Rodent Foraging Research Articles

Rodent seed predation and GUDs: effect of burning and topography

We examined the relationships between seed predation and the habitat into which a seed falls, abundance of rodents within that habitat, and foraging pattern of rodents within that habitat. Using seed plots, we assessed seed predation in burned and unburned tallgrass prairies at biweekly intervals between May and September in 2001 and 2002. Significantly more seed was removed from plots in burned than unburned prairies. Rodent abundance did not differ between burned prairie and unburned prairie, although the abundance of omnivorous–granivorous rodents (herbivores excluded) was greater in burned than unburned prairie. Proportion of seed removed in burned and unburned prairies was independent of both total rodent abundance and abundance of omnivorous–granivorous rodents. We also measured giving-up density (GUD) of rodents in burned and unburned prairies during the spring and summer of 2002. GUDs did not differ significantly in burned and unburned prairies. However, rodents had a higher GUD in uplands than in limestone breaks or lowland habitats. Our results suggest that rodent foraging in tallgrass prairie is affected by microhabitat and that rodent abundance is not sufficient to predict seed predation.

Rodent foraging is affected by indirect, but not by direct, cues of predation risk

We used foraging trays to determine whether oldfield mice, Peromyscus polionotus, altered foraging in response to direct cues of predation risk (urine of native and nonnative predators) and indirect cues of predation risk (foraging microhabitat, precipitation, and moon illumination). The proportion of seeds remaining in each tray (a measure of the giving-up density [GUD]) was used to measure risk perceived by mice. Mice did not alter their GUD when presented with cues of native predators (bobcats, Lynx rufus, and red foxes, Vulpes vulpes), recently introduced predators (coyotes, Canis latrans), nonnative predators (ocelots, Leopardus pardalis), a native herbivore (white-tailed deer, Odocoileus virginianus), or a water control. Rather, GUD was related to microhabitat: rodents removed more seeds from foraging trays sheltered beneath vegetative cover compared with exposed trays outside of cover. Rodents also removed more seeds during nights with precipitation and when moon illumination was low. Our results suggest that P. polionotus used indirect cues rather than direct cues to assess risk of vertebrate predation. Indirect cues may be more reliable than are direct scent cues for estimating risk from multiple vertebrate predators that present the most risk in open environments.

Granivory and microhabitat use in Australian desert rodents: are seeds important?

The diet and microhabitat use of two species of native Australian desert rodents, the spinifex hoppingmouseNotomys alexis and sandy inland mousePseudomys hermannsburgensis, were studied in the Simpson Desert, south-western Queensland. Contrary to expectation, both species were confirmed from analyses of their stomach contents to be omnivorous. The diets of both species varied through time in a similar manner; seeds were important in summer and especially in winter, but in autumn invertebrates constituted nearly 50% and 60% of the diet ofN. alexis andP. hermannsburgensis, respectively. Other plant material (root, leaf, floral part, stem) was found in appreciable amounts in the stomach contents of both species, and fungi were identified from a small number of individuals. Both species showed a high degree of overlap in the broad types of food they ingested (seed, plant material, invertebrates); however, there was considerably less overlap in the species of seeds eaten. Analysis of microhabitat use suggested that this difference was due to differential foraging between the species; the larger, bipedalN. alexis forages in the open more than the smaller, quadrupedalP. hermannsburgensis, which is found more commonly in or under hummocks of spinifex grass. Although our findings parallel patterns of morphological specialisation and differential foraging on seeds that have been described within communities of North American heteromyid rodents, we found little evidence that the foraging economics ofN. alexis orP. hermannsburgensis should depend solely or primarily on the distribution patterns of seeds. In the absence of dietary information, we suggest that ecological studies of desert rodents which focus solely on granivory, and neglect other important aspects of rodent foraging, can lead to a misinterpretation of species coexistence and community structure.

Mechanisms of Species Coexistence of Optimal Foragers: Temporal Partitioning by Two Species of Sand Dune Gerbils

Mechanistic approaches to understanding species coexistence and community structure have recently proved highly successful. We apply this approach to a sand dune community containing two common species of gerbils, Gerbillus allenbyi and G. pyramidum. Previous work suggested that coexistence is based on temporal variability in seed resource density on a daily time scale and a tradeoff of foraging efficiency at high versus low resource abundances. We tested the predictions of this mechanism by quantifying rodent foraging activity and its timing during the night over 6 nights using sand tracking plots, sand tracking strips, and seed trays. We demonstrated temporal partitioning with all three methods

Rodent seed predation in cereal crop areas of central Spain: effects of physiognomy, food availability, and predation risk

Patterns of rodent seed predation in extensive cereal croplands of central Spain were investigated by measuring rodent predation rates on artificial seed patches, together with seed availability, rodent abundance and habitat physiognomy Sampling was designed to cope with the spatial and temporal variability of factors potentially affecting rodent activity (natural and man‐made habitat features, season and moonlight) Rodent predation was unpredictably distributed in summer In winter, rodents foraged on average in the patches least used by man. moonlight, however, did alter this pattern, so that rodent predation was closely associated with shrubs in the bright nights and evenly distributed in the dark ones I conclude that the need of stable underground refuges and predation risk in the winter period seemed to be the mam factors constraining rodent foraging activity in the man‐made ecosystem studied

Indirect Facilitation of Granivorous Birds by Desert Rodents: Experimental Evidence from Foraging Patterns

In order to quantify the response of birds to experimental manipulations of seed availability and densities of granivorous rodents and ants, we counted granivorous birds and measured diurnal and nocturnal seed removal on 24 plots during winter months in the Chihuahuan Desert. Removal of single, widely spaced millet seeds provided a reliable measure of bird and rodent foraging activity. Avian foraging activity increased in response to supplemental seeds, but decreased in response to long—term removal of all rodents and all ants. Although birds potentially compete for seeds with rodents and ants, these results suggest that, in the long term, indirect facilitation dominates the interactions among all three taxa. The positive effect of the other granivores on birds may be mediated through changes in habitat structure (e.g., reduction in the density of annual plants). The increase of avian foraging in response to seed addition and the high spatial and temporal variance in the patterns of seed removal by birds indicate that in desert habitats granivorous birds use their mobility to find and exploit high concentrations of seeds. Thus, birds may reduce the spatial variation in seed abundance and reduce the densities of seed available to other granivores. The foraging behavior of birds and rodents revealed by these experiments clarifies the response of granivores to experimental manipulations reported earlier, such as the lack of biomass compensation by rodents in response to seed addition.

Distribution of Seeds in Sonoran Desert Soils: Implications for Heteromyid Rodent Foraging.

We used a hierarchical sampling design to investigate temporal and spatial patterns of variation in the topsoil seedbank at a site on the Santa Rita Experimental Range, 50 km south of Tucson, Arizona. Replicate sets of contiguous 4 ° 4 cm samples to 2 cm depth ("transects") were collected three times per year, from 1980 to 1983, from four microhabitats that are differentiated by desert heteromyid rodents: large and small open spaces, under canopies of large shrubs, and under canopies of small trees. We also analyzed texture and organic content of soils from the four microhabitats. Seeds from 54 plant taxa were encountered, most of them rare. Average seed mass across species was 1.28 mg/seed, but because tiny seeds were most numerous, the abundance-weighted average was 0.16 mg/seed. Total seed abundance was highly variable, ranging from 0 to 256 seeds and from 0 to 146 mg per sample. The fourfold temporal variation in mean mass or number of seeds per sample was largely due to between-year rather than between-season effects. Seed standing crops were positively correlated with rainfall during the previous 6-mo rainy period, and were lowest in fall and winter of 1982 after 2 yr of poor winter rains. Mean seed number per sample, which reflects primarily abundance of tiny seeds, did not vary among microhabitats. Mean per-sample seed mass, which reflects abundance of the large seeds eaten by rodents, did vary among microhabitats, however, with values being higher under shrubs and trees than in open spaces. The low mean abundance in open spaces was due more to a high frequency of seedless samples than to low maximum per-sample abundance. Hence, profitable seed patches do occur in open spaces, but are rarer than under shrubs or trees. Within microhabitats there was significant variation among replicate transects and among samples within transects. On a local scale, seeds occurred in patches 12 cm in diameter in all microhabitats and sampling periods. Seed species composition varied seasonally and among microhabitats, and there was an overall correlation between seed and adult microhabitat distribution for spring ephemerals. Soil from open spaces was finer and had lower organic content than that under shrub or tree canopies. Our results suggest that the resource upon which desert granivores depend is highly variable in time and space. Microhabitat is one of the most conspicuous sources of variation, and heteromyid rodent species differ in use of those microhabitats (open spaces vs. areas under canopies of perennial plants) that differ most noticeably in seed abundances, species composition, and soil characteristics.

Rodent Predation on Larvae of Coleophora parthenica (Lepidoptera: Coleophoridae), a Moth Imported for the Biological Control of Russian Thistle

Rodent predation of stem-boring larvae of Coleophora parthenica Meyrick, a moth imported for the biological control of Salsola australis R. Brown, was studied at Indio, Calif. The frequency, extent, and distribution of this predation were determined. Field trapping and laboratory feeding trials identified the house mouse, Mus musculus L., as the cause of this predation. Predation was seasonal and restricted to overwintering larvae in branches. Significantly more predation occurred in clumped than in solitary plants. Branch dissections indicated that rodent foraging was directed, although the overall success rate for removing the larvae was only 50%. Rodents preferred to forage for larvae within the thinner, less woody, secondary branches in the plant crowns. Rodents killed and removed 25.4% of the overwintering larvae within sampled branches. Surveys indicated that the rodent predation was restricted to the 30-ha study site located near the original release point for the moth at Indio.

Desert rodent foraging: Caching based economy

Desert rodent foraging: Caching based economy