Search

Frugivory (animals ingest all or part of fleshy-fruits and defecate or regurgitate seeds) and scatter-hoarding (animals store seeds in small caches in soil) are two important vertebrate-mediated seed dispersal syndromes. In both instances, there is an exchange of food for seed transport, but there are many important differences. For example, the seeds of frugivore-dispersed plants are often clumped in feces or under roosts and the microsite of depostion is often unsuitable for seedling establishment. However, frugivores can transport seeds long distances allowing plants to colonize new areas and promoting gene flow between populations. Scatter-hoarding animals, on the other hand, actively space seeds in microsites that often favor seedling establishment, but don’t move seeds very far. Both modes of seed dispersal can be very effective, but in different way. Some species of plants have evolved propagules that take advantage of both modes of dispersal in two separate phases (i.e., diplochory), apparently to obtain both types of benefits.

Western chokecherry (Prunus virginiana var. demissa, Rosaceae) is dispersed by frugivorous birds and carnivores, but it has large seeds that are potentially attractive to rodents that could act as seed predators and dispersers. Here, we quantify the benefits of primary dispersal by birds and secondary dispersal by scatter-hoarding rodents. In the fall, avian frugivores (mostly American robins, Turdus migratorius, and cedar waxwings, Bombycilla cedrorum) consumed 87% of the fruit crop and dispersed 67% of the fruit crop away from parent plants. Rodents removed 89% of seeds that simulated bird-dispersed seed rain from transects in riparian zones and 58% from transects in upland habitats. Rodents scatter-hoarded 91.6% of the seeds they removed, burying most in small caches (two to eight seeds) 8-25 mm deep. About 39% of the seeds in spring caches produced seedlings. Inside rodent-proof exclosures, 52.1% of seeds buried to simulate rodent caches produced seedlings, 29.7% of which were still alive after 1 year. In contrast, only 3.8% of seeds placed on the soil surface, simulating dispersal by avian frugivores, produced seedlings. Seed dispersal by frugivorous birds likely contributes to colonization of unoccupied habitat through long-range dispersal and to escape from distance-dependent seed mortality near the parent plant. Despite seed losses, rodents offer short-range seed dispersal and bury seeds in more favorable sites for germination, improving seedling emergence and establishment. The combined mechanisms of seed dispersal significantly enhanced chokecherry seedling recruitment by providing more dispersal-related benefits than either frugivorous bird or scatter-hoarding rodents could provide alone.

Summary 1. The seeds of many plants are dispersed by animals, but the nature of these plant–animal mutualisms is often moulded by the abiotic environment. Here, we show that desert peach (Prunus andersonii), with dry fruits and large seeds, relies on scatter-hoarding rodents for dispersal and that this form of seed dispersal maintains the effectiveness of dispersal while reducing water expenditure. 2. The fruit pulp of desert peach dries and dehisces at maturity in early summer. No vertebrate frugivores consumed the fruits, but rodents quickly harvested the nuts. Nearly 75% of the nut crop was removed from plant canopies by scansorial rodents like white-tailed antelope squirrels (Ammospermophilus leucurus), which scatter-hoarded nuts in 1–2 seed caches 10–30 mm deep. Deer mice (Peromyscus maniculatus) also made many shallow one-nut caches. 3. Heteromyid rodents (Great Basin pocket mouse, Perognathus parvus; Panamint kangaroo rat, Dipodomys panamintinus) primarily larder-hoarded nuts (c. 60%) in burrows too deep for seedling emergence, but also scatter-hoarded nuts in a few, large caches 10–40 mm deep. 4. Antelope squirrels were the most effective dispersers and deer mice and Panamint kangaroo rats were less effective. Abiotically dispersed nuts had virtually no recruitment (

Many studies of postdispersal seed fate use seed removal as an index of seed predation. However, following primary seed dispersal, some seeds are transported intact by ants, dung beetles, scatter-hoarding animals, or abiotic processes to new microsites (secondary dispersal) where germination is possible. Despite a growing realization that secondary seed dispersal can play an important role in plant recruitment, many researchers continue to use seed removal as a proxy for seed predation and are focused too intently on only the initial step of seed fate. We describe, using examples from the recent literature, how the results of some seed removal studies may have been misinterpreted, present plausible, alternative explanations for the fate of seeds in those studies, and discuss the importance of detailed studies of seed fates. Following the fates of seeds can be difficult, but such studies contribute much more to our understanding of seed dynamics and plant fitness.