Mast Production Research Articles

Hard Mast Production Before and After the Chestnut Blight

Abstract We estimated hard mast production of a Southern Appalachian forest for two 10 yr intervals: one before and one, 35 yr after, the chestnut blight fungus (Cryphonectria parasitica) (Murr.) Barr, had killed all mature chestnut trees. The basal area of hard mast-producing trees in the postblight forest was 28% less than in the preblight forest. The estimate of hard mast output was 34% less after the chestnut blight. Postblight production was less than preblight production for 8 of 10 yr. During 5 of these years, postblight production was only 5-27% of preblight production. Annual preblight mast production was relatively stable, whereas annual postblight production fluctuated substantially. Our findings suggest that the loss of mature chestnuts (Castanea dentata) markedly reduced the Southern Appalachian forest's carrying capacity for certain wildlife species. South. J. Appl. For 24(4):196-201.

Population viability analysis of a Japanese black bear population

AbstractA population viability analysis (PVA) was conducted for a Japanese black bear population in Shimokita Peninsula, northern Japan, using an individual‐based simulation model. Demographic stochasticity was incorporated in the model as well as the environmental stochasticity from the fluctuation of annual mast production. The extinction risk of the population was estimated with an emphasis on the effect of carrying capacity reduction and hunting pressure. The results suggest that the population has a high risk of extinction. Even if there is no further reduction of the carrying capacity and no hunting at all, the present size of the population cannot pass the test of the minimum viable population size (MVP) concept. Considering possible carrying capacity reduction in the future and actual hunting pressure, the population will fail to survive for 100 years at a very high probability. Because of deterioration of habitat and loss of the corridor between habitat areas, the population has become very sensitive to demographic impacts, including hunting pressure.

Influence of site conditions on the survival of Fagus sylvatica seedlings in an old‐growth beech forest

Abstract. Following a full mast production in autumn 1995 in the old‐growth beech forest of la Tillaie (France), cupules, live and dead 1‐yr old seedlings were counted in September 1996 in 40 plots, representing a wide range of ecological conditions. The influence of geomorphology and forest stage on mast production and on seedling establishment and survival was studied. Maximum seedling abundance did not occur in areas with the largest cupule abundance, but this result was not statistically significant. The presence of a shallow sandstone table under Fontainebleau sand, where beech is far from its ecological optimum, positively influenced the production of mast but negatively influenced seedling survival. Contrary to expectation, the early biostatic rather than the late biostatic phase seemed to be the best stage for beech regeneration. Gaps also provide good environmental conditions for seedling establishment. Humus and light conditions, water availability and competition between beech individuals may explain the results. Light was the main factor influencing mast production in mature stages, and drought was an important factor causing seedling mortality. This study points out the importance of seedling survival for regeneration patterns in beech forests.

THE INFLUENCE OF ACORN CROPS ON ANNUAL VARIATION IN RODENT AND BIRD POPULATIONS

I recorded mast production by oaks (Quercus sp.) at 12 forested sites in western Virginia for 6–12 yr and measured its impact on the abundance of small mammals, understory vegetation, and artificial-nest predation. White-tailed deer (Odocoileus virginianus) were excluded from half the 4-ha sites after at least one season of data collection. My hypothesis was that annual variation in acorn crops affected multiple species and that the strength of those interactions is mediated by white-tailed deer. The acorn crop was variable across sites and year, with some of the between-site variability explained by differences in elevation. All sites experienced at least one mast failure, and mast failure years were generally consistent across sites. White-footed mouse (Peromyscus leucopus), eastern chipmunk (Tamias striatus), and gray squirrel (Sciurus carolinensis) populations were significantly correlated with annual fluctuations in the acorn crop. The exclusion of deer had a significant impact on P. leucopus and T. striatus populations by increasing the number of animals captured following low acorn mast years. Annual fluctuations in the acorn crop, but not in rodent densities, were significantly correlated with the rates of predation on artificial nests the next summer. There was no significant interaction between predation rates and the exclusion of deer. An index from the Breeding Bird Survey (BBS) for Virginia was used to measure regional numbers for 11 common species captured at the sites. The index for two understory species was significantly negatively correlated with the mean acorn crop measured 2 yr previously. The effect of white-tailed deer on the forest community was not consistent across all conditions, as sites with large acorn crops were not strongly influenced by deer. These data are consistent with the hypothesis that mast crops from oaks serve as important determinants of community function within Appalachian forests.

Effects of Forest Fragmentation on Population Attributes of White-Footed Mice and Eastern Chipmunks

We examined differences between populations of white-footed mice ( Peromyscus leucopus ) and eastern chipmunks ( Tamias striatus ) in woodlot fragments and unfragmented forests and attempted to discriminate among potential causal mechanisms. White-footed mice showed increased population density and body mass in woodlots but otherwise no differences in population attributes between woodlots and forests. Eastern chipmunks showed decreased survival rates in woodlots but no other differences in population parameters between woodlots and forests. Mast production was variable among sites but showed no differences between woodlot and forest sites. Likewise, total biomass of mammalian granivores was similar between woodlot and forest sites, but woodlots contained an impoverished community of granivores. White-footed mice and eastern chipmunks may be affected differentially by forest fragmentation, presumably due to differences in their life-history stategies. Our results suggest that white-footed mice thrive in woodlot fragments due to increased mast availability resulting from decreased biomass of competing granivores. In contrast, eastern chipmunks may be influenced negatively by forest fragmentation, possibly because they are more susceptible to increased rates of predation occurring in woodlots than white-footed mice.

Mast seeding and Lyme disease

We wish to comment on two issues relating to a prediction raised in the article by Randolph[1xRandolph, S.E. Trends Ecol. Evol. 1998; 13: 301–303Abstract | Full Text | Full Text PDF | PubMed | Scopus (7)See all References[1]about our work[2xJones, C.G. et al. Science. 1998; 279: 1023–1026Crossref | PubMed | Scopus (255)See all References[2]. Randolph argues that because `low acorn production and moderate mouse densities are the norm [our] data do not explain the cause of the severe acorn failures and contingent crash in mouse populations that might initiate [gypsy] moth outbreaks'. We made no attempt to explain masting periodicity, but autumnal mast production does predict white-footed mouse (Peromyscus leucopus) density the following summer[3xWolff, J.O. J. Mammol. 1996; 77: 850–856CrossrefSee all References, 4xOstfeld, R.S., Jones, C.G., and Wolff, J.O. Bioscience. 1996; 46: 323–330CrossrefSee all References, 5xElkinton, J.S. et al. Ecology. 1996; 77: 2332–2342CrossrefSee all References]. Moderate mouse densities are indeed the norm. In most summers, densities are at or above c. 10 mice ha−1, which is sufficient to keep gypsy moth (Lymantria dispar) populations low via pupal predation[4xOstfeld, R.S., Jones, C.G., and Wolff, J.O. Bioscience. 1996; 46: 323–330CrossrefSee all References, 5xElkinton, J.S. et al. Ecology. 1996; 77: 2332–2342CrossrefSee all References, 6xElkinton, J.S. and Liebhold, A.M. Annu. Rev. Entomol. 1990; 35: 571–596CrossrefSee all References]. However, mouse populations do periodically collapse to below 10 ha−1 for one to two summers[3xWolff, J.O. J. Mammol. 1996; 77: 850–856CrossrefSee all References, 4xOstfeld, R.S., Jones, C.G., and Wolff, J.O. Bioscience. 1996; 46: 323–330CrossrefSee all References]. Evidence indicates that this is when moth populations, with their high fecundity, can rise to levels mice cannot suppress[2xJones, C.G. et al. Science. 1998; 279: 1023–1026Crossref | PubMed | Scopus (255)See all References, 4xOstfeld, R.S., Jones, C.G., and Wolff, J.O. Bioscience. 1996; 46: 323–330CrossrefSee all References, 5xElkinton, J.S. et al. Ecology. 1996; 77: 2332–2342CrossrefSee all References]. Mouse population collapses tend to occur if major masting events, which result in very high mouse densities, are followed by mast failure and food limitation. These events occur with a frequency similar to moth outbreaks[3xWolff, J.O. J. Mammol. 1996; 77: 850–856CrossrefSee all References, 4xOstfeld, R.S., Jones, C.G., and Wolff, J.O. Bioscience. 1996; 46: 323–330CrossrefSee all References].Randolph challenges our conclusion that white-footed mice play the major role in infecting Ixodes scapularis ticks with Borrelia burgdorferi. However, in the eastern United States, P. leucopus is both the most abundant host for ticks and by far the most competent reservoir for B. burgdorferi[7xSee all References[7]. Furthermore, Mather and Ginsberg[8xSee all References[8]demonstrated that the prevalence of spirochete infection in nymphal I. scapularis ticks strongly correlates with white-footed mouse density in the previous year. In our forests, acorns markedly affect mouse density, the density of host-seeking larval ticks and the number of ticks attached to mice[2xJones, C.G. et al. Science. 1998; 279: 1023–1026Crossref | PubMed | Scopus (255)See all References[2]. Therefore, we conclude that acorn production should allow epidemiologists to predict Lyme disease risk well in advance, here in the USA[9xOstfeld, R.S. Am. Sci. 1997; 85: 338–346See all References[9]. The European situation, in which several tick hosts are competent reservoirs, will probably make predicting Lyme disease risk more difficult. Nevertheless, we hope that epidemiologists will test the power of acorn production as a predictor of Lyme disease risk in European oak forests.

Post-dispersal seed predation: consequences for plant demography and evolution

Abstract Post-dispersal seed predation is only one of many factors underlying plant demography and evolution. Nevertheless, the generalist feeding habits of many post-dispersal seed predators and the limited ability of plants either to compensate for or to respond to post-dispersal seed losses directly suggest that post-dispersal seed predation may have a considerable impact on plant populations. Seed predators probably have little direct influence on the demography of plants that regenerate exclusively by vegetative means or are buffered by a large active seed bank, but such species are only a minority in most plant communities. In general, ants are significant post-dispersal seed predators in arid and semi-arid ecosystems while they act mainly as seed dispersers rather than as predators in temperate ecosystems. Although studies have probably underestimated the importance of invertebrates and birds as seed predators, rodents appear to have greater potential to influence seed dynamics, and are particularly important in temperate ecosystems. For example, production of mast seed crops is more effective at satiating specialist invertebrate seed predators than generalist vertebrates, and recruitment may be limited by post-dispersal seed predation even during mast years. Both spatial variation in post-dispersal seed predation and differences in predation between species are important elements which facilitate the coexistence of different plant species. Where microsites are limiting, selective post-dispersal seed predators can influence pre-emptive competition for these microsites. Seed size determines the extent of density-dependent predation and the exploitation of buried seed. This suggests that post-dispersal seed predators may also play a role in the evolution of seed characteristics. However, conclusions regarding the ecological and evolutionary impact of post-dispersal seed predators will remain speculative without a more substantial empirical base.

Integrative ecology and the dynamics of species in oak forests

Lyme disease and gypsy moth outbreaks plague many temperate oak forests. Over the past decade, we have developed models and hypotheses designed to allow us to predict irruptions of both gypsy moths and the tick vector of Lyme disease. We have documented a web of connections involving mast production by oak trees, population responses by white-footed mice, habitat selection by white-tailed deer, and population dynamics of both tick parasites and defoliating insects. In patchy landscapes typical of the northeastern U.S., dispersal by mice, deer, and attached ticks between oak and nonoak forests creates dynamics that would not be predictable by focusing on a single patch type. We would not have uncovered these interactions without adopting a research approach that comprised: (1) the inclusion of diverse taxa of animals, plants, and microbes; (2) the integration of individual, population, community, and ecosystem levels of organization; (3) the incorporation of more than one patch type in a heterogeneous landscape; and (4) a combination of long-term monitoring and manipulative field experiments.

Visual Counts of Acorns of California Black Oak (Quercus kelloggii) as an Indicator of Mast Production

Abstract In 1995, acorn production of California black oak(Quercus kelloggii) was measured on 20 mature trees located in two stands in Placer County, California. Acorn production of each tree was measured using three 0.8 m² cone traps and a single 30 sec visual count. Visual counts were compared with trap data to develop statistical relationships between the two methods because visual counts have some advantages over traps, and we desired an efficient measure of the amount of acorns available as food for wildlife. Visual counts were positively correlated (P < 0.020) with several trap measures including wet acorn weight, weight of sound acorns, dry acorn weight, and total number of sound acorns. Linear regression of square-root transformed data found that visual counts could be used to predict total weight of sound acorns and total weight of dry acorns (P < 0.003). These results indicate that visual counts are adequate surrogates for more detailed measures of acorn production. West. J. Appl. For. 13(1):27-31.

A sixteen-year record of regional and temporal variation in the fruiting of beech (Fagus sylvatica L.) in England (1980-1995)

Summary Annual production of mast by the beech is highly variable, yet there are few long-term records of the extent of masting which might help to explain the masting phenomenon. In this 16-year study, beech mast has been sampled from 100 trees by 7-min samples collected from the ground and from low-growing branches at sites ranging from the south to the north of England, and varying from closed canopy beechwood to shelter belts, avenues and isolated trees in parks. Variation in production of viable seed is much greater from year to year than from north to south. Good masting occurred in 1980, 1982, 1984, 1990 and 1995: in these years at least one year of very bad masting normally followed. Otherwise, prediction of masting is unreliable. No full mast was found in 1981. Overall there was very little full mast in five other years, but even in these years, some sites or some trees produced an appreciable amount. All trees produced empty pericarps as well as full mast, especially on lower or shaded branches. Isolated trees produced more empty pericarps than trees in groups; this is likely to result from a lack of cross pollination. It is concluded that ground sampling for a fixed period affords a rapid and effective method of assessing masting despite the factors intervening between mast shedding and collection.

Coexistence of white-footed mice and deer mice may be mediated by fluctuating environmental conditions.

White-footed mice, Peromyscus leucopus noveboracensis, and deer mice, P. maniculatus nubiterrae, occur sympatically throughout much of the Appalachian Mountains of the eastern United States. Previous studies have shown that these two species are behaviorally and ecologically similar and do not partition food or microhabitat. In this paper I use a 14-year data set to demonstrate that the two species have differential population growth and survival rates in response to food abundance and season, which may mediate their coexistence. The ratio of white-footed mice to deer mice ranged from 0.5:1 to 6:1. During summer and times of tood abundance, white-footed mice gained a numerical advantage over deer mice in 10 of 14 years, whereas following winter and poor food production, deer mice had higher survival in 9 of 13 years. The major decline in white-foote mice, but not deer mice, was associated with poor mast (acorn) production in autumn. Differential survival of deer mice may be due to their physiological adaptations to cold temperature and efficient use of torpor during food shortage. Inter-year variance in food production and climatic conditions appear to change the competitive advantage of each species often enough to permit coexistence. Coexistence of these two ecologically similar species may be maintained by different physiological limitations in a fluctuating environment.

Population Fluctuations of Mast-Eating Rodents Are Correlated with Production of Acorns

I used a 14-year dataset on dynamics of mast-consuming rodents from an eastern deciduous forest to determine the relationship between population fluctuations of white-footed mice ( Peromyscus leucopus ), deer mice ( P. maniculatus ), and eastern chipmunks ( Tamias stria-tus ) and production of acorn mast. Mast (acorn) production was episodic with four excellent crops produced in 14 years. Densities of rodents in summer ranged from 3 to 103 animals/ha and correlated positively with production of mast the previous autumn (all r 2 > 0.56). During years of high production of mast, stores of acorn lasted throughout winter, whereas in most years, acorns were gone by January. During years of high production of mast, mice bred all winter, which resulted in high densities the following summer. Episodic production of mast and resulting fluctuations in consumers of mast have implications for the predator-satiation hypothesis and other community processes.

Foods Used by Male Mallards Wintering in Southeastern Missouri

Although winter foods of mallards (Anas platyrhynchos) have been documented in several studies, the importance of ecological or biological factors on the consumption of specific food groups often was ignored. Consequently, we evaluated whether age, pair status, molt status, habitat, year, or season influenced foods consumed by male mallards in southeastern Missouri during winters 1983-86. Seeds of moist-soil plants composed 61.4 and 46.0% of the aggregate dry mass diet of ducks collected in 1983-84 and 1984-85. Agricultural grain made up 33.8% of the aggregate dry mass diet in 1984-85, and acorns accounted for 64.5% of the diet in 1985-86. Our analysis revealed that habitat where birds were collected (P < 0.01) and annual variation (P < 0.01) were predominate factors influencing male mallard diet during winter. We attribute annual differences in food consumption primarily to annual variation in mast production. Invertebrates were present in 82% of 156 food samples, but composed only 7.3% dry mass of all ducks collected. Invertebrate consumption was greater during mid-winter than during other portions of winter (P < 0.01), probably a result of population growth and life history strategies of invertebrate species. Consumption of food groups did not differ among adult and immature males (P = 0.75), paired and unpaired males (P = 0.15), or males of different molt status (P = 0.22). These results suggest that age and physiological factors are less important than environmental factors in determining food use by male mallards during winter. Providing a diversity of habitats and suitable foods may be the best management approach to compensate for annual variation in availability of individual food resources.

Thirty years of seed production in a subalpine Norway spruce forest: Patterns of temporal and spatial variation

Norway spruce seed production was studied over 30 years in a subalpine forest of the south-eastern Alps. Thirteen locations were selected along a gradient of elevation and aspect. During mast years, seed production declined on average by about 100 seeds m −2 year −1 per 100 m elevation. The increase in elevation was associated with a reduction in mast year frequency and average mast production. A complex of climatic and edaphic factors appeared to be responsible for the reduction in seed production along the elevation gradient. North-facing locations produced significantly more seeds per square metre per year than south-facing locations. This difference was probably linked with frequent water stresses on south-facing slopes. Variability in seed production within the forest was pronounced and unpredictable in low-production years. The tendency to concentrate seed crops, especially during mast years was not influenced by stand characteristics. The proportion of full seeds and the proportion of seeds which survived vertebrate predation were higher during mast years. These results are interpreted in the context of Norway spruce population dynamics.

Ecology of Lyme Disease: Habitat Associations of Ticks (Ixodes Scapularis) In a Rural Landscape

Human activities often result in the creation of patchy landscapes, which may influence distribution and abundance of some wildlife species and their ectoparasites. Risk of exposure to Lyme disease is a function of the abundance of ticks (Ixodes scapularis, formerly I. dammini), which in turn may be determined by the distribution of key vertebrate hosts within landscapes. We used transect drag sampling and small‐mammal trapping to estimate, respectively, the abundance of host‐seeking and attached ticks in a rural landscape (southeastern New York) consisting of a mosaic of several discrete habitat types. Forested habitat types supported higher densities of host‐seeking ticks than herbaceous or shrub‐dominated habitats. However, in patches of little bluestem grass and gray dogwood shrubs, small mammals had high tick burdens despite low densities of host‐seeking ticks. There was an outbreak of larval ticks limited to oak‐dominated habitats in summer, 1992, which we postulate was related to unusually heavy acorn (mast) production attracting white‐tailed deer and attached adult deer ticks, in autumn 1991. This hypothesis was supported by low densities of larval ticks in oak patches in summer, 1993, following poor mast production the previous autumn. Instead, the 1993 larval peak shifted to maple‐dominated habitats, which may result from intensive use of these patches by deer in nonmast years. The abundance of host‐seeking nymphs was strongly correlated with the abundance of white‐footed mice the prior summer. Both the high tick burdens in little bluestem and dogwood patches, and shifting locations of larval outbreaks, appear to be functions of landscape configuration, especially patch size and juxtaposition.

White-Tailed Deer Foraging in Relation to Successional Stage, Overstory Type and Management of Southern Appalachian Forests

Year-round foraging of white-tailed deer (Odocoileus virginianus) on the na- tional forests of the Southern Appalachian mountains in Georgia, North Carolina and Ten- nessee was determined by analysis of rumen samples from 581 deer taken over 5 years and by sampling forage availability and evidence of browsing in selected habitat types. Spring and summer diets consisted mainly of green leaves and succulent twig tips of deciduous woody plants (58% in spring, 54% in summer). These forages were more abundant and used more intensively by deer in and around clearcuts than in adjacent older forests. Most other im- portant foods in these seasons (i.e., fruits, forbs and fungi) also were much more abundant in the clearcuts. Flowers of yellow-poplar (Liriodendron tulipifera), which dominated the diet in late May and earlyJune, and squawroot (Conopholis americana), a parasitic herb associated with red oaks ( Quercus spp.) and an important secondary food throughout most of the spring and summer, were more available in older forests. Fall and winter diets were influenced greatly by the availability of mast, especially acorns. When mast was abundant, it dominated the diet. When mast was scarce, deer fed mainly on the leaves of broadleaf evergreen woody plants, especially rosebay rhododendron (Rhododendron maximum). Twig ends were used little by deer during fall and winter. Older forests generally provided best foraging conditions for deer in fall and winter, being the primary source of mast and also producing about the same quantity of broadleaf evergreen foliage as clearcuts. Clearcuts and older forests provide complementary benefits to deer. Forests of intermediate age (after crown closure reduces browse availability and before onset of significant mast production) contribute much less to the deer forage resource than either clearcuts or older forests. Specific contributions of different forest age classes to the forage base vary with site characteristics. Implications of changing forest management policy are discussed.

Comparison of total lipids, fatty acids, sugars and nonvolatile organic acids in nuts from four Castanea species

AbstractTotal lipid percentage and fatty acid ratios in nuts from Castanea dentata (Marsh) Borkh (American), C sativa Mill (European), C mollissima B1 (Chinese) chestnuts and C pumila (L) Mill (chinkapin) were significantly different among all species and among individuals within species. Total lipids and fatty acids were greatest in American chestnuts followed by chinkapins, then European chestnuts, and lowest in Chinese chestnuts. Palmitic, stearic, oleic, linoleic and linolenic acids comprised the fatty acid complement in all species. Free sugars (fructose, glucose and sucrose) and the sugar‐alcohol inositol did not differ significantly (P &gt; 0.05) by species except in the European chestnuts where fructose and glucose were absent. Citric acid was present in all species except the European chestnuts. Malic acid was present in all species except in the American chestnuts. These results can be used to test nuts of new hybrids being bred for nut orchards and for wildlife mast production.

Fibroblast-Derived Factors Induce Different Mast Cell Characteristics in Human Myeloid Cell Lines and Peripheral Monocytes.

Mast cell differentiation markers were studied by culturing monocytic (U937, THP1) a promyelotic (HL60) and a human mast cell line (HMC1) and peripheral human blood monocytes with fibroblast supernatants and feeder layers. Mast cell differentiation occurred on the basis of metachromasia, chloroacetate esterase, expression of mast cell-specific antigens (APAAP) and production of tryptase in all cell types, but to varying degrees and not at all with a FcεRI marker in monocytic lines. Direct cellular contact is thus not necessary for induction of mast cell differentiation by fibroblasts.

WEIGHTS AND HEMATOLOGY OF WILD BLACK BEARS DURING HIBERNATION

We compared weights and hematological profiles of adult (greater than 3-yr-old) female black bears (Ursus americanus) during hibernation (after 8 January). We handled 28 bears one to four times (total of 47) over 4 yr of varying mast and berry production. Mean weight of lactating bears was greater (P less than 0.0001) than that of non-lactating females. White blood cells (P less than 0.05) and mean corpuscular volume (P = 0.005) also differed between lactating and non-lactating bears. Hemoglobin (P = 0.006) and mean corpuscular hemoglobin concentration (P = 0.02) varied among years; values were lowest during 1975, following decreased precipitation and the occurrence of a second year of mast and berry crop shortages in a three-year period. Significant (P less than 0.05) interaction between reproductive status (lactating versus non-lactating) and study year for hemoglobin, red blood cells, and packed cell volume, and increased mean corpuscular volume, suggested a greater nutritional challenge for lactating females compared to non-lactating females during the 1975 denning season. Our data suggest that hematological characteristics of denning bears may be more sensitive than weights as indicators of annual changes in nutritional status; however, other influential factors, in addition to mast and berry crop production, remain to be examined.

Consequences of a Temporally and Spatially Variable Food Supply for an Unexploited Gray Squirrel (Sciurus carolinensis) Population

-The demography and spatial distribution of a gray squirrel (Sciurus carolinensis) population was studied with respect to differences in habitat quality and food production in a heterogeneous Delaware woodlot from 1972-1973. In 1971 a large mast crop was produced, followed by a poor 1972 crop and a partial recovery in 1973. The squirrel population declined from 116 individuals in summer 1972 to 82 in fall 1973. Major components of the decline were losses of 1972 juveniles and 2-5-year-old females, and curtailed breeding in 1973. Squirrels were segregated among five study plots that represented areas of differing habitat quality and food production within the woodlot. The distribution of the sexes among the plots was significantly heterogeneous in summer and fall 1972 and summer 1973 (P < 0.10, G-test); plots with poorer mast production had a preponderance of females (R percent of individuals = 62%) while males predominated in plots with the best mast resources (R = 64%). In particular, adult males and yearlings (both sexes) were skewed towards high-mast plots while adult females were more abundant in low-mast plots. Juveniles showed no discernable pattern of distribution among plots. Losses were greater than expected from low-mast plots and less than expected from high-mast plots, especially for juveniles, yearlings, and females. The pattern of spatial variation of food abundance, sex (and possibly age) ratios and disappearance rates suggests a model of population regulation in which subordinates are relegated to suboptimal sites and bear major stress and losses when population density is high and food resources dwindle.