A non-native earthworm shifts the seed predation dynamics of a native weed

Seed predators both consume and disperse seeds, with important consequences for the population dynamics of many plant species.  The net effect of multiple seed predators depends on the relative proportion of the seed pool each predator obtains, and this proportion should reflect species-specific habitat preferences.  We studied the effect of the non-native earthworm, Lumbricus terrestris, on seed loss dynamics in the native weed, Ambrosia trifida (giant ragweed).  Giant ragweed seeds are predated by mice, but L. terrestris may protect the seeds against rodent predation by caching them in its burrows.  We investigated these interactions, as well as how environmental factors affected net seed losses by competing seed predators.

A two-year field study was conducted in which we measured removal of experimentally dispersed giant ragweed seeds by earthworms and mice in habitats varying in plant cover.  We analyzed the relative proportion of seeds taken by each species under the varying ex...