Cryptic Consequences of a Dispersal Mutualism: Seed Burial, Elaiosome Removal, and Seed-Bank Dynamics

Abstract

Abstract. In moving seeds from one location to another, dispersers define the ecological context that a plant will experience throughout its lifetime. Because seed deposition sites may benefit one plant life cycle stage but not others, dispersal may give rise to a conflict between a plant's dispersal needs (e.g., predator escape) and its requirements for successful establishment (e.g., suitable habitat). In this study, we assessed the effects of two components of seed dispersal by ants (seed burial depth and elaiosome removal) at several stages during the recruitment of Leucospermum truncatulum, an ant-dispersed plant from the fynbos shrublands of South Africa. A seed-predator exclusion experiment revealed that the removal of elaiosomes significantly reduced rodent predation on seeds buried 1 cm deep and increased the viability of seeds that were not consumed. In contrast, we found that elaiosomes had no effect on the probability of a living seed emerging as a seedling. In a seed burial depth experiment in which predators were not excluded, deeper burial significantly enhanced seed survival, but this benefit came at the expense of reduced seedling emergence, delayed emergence, and smaller cotyledon size. Despite the potential importance of these seedling characteristics, elaiosomes and burial depth had no significant effect on seedling survival through the first year of this study. In contrast, burial depth had strong positive effects on the fraction of seeds that persisted in the seed bank. Although dormant individuals may die before germinating and reproducing, those that persist at greater soil depths can play a crucial role in rescuing populations from local extinction in unpredictable environments. Given the extreme variability in fire frequency in fynbos, the net effect of seed dispersal by ants on plant populations will depend on how temporal fluctuations in fire regimes influence cost-benefit thresholds related to seed dormancy and seed mortality.

The mixed effects of experimental ant removal on seedling distribution, belowground invertebrates, and soil nutrients

“…In the process of handling seeds, ants may damage the seed coat (Christian andStanton 2004, Zettler et al 2001) and increase fungal infection. Ants may also deposit seeds into unfavorable germination sites (Rice andWestoby 1986, Christian andStanton 2004) such as logs or move seeds into marginal habitat (Giladi 2004). The distribution of H. arifolia in the study area is patchy, with distinct boundaries between occupied and unoccupied habitats (Giladi 2004, Warren et al 2010, suggesting that the distribution of suitable habitat is not continuous.…”

The relevance of ants as seed rescuers of a primarily bird-dispersed tree in the Neotropical cerrado savanna

“…Costs of the interaction with ants possibly include some seed predation by Pheidole spp. (but see Levey and Byrne 1993), deposition at deep soil levels inappropriate for germination (Christian and Stanton 2004), or death due to fungal infection (Wirth et al 2003). This reinforces the dual role of Atta spp.…”

Seedling establishment in eelgrass: seed burial effects on winter losses of developing seedlings

“…Seed burial has generally been viewed as important mostly for minimizing seed predation in terrestrial and submersed angiosperms (Fishman & Orth 1996, Hulme & Borelli 1999, Christian & Stanton 2004. In the Chesapeake Bay region, seeds distributed in October have shown higher establishment rates than seeds present in the summer (Marion & Orth 2010a) when seed predators are abundant and active (Fishman & Orth 1996), and seed burial ).…”