The distribution and frequency of various color morphs were determined in the population of moor frog, Rana arvalis Nilss, on the Middle Ural. The color polymorphism has been established to correlate with some demographic traits such as migration and the life-span. The relative stability of polymorphism within the population is assumed to be determined by ecological mechanisms, i.e., the dynamics of numbers and spatial and age structure of the population.
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293The moor frog (Rana arvalis) inhabits the largest territory of all Eurasian true frogs (Ranidae), and its east-west extension spans more than 7200 km, from northern France to beyond Lake Baikal. Within this area, the moor frog shows pronounced morphological and autecological (aquatic and terrestrial) variation, and at least in southeastern Europe a large amount of genetic variation. Nevertheless, no geographic subspecies can be delineated except the partly disputed R. a. arvalis and R. a. wolterstorffi. The latter inhabits a small area in the Pannonian region, whereas the former covers the reminder of the distribution range. The genetic-taxonomic status of marginal populations in the Balkans (Slovenia, Croatia) and the Ukraine remains as yet unresolved. A special feature of the moor frog is the purple or blue colouration of males during the breeding season, whose origin as well as function is as yet unknown. In northern Scandinavia, as well as some southern populations, this colouration is missing or only observed in some years. Suitable habitats for the moor frog are very diverse, and encompass moor edges, heath ponds, riverine forests, meadows and pastures, and even dry pine forests. Regional habitat specialisations are noted towards the margins of the distribution area, whereas the moor frog is rather a generalist in core areas. Habitat specialisation in the densely populated western border of its distribution constitute a major threat, as only unsuitable areas remain following habitat destruction. Rana arvalis is therefore in part highly endangered or at risk of extinction in France and southwest Germany, and sustainable and comprehensive conservation programmes are thus urgently necessary. Large-scale agricultural extensification measures and the creation of new breeding sites are key towards establishing connectivity between remaining populations and a restauration of their habitats. Additionally, further research into the speciesí conservation biology is necessary.
In 1989 and 1990, the migration and survival rates and growth of Rana temporaria and R. arvalis juveniles were examined by means of the group marking method applied to recently metamorphosed individuals, and by recapture of juveniles along two different transects, each 700 m long. As compared with 1990, in 1989, juveniles of R. arvalis had smaller body size upon metamorphosis and higher density near the pond, with higher mortality rate in close proximity to it (up to 200 m) and higher survival rate at a considerable distance from the pond. In both years, the froglets that left the pond earlier had advantage of higher survival rate, but only at a distance from the pond exceeding 200 m. Among the early metamorphosed juveniles, larger individuals better survived in 1990, but not in 1989 (because of the higher density). Among the individuals that left the pond later, the survival rate was higher in large-sized juveniles in both years. Dispersing away from the pond, the juveniles attained larger average sizes in 1989, compared with 1990, and more completely compensated for the initial body size delay. The body sizes attained by the end of the season were the same for early small-sized and late large- and medium-sized individuals. In R. temporaria, the growth rate is higher than that in R. arvalis and compensation for the initially small body size of juveniles is practically complete.
Influence of changing illuminance on the growth of fish juveniles and grass frog tadpoles was investigated. The maximum growth rate of all the species is observed under conditions of illuminance oscillations about certain values. For the fish growth, the regimes with 12- and 24-hour oscillations are the best. In the optimal varying regimes, the lower lethal oxygen level declines. Change of the darkness (0 lx) to bright light decreases the growth rate of fishes. Similar results are obtained in experiments with grass frog larvae
