Population fluctuations of light-attracted chrysomelid beetles in relation to supra-annual environmental changes in a Bornean rainforest

In Southeast Asian tropical rainforests, two events, severe droughts associated with the El Ni?o-Southern Oscillation and general flowering, a type of community-wide mass flowering, occur at irregular, supra-annual intervals. The relationship between these two supra-annual events and patterns of insect population fluctuations has yet to be clearly elucidated. Leaf beetles (Chrysomelidae) are major herbivores and flower-visitors of canopy trees, affecting their growth and reproduction and, in turn, affected by tree phenology; but their population fluctuations in the Southeast Asian tropics have not been extensively investigated. We examined population fluctuation patterns of the 34 most dominant chrysomelid species in relation to the two supra-annual events by conducting monthly light-trapping over seven years in a lowland dipterocarp forest in Borneo. Our results showed large community variation in population fluctuation patterns and a supra-annual (between-year) variation in abundance for most of the dominant chrysomelids that was significantly larger than the annual (within-year) variation. Specifically, in response to a severe drought in 1998, chrysomelid species exhibited different population responses. These results show that population fluctuations of individual species, rather than the entire assemblage, must be analyzed to determine the effects of changes in environmental conditions on the structure of insect assemblages in the tropics, especially in regions where supra-annual environmental changes are relatively more important than seasonal changes.     

Annual changes in the population size of the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) on high-seas Pacific Salmon (Oncorhynchus spp.), and relationship to host abundance

The population size of the salmon louse, Lepeophtheirus salmonis, was monitored annually in the summers of 1991–1997 by examining six species of Pacific salmon (Oncorhynchus spp.) caught by surface long-lines in oceanic offshore waters of the North Pacific Ocean and Bering Sea. The annual copepod population size on all salmonids caught was estimated by combining the calculated number of copepods carrying on each salmonid species. The copepod population fluctuated markedly from year to year, which resulted largely from marked annual changes in abundance of pink salmon (O. gorbuscha). Since pink salmon were most frequently and heavily infected and since their abundance changed every year, the copepod population was high in the years when this salmonid species was abundant, but low when it was rare. On the contrary, chum salmon (O. keta) did not show high prevalence and intensity of infection, but the annual abundance of this host species was consistently high, i.e. chum salmon carried many copepods every year. Copepods on other salmonid species (sockeye salmon O. nerka, coho salmon O. kisutch, chinook salmon O. tshawytscha, and steelhead trout O. mykiss) constantly formed a small percentage of the total copepod population. Both chum and pink salmon are the most important hosts in terms of their substantial contribution to support the copepod population, but the importance as hosts of each species is definitely different between the species. Chum salmon is a stable important host supporting the copepod population at a relatively high level every year, while the number of copepods on pink salmon annually exhibits marked fluctuations, and this salmonid species is regarded as an unstable important host.     

Significance of intra-inflorescence variation on flowering time of a spring ephemeral, <Emphasis Type="Italic">Gagea lutea</Emphasis> (Liliaceae), under seasonal fluctuations of pollinator and light availabilities

I studied the relationship between seed-set patterns within inflorescences and temporal variations in light and pollinator availabilities for 2 years in the spring ephemeral species Gagea lutea in a deciduous forest. Timing of canopy closure and seasonal trend of pollinator frequency did not synchronize with the annual fluctuation in flowering phenology. In the early snowmelt year, seed-set success reflected the seasonal pollinator abundance from early to middle flowering periods. In the late snowmelt year, however, seed-set rates were independent of pollinator activity and decreased with canopy closing even after hand pollination. The restricted seed production by defoliation and the increase in seed-set rates at the forest edge suggested that seed production was supported by current photosynthetic carbon gain. Thus, annual fluctuations of reproductive success can explain the variation in flowering phenology within a population although seasonal light deterioration would serve as a selective force for flowering in the early season.     

Seasonal and annual dietary changes in Lesser Kestrels Falco naumanni wintering in Lesotho

The diet of Lesser Kestrels Falco naumanni wintering in an agriculturally-transformed area in Lesotho was studied by means of pellet analysis. Orthopterans, beetles and solifugids (sun spiders) comprised the staple food of the wintering Lesser Kestrels. Small vertebrates, termite alates, earwigs and scolopendrans supplemented the diet. The proportion of pellets containing scarabaeid and carabid beetles, as well as those containing locusts and crickets, increased as the wintering season progressed, while the proportion of pellets containing solifugids decreased during the same period. Significant differences in diet composition were recorded between the 1998/1999 and 1999/2000 wintering seasons.     

Sequential flowering of neighboring goldenrods and the movements of the flower predator Epicauta pennsylvanica

Summary As neighboring plants flower sequentially, do flower feeders preferentially remain in the area, rather than move to another area with flowering plants? I examined the movements of the meloid beetle Epicauta pennsylvanica, a flower predator specializing on Solidago, in four types of replicated experimental plots — monocultures of Solidago altissima, or S. altissima interplanted with members of the same genus, same family, or different taxonomic orders. I released marked beetles only in the genus plots, which contained four species of Solidago, two that bloom before S. altissima. The number of beetles in the genus plots declined steadily as S. altissima came into flower in all the plots; the total number of beetles in all the plots remained fairly constant. I found no evidence that plant neighborhoods affected beetle distribution. Beetles foraging on the early blooming Solidago species did not remain in the genus plots as S. altissima came into flower. In addition, beetles that left the genus plots did not differentially accumulate in any of the other plot types, even though one type of plot was a monoculture with four times the density of S. altissima than the other plots.     

Habitat Specificity and Variation of Coleopteran Assemblages Between Habitats in a Southern African (Swaziland) Agricultural Landscape

Assessment of Coleopteran diversity and abundance was carried out in the lowveld region of Swaziland by pitfall trapping in five distinct habitats. Additionally, the study was to ascertain if any of the families collected illustrated habitat fidelity. 18 coleopteran families, comprising 2903 individuals were collected, with an additional 29 unidentified specimens, totalling 2932 beetles. Numerically, the top five families were the Scarabaeidae (2425), Carabidae (211), Tenebrionidae (149), Nitidulidae (37) and Curculionidae (22). 66.6% of all specimens collected were harboured within the pine windbreak while the lowest number (2.6%) was collected from the mature citrus orchard. The highest proportion (77%) of scarabaeid beetles collected occurred within the pine windbreak. Habitat specificity was illustrated by one family, Meloidae, which was found only in the young orchard. Community analysis was further carried out to ascertain distribution patterns of the dominant coleopteran families. Three scarabaeid species were found only in the pine windbreak while three carabid species occurred only in the indigenous savanna. Significant differences between habitats were observed in the number of beetles collected while no significant differences were observed in terms of the number of families observed in each habitat (p<0.05). Results indicate that conservation of the various habitat patches within the mosaic studied could facilitate conservation of whole communities rather than individual species thus facilitating effective conservation of the agricultural landscape.     

The infestation and dispersion patterns of Carcinonemertes spp. (Nemertea) on their crab hosts

Seasonal changes in the infestation and dispersion patterns of egg predatory nemerteans on their crab hosts were analyzed. Marked differences in the seasonal patterns of infestation were noted between worm species, yet, common patterns in the aggregation of the worms were found. Worm aggregation increased at the onset of the reproductive seasons of the hosts, and at the nadirs of the reproductive seasons for those hosts with year round breeding. The aggregation patterns of two worm species fluctuated with the physical environment of their estuarine hosts. Salinity changes as a result of seasonal rains may have caused changes in the underlying dispersion patterns of Carcinonemertes epialti on Hemiarapsus oregonensis, and C. mitsukurii on Portunus pelagicus. Lastly, the embryogenic cycle of the host species was significant in shaping the infestation and aggregation patterns of C. epialti on Cancer anthonyi and C. regicides on Paralithodes camtschaticus. Worm immigration and emigration were linked to crab embryogenesis and directly influenced the dispersion patterns of the worms.     

Communities of arbuscular mycorrhizal fungi in grassland: Seasonal variability and effects of environment and host plants

The seasonal dynamics of a community of endomycorrhizal fungal morphotypes in the roots of three grassland species (Achillea millefolium, Poa angustifolia, Plantago lanceolata) was evaluated, together with the effects of experimental treatment (mowing and phosphorus application) and the host plant properties. Strong seasonal variability was found in the fungal community, where clear seasonal patterns can be distinguished for several fungal morphotypes. The sampling date explained 20 to 30% of the total compositional variability for all three host species. ThePlantago roots host the highest number of arbuscular mycorrhizal (AM) fungal populations. There are two co-dominant fungal morphotypes inAchillea roots (assigned to the generaScutellospora andGlomus) and only one strongly dominant morphotype (assigned toGlomus), in thePoa roots. All three host species have a comparable pattern of richness of AM morphotypes with a single peak in the summer, possibly aligned with the flowering time of the host.     

Differences in morphology and reproductive traits of Galerucella nymphaeae from four host plant species

The water lily beetle Galerucella nymphaeae L. (Coleoptera: Chrysomelidae) exploits different hosts, including Nuphar lutea Sm. and Nymphaea alba L. (both Nymphaeaceae), as well as Polygonum amphibium L. and Rumex hydrolapathum Hudson (both Polygonaceae). The present study investigates whether within-species differences in morphological and reproductive traits are associated with differences in host species exploitation. A total of 1103 adult beetles were collected from 11 localities in The Netherlands, one of which contained all four hosts and three other localities contained hosts from both families (sympatric localities). Adults originating from Nuphar and Nymphaea were on average darker in colour and larger in size and had disproportionally bigger mandibles than beetles originating from Polygonum and Rumex across the 11 localities. Head capsules of first instar larvae from Nymphaeaceae hosts were between 17% and 28% larger than those of larvae from Polygonaceae hosts. Furthermore, beetles from Nuphar and Nymphaea laid larger sized eggs, but fewer eggs per clutch than beetles originating from Polygonum and Rumex. Although host related variation was less pronounced at the sympatric localities than in the allopatric localities, differences in larval and adult size were still highly significant at the sympatric localities. It is not clear whether the observed differences are genetically based, as opposed to host induced. However, leaf toughness varied among species in a way suggesting that leaf toughness may be partly responsible for host related differences in G. nymphaeae.     

Mortality pattern and age structure in two carabid populations with different seasonal life cycles

1. Adult populations of two carabid species, a spring breeder, Carabus yaconinus, and an autumn breeder, Leptocarabus kumagaii, were studied in a lowland habitat (area: 16,500 m²) by pitfall sampling and mark-recapture method. The seasonal change in population number, age structure and mortality pattern were clarified and related to their seasonal life cycles.
2. The survival rate of new adults from emergence to the first reproductive season was on the average 48% in C. yaconinus and 55% in L. kumagaii. In C. yaconinus, beetles which emerged later in the season survived more to the first reproductive season than those emerged earlier. C. yaconinus which had survived the pre-reproductive period mostly died out during the first reproductive season of 5 months, and about 8% survived until the second season. In L. kumagaii which had a short reproductive period in autumn, about 20% survived to the second reproductive season, and a small proportion even to the third reproductive season. Accordingly, the proportion of old beetles in the reproductive population was higher in L. kumagaii than in C. yaconinus.
3. The reproductive population of C. yaconinus contained on the average 1600 beetles and produced 3300 new adults. the L. kumagaii population contained on the average about 530 reproductives in autumn, and about 820 beetles emerged in the following year. The recruitment rate of new adults of C. yaconinus was higher than that of L. kumagaii, and this resulted in its higher population density. In L. kumagaii, however, the high adult survivorship and iteroparous reproduction were important for its population growth.
4. Relationship between seasonal adaptation and demographic strategies in the carabid populations were discussed.

     

Component community dynamics of larval trematodes in the freshwater snail Semisulcospira nakasekoae in the Uji River, central Japan

The component community of larval trematodes in the freshwater snail Semisulcospira nakasekoae (Caenogastropoda: Sorbeoconcha: Pleuroceridae) was surveyed over 13 months from April 1996 to April 1997 inclusive. Temporal and spatial fluctuation of trematode prevalence, the frequency of multiple infections, and the duration of cercarial shedding were examined as factors that might affect trematode community structure. The spatial prevalence of some species varied significantly, but the dynamics were too small to allow an explanation of the overall pattern. The prevalence of sanguinicolids fluctuated temporally, despite a stable size distribution in the host populations (> 6.0 mm shell width), suggesting the life-cycle phenology of this species. Some pairs of species had statistically positive associations, but no pairs had negative associations. This shows the importance of positive association possibly as a result of suppression of the host defensive response on trematode community structures in molluscan hosts. The length of the patent period, which is part of the persistent period, varied among trematode species, suggesting it to be one of the factors determining prevalence in the host population.     

Seasonal variation in life history traits in two Drosophila species

Seasonal environmental heterogeneity is cyclic, persistent and geographically widespread. In species that reproduce multiple times annually, environmental changes across seasonal time may create different selection regimes that may shape the population ecology and life history adaptation in these species. Here, we investigate how two closely related species of Drosophila in a temperate orchard respond to environmental changes across seasonal time. Natural populations of Drosophila melanogaster and Drosophila simulans were sampled at four timepoints from June through November to assess seasonal change in fundamental aspects of population dynamics as well as life history traits. D. melanogaster exhibit pronounced change across seasonal time: early in the season, the population is inferred to be uniformly young and potentially represents the early generation following overwintering survivorship. D. melanogaster isofemale lines derived from the early population and reared in a common garden are characterized by high tolerance to a variety of stressors as well as a fast rate of development in the laboratory environment that declines across seasonal time. In contrast, wild D. simulans populations were inferred to be consistently heterogeneous in age distribution across seasonal collections; only starvation tolerance changed predictably over seasonal time in a parallel manner as in D. melanogaster. These results suggest fundamental differences in population and evolutionary dynamics between these two taxa associated with seasonal heterogeneity in environmental parameters and associated selection pressures.     

A time series and geographical analysis of population dynamics of the red-backed vole in Hokkaido,Japan

Summary A time series and geographical analysis of the long term (25-years and 16-years) census data of the red-backed vole, Clethrionomys rufocanus bedfordiae, populations in Hokkaido, Japan was carried out. Eighty seven populations from all over Hokkaido were grouped into the following 4 types according to their flucturation patterns: type A: low density-constant type; type B: medium density-gradual increase type; type C: medium density-wavy change type; type D: high density-large amplitude type. The border between type B and type C was not clear. Although the distribution of the fluctuation types did not show any geographical cline, the high density type (type D) occurred in limited areas where the winter was severe and spring came later and almost all the populations in the Oshima peninsula were the low density type (type A). The most common type of population in Hokkaido, type C, greatly fluctuated from year to year with the maximum density level/the minimum one being over 10. The periodicity of the peak years was not statistically significant, although peaks often occurred at 3 or 4 year intervals. The population grew from spring to autumn in almost all years so that the pattern of the seasonal change was qualitatively constant. The population density levels in spring were not significantly different between peak years and others, while those in autumn were greatly different between them, so that the population growth rates from spring to autumn were variable from year to year. This differential pattern was also found between high and low density areas.     

Seasonal abundance of Tuberolachnus salignus and its effect on flowering of host willows of varying susceptibility

The giant willow aphid Tuberolachnus salignus Gmelin is a large phloem-feeding insect which colonizes the stems of willow trees. This aphid is a new invasive species in New Zealand and there is limited knowledge of its inter-annual population patterns and the damage it can cause to willow hosts. Our study investigated the T. salignus population dynamics and its effects on the flowering parameters of fifteen willow species and hybrids in a field trial. The aphid population levels were found to vary among the willow species and hybrids. Based on the aphid population levels, the willow species and hybrids were classified as resistant, moderately resistant, susceptible or highly susceptible. T. salignus infestation had no effect on the flowering of resistant and moderately resistant willows, but significantly delayed the flowering time, extended the flowering duration, and decreased the catkin length in susceptible species and hybrids. Interestingly, aphid infestation was found to increase the catkin number and total floral output of some willow species and hybrids. It can be concluded that aphid populations and their effects on flowering are host-specific, with large differences between resistant and susceptible host plants.     

Timing of reproduction in a prairie legume: seasonal impacts of insects consuming flowers and seeds

Summary Seasonal patterns of insect damage to reproductive tissue of the legume Baptisia australis were studied for three years in native tallgrass priairie. Contrasting seasonal patterns of damage were associated with the major species of insect consumers. The moth Grapholitha tristegana (Olethreutidae) and the weevil Tychius sordidus (Curculionidae), which together infested 80–100% of developing fruits (pods), consistently damaged more seeds on average in early than in late maturing pods. But while late opening flowers were less subject to attack from moths and weevils, they were more subject to attack from chewing insects, particularly blister beetles (Epicauta fabricii, Meloidae), which destroyed >80% of all flowers and developing young pods (including moth and weevil larval inhabitants). The blister beetles arrived late in the flowering season and fed particularly on young reproductive tissue, allowing larger, older pods that had developed from early opening flowers to escape destruction. The relative abundances and impacts of blister beetles, moths, and weevils varied from year to year. Adding to the uncertainty of reproductive success of the host plant were the large and variable amounts of damage to immature buds inflicted by insects (including the blister beetles and weevil adults) and late killing frosts. Thus, timing of flowering is critical to success in seed production for B. australis. The heavy impacts of insects and weather can result in a very narrow window in time (which shifts from year to year) during which B. australis can flower with any success. The opposing pressures exerted by insects and weather on floral reproductive success may act in concert with other features of the plant's biology to foster the maintenance of considerable diversity in flowering times among individuals in local populations of B. australis.     

盐池荒漠草地拟步甲昆虫群落时间结构和动态

从2009年3月到10月采用巴氏罐诱导法调查了宁夏盐池四墩子6个不同生境中的拟步甲的群落组成以及时间动态,结果表明,本次调查共采集拟步甲昆虫5431只,计10属20种,个体数最多的是弯齿琵甲Blapsfemoralis femoralis Fischer-Waldheim和克小鳖甲Microdera kraatzi kraatzi Reitter,分别占总数的47.30%和40.66%,不同季节的优势种类不同。从时间动态上看,拟步甲物种数和个体数成显著正相关(r=0.887,P=0.003),表现为5月和7—8月2个发生高峰期,且5月最高。从整个景观来看,优势种克小鳖甲的盛发期在5月和7月,弯齿琵甲的盛发期在5月和8月,不同景观样地略有差异。物种-时间对应分析表明,拟步甲成虫发生可以分为春季发生型、春夏发生型、夏季发生型、夏秋发生型和全年发生型5类。5月拟步甲群落多样性和丰富度最高,不同月的拟步甲群落相似性可以聚为3类,由于植被类型和干扰程度的差异,月间拟步甲群落相似性会有所差异。     

ECOLOGY AND SYSTEMATICS OF HYPOXIS SESSILIS AND H. WRIGHTII (HYPOXIDACEAE) IN SOUTHERN FLORIDA

Fire acts as a strong flowering stimulus for Hypoxis sessilis and Hypoxis wrightii in southern Florida. Flowering intensity reaches a peak during the period 6–12 weeks postburn. Thereafter, reproductive activity decreases and follows a seasonal pattern with maximum intensity observed during the summer months. Some plants in each population are reproductively active throughout the year. In addition to increasing reproductive intensity, fire also influences the morphology of the inflorescence. Those inflorescences produced shortly after the burn are larger, more likely to have two flowers, and have chasmogamous flowers. Within three weeks after the start of flowering, all flowers produced by the plants are cleistogamous. Inflorescence size decreases soon afterward. Easy recognition of the two species is hampered by this morphological plasticity, but they retain enough distinguishing characteristics in southern Florida to be considered separate species.     

Plant-pollinator interactions in tropical monsoon forests in Southeast Asia

Forests with different flora and vegetation types harbor different assemblages of flower visitors, and plant-pollinator interactions vary among forests. In monsoon-dominated East and Southeast Asia, there is a characteristic gradient in climate along latitude, creating a broad spectrum of forest types with potentially diverse pollinator communities. To detect a geographical pattern of plant-pollinator interactions, we investigated flowering phenology and pollinator assemblages in the least-studied forest type, i.e., tropical monsoon forest, in the Vientiane plain in Laos. Throughout the 5-year study, we observed 171 plant species blooming and detected flower visitors on 145 species. Flowering occurred throughout the year, although the number of flowering plant species peaked at the end of dry season. The dominant canopy trees, including Dipterocarpaceae, bloomed annually, in contrast to the supra-annual general flowering that occurs in Southeast Asian tropical rain forests. Among the 134 native plant species, 68 were pollinated by hymenopterans and others by lepidopterans, beetles, flies, or diverse insects. Among the observed bees, Xylocopa, megachilids, and honeybees mainly contributed to the pollination of canopy trees, whereas long-tongued Amegilla bees pollinated diverse perennials with long corolla tubes. This is the first community-level study of plant-pollinator interactions in an Asian tropical monsoon forest ecosystem.     

Diversity of dung and carrion beetles in a disturbed Mexican tropical montane cloud forest and on shade coffee plantations

This paper analyzes the diversity of dung and carrion beetles (Scarabaeinae and Silphidae) in four human-induced habitats of a disturbed tropical montane cloud forest: polyspecific shade coffee plantations, monospecific shade coffee plantations, tropical montane cloud forest fragments, and clear cuts. The four habitats had similar richness, species composition, and assemblage structure of dung and carrion beetles. Differences were found in abundance and biomass levels for the four dominant species in the landscape. Dung beetles were more abundant than carrion beetles, but the biomass was higher for the latter. Carrion beetles were seasonal, while dung beetles were clearly not. When forest fragments and shade coffee plantations were compared to other similar habitats in the region, the same general pattern was observed. However, forests with high disturbance and monospecific shade coffee plantations had lower species richness than forests with low and medium disturbance and polyspecific shade coffee plantations. Thus shade coffee plantations maintain connectivity between patches of cloud forest in a landscape that is strongly affected by human activities. Protecting landscape diversity appears to ensure high species richness.     

Phoretic Poecilochirus mites specialize on their burying beetle hosts

Recurring species interactions can cause species to adapt to each other. Specialization will increase the fitness of symbionts in the coevolved association but may reduce the flexibility of symbiont choice as it will often decrease fitness in interactions with other than the main symbiont species. We analyzed the fitness interactions between a complex of two cryptic mite species and their sympatric burying beetle hosts in a European population. Poecilochirus mites (Mesostigmata, Parasitidae) are phoretic on burying beetles and reproduce alongside beetles, while these care for their offspring at vertebrate carcasses. While Poecilochirus carabi is typically found on Nicrophorus vespilloides beetles, P. necrophori is associated with N. vespillo. It has long been known that the mites discriminate between the two beetle species, but the fitness consequences of this choice remained unknown. We experimentally associated both mite species with both beetle species and found that mite fitness suffered when mites reproduced alongside a nonpreferred host. In turn, there is evidence that one of the beetle species is better able to cope with the mite species they are typically associated with. The overall fitness effect of mites on beetles was negative in our laboratory experiments. The Poecilochirus mites studied here are thus specialized competitors or parasites of burying beetles.