The Effects of a Natural Increase in Food-Supply on a Wild Population of House Mice

Changes in density and breeding of the house mouse (Mus musculus) in a New Zealand forest dominated by hard beech (Nothofagus truncata) were monitored for 2.5 years. Mice bred during winter and increased dramatically in density only during a beech mast year. Mice readily ate the endosperm and embryo of hard beech seed in die laboratory and chemical analysis showed it to be a very nutritious food source, similar in quality to Fagus beech seed in the northern hemisphere. Thus the mouse, introduced to New Zealand, responds to a Nothofagus mast year in a similar way to other rodent species in the northern hemisphere during a Fagus mast year.     

Differential spatial responses of rodents to masting on forest sites with differing disturbance history

Mast seeding, the synchronized interannual variation in seed production of trees, is a well‐known bottom‐up driver for population densities of granivorous forest rodents. Such demographic effects also affect habitat preferences of the animals: After large seed production events, reduced habitat selectivity can lead to spillover from forest patches into adjacent alpine meadows or clear‐cuts, as has been reported for human‐impacted forests. In unmanaged, primeval forests, however, gaps created by natural disturbances are typical elements, yet it is unclear whether the same spillover dynamics occur under natural conditions. To determine whether annual variation in seed production drives spillover effects in naturally formed gaps, we used 14 years of small mammal trapping data combined with seed trap data to estimate population densities of Apodemus spp. mice and bank voles (Myodes glareolus) on 5 forest sites with differing disturbance history. The study sites, located in a forest dominated by European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba), consisted of two primeval forest sites with small canopy gaps, two sites with larger gaps (after an avalanche event and a windthrow event), and a managed forest stand with closed canopy as a control. Hierarchical Bayesian N‐mixture models revealed a strong influence of seed rain on small rodent abundance, which were site‐specific for M. glareolus but not for Apodemus spp. Following years of moderate or low seed crop, M. glareolus avoided open habitat patches but colonized those habitats in large numbers after full mast events, suggesting that spillover events also occur in unmanaged forests, but not in all small rodents. The species‐ and site‐specific characteristics of local density responding to food availability have potentially long‐lasting effects on forest gap regeneration dynamics and should be addressed in future studies.     

Ecological consequences of an unusual simultaneous masting of Araucaria araucana and Chusquea culeou in North‐West Patagonia,Argentina

A simultaneous masting of two abundant species in the temperate forests of North‐West Argentinean Patagonia occurred in 2013 for the first time ever recorded: the semelparous bamboo grass Chusquea culeou (colihue), dominating the understory, flowered and set seed across 1100 km² while pehuén (Araucaria araucana), an endemic conifer co‐dominating the tree layer had the highest regionally synchronized mast event in the last 30 years. Strong trophic effects were expected as a consequence of this extraordinary amount of seed, such as rodent outbreaks (ratadas) that followed previous Chusquea spp. mast events and included Oligoryzomys longicaudatus, the main reservoir of the Andes virus causing the Hantavirus Pulmonar Syndrome. From March 2013 to May 2014, we sampled relative abundance and activity of seed‐eaters and carnivores at four study sites with different proportions of both masting species. Surprisingly, total rodent capture rates never exceeded 14% in wild habitats and 8% in peridomestic areas showing low overall density in spite of some heavy O. longicaudatus males extending their reproductive activity into winter. Total abundance and relative proportion of granivorous birds peaked at the four sites in winter or spring, when they are usually scarce. Other surveyed organisms (native and exotic seed‐eaters, ungulates and carnivores) showed moderate responses at most, probably through aggregation from surrounding areas rather than reproduction. Seed removal from experimental seed stations varied in time and space though never peaked. The clearest pattern of community responses, though much subtler than expected, occurred at the site where colihue was abundant and pehuén scarce. This is the first systematic study that reports such a simultaneous double masting and our surveys revealed no widespread community consequences. We propose that either contingent events, such as an unprecedented drought, or permanent environmental features or contextual characteristics may explain the lack of a rodent outbreak in this area.     

Mast Pulses Shape Trophic Interactions between Fluctuating Rodent Populations in a Primeval Forest

How different functional responses of consumers exploiting pulsed resources affect community dynamics is an ongoing question in ecology. Tree masting is a common resource pulse in terrestrial ecosystems that can drive rodent population cycles. Using stable isotope (δ¹³C, δ¹⁵N) analyses, we investigated the dietary response of two fluctuating rodent species, the yellow-necked mouse Apodemus flavicollis and the bank vole Myodes glareolus, to mast events in Białowieża Forest (NE Poland). Rodent hair samples were obtained non-invasively from faeces of their predators for an 11-year period that encompassed two mast events. Spectacular seed crops of deciduous trees, namely oak Quercus robur and hornbeam Carpinus betulus, occur after several intermediate years of moderate seed production, with a post-mast year characterised by a nil crop. While a Bayesian isotopic (SIAR) mixing model showed a variety of potential vegetation inputs to rodent diets, the isotopic niche of the yellow-necked mouse was strongly associated with mast of deciduous trees (>80% of diet), showing no variation among years of different seed crop. However, bank voles showed a strong functional response; in mast years the vole shifted its diet from herbs in deciduous forest (∼66% of diet) to mast (∼74%). Only in mast years did the isotopic niche of both rodent species overlap. Previous research showed that bank voles, subordinate and more generalist than mice, showed higher fluctuations in numbers in response to masting. This study provides unique data on the functional response of key pulse consumers in forest food webs, and contributes to our understanding of rodent population fluctuations and the mechanisms governing pulse–consumer interactions.     

Population dynamics ofClethrionomys glareolus andApodemus flavicollis: seasonal components of density dependence and density independence

Using long-term data on two forest rodent species [the bank voleClethrionomys glareolus (Schreber, 1780) and the yellow-necked mouseApodemus flavicollis (Melchior, 1834)] from the Białowieża Primeval Forest (E Poland), we decompose the annual density-dependent and density-independent structures into their seasonal components. For this purpose we adopt a state-space modelling approach explicitly incorporating sampling stochasticity. As density-independent factors we use the North Atlantic Oscillation (NAO) — a proxy variable for the overall climatic condition — and data on annual seed production. We find a weak effect of the NAO in the annual models for both species as well as during the winter in the seasonal model forC. glareolus. The effect of the NAO disappears, however, when seed-crops are incorporated into the models (for both the annual and the seasonal — suggesting that NAO primarily affects seed production). Seed production enters the models with a positive effect during the winter only, suggesting that the among-year variation in rodent density is primarily accounted for by differences in seed-production, particularly oak seeds. ForA. flavicollis, a slightly positive effect of hornbeam also appears in the summer dynamics. The obtained results are discussed on the basis of earlier studies on the same populations, on the same species studied elsewhere as well as on the basis of general ecological insight.

     

Effects of mast seeding and rodent abundance on seed predation and dispersal of <Emphasis Type="Italic">Quercus aliena</Emphasis> (Fagaceae) in Qinling Mountains,Central China

Rodents act as seed predators and dispersers and play an important role in the regeneration of plants. Seed production and rodent abundance may influence caching rodents’ decision to consume or cache seeds. We studied how did seed production and rodent abundance co-influence seed predation and dispersal by rodents in the mast seed years (2011 and 2013) and non-mast seed years (2012 and 2014) in the Qinling Mountains of Shaanxi Province, Central China. We found that: (1) The seed removal rates were much faster in the non-mast seed years than in the mast seed years. (2) Although the total number of seeds consumed (including eaten in situ and after removal) was higher in the non-mast seed years than in the mast seed years, no significant differences were found in the seeds that were eaten in situ and after removal among the 4 years. (3) Significant differences were observed in seeds that were cached among the 4 years, and more seeds were cached in the non-mast seed years than in the mast seed years. (4) The primary and secondary seed dispersal distances (including cached and eaten) were all longer in the non-mast seed years than in the mast seed years. Overall, these results indicate that non-mast seeding with low per capita seed availability could increase both seeds consumption and caching by rodents. Our results are partially supporting the predator satiation hypothesis.     

Marten and fisher responses to fluctuations in prey populations and mast crops in the northern hardwood forest

Many forest tree species produce seed (mast) crops that are consumed by a variety of wildlife species and these pulsed resources may mediate interactions among predator and prey populations. In the northern hardwood forests of New York, we investigated interactions among mast production, prey abundance, and harvests of American martens (Martes americana) and fishers (Martes pennanti) during 1988–2009. Mast production for beech (Fagus grandifolia), sugar maple (Acer saccharum), and mountain ash (Sorbus americana) was synchronous and an alternate-year pattern in production was evident for most of the time series. We documented considerable temporal variation in summer small mammal relative abundance and our numerical response models received substantial support for 5 of the 8 species, indicating lagged responses to autumn mast crops. Trap response of martens to the autumn production of beech mast and mountain ash berries was immediate and numerical responses to the relative abundance of small mammal prey occurred during the preceding summer. The age structure of the marten harvest differed based on the dominant alternate-year pattern of summer prey relative abundance and autumn mast production (χ²₄ = 33.06, P < 0.001). The proportion of juvenile marten in the autumn harvest was 52% and 34% following summers when small mammal relative abundance was high and low, respectively and these differences resulted in a persistent cohort effect that was apparent until age 3.5. Trap response of fishers to the autumn production of beech mast was immediate and numerical responses to the relative abundance of Sciurid prey occurred during the preceding summer. Marten and fisher harvests fluctuated similarly among New York, Maine, and New Brunswick, which may indicate regional synchronization of mast crops and responses of martens and fishers to similar prey dynamics. A better understanding of how food availability influences demographic responses and trapping vulnerability of martens and fishers would aid our ability to manage harvests of these species on a sustained yield basis. © 2011 The Wildlife Society.     

Strong “bottom‐up” influences on small mammal populations: State‐space model analyses from long‐term studies

“Bottom‐up” influences, that is, masting, plus population density and climate, commonly influence woodland rodent demography. However, “top‐down” influences (predation) also intervene. Here, we assess the impacts of masting, climate, and density on rodent populations placed in the context of what is known about “top‐down” influences. To explain between‐year variations in bank vole Myodes glareolus and wood mouse Apodemus sylvaticus population demography, we applied a state‐space model to 33 years of catch‐mark‐release live‐trapping, winter temperature, and precise mast‐collection data. Experimental mast additions aided interpretation. Rodent numbers in European ash Fraxinus excelsior woodland were estimated (May/June, November/December). December–March mean minimum daily temperature represented winter severity. Total marked adult mice/voles (and juveniles in May/June) provided density indices validated against a model‐generated population estimate; this allowed estimation of the structure of a time‐series model and the demographic impacts of the climatic/biological variables. During two winters of insignificant fruit‐fall, 6.79 g/m² sterilized ash seed (as fruit) was distributed over an equivalent woodland similarly live‐trapped. September–March fruit‐fall strongly increased bank vole spring reproductive rate and winter and summer population growth rates; colder winters weakly reduced winter population growth. September–March fruit‐fall and warmer winters marginally increased wood mouse spring reproductive rate and September–December fruit‐fall weakly elevated summer population growth. Density dependence significantly reduced both species' population growth. Fruit‐fall impacts on demography still appeared after a year. Experimental ash fruit addition confirmed its positive influence on bank vole winter population growth with probable moderation by colder temperatures. The models show the strong impact of masting as a “bottom‐up” influence on rodent demography, emphasizing independent masting and weather influences; delayed effects of masting; and the importance of density dependence and its interaction with masting. We conclude that these rodents show strong “bottom‐up” and density‐dependent influences on demography moderated by winter temperature. “Top‐down” influences appear weak and need further investigation.     

Composition of cyclic and non-cyclic vole populations: On the causes of variation in individual quality among Clethrionomys glareolus in Sweden

A cyclic Clethrionomys glareolus population from north Sweden was compared with a non-cyclic population from south Sweden regarding age structure, body weight, reproductive development and suppression, and sex ratios.The non-cyclic population, after years with winter breeding, was characterized by especially early and intense breeding in spring and many post-reproductive animals in autumn. Non-cyclic populations with no winter reproduction were similar to increase years in cyclic populations. In peak and especially in decline phases of cyclic populations reproduction decreased clearly below the level in non-cyclic populations. Animal weights varied insignificantly between years in the non-cyclic population but changed greatly in the cyclic population.A unifying hypothesis for explaining variations in animal quality between different populations is proposed: Maternal conditions related to food supply are assumed to affect body growth and sexual maturation of the young. Predictions from this hypotheses are outlined and compared with those from competing ideas.     

Mast-seeding in the cycad genus Encephalartos: a test of the predator satiation hypothesis

Mast-seeding behaviour was monitored in 18 populations of eight species of the African cycad genus Encephalartos between 1988 and 1991. The coefficient of variation (V) in annual cone production for each population ranged between 88 and 200, indicating large fluctuations in reproductive effort between years. Data were collected to determine whether mast-seeding reduced levels of predispersal seed predation by satiating seed predators in mast years and whether it resulted in a reproductive advantage over plants which reproduced more frequently. Masting intensity was greatest in those populations in which individual plants suffered the highest levels of predispersal seed predation in years when only a few plants produced seeds. The principal seed predators were two congeneric weevil species, Antliarhinus zamiae and A. signatus, which develop exclusively on cycad seeds. The lowest intensity of mast-seeding was recorded for cycad populations with low levels of seed predation and in which A. zamiae and A. signatus occurred only in low numbers or were entirely absent. Larger seed crops appeared to result in lower levels of seed predation by A. zamiae and A. signatus in four populations of E. altensteinii, and differences in seed crop size accounted for 48–66% of variation in levels of seed predation in populations of five cycad species. In one population of E. altensteinii, lower levels of seed predation in plants reproducing periodically resulted in a reproductive advantage over plants reproducing more frequently. These results are consistent with the predator satiation hypothesis. However, in most cycad populations, numbers of seed predators did not appear to decrease significantly after a period of 2–8 years between reproductive episodes and, in two of three populations examined, periodic reproduction did not increase the number of seeds surviving to dispersal over a 4-year period. These results are interpreted to mean that periodic reproduction has not evolved in response to selection imposed by seed predators, but that selection may favour those plants which experience lower levels of seed predation by coning in synchrony with the majority of plants in the population.     

Is there a higher risk for herbivore outhreaks after cold mast years? An analysis of two plant/herbivore series from southern Norway

Historical data on two plant‐herbivore interactions from southern Norway were used to test the hypothesis that the degree of herbivore outbreaks in post‐mast years is negatively related to summer temperatures in the mast year, because plants are more depressed after a high seed production if temperatures and thus the photosynthetic activity is low. The plant species were the sessile oak Quercus petraea and the bilberry Vaceinium myrtillus. For the former species post‐mast years were identified from reports given by the local forest authorities for the period 1930–48, and from acorn export curves for the period 1949–98, For the latter species, post‐mast years were identified mainly from bilberry export curves for the period 1920–31, from game reports for the period 1932–78. and from diary notes for the period 1979–87. The herbivore species used were the green oak leaf roller moth Tortrix viridana and the capercaillie Tetrao urogallus. Eight moth outbreaks on oak forests were reported by the forest authorities in the period 1930–98, and they all started in a post‐mast year of the sessile oak. There were however also eleven post‐mast years without moth outbreaks. According to game reports, observations and autumn counts, all increases in the autumn population size of capercaillie during 1920 88 occurred in or after a year with high bilberry production. Among i8 post‐mast years, there were seven with strong increase, seven with slight or moderate increase, and four with no increase. For both herbivore species, post‐mast years with marked population increases had significantly lower summer temperatures in the preceding (mast) year than had post‐mast years with no or slight increases. For moth populations there also was a negative effect of high temperatures in April, possibly because moth eggs tend to hatch too early relative lo budburst if spring temperatures are high. For the capercaillie, high amount of precipitation in June – July seemed to have some negative impact on the autumn population sizes, as also found in previous studies.     

Seed survival on experimental dishes in a central European old‐growth mixed‐species forest – effects of predator guilds,tree masting and small mammal population dynamics

Predation of tree seeds can be a major factor structuring plant communities. We present a three year study on tree seed survival on experimental dishes in an old‐growth forest in central Europe in Austria. We addressed species specific, spatial and temporal aspects of post‐dispersal seed predation. Seeds of Norway spruce Picea abies, European beech Fagus sylvatica, and silver fir Abies alba were exposed on dishes in different types of exclosures which allowed access only to specific guilds of seed predators. Removal experiments were carried out in two old‐growth forests and a managed forest (macro‐sites), including micro‐sites with and without cover of ground vegetation. We conducted the experiment in three consecutive years with a mast year of beech and spruce before the first year of the study. The seed removal experiments were combined with live trapping of small mammals being potential seed predators. Our experiments showed a distinctly different impact of different predator guilds on seed survival on the dishes with highest removal rates of seeds from dishes accessible for small mammals. We observed differing preferences of small mammals for the different tree species. Seed survival in different macro‐ and micro‐habitats were highly variable with lower seed survival in old growth forests. In contrast to our assumption, and in contrast to the satiation hypothesis which assumes higher seed survival in and directly after mast years, seed survival was lower in the year following the mast year of beech when a population peak of small mammals occurred and higher in intermast periods when subsequently small mammal population crashed. This suggests a higher importance of sporadic masting shortly after mast years in intermast periods for establishment of forest trees provided that pollination efficiency is high enough in such years. Combined with the high seed mortality observed after the mast year, this corroborates the important role of seed predation for forest dynamics. An altered synchrony or asynchrony of masting of different tree species and changed masting frequencies through climate change may thus lead to strong and non‐linear effects on forest dynamics.     

Synchronicity,periodicity and bimodality in inter‐annual tree seed production along an elevation gradient

Distinctive inter‐annual patterns of tree seed production can include spatial synchronicity, periodicity, and high variability among individuals within a population. Synchronicity and high variability are now commonly used to define mast seeding, with ‘strict’ mast seeding further distinguished by annual seed production that is either often large or nil and thus bimodal. Here we test for synchronicity, periodicity, and bimodality using 43 years of annual total and viable seed counts, along four transect lines, sampling an elevation gradient (480–1340 m) in a monospecific New Zealand mountain beech Nothofagus solandri var. cliffortioides forest. We expect most support for periodicity and bimodality at relatively high elevation sites that are most resource limited and known to have the greatest variability in seed production. While there was weak evidence for differences in viable seed counts along the elevation gradient, this was not the case for total seed counts. A significant year‐effect on seed counts provided some evidence for synchronization, but the correlations of total or viable seed counts rapidly declined (from 0.96 to 0.58) with increasing elevation difference among transect lines. Although we detected a seven‐year periodicity in total and viable seed counts at each elevation, we also detected other period lengths at most elevations. We did not find evidence for our expectation of increased period length and bimodality in relatively unproductive high elevation mountain beech forests because they would take more time to recover from seeding events. As a consequence, if resource limitation is an important driver of mountain beech seed production its influence must be strongly regulated by other factors to determine the distinctive characteristics (periodicity and synchronicity but not bimodality) of inter‐annual variation in seed production.     

Is energy supply the trigger for reproductive activity in male edible dormice (<Emphasis Type="Italic">Glis glis</Emphasis>)?

In edible dormice (Glis glis) reproduction is synchronised with the intermittent masting of the European beech (Fagus sylvatica). In years of mast failure dormouse males seem to anticipate future low food availability and fail to develop functional testes. We hypothesised that the availability of high-quality food is linked to male reproductive capacity, because of high male energetic demands during gonad maturation. We therefore evaluated the relationship between beech seed production and male reproductivity in the field between 1993 and 2005. In order to know whether the energy content of the food as such triggers sexual capacity, we supplemented high-quality food in the field for 3 years and investigated reproductive output, reproductive capacity, and body mass changes. Results revealed that male reproductive capacity was positively linked with beech seed production. Body mass changes of reference males during the high reproductive year further revealed high energetic demands of male reproduction, which were counter balanced in food-supplemented males. However, in contrast to our assumptions, artificial food supply during a year of mast failure failed to evoke high reproductivity in edible dormice. The availability of high-quality food can therefore be ruled out from being the primary trigger for sexual activity in male edible dormice.     

A mast‐seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers

Granivorous rodent populations in deserts are primarily regulated through precipitation‐driven resource pulses rather than pulses associated with mast‐seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast‐seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5‐year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush‐dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush‐dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush‐dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource‐rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource‐poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem.     

Main determinants of rodent population fluctuations in managed Central European temperate lowland forests

Whilst studies have shown that climatic (North Atlantic Oscillation (NAO)) and biotic (acorn production) factors influence rodent populations, mechanisms driving temporal and spatial fluctuation of rodent populations are understudied. This study evaluates relationships between the influence of environmental factors (biotic and abiotic) and phenotypic characteristics across two rodent feeding guilds (granivorous and non-granivorous species) represented by four species of rodents in Central Europe. We hypothesise that the relationship between acorn density and population growth rate are indirectly affected by climatic factors (winter NAO) and that these effects differ amongst herbivorous and granivorous species. In addition, we also tested whether effects of weather and competition on individual phenotype characteristic vary amongst mast and non-mast years. Rodent populations were estimated by catching individuals in snap traps during the growing season (from March to November) over a period of 9 years at three sites. The results of the generalised linear model provide evidence that acorn production best explained the population fluctuations. We therefore conclude that the between-year population fluctuations in rodent abundance were governed by density dependence and initiated primarily by acorn mast years. Auto-regressive models also revealed direct density dependence in combination with the direct effects of mast years. Therefore, strong intraspecific competition for food is likely in years following mast years. Our results also showed that abundance of non-granivorous species is mainly influenced by local weather conditions which could regulate food quality and abundance. On the other hand, population dynamics of granivorous species are caused directly by acorn density and indirectly by climatic condition influencing acorn production.     

Effects of predator removal on vertebrate prey populations: birds of prey and small mammals

We studied the effects of removal of breeding nomadic avian predators (the kestrel, Falco tinnunculus and Tengmalm's owl, Aegolius funereus) on small mammals (voles of the genera Microtus and Clethrionomys and the common shrew, Sorex araneus) during 1989–1992 in western Finland to find out if these predators have a regulating or limiting impact on their prey populations. We removed potential breeding sites of raptors from five manipulation areas (c. 3 km² each), whereas control areas had nest-boxes in addition to natural cavities and stick-nests. Densities of small mammals were monitored by snap-trapping in April, June, and August, and densities of mammalian predators (the least weasel, Mustela nivalis nivalis, the stoat, M. erminea and the red fox, Vulpes vulpes) by snow tracking in early spring and late autumn. The yearly mean number of raptor breeding territories was 0.2–1.0 in reduction areas and 3.0–8.2 in control areas. Breeding raptors alone did not regulate prey populations in the long term, but probably caused short-term changes in the population dynamics of both the main prey, the sibling vole (Microtus rossiaemeridionalis) and an alternative prey (the common shrew). The densities of an alternative prey, the bank vole (Clethrionomys glareolus) decreased in raptor reduction areas, most likely due to increased least weasel predation pressure in the absence of breeding avian predators.     

Winter breeding in three rodent species, the bank vole Clethrionomys glareolus, the yellow-necked mouse Apodemus flavicollis and the wood mouse Apodemus sylvaticus in southern Sweden

Winter breeding, as judged from heavy reproductive organs in both males and females, was observed in bank voles, yellow-necked mice and wood mice in south Sweden during the winter of 1976–1977. The breeding was probably a result of unusually favourable feeding conditions created by an extremely rich beech mast crop.     

Predicting the incidence of mohua predation from the seedfall,mouse, and predator fluctuations in beech forests

Abstract

Predator control will be required to save many mohua (Mohoua ochrocephala) populations from extinction. However, control may be required only in years when stoat (Mustela erminea) densities are high. To manage local stoat populations effectively, a reliable predictor of high risk years is required. We examined whether different levels of beech seedfall and mouse capture rates were related to the levels of mohua predation recorded in the Hawdon Valley, Arthur's Pass National Park, and the Eglinton Valley, Fiordland National Park, between 1989 and 1994. During this period there was only one full beech mast year in each study area during autumn. The full mast seedfall in Hawdon Valley was predominantly of mountain beech (Nothofagus solandri var. cliffortioides) and red beech (N. fused), and in Eglinton Valley it was predominantly silver beech (TV. menziesii). During the following summer, mouse and stoat densities, and the predation rate of adult mohua, all increased considerably. There was very little predation on adult mohua in the summers following poor seedfalls when mouse and predator densities remained low. In 1993, a partial mast did not trigger a mouse or stoat irruption.

We conclude that counts of beech seedfall and indices of mouse density are potential predictors of an impending irruption of key predators. Winter mouse density appeared to be the most reliable indicator, because neither stoats nor mice respond to seedfall alone. A combination of these indicators could be used as a basis for management decisions on whether to undertake stoat control to protect mohua populations in the future. However, more information is required on the seedfall thresholds that may trigger sufficient increases in mouse and stoat numbers and, consequently, bird predation.     

Distribution of Acanthaster planci outbreaks on the Great Barrier Reef between 1966 and 1989

Analysis of data from 1966 to 1989 indicates 2 periods of abundant starfish outbreaks on the Great Barrier Reef (GBR). While the data for the first peak of activity (1966–1975) are relatively limited, the data for the most recent peak of activity (1981–1989) support the hypothesis of southward moving waves of outbreaks. The southward drift of outbreak activity is consistent with speed and direction of average summer currents on the GBR but the concept of a discrete seed area to initiate the wave is not substantiated, nor testable, with presently available data. As the present wave of outbreaks appears to be declining in the central section of the GBR (17–19°S) small residual populations may remain. If the outbreaks are coupled to coral recovery patterns then the next period of high starfish activity in the central section would be expected in the late-1990's.