Authors: Kurtulus Olgun, Varol Tok, J. W. Arntzen And Oguz T0rkozan

Authors:James R. Mccranie And Larry David Wilson 

Authors: Ulrich Sinsch

Abstract: The metamorphic success oflarval cohorts and the post-metamorphic growth of toad lets were studied in a large metapopulation of natterjack toads (Bufo calamita) in the Rhinelands, Germany. Larval density was greater in the cohorts studied in 1 99 1 than in those studied in 1992 and metamorphs were smaller in 1991 than in 1992, indicating short-term carry-over effects. Metamorphic success and average snout-vent length were larger in the cohort originating from the early breeding period than in those from the main breeding period in the previous year. The further terrestrial development of three metamorph cohorts was followed until adulthood using commercial fish marks (microtags) for batch-tagging. Microtags are small pieces of wire which are injected below the skin. Their presence is determined using a hand-wand metal detector. The short- and long-term effects of this new marking technique on growth and survival of almost 2000 free-ranging toadlets are reported. The results obtained indicate that microtagging is a useful and harmless technique for the study of metamorphs.

Authors: Wolfgang Bohme And Thomas Ziegler

Abstract: The status of the two nominal subspecies of Varanus niloticus (Linnaeus, 1766), viz. V. n. niloticus and V. n. ornatus (Daudin, 1803) is re-evaluated based on morphological (colour pattern, scalation, dimensions, outer genitals), ecological, and distributional data. Evidence is presented that both forms have markedly surpassed the subspecific level and have to be treated as two distinct, though closely related, species.

Authors: Gillian C. Baker And Trevor J . C. Beebee

Abstract: Previous laboratory and replicated pond experiments have implicated Prototheca richardsi, a unicellular alga, in interference competition within larval anuran assemblages. We investigated the extent of interspecific competition between Rana temporaria and Bufo bufo larvae, and the occurrence of P. richardsi, in small fish-ponds where initial tadpole densities were high. Mortality of both R. temporaria and B. bufo larvae was high during the early stages of development, and interspecific competition was negligible in these ponds and in mesh cages suspended in them. However, growth of B. bufo larvae was reduced when they were raised with R. temporaria larvae at natural densities in plastic cages within the ponds. P. richardsi was positively associated with the plastic cage treatments, but was much less frequent in the ponds outside or in the mesh cage treatments. Predation appears to be a much more important structuring force than either resource competition or Prototheca-mediated interference competition in the anuran communities inhabiting these fish-ponds.

Authors: John Davenport , Nina De Verteuil And Shona H. Magill

Abstract: Young green turtles, Chelonia mydas responded to increasing current velocities by swimming upstream for a greater proportion of the time. At temperatures of 21-25°C currents equivalent to 1-2 body lengths s^·1 induced continuous upstream swimming. At low current velocity the turtles usually employed ' dog-paddle' (ipsilateral synchronized) swimming. At swimming speeds of 0.8-1.4 body lengths s^·1 they switched to synchronized forelimb flapping, with stationary rear limbs. Maximum dog-paddle speed was about 40% of maximum speed using synchronized foretlippers: the latter mechanism is clearly capable of generating far more propulsive power. Maximum sustained swimming speeds at 25°C, 21°C and 15°C were 3.3 1, 2. 96 and 2.09 body lengths s^·1 respectively; the speed at 15°C was significantly lower than at the other two temperatures, and could not be sustained for more than 2-4 min before instability in pitch, roll and yaw prevented the animal from swimming upstream. A detailed analysis of the swimming mechanism at different temperatures is presented. This demonstrated a significant degradation of co-ordination of swimming at 15°C, even though the lethal temperature of green turtles is well below 10°C. The significance of this finding is discussed in terms of vulnerability of the species to cold.

Authors: Michael R. K. Lambert