Species host numerous parasites, yet most studies still focus on pairwise host-parasite interactions.  Recent evidence suggests that ignoring the community ecology of parasitism can limit our understanding of the drivers of epidemics in natural populations.  In this study, we analyze patterns of infection of a suite of parasites of lake Daphnia populations to look for evidence of competition among parasites at both the individual- and population-levels.  We tracked infections in 18 lake populations of Daphnia dentifera from 2002 through 2007; lakes were sampled biweekly in summer and autumn.  During this time, four parasites were particularly common: the yeast Metschnikowia bicuspidata, the bacteria Pasteuria ramosa and Spirobacillus cienkowskii, and a fungal brood parasite.  
Results/Conclusions

We looked for evidence of individual-level competition by comparing the number of co-infected individuals with the number expected based on infections prevalences in the lake population.  We found significant evidence for individual-level competition (i.e., significantly fewer co-infected individuals than expected) for some parasite combinations (e.g., Metschnikowia and Spirobacillus), but not for others (e.g., Metschnikowia and the brood parasite).  Preliminary results from the population-level analysis suggest that factors other than ecological interference among parasites are more likely to be important in determining patterns of epidemics in Daphnia populations.