Larval Development of Two Syntopic Amphibian Species (Bombina orientalis, Anura, Bombinatoridae and Dryophytes japonicus, Anura, Hylidae) Living Separately or Jointly in the Far East, Based on the Results of Laboratory Studies

Competition is known to render significant impacts on both the population dynamics and the community structure. As has traditionally been believed, Dryophytes japonicus larvae inhibit Bombina orientalis larvae when cohabiting. This paper is devoted to study of the influence of these species on the development of each other in experimental conditions. The larvae were grown before metamorphosis in three variants: with single maintenance, together with conspecifics at different densities, as well as with the joint maintenance of individuals of the two species. When kept alone, B. orientalis larvae, in comparison with D. japonicus, are characterized by a higher survival rate (100% vs. 85%), a shorter duration of larval development, and a longer body length of individuals during the period of metamorphosis. With an increase in the duration of larval development, the size of D. japonicus juveniles increased. There are no differences in the survival rate when growing larvae of each species at different densities. The duration of larval development varied significantly in different experimental groups. In both species, the duration of development correlated with the initial density per unit volume of water and per unit area of the bottom. With increasing density, the length and mass of the larvae decreased. The bottom area renders a greater impact on the duration of larval development as well as the length and body weight of B. orientalis juveniles than the volume of water. According to the results of regression analysis, with an increase in the initial stocking density of B. orientalis by 100 specimens per square meter of the bottom, the duration of larval development increased by 4.7 days, the body length decreased by 0.83 mm, and the weight dropped by 0.06 g. The volume of water has a greater influence on the same indicators of larval development of D. japonicus. With an increase in the initial density by one specimen per liter of water, the duration of larval development of D. japonicus increased by 11.7 days, the body length decreased by 0.37 mm, and the weight dropped by 0.07 g. When the larvae of the two species were grown together with an increased proportion of one of them, no negative impact was observed neither on the survival nor on the development, nor on the growth of the other species. On the contrary, with an increased number of conspecifics in the container due to a decrease in the number of individuals of the other species, the development and growth of larvae of the former species was inhibited. Thus, in laboratory conditions, no noticeable interspecific competition was observed between the larvae of B. orientalis and D. japonicus. The authors suggest that a successful coexistence of these two species is associated with pronounced intraspecific competition in each of them, which was previously noted for other animal taxa.