Here I report the results of two years of field manipulations in which I investigated the role of the small, annual hemiparasite, Triphysaria pusilla (Benth.) Chuang & Heckard (formerly known as Orthocarpus pusillus; Scrophulariaceae; hereafter, Triphysaria) in a coastal prairie community.
This area is dominated by annual species: annuals constituted 70.5 [+ or -] 2.3% (mean [+ or -] 1 SE) of the dicot biomass (not including Triphysaria) harvested in the parasite removal experiment, and annual grasses made up 86.5 [+ or -] 2.4% of graminoid biomass (based on a pilot study with 20 plots; M.
The parasitic plants at this site, mostly Triphysaria pusilla (but also a few T.
To examine the role of Triphysaria in the coastal prairie community, I selected 21 blocks, each 1 x 1 m, of low-growing prairie vegetation in early March 1994 after most germination was complete.
Finally, I calculated the Shannon-Wiener index of species diversity for each plot and used a sign test to examine whether Triphysaria removal altered host diversity in any consistent direction.
In addition to effects of Triphysaria on various host species, I also evaluated (1) the effect of different hosts and host combinations on Triphysaria performance and (2) the competitive interactions among pairs of hosts in the presence and absence of Triphysaria.
Host taxa Parasite (Triphysaria Hypochaeris Lupinus pusilla) Grasses glabra nanus X - - - X X - - X - X - X - - X X X X - X X - X - X - - - - X - - - - X - X X - - X - X I concentrated on the three most abundant annual host taxa: a native, nitrogen-fixing annual, Lupinus nanus; an introduced annual, Hypochaeris glabra (Asteraceae); and a mix of mostly introduced annual grasses.
On 21 January 1995, I searched for 10 areas at least 1.5 m in diameter that contained seedlings of all four focal taxa: Triphysaria, Lupinus, Hypochaeris, and grasses.
I also included a treatment of Triphysaria grown in the absence of any hosts to assess the extent of host dependence for this partially autotrophic parasite.
To assess whether there were any initial differences among the experimental treatments, I recorded the number of individuals of Lupinus, Hypochaeris, and Triphysaria as well as the percentage cover of grasses on 18 February.