Population structure of the dogbane beetle Chrysochus auratus: effects of patch size, isolation, and quality

In this study, we examined how patch size, isolation, and quality influence interpatch movement of the dogbane beetle, Chrysochus auratus. We conducted regular censuses of dogbane beetle abundance in patches of dogbane and conducted a mark-recapture experiment track their movement among patches. The first step in the study was identifying natural patches of A. cannabinum in Blandy Experimental Farm’s (Clarke County, Virginia) native plant meadow. A.cannabinum stems separated by less than 2 meters were considered part of the same patch. Forty of 115 patches identified in the meadow were studied.Only 40 of about 115 patches were used to conduct the project in a meadow area. The size of A. cannabinum patches was estimated calculated by counting the number of stems. The isolation of each patch was estimated as the median edge-to-edge distance to the 3 nearest-neighboring patches. We assessed patch quality by measuring the mean stem height per patch as well as the proportion of stems in flower.

We conducted weekly surveys of the number of dogbane beetles in each A. cannabinum patch. The surveys were conducted starting at 8:00am. All beetles encountered were collected and taken to the laboratory. Beetles were then measured and given an individual marking on their elytra with Testors model enamel. Each dogbane beetle was given a unique pattern of ordered colored dots. Beetles were released back into the patch they were collected from. For each patch, we computed the number of immigrants received and the proportion of individuals that emigrated to another patch.