No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The development of natterjack toad (Bufo calamita Laurenti) tadpoles was monitored under two levels of food and with or without competitors (Rana temporaria L.) using a replicated pond system. The design prevented physical interactions between species but allowed B. calamita access to R. temporaria faeces. 2. Food supplements accelerated growth with or without competitors. The presence of competitors depressed B. calamita growth, even under conditions of high food. 3. B. calamita raised under high food metamorphosed earlier than those raised under low food, but neither food nor competitors affected survival. 4. The growth-inhibiting alga, Prototheca, was detected in the faeces of both R. temporaria and B. calamita. B. calamita raised with R. temporaria for several weeks produced larger numbers of protothecan cells in their faeces than those raised without competitors. 5. Inferior competitors may be diverted from high quality food resources by the attractive properties of Prototheca in faeces. In such a situation superior competitors may exert a negative effect even under high food levels.

No abstract

No abstract

SUMMARY 1. Numbers of the contramensal alga Prototheca richardsi were high in spring in two ponds used for breeding by anuran amphibians, but lower at other times of year and undetectable in two ponds not used by anurans. 2. Prototheca richardsi became abundant in the silt of eight experimental ponds which contained tadpoles, but remained undetectable in four otherwise identical ponds lacking tadpoles. 3. Prototheca richardsi numbers in laboratory microcosms remained stable for many days in sterile tap water, but declined with a half‐life of about 6 days in pond water at 20°C. 4. Further studies with microcosms using antibiotics and electron microscopy indicated that mortality of P. richardsi was caused primarily by pathogenic bacteria.