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.
Summary1. 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 (<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.
We used a hierarchical approach to describe habitat characteristics of song posts and foraging sites used by Varied Thrushes (Ixoreus naevius) in coastal redwood (Sequoia sempervirens) forests of northwestern California. We measured mesohabitat (0.04-ha circular plots) and microhabitat (0.5-m radius) scale attributes centered on occupied and random song posts and foraging locations at four study sites during March–August of 1994 and 1995. Ninety-five percent of song posts were in trees or snags. Male thrushes used song posts with low foliage density near the top of large conifers (microhabitat scale), located on steeper slopes, surrounded by a high density of trees, and centered in drainages closer to water (mesohabitat scale) as compared to random locations. Varied Thrushes foraged predominantly on the ground early in the breeding season, then subsequently included fruit in their diet after the young had fledged. Although many variables were correlated with ground foraging locations, microhabitat foliage density had the greatest explanatory power, indicating thrushes selected foraging locations primarily at the microhabitat scale, and emphasizing the importance of measuring habitat characteristics at the appropriate spatial scale. Abrupt forest edges, such as those produced by clearcuts, may reduce habitat suitability for Varied Thrushes possibly explaining their absence from small forest fragments during the breeding season.
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