Zoonotic diseases may be affected by the diversity of host and/or vectors of a disease agent, as species are differentially able to both host and transmit the causative agent. These differential abilities can dilute the risk of disease. However, it is not clear how the diversity of different community components interact to affect disease risk.  We hypothesized that the West Nile virus may show such sensitivity to diversity, because the host (birds) and the vector (mosquitoes) can have high diversity that might affect transmission. We further hypothesized that the plant community diversity in wetland patches may be the overall controlling factor of biodiversity dilution effects for this disease, as the plant community provides the environmental structure that in turn is thought to have strong effects on the diversity of both hosts and vector.   We quantified plant, bird and mosquito diversity in four urban wetland patches, including two large (>100 ha) and two small (10 ha) in New Jersey during the breeding and fall migration seasons, using point-based census methods.  Birds and mosquitoes were also quantified in the adjacent suburban residential matrix.

Results/Conclusions

We expected that diversities of plants, birds and mosquitoes would be higher in larger patches, but found that local richness per sample point did not show such pattern (bird diversities were 15.6±0.8 and 15.0 ±10 spp/point in large sites, and 17.5±0.5 and 11 (n=1) in the small sites; 13±0.9 mosquito species per point in large sites vs. 15.5±0.3 per point in small sites; and 36±2.3 plant species per point in large sites vs. 27±3.4 spp/site).  However, although the overall richness (total number of species observed) of both plants and birds was higher at the large sites than the small sites, no such pattern was observed for mosquito diversity.  Both bird and mosquito diversity decreased with distance from the wetland edge.  Culex complex mosquitoes, the primary bird-to-human viral vector, was most abundant at 50 m from the wetland edge. The results suggest that plant community diversity may not be a good predictor of the potential for biodiversity dilution of West Nile risk.