Abstract
•Parasite and host abundance exhibited a clumped dispersion•Parasite cover increased with longer hydroperiods•Host traits changed along the hydroperiod gradient and with infection•Infection of hosts increased with longer hydroperiods•Hydroperiod gradient had direct and indirect relationships with infection
Understanding host-parasite interactions is a central question in ecology. The distribution and abundance of plant hosts and parasites tend to be less studied in natural ecosystems. In California, vernal pools are seasonal wetlands that are habitat to the plant parasite Cuscuta howelliana (Bogg’s lake dodder) and its most common host, Eryngium castrense (Coyote thistle). Previous research has identified the interaction and its community effects, but little research has been conducted on their distribution, abundance, and infection patterns, as well as how these change, along a hydroperiod gradient. Ten vernal pools were sampled using 5 random quadrats along 2 transects. Both Cuscuta and Eryngium displayed clumped dispersion patterns within pools. Cuscuta cover had a strong positive association with inundation period and Eryngium traits (height and inflorescence number) had a strong positive association with inundation period. Eryngium plants were smaller at higher densities. Eryngium characteristics were significantly smaller in the presence of Cuscuta infection but highly variable across pools. Path analysis showed that there were significant direct and indirect pathways from hydroperiod to infection rates. The strongest pathway was the increased hydroperiod to increasing Cuscuta cover to increasing infection. These results highlighted the complex interactions among parasite, host, and the environment. This will help understand the spatial ecology of parasite-host interactions along an environmental gradient of this imperiled and diverse ecosystem.