Relative prey capturing efficiency between two species of sundew: Drosera linearis and Drosera rotundifolia.

Abstract

Members of the genus Drosera (sundews) are notorious for their ability to capture insects in order to supplement low levels of nutrients in the habitats in which they live. Two species, Drosera linearis and Drosera rotundifolia use the same mechanisms to capture prey, but are distinctly different in the shapes of their leaves and their preferred habitats. I aimed to determine whether one species was more efficient at capturing insects than the other, and if so, ascertain the reasons for such a disparity. In a rich fen in the northern lower peninsula of Michigan, I estimated, for both species, populations in relation to the area of exposed soil, calculated percentages of leaves containing insects and counted the numbers of insects captured by these leaves per unit-area. Populations of the two species were found in two different micro-habitats; however the correlation between exposed soil and species abundance was not statistically significant. Drosera linearis individuals had a higher percentage of leaves containing insects and caught an average of four times as many insects as D. rotundifolia per leaf. Drosera linearis was 2.3 times more efficient at capturing insects than D. rotundifolia per mm2. These results are most likely due to differences in the orientation and shape of leaves as well as differing moisture levels, acidity and interspecies competition between micro-habitats.