Growth, survival and activity patterns of recently metamorphosed Bufo marinus

Abstract

We examined factors affecting the growth and survival of postmetamorphic Bufo marinus using sampling and experiments. Bufo metamorphs, defined as newly emerged terrestrial toads of 9-29mm snout-ischium length (SIL), were classified into four stages on the basis of colour and size. Stage 1 were uniformly black and about 9-12 mm SIL, stage 2 were mottled with orange spots and about 12-16mm SL, stage 3 had a white mid-dorsal line and were about 16-25mm SIL, and stage 4 had enlarged parotoid glands and were about 25-29 mm SIL. We determined the density of each stage at three distances (0-1, 2-3, 4-5m) from their larval habitat using 1 x 1-m quadrat samples. The mean densities of all metamorphs within 1 m of water were 2.6m-2 and 2.1m-2 for the wet and early dry seasons, respectively. The mean densities of all metamorphs during both seasons at 2-3m and 4-5m from water were 0.8m-2 and 0.6m-2, respectively. Stage 2 metamorphs were most common in samples. Most stage 1 metamorphs occurred within 1m of the water in both seasons (98% wet; 95% dry). Increasing percentages of stage 2, 3 and 4 metamorphs occurred in samples 2-3 and 4-5m from water (38, 49 and 80%, respectively, averaged over both seasons). Three experiments examined the response of metamorph growth and survival rates to density in open-topped flyscreen enclosures. Stage 1 or 2 metamorphs were established at initial densities of 3.3, 6.7 and 16.7m-2. Metamorphs in the lower-density enclosures grew more rapidly than metamorphs in the higher-density enclosures. A profile analysis showed that daily survival rate was not densitydependent. Correlation analyses showed that daily metamorph survival was influenced by daily maximum and minimum temperatures. Metamorphs at lower densities attain juvenile size (30mm) more rapidly; because they survive at the same daily rates as metamorphs at higher densities they experience lower cumulative mortality as metamorphs.