the case with the newts and common toad in the Volga-Kama region. Extensive use of insecticides and mineral fertilizers in agriculture proves especially ruinous for the fauna, and floods of water polluted after washing the fields cause death of amphibian spawn and larvae. The similar negative role is played by the industrial wastes and even by the destruction of swamps, banks of lakes, and ponds due to uncontrolled cattle grazing. Breeding of fish in small water bodies, and, especially that of Percottus glehni also has negative consequences. Many fishes devour amphibian spawn and larvae, especially those of the newts.
Finally, uncontrolled catching has negative consequences for amphibian population. For a long time the subject to it were the species used in medicine, in schoolchildren and students' education, and in scientific studies. They were European species of frogs, common and green toad, and to less extent - smooth and crested newts. During last years (due to declared nature conservation) their capture (especially for educational purposes) was diminished. At the same time, the catching of the most beautiful and rare species for the terrariums has sharply increased. Besides, some new private firms in Russia are trying to profit from the export of toad venom.
However, the main threat for amphibians comes from urbanization. In majority of large cities their number is not high, species diversity is low. As a rule, the new living districts possess more amphibians than the old ones. This is due to the destruction of small ponds and urban planning and organization of public services. Larger ponds are subject to cleaning, their shores are made vertical and concreted, so that they become unaccessible for animals. Besides that, the building of asphaltic roads disrupts the population into smaller parts, many species die on the highways. As a result some populations disappear and the others become more isolated. This makes them more vulnerable and the probability of their extinction due to inbreeding, unfavorable environmental conditions and vandalism increases.
Moscow is a good illustration of this. In the center amphibians disappeared already before the '40s. Subsequently, the decrease of their number and species diversity was completely dependent on house building. Up till now the main concentration of these species retained only in some parks on the outskirts of Russia's capital. However, even there the amphibians' number is gradually declining due to the construction of recreation facilities.
As was indicated above, amphibians' vulnerability to unfavorable living conditions depends on their species. For example, the ploughing up of fields can lead to local increase of the number of the common spadefoot, which conducts digging mode of life. Amelioration works accompanied by the establishment of channels, ditches, network of small ponds are favorable for the populations of grass frog, moor frog, aquatic green frogs, green toad. Among them, the marsh frog (Rana ridibunda) is especially adaptable. On the south of range margin: in Kalmykia, Lower Povolzhye, the Caucasus the species readily populated the channels and fish ponds, which may be used for the establishment of the "frog farms". At the same time. discharge of warm industrial and municipal waters into natural and artificial water bodies enabled this southern species to form populations in the conditions of cold climate of the Urals (Verkhny Tagil, Yekaterinburg), Yakutsk, Gorno-Altaisk.
Thus, the intensive anthropogenic destruction of natural environment may cause total extinction of amphibians in the entire regions. On the other hand, the same anthropogenic influence leads to change of amphibian fauna. Now some localities possess only one-two species, as a rule, of frogs and toads only.
All this can hardly be accepted as satisfactory Amphibians are very sensitive indicators of the environmental conditions - both terrestrial and aquatic. They react to deterioration of the ecological situation much earlier than the people can notice this. This is why the decline of their populations is an alarm signal which must not be ignored.
In general, the problem of amphibians' maintenance is far from resolution. It is not clear, whether these are global, or just local declines? What is the rate of decline of separate species? What are the impacts of natural and anthropogenic factors on this? These problems are important not only for the specialists from Russia. This is one of the reasons for the establishment of the Declining Amphibian Populations Task Force under the Species Survival Commission of International Union for Conservation of Nature (IUCN). The members of the DAPTF are researchers from Europe, Asia, America and Australia. In 1992, the Working Group of the Community of Independent States within the DAPTF was established. It included scientists from Byelorus, Georgia, Kazakhstan, Russia, Uzbekistan and Ukraine. We hope that this cooperation of zoologists from different states and regions will not only permit to solve the problem of global number dynamics of these species, but also make an impact on the preservation of their biodiversity on our planet.
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