O. J. Reichman

Impact of Pocket Gopher Burrows on Overlying Vegetation

The impact of pocket gopher burrows on overlying vegetation was examined by analysis of plant samples taken from quadrats directly over active and vacant Geomys bursarius burrows, adjacent controls, and samples from the surrounding fields at sites in Kansas and Minnesota. The pocket gophers burrowed in that portion of the field which exhibited the greatest plant biomass. The biomass of plants (roots, stems, and both) directly over active burrows was, however, reduced by over one-third. The depletion was somewhat less over old, vacant burrows. The dominant forb species, with a tap root, was significantly more affected than the dominant grass, with a diffuse root system.

Responses to Simulated Leaf and Root Herbivory by A Biennial, Tragopogon Dubius

Removal of 25 or 75% of leaf or root tissue, and 25% of both, was used to simulate above- and belowground herbivory on Tragopogon dubius. Plants with 25% of their leaf tissue removed did not differ significantly from controls in total biomass; those with any root tissue trimmed produced significantly less biomass while the 75% leaf removal treatment was intermediate. A similar pattern was exhibited for plant mortality and flower production. Plants that had one or more flowers removed by herbivores grew significantly larger and produced significantly more flowers than plants that lost no flowers, regardless of treatment. The greatest differences between treatments in nutrient allocation patterns occurred 1 d after manipulations were applied. Subsequently, differences between treatments mod- erated, and values tended to converge by 98 d postmanipulation, when the plants were harvested. Seeds had significantly higher nitrogen concentration levels than leaf or root tissue.

Ecological and Mycological Characteristics of Caches in the Mounds of Dipodomys spectabilis

Banner-tailed kangaroo rats ( Dipodomys spectabilis ) are primarily granivorous and store large quantities of seeds in underground caches. We found that a majority of these caches occurred near 30 cm in depth or below 50 cm. Most caches were approximately one third of the distance from the mound center to the edge and were on the north or northwest side of the mounds. There was no obvious temporal relationships between use of seed and when they were gathered. Seeds stored early and late in a four-month period were significantly depleted after the four months while those stored during the middle of the experimental period, when native seeds were abundant, were not depleted. Mycological analyses of the caches revealed at least 23 species of fungi. Fungal colonists were more abundant and diverse in caches made in the middle of a four-month caching period than early or late in the period.

Caching behaviour by eastern woodrats, Neotoma floridana, in relation to food perishability

Abstract Two experiments were conducted on eastern woodrats to determine whether the preference for food items gathered for their caches and the sequence of use of items in the cache varied with perishability. In the first experiment, woodrats were given either 2 kg each of two non-perishable items, laboratory chow and bur oak acorns (which they used more than chow), or 2 kg each of preferred, but perishable, grapes and the non-perishable chow. As hypothesized, the woodrats both ate and stored acorns when they were paired with chow (there would be no advantage to either eating or storing the less-used chow). In contrast, when given grapes and chow, the woodrats continued to eat grapes but stored primarily chow. That is, the utility of the items appeared to change depending on whether they were to be eaten or stored. In the second experiment, woodrats were given excess amounts of chow or grapes that were 2, 4, 6 and 8 days old. They ingested chow in the proportions available, as the chow did not spoil with age. However, the consumed grapes in proportions significantly different from those available. It was anticipated that they would eat the oldes grapes first and store the freshest grapes, but neither this pattern nor any other was obvious in ralation to the age of the grapes. The results suggest that woodrats discriminate between food items based on their perishability, and vary their decisions about what to ingest and store accordingly.

Management of sterile and mouldy seeds by a desert rodent

Abstract Banner-tailed kangaroo rats (Dipodomys spectabilis) are known to store large quantities of seeds in underground caches. Over 20 species of moulds have been found in the caches, and experiments have shown that the kangaroo rats prefer to ingest slightly mouldy seeds over non-mouldy and very mouldy seeds. Laboratory experiments were designed to test the hypothesis that these rodents manage seeds to promote an intermediate level of seed mouldiness. The experiments revealed that rodents tended to move sterile seeds to the highest humidities available. The same individuals moved seeds with the preferred level of mouldiness to humidities below the threshold for further mould growth. We interpret these activities as adaptive attempts to increase mould growth on sterile seeds and inhibit further growth on sufficiently mouldy seeds.

The Influence of Three Sympatric Species of Fossorial Mole-Rats (Bathyergidae) on Vegetation

Samples of vegetation revealed that total plant biomass was reduced by almost 30% directly above burrows of mole-rats (Bathyergidae) compared with control samples. Bulbs and roots of dicots especially were reduced above burrows. We predicted that mole-rats would inhabit portions of the study site with greater than average plant biomass than indicated by random samples on the field site; this was not the case. Burrows underlay 10.7% of the study area and mounds produced during excavation of burrows covered another 28.2% of the field. Thus, the potential impact of burrowing activity of mole-rats on the plant community is substantial, through both direct consumption of plant material and physical alteration of the habitat.

Effects of Food Perishability, Distance, and Competitors on Caching Behavior by Eastern Woodrats

Four experiments were performed to determine whether eastern woodrats ( Neotoma floridana ) differentially consumed and cached perishable and persistent food under different sets of conditions. We predicted that adding the factors of distance and competition to perishability would change the way in which foods were selected. In experiment 1, woodrats differentially consumed more-perishable fresh apple slices, whereas in experiment 2 they differentially cached less-perishable dry apple slices. In experiment 3, when given the choice between fresh and dry slices at locations both nearby and distant from their cache sites, woodrats cached nearby dry items before nearby fresh items or fresh and dry items from the distant location. Experiment 4 revealed that presence of a putative conspecific competitor shifted behavior toward securing nearby dry and distant dry items before fresh items from either distance. Results of the order in which items were eaten and cached in experiments 1 and 2 are consistent with predictions concerning trade-offs of the cost of food with respect to perishability. Results of experiment 3 were in partial agreement with predictions concerning the order of acquisition when perishability and distance were considered. Results of experiment 4 were not in agreement with predictions when perishability, distance, and competition were considered.

Seed preferences by desert rodents based on levels of mouldiness

Abstract Large species of kangaroo rats (family Heteromyidae) make extensive underground caches of seeds. During collection and storage, seeds become inoculated with fungal spores, most of which are common pernicious storage moulds in human agriculture systems. The moulds and their metabolites may be beneficial or detrimental, depending on the species of mould and the growth conditions. Feeding experiments were conducted to determine the preferences for mouldy seeds by Dipodomys spectabilis . Results showed that kangaroo rats prefer slightly mouldy seeds over very mouldy seeds, dry seeds, and unmouldy, imbibed seeds, apparently taking advantage of beneficial effects of moulds while avoiding the liabilities.

Characteristics and Significance of the Caches of Eastern Woodrats (Neotoma floridana)

Caches from eastern woodrat ( Neotoma floridana ) dens were analyzed for plant-species composition, abundance, and energy content. Body mass and sex of den residents and the den volume were measured to determine correlations with energy content of caches. We found no difference between males and females in den volume or energy content of caches. However, a positive correlation existed between body mass of the cache owner and the amount of energy stored in the cache, such that larger individuals had a disproportionately greater reserve of energy stored in caches than did smaller individuals. The disparity suggests that small individuals are forced to forage outside the den more often than large individuals.

Influence of maternal diet and perishability on caching and consumption behavior of juvenile eastern woodrats

We tested the hypotheses that juvenile eastern woodrats ( Neotoma floridana ) learned to select appropriate foods to cache by cues from the maternal diet and that the effect of perishability affected caching and consumption behavior of juvenile woodrats. In May 1993, female woodrats were mated and placed on a diet of garlic-flavored chow. Females in group A were fed garlic-flavored chow until offspring were weaned. Females in group B were fed garlic-flavored chow until parturition and then were placed on a diet of standard laboratory chow. All offspring were weaned at 45 days postpartum and maintained on a diet of standard laboratory chow. In October and November 1993, juveniles were tested to determine their preference for caching and consumption of garlic-flavored chow or a novel (mint) flavored chow. Juveniles in group A cached more garlic-flavored chow than juveniles in group B ( P = 0.04). There was no difference between groups in the amount of garlic chow consumed ( P = 0.5). Naive juveniles preferred to cache dry apple ( P = 0.01) but preferred to consume fresh apple ( P = 0.01). The outcome of our experiments suggests that maternal diet influences the cache-food selection of naive woodrats. Further, naive juvenile woodrats treat perishable and non-perishable foods in a manner similar to adults suggesting that their response to such foods is not learned.