. As these foundress wasps pollinate the flowers, they also oviposit in some of them. Usually the foundresses die inside the syconium, and then both their offspring and the seeds begin to develop. Finally, after maturation, the offspring mate, and then the mated females collect pollen, leave their natal syconium, and fly off to find a receptive tree and begin the cycle anew.The fig-wasp mutualism is both ancient and diverse, originating Ϸ90 million years ago (5) with Ͼ700 extant species of figs currently recognized (6). Both morphological (7,8) and recent molecular studies (5, 9-11) broadly support the proposition of cocladogenesis and coadaptation between recognized genera of pollinating wasps and their respective sections of figs. These studies also suggest that finer-scale cospeciation of individual fig and wasp species is widespread. Furthermore, major fitness components in both the fig and the wasps are relatively easy to measure and interpret (4,(12)(13)(14). Combined, these attributes of figs and wasps provide a model system for both focal and comparative studies of the coevolution of costs and benefits involved in a mutualism (4, 12-15). Moreover, fig-pollinating wasps have been exploited extensively to both develop and test theories of sex allocation under conditions of local mate competition (LMC) (16-23). Here this theory predicts that, both within and among wasp species, as the number of foundresses that contribute to shared broods within syconia increases, the proportion of males (brood sex ratio) should increase from the extreme female bias expected with only one foundress. These studies have been generalized to investigate precision of adaptation and the situations promoting adaptive behavioral plasticity (20-23).With few exceptions (2,7,8,(24)(25)(26), these previous studies have either suggested or assumed one species of pollinator wasp per host fig species. The degree to which this key assumption of host specificity is violated has profound implications for the understanding of fig-pollinator wasp interactions in particular as well as studies of adaptive sex allocation and of the coevolution of mutualisms in general. In this study we use recently developed microsatellite markers (27, 28) in combination with mitochondrial sequence analyses to show that the assumption of one species of pollinator wasp per host fig species is routinely violated. We discuss the implications of these findings with respect to our understanding of the fig-wasp mutualism. In addition we document their effects on the fit between observed sex ratios and the values predicted from LMC theory. (27,28). These analyses revealed previously undetected cryptic species (see below). Subsequently, the mitochondrial cytochrome oxidase subunit I (COI) gene was sequenced from one to eight individuals per species in this sample to confirm the species status. Further, these data were combined with sequences from earlier studies for phylogenetic analyses (5). Where undescribed cryptic wasp species were confirmed, we used the name of the...

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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. Summary1. The aggregation model of coexistence states that intraspecific aggregation over patches stabilizes species coexistence and allows high diversity in patchy systems.The model is reviewed, with emphasis on the methods of analysis of aggregation data. Essential improvements in existing methods of analysis are presented. 2. The density, rather than the number, of competitors is important when patches differ in size. Measures of intraspecific and interspecific aggregation, J and C, are modified to take account of variable patches. The discrete negative binomial distribution is not suitable to quantify crowding on variable patches. A new criterion for coexistence in a patchy environment is developed that is a necessary and sufficient condition for the persistence of a specified species in the presence of other species. A previous criterion, the 'relative strength of intraspecific aggregation', A, represents only a necessary condition for the coexistence of two species.4. The stability of coexistence is affected by clutch sizes. Existing methods to estimate clutch sizes are not satisfactory. The analyses are most sensitive to errors in the estimated clutch size when clutches are large relative to the number of individuals per patch.When suitable habitat occurs in patches, the assumption of complete mixing of individuals made by simple population models is violated. Individuals in the same patch interact, but individuals in different patches do not. If species that use the same type of resource differ in their distribution over patches in such a way that interspecific interactions are reduced relative to intraspecific interactions, then species coexistence is facilitated. This idea has been formalized as the 'aggregation model

Summary1. Previous work has suggested that species diversity in resource-limited insect communities on patchy resources is maintained by spatial aggregation, not by resource partitioning. The most comprehensive test of this claim to date was by Shorrocks & Sevenster (1995), but some of their datasets included only a few resource types, which reduces the likelihood of ®nding a strong eect of resource partitioning. Also, methods of analysis have since been re®ned, e.g. to account for patch size. 2. We collected 733 mushroom samples belonging to 66 taxa in a Dutch woodland area. From these mushrooms, 38,891 insects were reared, belonging to 60 taxa of Diptera and Hymenoptera. Drosophilid species and their parasitoids were identi®ed to the species level; other taxa to the family level. We argue that the community is resource limited. 3. Generally, the insects have fairly narrow diets, including only a few of the available mushroom species. The degree of niche overlap varies widely in this community. 4. Within single resource types, co-existence can be explained by intra-speci®c aggregation over patches alone, in accordance with previous studies. 5. This conclusion remains unchanged for the mycophagous community as a whole: intra-speci®c aggregation of competitors is a sucient and necessary mechanism for co-existence in this diverse community, while resource partitioning does not contribute detectably to species diversity. This is the ®rst time that this pattern has been demonstrated in a dataset involving such a large number of resource types. 6. Our conclusions are strongly supported by data manipulations in which we removed or intensi®ed the eect of resource partitioning and spatial aggregation. 7. We argue that this community may be close to saturation, but we emphasize that saturation is a gradual phenomenon in patchy systems. 8. Since dierential use of resource types does not reduce competitive interactions among the insects, it seems unlikely that inter-speci®c competition constitutes the selective pressure favouring specialization.

Parasitic wasps lay their eggs in or on other insects. Allocation of resources to reproduction (eggs) and survival (life span) should maximize reproductive success, but stochasticity in the number of hosts encountered precludes an exact match of allocation with reproductive opportunity. We study optimal egg loads using a general model for pro-ovigenic parasitoids (which only mature eggs before adult life) and a dynamic programming model for synovigenic parasitoids (which can mature additional eggs during adult life). We find that stochasticity has a major effect on optimal egg loads and that the patchy distribution of hosts is the major source of stochasticity in reproductive opportunities. In a stochastic world, the further "relative habitat quality" (expected number of oviposition opportunities gained by reducing reproductive investment by one egg) is below unity (as we argue it generally is), the more the optimal egg load exceeds the expected number of hosts. In unusually rich environments, however, stochasticity decreases optimal egg loads. Although synovigenic parasitoids can adjust to the conditions they encounter, they too have to invest for an uncertain future. Because they can replenish their egg supply throughout life, the incidence of egg limitation is even lower than in pro-ovigenic parasitoids.

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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. Within taxa at the class or family level, the developmental period is often proportional to adult life span. In Drosophila species, a short developmental period increases larval competitive ability. Species with a long adult life, however, may have a better chance to reach new breeding sites in time and space. In another paper (Sevenster & Van Alphen 1993), we presented a model incorporating this trade-off. It shows that fast larval developers ('fast species') are dominant when breeding opportunities are frequent, and that good adult survivors ('slow species') are dominant when breeding opportunities are scarce. Moreover, the model demonstrates that a fast and a slow species may coexist in intermediate environments. In this paper we show that data from experiments and the field support the model. The trade-off between larval developmental rate and adult survival is established in a guild of frugivorous Drosophila species from Panama. 3. The interval between provisioning with larval food in population cages influences the outcome of competition between a fast and a slow species roughly as predicted by the model. 4.In the field, slow species are more abundant among adults than among recruits, as is expected from differential survival of adults and from differential competitive ability of larvae. 5. The guild composition in the field shifts towards fast species when fruits are abundant, and towards slow species when fruits are scarce. 6. Specialized species, which perceive a lower abundance of breeding sites than generalists, are slower species than are the generalists. 7. We conclude that there is ample evidence that differences in life-history strategy influence the structure of natural communities in a predictable way and promote the coexistence of species using similar resources.

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