Olfaction plays an important role in the foraging behavior of rodents, but little is known about how this sense varies among taxa that evolved in different ecological settings. Field experiments were conducted in 10- by 10-m enclosures to test for interspecific differences in foraging success for ponderosa pine (Pinus ponderosa) or sunflower seeds, based on olfaction, of 4 rodent species: 2 heteromyid rodents (Panamint kangaroo rat, Dipodomys panamintinus, and Great Basin pocket mouse, Perognathus parvus) and 2 nonheteromyid rodents (yellow pine chipmunk, Tamias amoenus, and deer mouse, Peromyscus maniculatus). All species found large, shallow caches more frequently than small, deep caches. Chipmunks had the lowest foraging success for buried sunflower seeds under dry conditions. Deer mice did as well as the heteromyid rodents on large shallow caches but found relatively few small, deep caches. The heteromyids were the only species that found small, deep sunflower seed caches under dry conditions, and Panamint kangaroo rats always found more caches than did Great Basin pocket mice. These results confirm that olfaction plays an important role in foraging of rodents for buried seeds and support the notion that the olfactory sense of rodent species has evolved greater sensitivity to seeds in different ecological contexts.
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.
The dispersal behavior of female snow melt mosquitoes was studied in two forests in Rhineland-Palatinate, Germany, from April to August 1993. Both CDC-light-traps and human bait collections were used to collect mosquitoes. Sampling sites were chosen along a west-east and a north-south transect in treated and untreated parts of a forest with a village in its center. Around this settlement, breeding sites within a radius of 1.5 to 2.5 km were treated. It could be shown that this buffer zone is sufficient to prevent a nuisance caused by snow melt mosquitoes in the village. The results lead to the conclusion that snow melt mosquitoes do not regularly migrate over large distances but stay near their breeding sites. In a detailed study of the behavior of Aedes rusticus, it could be observed that these mosquitoes were resting in the interior of the forest during daytime and leaving it with increasing dusk up to 50 m from the forest edge. A comparison of landing rate counts near a row of trees and in the open field showed higher activity near the row of trees indicating visual orientation of the mosquitoes. Although the Ae. rusticus females left the forest regularly, no nuisance occurred in nearby villages. The treatment of breeding sites near settlements appeared to be sufficient to prevent a nuisance caused by the snow melt mosquitoes.
Deer mice ( Peromyscus maniculatus) are known to larder hoard food, but their scatter-hoarding behav- ior is poorly documented. Eleven deer mice were each presented with 150 Jeffrey pine {Pinus jeffreyi) seeds in 10 x 10- m enclosures in Jeffrey pine forests on the east slope of the Sierra Nevada. Subjects made a mean ± 1 s of 31.2 ± 30.0 caches per trial. Caches were shallow (most 2-12 mm deep) and usually contained only 1 or 2 seeds. Most caches were made at the edge of antelope bitterbrush ( Purshia tridentata) shrubs in mineral soil or in thin layers of plant litter. These results suggest that deer mice might make a significant contribution to the dispersal of Jeffrey pine.
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 (<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 scatter‐hoarding 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.
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.
