Seed dispersal by scatter-hoarding rodents in arid environments

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 (Ammo-spermophilus 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 mmdeep. 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 (< 1% emergence), but nuts buried in soil to simulate rodent caches had 32% emergence and 5.6% survived after 1 year. Scatter-hoarding rodents are responsible for virtually all recruitment in desert peach. 5. Synthesis. Desert peach arose from a fleshy-fruited ancestor that was probably dispersed by endozoochorous frugivores. About 35 species of dry-fruited Prunus occur in arid environments across North America and Eurasia. The most parsimonious explanation for the evolution of dry-fruited Prunus is the loss of frugivory in a diplochorous ancestor (i.e. combined frugivore and scatterhoarding dispersal) to maintain the effectiveness of seed dispersal while reducing the demand for water in arid environments.