Dependence of the dwarf sundew (Drosera brevifolia) on burrowing crayfish disturbance

Abstract

Disturbance is necessary for the survival of most species of carnivorous plants to reduce competition and expose bare soil for germination. Historically, fire was the most widespread form of disturbance. Today, prescribed burns and mowing are the primary anthropogenic forms of disturbance maintaining populations of carnivorous plants. Other natural forms of disturbance have received little consideration such as grazing and small-scale disturbance by burrowing crayfish. In Mississippi, burrowing crayfish are beneficial to both sundews (Drosera capillaris) and bladderworts (Utricularia juncea). Because burrowing crayfish are found throughout much of southeastern North America, they may provide a vital form of disturbance for smaller species of carnivorous plants to the point of being ecosystem engineers. In this study, we investigated if the Kentucky state-endangered dwarf sundew (D. brevifolia) benefits from bare patches of soil created experimentally by us and naturally by the endemic Bluegrass crayfish (Cambarus batchi). We observed colonization of sundews on crayfish mounds, chimneys, and eroded chimneys (= flat mounds) over 16 months. We also observed colonization of patches of soil we scraped clear of plants. We found that dwarf sundews quickly colonized bare soil, and that bare patches created by burrowing crayfish may be an essential small-scale form of disturbance for these sundews. Dwarf sundews have a life history predicted by the colonization hypothesis that being, they grow in a restricted niche space within the meadow and appear to have a disturbance-mediated coexistence with crayfish. They are small, fast growing, and short lived, and produce a seed bank. Dwarf sundews are a “fugitive species” that quickly colonize intense, small-scale disturbed sites to temporarily escape competition. We briefly discuss other potentially important, yet over-looked, disturbance that historically has been beneficial to carnivorous plants in southeastern North America.