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. We tested for the importance of priority effects on the interactions between immatures of the mosquito, Culiseta longiareolata, and immatures of the green toad, Bufo viridis, the two most abundant species of many temporary pools of the Negev Desert, Israel. Previously, we reported that when these two taxonomically distant species were placed together as early stage larvae, they competed strongly and when Culiseta larvae had the size advantage, they preyed on Bufo hatchlings. Here, we tested the interaction between these two species in artificial pools when Bufo enters first and develops prior to Culiseta entering. 2. We also tested for intra-specific competition and for the impact of both mosquito larva and tadpole on invading species. 3. We assessed these interactions by experimentally manipulating various combinations and densities of Bufo and Culiseta. We introduced early stage Bufo larvae 12 days prior to introducing first instar Culiseta larvae. 4. Bufo exhibited a strong intraspecific density-dependent effect: tadpoles were smaller and reached metamorphosis later at the higher density. We did not demonstrate an intraspecific density-dependent effect in Culiseta. Culiseta larvae affected neither survival nor development rates of the larger Bufo.Early stage Culiseta larvae were vulnerable to predation by the larger Bufo but later instar Culiseta larvae were no longer vulnerable. Bufo reduced larval development rate of Culiseta but did not affect pupal size. 6. Bufo tadpoles virtually eliminated, and Culiseta larvae strongly reduced, the number of individuals of an invading ceratopogonid midge species reaching the pupal stage. 7. The work here, combined with our previous work, demonstrates the importance of priority effects with respect to the outcome of competition and intraguild predation. change the symmetry of the competitive interaction and the larger tadpoles, although largely periphyton scrapers, may also become opportunistic predators on Culiseta larvae. At the same time, we also tested for intraspecific density-dependent effects on growth and survival and the impacts of these two species on other colonizing species. 78

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