Ephemeral ponds are doubly insular habitats in that they are discrete in time as well as in space. Predicting species richness based on pond size has been attempted using measures of both spatial extent and habitat duration, but habitat qualities alone only drive community composition under the speciessorting metacommunity paradigm. We tested the hypothesis that community composition in temporary ponds is driven by species sorting due to pond duration. In order to eliminate bias due to undersampling, we sampled 34 pools distributed among 3 complexes in every ponding event over a period of six years, and identified every individual for the microcrustacean taxa. Our data were consistent with most of the predictions of the species-sorting hypothesis. There was a clear pattern of difference between ponds in species richness as well as higher species richness in years with higher rainfall. The set of crustacean species that we found in the pools was highly significantly nested across the region, but not necessarily within localized groups of ponds (complexes). We also found differences in community composition among complexes. Pond depth was the best predictor of species richness when data were summarized over the whole study, but in one year with unusually high rainfall, pond area and hydroperiod were significant but depth was not. We did find some species in all ponds. It is likely that given their short development time, ponds do not differ in habitat quality for these few species. These results taken together emphasize the variability inherent in ephemeral pond ecology, with detectable differences in crustacean communities and the factors influencing them between years as well as between ponds, and at scales of meters as well as kilometers. Although our data provide further evidence that species sorting on pond permanence is an important factor structuring temporary pond crustacean communities, our assumption that dispersal is not limiting still needs to be tested.

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1. Ephemeral wetland habitats provide a useful model system for studying how lifehistory patterns enable populations to persist despite high environmental variation. One important life-history trait of both plants and crustaceans in such habitats involves hatching/germination of only some of the eggs/seeds at any time. This bet-hedging leads to the development of a bank composed of dormant propagules of many ages. 2. The San Diego fairy shrimp, Branchinecta sandiegonensis (Crustacea: Anostraca), a dominant faunal element of ephemeral ponds in San Diego, California, is a suitable organism for studying the consequences of highly fluctuating environmental conditions. As a result of large-scale habitat loss, the species is also endangered, and this motivated our specific study towards understanding the hatching dynamics of its egg bank for planning conservation efforts such as pool restoration and re-creation. 3. We formulated a matrix population model using egg age within the bank to study the relationship between adult survival and reproduction, and survival in and hatching from the egg bank. As vital rates for fairy shrimp are only poorly known, we generated 48 matrices with parameters encompassing ranges of likely values for the vital rates of B. sandiegonensis. We calculated population growth rates and eigenvalue elasticities both for a static model and a model with periodic reproductive failure. 4. The model shows that in good filling events, population growth rate is very high and the egg bank is increased dramatically. While population growth rate is insensitive to long-term survival in the egg bank in our static deterministic model, it becomes sensitive to survival in the egg bank when a regime of periodically failed reproductive events is imposed. 5. Under favourable conditions, it was best for shrimp to hatch from eggs as soon as possible. However, under a regime where failed reproductive events were common, it was best to hatch after several pool fillings. Because conditions change from favourable to unfavourable unpredictably, variation in age within the egg bank appears to be critical for the persistence of the population. This attribute needs to be carefully considered when restoring or creating new pools for conservation purposes.

Reproductive modes in marine invertebrates can be generally grouped into two types: those brooding larvae and those broadcast‐spawning gametes into the water. We asked if these different life‐history strategies differ based on how contribution to fitness is partitioned between growth, stasis, and reproduction. To investigate this question, we used published demographic data on ten diverse species of marine bivalves. We parameterized simple matrix‐population models and calculated the sums of elasticities to growth, stasis, and reproduction parameters and plotted the results on triangular axes. We also assessed whether contribution patterns were correlated with reproductive mode and tropical, temperate, or polar environments. We found that some of the broadcast spawners fell in the region of the plot with high elasticities for stasis and that some of the brooders fell in the region of the plot with higher growth and reproduction elasticities than stasis ones. However, instead of a sharp dichotomy, we found a continuum in contributions of stasis parameters with long‐lived brooders and short‐lived broadcast spawners in the same region of the plot. There was no clear pattern of reproductive mode associated with any particular environment, but we think these preliminary results are intriguing and that further work on comparative demography of marine invertebrates is warranted.