Non-mast Years Research Articles

Long-term comparison of food availability and reproduction in the edible dormouse (Glis glis)

Summary Individuals of animal populations that are controlled by food availability should be favored if they were able to reduce the lag phase between the occurrence of high food availability and the production of offspring. Edible dormice ( Glis glis ), small hibernating rodents from central and southern Europe, show fluctuation in reproductive output that seem to be timed to coincide with future food supply. We report predictable lows of reproductive rates in edible dormice after years of mast fruiting (i.e., when animals are in perfect condition) and high reproductive rates in the spring of years that will see mast fruiting trees (oaks, beech) later in the same year. Because trees are unlikely to produce mast crops two years in a row, we hypothesize that the lack of or the reduced reproduction in the spring after mast years is an adaptation to the predictable low food availability of a “non-mast” year after a mast year. Since, the other way round, there is a high probability that a mast year will follow a non-mast year in central Europe, reproductive success is likely to be increased by reproducing in the spring of the year after a non-mast year, thus anticipating future food supply in fall. In years of no or reduced reproduction males did not develop functional testes after hibernation. Thus, the sexual inactivity of male dormice is likely to be the major cause for reproductive failure.

Seed scatterhoarding by white-tailed rats: consequences for seedling recruitment by an Australian rain forest tree

The role of white-tailed rats (Uromys caudimaculatus) as dispersers of seeds of the Australian tropical rain forest tree Beilschmiedia bancroftii, (Lauraceae) was investigated by following the fates of seeds and seedlings over 2 y. Fruits of this tree are too large to be consumed by any avian frugivore except the southern cassowary (Casuarius casuarius), and the only other native mammal capable of dispersing the seeds is the musky rat kangaroo (Hypsiprimnodon moschatus). However, neither of these species has been documented to disperse the seeds of this tree. During a mast year, white-tailed rats cached seeds an average of 13 m from parent trees in a variety of microsites. Although none of the 61 cached seeds followed in this study survived to germination, comparison of seed, cache and seedling distributions suggested that most seedlings arose from rat-cached seeds. White-tailed rats cached seeds in both mast and non-mast years, but the time seeds remained on the forest floor and in caches was significantly shorter in non-mast years, suggesting that synchronous seed production increases the probability that some caches survive to germination. Because white-tailed rats are the most common and widespread native mammal capable of dispersing large-seeds, this study suggests that they may play an important role in the seed and seedling dynamics of large-seeded tree species in Australian tropical rain forests.

Seed dynamics of the mast seeding tussock grass Ampelodesmos mauritanica in Mediterranean shrublands

Summary 1 The Mediterranean perennial grass Ampelodesmos mauritanica may have the potential to expand its range. We analysed temporal variability of its reproductive components (seedfall, seed bank, seed predation, seed germination, seedling emergence, survival and growth) in three microsites (open areas, beneath Ampelodesmos and beneath shrubs) at two sites. 2 Reproductive components prior to seedling emergence were both closely linked and very similar between microsites within a site. Seedling survival and growth differed between microsites, being lowest in open areas. Recruitment patterns cannot therefore be predicted from seedfall. 3 Abundant seed production in 1996 was followed by successful germination and high seedling survival. In the following (non-masting) year, although Ampelodesmos has a low-density persistent seed bank, recruitment was much lower because germination was low and post-dispersal seed predation was high. 4 Our results suggest that Ampelodesmos reproduction is episodic. Expansion of its distribution may be triggered by intermittent seedling recruitment following masting, but is otherwise constrained by seed limitation, post-dispersal seed predation and a loss of viability in the seed bank.

Pollen Coupling of Forest Trees: Forming Synchronized and Periodic Reproduction out of Chaos

Many of the tree species in mature forests show masting; their reproductive activity has a large variance between years and is often synchronized between different individuals. In this paper, we analyse a globally coupled map model in which trees accumulate photosynthate every year, produce flowers when the energy reserve level exceeds a threshold, and set seeds and fruits at a rate limited by pollen availability. Without pollen limitation, the trees in the forest show independent chaotic fluctuation. Coupling of trees via pollen exchange results in reproduction being synchronized partially or completely over the forest. The whole forest shows diverse dynamical behaviors determined by the values of two essential parameters; the depletion coefficient k and the coupling strength β. We find perfectly synchronized periodic reproduction, synchronized reproduction with a chaotic time series, clustering phenomena, and chaotic reproduction of trees without synchronization over individuals. There are many parameter windows in which synchronized reproduction of trees shows a stable periodic fluctuation. For perfectly synchronized forests, we can calculate all the Lyapunov exponents analytically. They show that synchronized reproduction of all the trees in the forest can only occur when trees flower at low (but positive) levels in a significant fraction of years, resulting in small fruit sets due to outcrossed pollen limitation. This is consistent with the observation that the distinction between mast years and non-mast years is often not clear cut.

DEMOGRAPHY OF THE YELLOWSTONE GRIZZLY BEARS

We undertook a demographic analysis of the Yellowstone grizzly bears (Ursus arctos) to identify critical environmental factors controlling grizzly bear vital rates, and thereby to help evaluate the effectiveness of past management and to identify future conservation issues. We concluded that, within the limits of uncertainty implied by the available data and our methods of data analysis, the size of the Yellowstone grizzly bear population changed little from 1975 to 1995. We found that grizzly bear mortality rates are about double in years when the whitebark pine crop fails than in mast years, and that the population probably declines when the crop fails and increases in mast years. Our model suggests that natural variation in whitebark pine crop size over the last two decades explains more of the perceived fluctuations in Yellowstone grizzly population size than do other variables. Our analysis used demographic data from 202 radio-telemetered bears followed between 1975 and 1992 and accounted for whitebark pine (Pinus albicaulis) crop failures during 1993–1995. We used a maximum likelihood method to estimate demographic parameters and used the Akaike Information Criteria to judge the significance of various independent variables. We identified no independent variables correlated with grizzly bear fecundity. In order of importance, we found that grizzly bear mortality rates are correlated with season, whitebark pine crop size (mast vs. nonmast year), sex, management-trapping status (never management-trapped vs. mangement-trapped once or more), and age. The mortality rate of bears that were management-trapped at least once was almost double that of bears that were never management-trapped, implying a source/sink (i.e., never management-trapped/management-trapped) structure. The rate at which bears move between the source and sink, estimated as the management-trapping rate (h), is critical to estimating the finite rate of increase, λ͞. We quantified h by estimating the rate at which bears that have never been management-trapped are management-trapped for the first time. It differed across seasons, was higher in nonmast than mast years, and varied with age. We calculate that λ͞ = 1.00 from 1975 to 1983 (four mast and five nonmast years) and 1.02 from 1984 to 1995 (seven mast and five nonmast years). Overall, we find that λ͞ = 1.01 ± 0.04 (mean ± 1 se) from 1975 to 1995. Our models suggest that future management should concentrate on the threats to whitebark pine, such as those posed by white pine blister rust, global warming, and fire suppression. As is currently widely recognized by Yellowstone land managers, our model also suggests that future management must compensate for the increased grizzly bear mortality that is likely to be caused by an increasing number of humans in Yellowstone.

Demography of the Yellowstone Grizzly Bears

We undertook a demographic analysis of the Yellowstone grizzly bears (Ursus arctos) to identify critical environmental factors controlling grizzly bear vital rates, and thereby to help evaluate the effectiveness of past management and to identify future conservation issues. We concluded that, within the limits of uncertainty implied by the available data and our methods of data analysis, the size of the Yellowstone grizzly bear population changed little from 1975 to 1995. We found that grizzly bear mortality rates are about double in years when the whitebark pine crop fails than in mast years, and that the population probably declines when the crop fails and increases in mast years. Our model suggests that natural variation in whitebark pine crop size over the last two decades explains more of the perceived fluctuations in Yellowstone grizzly population size than do other variables. Our analysis used demographic data from 202 radio-telemetered bears followed between 1975 and 1992 and accounted for whitebark pine (Pinus albicaulis) crop failures during 1993–1995. We used a maximum likelihood method to estimate demographic parameters and used the Akaike Information Criteria to judge the significance of various independent variables. We identified no independent variables correlated with grizzly bear fecundity. In order of importance, we found that grizzly bear mortality rates are correlated with season, whitebark pine crop size (mast vs. nonmast year), sex, management-trapping status (never management-trapped vs. mangement-trapped once or more), and age. The mortality rate of bears that were management-trapped at least once was almost double that of bears that were never management-trapped, implying a source/sink (i.e., never management-trapped/management-trapped) structure. The rate at which bears move between the source and sink, estimated as the management-trapping rate (h), is critical to estimating the finite rate of increase, λ͞. We quantified h by estimating the rate at which bears that have never been management-trapped are management-trapped for the first time. It differed across seasons, was higher in nonmast than mast years, and varied with age. We calculate that λ͞ = 1.00 from 1975 to 1983 (four mast and five nonmast years) and 1.02 from 1984 to 1995 (seven mast and five nonmast years). Overall, we find that λ͞ = 1.01 ± 0.04 (mean ± 1 se) from 1975 to 1995. Our models suggest that future management should concentrate on the threats to whitebark pine, such as those posed by white pine blister rust, global warming, and fire suppression. As is currently widely recognized by Yellowstone land managers, our model also suggests that future management must compensate for the increased grizzly bear mortality that is likely to be caused by an increasing number of humans in Yellowstone.

Masting Enhancement Makes Pecan Nut Casebearer Pecans Ally Against Pecan Weevil

Plant defense from phytophages by association with other phytophages is known, but presently considered unusual compared with chemical, morphological, injury repair, or escape mechanisms. Pecan escapes nut feeders by synchronously producing nuts in a 2 to 7-yr cycle. Nut production in nonmast years would increase carrying capacity for late-season nut feeders. The pecan nut casebearer, Acrobasis nuxcorella Neunzig, acts as a fruiting cycle enhancer in pecan by removing nuts early in years of low production, thereby denying late-season nut feeders such as pecan weevil, ClIrm/io caryae (Horn), food. Pecan nut casebearer benefits pecan by increasing estimated average lifetime nut production of an archetypical tree in the presence of pecan weevil by 71,116 nuts at a cost of 210 mature nut equivalents provided pecan nut casebearer, representing a 339:1 return on reproductive effort to pecan.

Masting and Pecan Interaction with Insectan Predehiscent Nut Feeders

Pecan, Carya illinoensis (Wang.) K. Koch, is a massing species that predominantly produces nut crops at 3- to 4-yr intervals. The pecan nut casebearer, Acrobasis nuxvorella Neunzig, removes nutlets in May in years of low production, thereby reducing the equilibrium level of the late season obligatory nut feeding pecan weevil, Curculio caryae (Horn). The pecan generally produces more viable nuts at dehiscence in mast years when pecan nut casebearer occurs with pecan weevil compared with when pecan weevil occurs alone. The pecan nut casebearer enhances massing by substantially reducing nuts in nonmast (low production) years without having much effect in mast (high production) years. This interaction benefits both the pecan and the pecan nut casebearer to the detriment of the pecan weevil.

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.

Trophic structure of bat communities in the understorey of lowland dipterocarp rain forest in Malaysia

ABSTRACTBat communities in the understorey of primary lowland dipterocarp forest in peninsular Malaysia and Sabah were sampled with mist nets and harp traps to estimate their trophic structure. Overall, 4 of 26 species (15%) at one site, and 6 of 33 species (18%) at the other site were frugivores, while the remainder were insectivores. In terms of individuals, 7–12% of all captures were frugivores. However, the true proportion of frugivores at both sites was probably closer to 1%, because the sampling procedures were strongly biased towards frugivores. In contrast, previously published studies indicate that frugivores comprise 34–48% of species, and up to 80% of individuals in bat communities in the understorey of Neotropical forest. These results support the hypothesis, developed from studies of bird communities, that the under-storey of Malaysian dipterocarp forest supports relatively few obligate frugivores, at least in non-masting years. However, further data are required on bats in the canopy, and on the foraging ranges of bats to compare the absolute densities of bats in Malaysian and Neotropical forests.

Seed Predation and Cross‐Pollination in Mast‐Seeding Beech (Fagus Sylvatica) Patches

In this study we examined cross—pollination and levels of insect and vertebrate predation on the seeds of beech as a function of stand size and tree size. Cross—pollination in this wind—pollinated species is positively correlated with stand size and flower density. In two mast years, 6—14% of seeds contained no kernels, and in a nonmast year the figure was 24%. Predispersal destruction of seeds by a moth (Cydia fagiglandana) was 3.1% in a mast year and 38% in a nonmast year. The variation in seed destruction by vertebrates was much less between mast (5.7%) and nonmast (12%) years. Destruction by the moth was negatively correlated with tree size, while that by vertebrates was positively correlated with tree size. Vertebrate seed predation was negatively correlated with stand size. In a large stand, <10% of the seeds were consumed by vertebrates by April in two mast years. Both cross—pollination and seed predation may have been important factors in the evolution of mast seeding in beech.