Asymmetric interspecific aggression in New Guinean songbirds that replace one another along an elevational gradient

A common pattern in tropical avifaunas is for closely related species to inhabit largely parapatric elevational distributions such that they replace one another along the elevational gradient. A long‐standing hypothesis for this pattern is that parapatry is maintained by interspecific interference competition mediated by interspecific aggression. However, empirical tests of this hypothesis remain scarce. We used reciprocal playback experiments to measure interspecific aggression in five species‐pairs of New Guinean passerine elevational replacements. We found evidence of interspecific aggression in three species‐pairs. In these three cases, interspecific aggression was asymmetric, with the lower elevation species more aggressive towards the upper elevation species than vice versa. Two patterns suggest that this interspecific aggression is a learned response to the presence of a heterospecific competitor rather than misdirected intraspecific aggression or an evolved response to a competitor. First, when present, interspecific aggression was always strongest at the upper elevation range margin of the lower elevation species (i.e. in the elevational zone in which the two species were found in close proximity and thus interacted with each other), and diminished over very short distances away from this zone. Secondly, the two species‐pairs that did not exhibit interspecific aggression had narrow ‘no man's land’ gaps between their elevational distributions such that heterospecifics did not encounter one another, possibly explaining the lack of interspecific aggression in these examples. Our results support the hypothesis that interspecific aggression is one factor influencing elevational limits in species‐pairs of New Guinean elevational replacements.     

Sexual niche partitioning in two species of New Guinean Pachycephala whistlers

Sex differences in foraging behavior have been widely reported in the ornithological literature, but few examples are available from tropical avifaunas. Differences between males and females in foraging behavior have been hypothesized to be a byproduct of sexual size dimorphism or a result of niche partitioning to reduce intersexual competition for food or different reproductive roles. From 2010 to 2013, I used foraging data and mist‐net capture rates from multiple study sites to examine possible sex differences in the foraging behavior of two New Guinean Pachycephala whistlers. I found that male Regent (Pachycephala schlegelii) and Sclater's (Pachycephala soror) whistlers consistently foraged in higher strata than females. It is unlikely that these differences are due to sexual dimorphism because these species exhibit little sexual dimorphism. Sex differences in foraging behavior were consistent across years and study sites and did not appear linked to breeding behavior, supporting the food‐competition hypothesis, but not the reproductive‐roles hypothesis. Male territorial defense often occurs in relatively high strata in Pachycephala whistlers, possibly influencing male foraging strata. However, male territorial behavior cannot explain why females predominately forage in lower strata. Instead, intersexual competition for food resources is likely the primary driver of differences in the foraging behavior of male and female Regent and Sclater's whistlers.     

Influence of Feed Components on Symbiotic Bacterial Community Structure in the Gut of the Wood-Feeding Higher Termite Nasutitermes takasagoensis

The influence of carbon sources on bacterial community structure in the gut of the wood-feeding higher termite Nasutitermes takasagoensis was investigated. 16S rRNA gene sequencing and terminal-restriction fragment length polymorphism (T-RFLP) analyses revealed that the bacterial community structure changed markedly depending on feed components at the phylum level. Spirochaetes was predominant in the clone libraries from wood- and wood powder-fed termites, whereas Bacteroidetes was the largest group in the libraries from xylan-, cellobiose-, and glucose-fed termites, and Firmicutes was predominant in the library from xylose-fed termites. In addition, clones belonging to the phylum Termite Group I (TG1) were found in the library from xylose-fed termites. Our results indicate that the symbiotic relationship between termite and gut microorganisms is not very strong or stable over a short time, and that termite gut microbial community structures vary depending on components of the feeds.     

Does Weeding Promote Regeneration of an Indigenous Tree Community in Felled Pine Plantations in Uganda?

The use of plantations to manage extensive tracks of deforested lands in the tropics is a conservation strategy that has recently received considerable attention. Plantation trees can promote seed dispersal by attracting dispersers and creating favorable site conditions, leading to increased germination and establishment of indigenous trees. Subsequently, plantation trees can be harvested for profit or left to senesce, leaving a native tree community. We evaluated the effect of vine, grass, and shrub cutting (weeding) over a 3‐year period on regeneration of indigenous trees subsequent to the removal of plantation softwoods in Kibale National Park, Uganda. Counter to what would be expected if weeding released trees from competition, we found no difference in the total number of stems or in the stems greater than 10 cm diameter at breast height between control and weeded plots; there were more stems greater than 1 cm diameter at breast height in the control plots. For species found in both control and weeded plots, the maximum size of individuals did not differ. At the end of the study, 61 species were found in the control plots and 43 species were found in the weeded plots, and in both types of plots the three most abundant species were the same. The number of species and stems classified as early or middle successional species did not differ between weeded and control plots. The fact that weeding did not promote regeneration of indigenous trees after the removal of plantation trees illustrates the importance of evaluating and field‐testing potential management options.     

Community level impacts of an ant invader and food mediated coexistence

Ant invasions exert a range of effects on recipient communities, from displacement of particular species to more complex community disruption. While species loss has been recorded for a number of invasion events, a little examined aspect of these invasions is the mechanisms for coexistence with resident ant species.The yellow crazy ant, Anoplolepis gracilipes (Smith), is considered one of the world’s worst ant invaders and has recently undergone rapid population growth in Tokelau. We surveyed the ground-dwelling ant fauna in two plots on each of five invaded and three uninvaded islands across two atolls in Tokelau to examine community characteristics of the ant fauna in areas with and without yellow crazy ants. We also used three types of food bait (tuna, jam and peanut butter) to experimentally test if species are able to coexist by consuming different food resources. Anoplolepis gracilipes was found to coexist with two to six other ant species at any one site, and coexisted with a total of 11 ant species. Four species never co-occurred with A. gracilipes. Non-metric multidimensional scaling showed significant differences in community composition and the relative abundance of species between areas that had, and had not, been invaded by A. gracilipes. The number of other ant species was significantly lower in communities invaded by the yellow crazy ant, but did not decline with increasing A. gracilipes abundance, indicating that impacts were independent of population density. The yellow crazy ant dominated all tuna and jam baits, but had a low attendance on peanut butter, allowing four other ant species to access this resource. Our results demonstrate community level impacts of an ant invader on a tropical oceanic atoll and suggest that differing use of food resources can facilitate coexistence in ant communities. Received 11 September 2006; revised 15 January 2007; accepted 22 February 2007.     

长苞铁杉天然林群落种内及种间竞争关系研究

通过各种竞争指数的比较筛选,得到较能客观反映长苞铁杉种内、种间竞争关系的竞争指数,定量地分析了长苞铁杉种内和种间竞争强度。结果表明:长苞铁杉种内竞争随胸径的增大而逐渐减少;种间与种内竞争关系顺序为:长苞铁杉-长苞铁杉>猴头杜鹃-长苞铁杉>青冈栎-长苞铁杉>其它树种-长苞铁杉。竞争强度与对象木的胸高直径服从双曲线回归关系,利用模型预测了长苞铁杉种内、种间的竞争强度。     

Analysis of the insect community in a stored-maize facility

Maize samples were obtained at two depths [0–30cm (top sample) and 30–60cm (bottom sample) from the maize surface] at 19–28 locations from a naturally infested maize storage facility in Wisconsin, USA. Based on identification of insects in stored-maize samples from 13 weekly sampling events, four topics were addressed: (i) the seasonal fluctuation in the insect community; (ii) ordination analysis was conducted to examine the association among insect taxa and to determine their distribution along abiotic and geographic gradients; (iii) the demographic characteristics of insect communities in maize samples with high abundance of either Plodia interpunctella (Plodia samples) or Sitophilus zeamais (Sitophilus samples); and (iv) to what extent natural enemies were spatially associated with their prey species. We identified a total of 18 different taxa, composed of adults and larvae of 14 determined species, and others identified to genus, family or order. Insect density was significantly higher in top samples compared to bottom samples, and the insect taxa occurred more frequently in top samples compared to bottom samples. In the ordination analysis, the three explanatory variables accounting for eastern, northern and vertical position of maize samples explained the largest part of the total variance. There was a gradual time trend with some of the insect species mainly occurring early or late in the monitoring period. Moisture content of the maize was the weakest of the significant explanatory variables, while temperature in the grain mass did not explain a significant part of the total variance. Plodia samples and Sitophilus samples had significantly different spatial distribution patterns and had markedly different insect species composition. Plodia samples were characterized by low abundance of all granivores and fungivores, except P.interpunctella. Conversely, Sitophilus samples had high abundance of T.castaneum, A.advena, and C.ferrugineus. Consequently, Sitophilus samples seemed to comprise more diverse insect communities than Plodia samples. Natural enemies were not significantly associated with their most common hosts. In a highly homogeneous habitat (stored maize), we demonstrated that stored-product insect species had significantly different distribution patterns mainly along geographic gradients. Stochasticity of the initial infestation process or interspecific competition are two of the possible explanations for the spatial segregation of stored-product insects, and the spatial segregation of insects on the same trophic level may have profound implications for the understanding of how these ecosystems develop over time and thereby how integrated pest management strategies are implemented to control insect pest populations.     

Interspecific variation in the defence secretions of Nasutitermes soldiers

Termite soldiers of the genus Nasutitermes (Isoptera, Termitidae, Nasutitermitinae) eject a viscous, sticky defense secretion composed of non-polar monoterpene hydrocarbons and polyoxygenated diterpenes from the frontal gland. Chemical compositions are described in detail for the East African species, N. kempae and N. infuscatus, and for the Neotropical species N. ephratae. Additional comparisons with the new world species N. costalis, N. rippertii and N. octopilis are presented. The structure of a new monohydroxykempene from N. ephratae is described, and a physicochemical model for the stickiness of the glue is presented. Although the structures of the individual secretion components vary within the genus, the glue-like nature of the secretion remains essentially unchanged. Chemical analysis of soldier defense secretions may be useful in studying the systematic biology of termites.     

Oviposition preference and larval performance in the exotic birch-leafmining sawfly Profenusa thomsoni

This study used experiments at several spatial scales to determine whether (1) intraspecific competition occurs among larvae of the leafmining sawfly Profenusa thomsoni (Konow) (Hymenoptera: Tenthredinidae) on birch (Betula spp.), (2) oviposition site preferences of P. thomsoni maximize offspring performance, and (3) early‐season damage by external folivores or the leafminer Fenusa pumila Leach (Hymenoptera: Tenthredinidae) affects oviposition preferences or larval performance of P. thomsoni. Larval P. thomsoni competed at natural densities; survival and weight of larvae were reduced under crowded conditions. Despite this, females of P. thomsoni tended to lay eggs on leaves already bearing eggs from other females and discriminated only weakly among leaves of different sizes on a branch. Both damage by F. pumila and artificial damage to leaves early in the season decreased survival of P. thomsoni larvae on the same branch, and ovipositing P. thomsoni females avoided damaged leaves but not other leaves on the same branch. In general, oviposition choices by P. thomsoni reduced larval survival. Possible reasons for the lack of a strong preference–performance relationship in P. thomsoni are discussed.     

Axial Differences in Community Structure of Crenarchaeota and Euryarchaeota in the Highly Compartmentalized Gut of the Soil-Feeding Termite Cubitermes orthognathus

Methanogenesis represents an important electron sink reaction in the hindgut of soil-feeding termites. This is the first comprehensive analysis of the archaeal community structure within the highly compartmentalized intestinal tract of a humivorous insect, combining clonal analysis and terminal restriction fragment (T-RF) length polymorphism (T-RFLP) fingerprinting of the archaeal communities in the different gut compartments of Cubitermes orthognathus. We found that the morphological and physicochemical heterogeneity of the gut is reflected in a large phylogenetic diversity and pronounced axial differences in the composition of the archaeal gut microbiota, notably among those clones or ribotypes that could be assigned to methanogenic taxa. Comparative analysis of the relative frequencies of different archaeal lineages among the small-subunit rRNA gene (SSU rDNA) clones and their corresponding T-RF indicated that the archaeal community in the anterior, extremely alkaline hindgut compartment (P1) consists mainly of members of the Methanosarcinaceae, whereas Methanobacteriaceae and Methanomicrobiales predominate in the subsequent, more posterior compartments (P3/4a and P4b). The relative abundance of Thermoplasmales increased towards the rectum (P5). SSU rDNA sequences representing Crenarchaeota, which have not yet been reported to occur in the intestinal tracts of arthropods, were detected in all gut sections. We discuss how the spatial distribution of methanogenic populations may be linked to axial heterogeneity in the physicochemical gut conditions and to functional adaptations to their respective ecological niches.     

珍稀濒危植物梓叶槭种群径级结构与种内种间竞争关系

该研究对四川省珍稀濒危植物梓叶槭(Acer catalpifolium)种群的主要分布区进行调查,分析梓叶槭种群径级结构与种内和种间的竞争关系,探讨竞争强度与径级和距离之间的关系。结果表明:(1)梓叶槭胸径与树高之间存在显著的幂函数关系;种群径级结构呈正态分布,中小径级树木较多,高径级树木较少。(2)梓叶槭种内和种间竞争强度分别占总竞争强度(222.87)的15.16%和84.84%,说明竞争主要来自种间。(3)梓叶槭与主要伴生种之间的竞争强度大小依次为柳杉桢楠白栎刺楸灯台树桦木杉木厚朴光皮桦;对象木和竞争木距离与竞争指数之间较好地服从指数函数关系,当对象木与竞争木距离小于1m时,竞争指数可达到5.5,随着距离逐渐增加,其竞争指数相应降低,并最终趋于平缓。(4)竞争强度随对象木胸径的增大而减小,当对象木胸径小于20cm时,受到的竞争压力最大,竞争指数最大的分别是梓叶槭与整个林分(234.98)以及梓叶槭与种间(184.01);当对象木胸径小于10cm时,竞争指数均可以达到18;当对象木胸径大于20cm时,竞争强度变化很小且竞争指数较低;竞争强度与对象木胸径服从幂函数关系(CI=AD-B)。(5)模型预测结果表明,随着梓叶槭胸径的增加,竞争指数均越来越小,竞争强度呈降低趋势;当梓叶槭胸径为0~5cm时,梓叶槭与整个林分受到的竞争强度最大,竞争指数为7.14,占总竞争强度的50%;当胸径大于20cm时,竞争指数变化不大;该模型能很好的预测梓叶槭种内和种间竞争强度。     

黄土高原马栏林区辽东栎林种内、种间竞争研究

利用Hegyi的单木竞争指数模型对黄土高原马栏林区辽东栎(Quercus liaotungensis)的种内和种间竞争强度进行了定量分析.结果显示:(1)辽东栎种内竞争强度与种间竞争强度的总和大致相等,其种内及种间竞争强度均随对象木胸径的增大而逐渐减小,其关系服从幂函数规律,竞争主要发生在胸径小于15 cm的幼树阶段.(2)各组成树种对辽东栎影响程度(竞争指数)的大小顺序为:辽东栎>油松(Pinus tabulaeformis)>白桦(Betulaplatyphylla)>山杨(Populus davidiana)>杜梨(Pyrus betulaefolia)>湖北山楂(Crataegus hupehensis)>茶条槭(Acer ginnala)>陕西鹅耳枥(Carpinus shensiensis)>葛萝槭(A.grosseri).(3)油松是该地区的次优势种,对辽东栎有较大的竞争压力,在群落发展中可能会形成以油松占优势的混交林.(4)辽东栎胸径小于15 cm时,种内种间竞争是导致大量个体死亡的主要原因;胸径超过15 cm时,人为砍伐可能是个体死亡的主要原因.研究结果认为马栏林区混交林油松的密度不宜过大,尤其是在与未成熟辽东栎种群混交时密度应合理,应对该林区的混交林进行人工抚育,及时择伐密度过大的油松,而在辽东栎胸径达到15 cm之前择伐长势较差的植株,以促使森林群落尽快趋于稳定.     

Comparison of the septal areas in New Guinean and European brains

In 1966, septal nuclei of unusual size in brains of kuru-diseased Fore people from the Eastern Highlands of New Guinea were reported (Beck and Gajdusek, 1966). Microscopic investigation which did not reveal any pathological changes in these nuclei led to the question of whether their large size could be a characteristic feature of the Fore (and perhaps also of other ethnic groups of New Guinea), rather than a consequence of the disease. We had at our disposal brains from patients of coastal areas of New Guinea who did not suffer from kuru. The septal areas of eight cases were investigated by serial sections and compared to those of nine European brains. No difference in size comparable to that reported in the earlier study could be detected. We conclude that a possible pecularity in the size of the septal nuclei of Fore people cannot be generalized to the entire population of New Guinea.     

Community Structure and Dynamics of Small Eukaryotes Targeted by New Oligonucleotide Probes: New Insight into the Lacustrine Microbial Food Web

The seasonal dynamics of the small eukaryotic fraction (cell diameter, 0.2 to 5 μm) was investigated in a mesotrophic lake by tyramide signal amplification-fluorescence in situ hybridization targeting seven different phylogenetic groups: Chlorophyceae, Chrysophyceae, Cryptophyceae, Cercozoa, LKM11, Perkinsozoa (two clades), and Fungi. The abundance of small eukaryotes ranged from 1,692 to 10,782 cells ml⁻¹. The dominant groups were the Chrysophyceae and the Chlorophyceae, which represented 19.6% and 17.9% of small eukaryotes, respectively. The results also confirmed the quantitative importance of putative parasites, Fungi and Perkinsozoa, in the small heterotrophic eukaryotic assemblage. The relative abundances recorded for the Perkinsozoa group reached as much as 31.6% of total targeted eukaryotes during the summer. The dynamics of Perkinsozoa clade 1 coincided with abundance variations in Peridinium and Ceratium spp. (Dinoflagellates), while the dynamics of Perkinsozoa clade 2 was linked to the presence of Dinobryon spp. (Chrysophyceae). Fungi, represented by chytrids, reached maximal abundance in December (569 cells ml⁻¹) and were mainly correlated with the dynamics of diatoms, especially Melosira varians. A further new finding of this study is the recurrent presence of Cercozoa (6.2%) and LKM11 (4.5%) cells. This quantitative approach based on newly designed probes offers a promising means of in-depth analysis of microbial food webs in lakes, especially by revealing the phylogenetic composition of the small heterotrophic flagellate assemblage, for which an important fraction of cells are generally unidentified by classical microscopy (on average, 96.8% of the small heterotrophic flagellates were identified by the specific probes we used in this study).Recently developed molecular methods based on the amplification and sequencing of rRNA genes have made it possible to investigate picoeukaryote assemblage composition (pigmented or nonpigmented unicellular eukaryotes with cell diameters of <2 μm or <5 μm according to the studies) in various aquatic systems, independently of morphological identification and cultivation (14, 23, 27, 28, 29, 39). The essential role of picoplankton (both eukaryotic and prokaryotic) as a contributor to plankton biomass and to carbon and nutrient cycling has long been established (9), but the unexpected diversity among the smallest eukaryotes (cell diameters, <5 μm) was only recently revealed. Most of these data were obtained in oceanic systems, but a few recent studies conducted in lakes have also highlighted the broad diversity of 18S rRNA sequences affiliated with numerous phylogenetic groups: Chlorophyceae, Chrysophyceae, Cryptophyceae, Cercozoa, Fungi, Choanoflagellida, Bicosoecida, Ciliophora, Haptophyceae, Perkinsozoa, LKM11, Hyphochytridiomycota, Katablepharidaceae, Dinophyceae, and Eustigmatophyceae (22, 23, 24, 34). Thus, it has been possible to observe clear seasonal changes in small-eukaryote structure in an oligomesotrophic lake (23), and the lake-based studies generally report a dominance of heterotrophic cells within the lacustrine small-eukaryote assemblage. Moreover, the recurrent presence of sequences affiliated with parasitic groups has been highlighted in lakes of various trophic statuses (22, 23). Lepère et al. (25) reported the unexpected importance of two groups: first, fungi affiliated with two clades of chytrids known as parasites of various groups of microalgae; and second, members of the phylum Perkinsozoa belonging to two clades closely related to Perkinsus marinus and Parvilucifera infectans, which are parasites of bivalves and dinoflagellates, respectively (30), and whose systematic position has been controversial, since they are phylogenetically related to the Apicomplexa or the Dinoflagellata (6, 13).Although these data brought new insight into the structural diversity of lacustrine small eukaryotes, the relative importance, dynamics, and functional roles of these microorganisms from various phylogenetic groups are still largely unknown. We now need to research specific in situ abundances of previously undetected taxa. In this study, specially developed oligonucleotide probes, designed on the basis of molecular data obtained from sequencing (20, 21, 22, 23, 24, 25, 34), were used for fluorescence in situ hybridization (FISH) coupled with tyramide signal amplification (TSA) to investigate the composition, abundance, and dynamics of lacustrine small eukaryotes (<5 μm) in the mesotrophic Lake Bourget over 1 year. Special attention was paid to the dynamics of putative parasitic groups (Perkinsozoa, Fungi, Cercozoa).     

鹤地水库浮游植物群落的结构与动态

鹤地水库位于雷州半岛北部(21°42'～22°22'N,109°54'～110°25'E),是一座中营养化的大型水库.为了研究其浮游植物群落的结构与变化特点,在水库设置5个采样点,并于2003年2、7、9、12月对其采样.鹤地水库浮游植物生物量变化为O.156～2.548 mg L~(-1),主要由蓝藻和硅藻组成.5个采样点的浮游植物生物量具有明显的季节变化,且变化趋势相同,即丰水期的生物量高于枯水期,主要是由于丰水期水温较高以及入库河水带入的营养盐.5个采样点的浮游植物生物量从主要入库河流至大坝区呈下降趋势,与磷浓度的降低直接相关.浮游植物优势种主要以热带代表性种类为主,且有明显的季节变化,枯水期主要为硅藻的根管藻(Rhizosolenia sp.)、小环藻(Cyclotella sp.)、颗粒直链藻(Melosira granulata)以及模糊直链藻(Melosira ambigua)等.丰水期为蓝藻的拟柱孢藻(Cylindrospermopsis raciborskii)、湖泊假鱼腥藻(Pseudanabaena limnetica)等,浮游植物优势种类的变化主要受磷浓度的影响.浮游植物前8个优势种的生物量占浮游植物群落生物量的850%～92%,显著低于温带地区浮游植物群落结构稳定的湖泊.     

Dynamics of the Abundance and Community Structure of Small Mammals in the Saratov Trans-Volga Region

A typical feature of the populations of small mammals in different areas of the Saratov Trans-Volga region is the long-term and constantly increasing abundance of Sylvaemus uralensis and its wide distribution in a variety of habitats. The maximal abundance of S. uralensis is 72.0 individuals per 100 trap-days, and its share in catches is 73.0%. The abundance of Microtus arvalis tends to increase. It was shown that Lagurus lagurus has been found again in the steppe zone, on fallow lands and fields, after a prolonged depression in 2012–2013, the average density of species being 4.0 individuals per 100 trap-days. A high abundance of other typical steppe inhabitants (Allocricetulus eversmanni and Ellobius talpinus) was noted as well. The highest indices of species diversity (H = 1.18) are typical of fallow lands.     

白颈长尾雉与白鹇秋冬季空间生态位比较

2008年9月-2009年2月,在江西官山国家级自然保护区对白颈长尾雉(Syrmaticus ellioti)和白鹇(Lophura nycthemera)及其栖息地生态因子进行调查,通过8个资源轴分析了2个种的多维生态位宽度、重叠及种间竞争.结果表明,白鹇和白颈长尾雉综合空间生态位宽度分别仅为0.268和0.294;白鹇的海拔和坡度空间生态位大于白颈长尾雉.而白颈长尾雉的坡向生态位宽度大于白鹇,在其他资源轴上二者接近;白颈长尾雉和白鹇的栖息地生态位相似性为0.425,竞争系数为0.584,竞争比较激烈.应加强低海拔地区植被及水源的保护,减少人为干扰.