Persistence in the seed bank: The effects of fungi and invertebrates on seeds of native and exotic plants

Fungal pathogens and invertebrate seed predators both may limit the establishment of persistent seed banks. Exotic plants may be less subject to attack by these natural enemies than are native species; if so, this may provide exotics with an important advantage by reducing seed mortality and enhancing the persistence of colonizing populations. We investigated this idea with a field experiment in which we used fungicides and screening to protect seeds of 39 native and exotic old field plants. The recovery of germinable seeds was improved by fungicide additions, but not by the exclusion of macroinvertebrates. The effects of fungicide varied among species and sampling dates, but the recovery of natives was not consistently improved more than the recovery of exotics. These results suggest that soil fungi have important impacts on the seed banks of many species, but that exotics are not consistently more resistant than natives to attacks by either fungal pathogens or invertebrates. Consequently, it is unlikely that the majority of invaders benefit from reduced pest loads at the seed bank stage.