Low Interspecific Competition Research Articles

Diet composition, niche overlap and partitioning of five sympatric rhinolophid bats in Southwestern China during summer

Understanding trophic niche differentiation is critical for exploring interspecific competition and stable coexistence among morphologically similar sympatric species. Bats are an ideal model for studying trophic niche differentiation among species because of their high taxonomic and ecological diversities, as well as their special life history traits. Although many factors can affect bat trophic niches, few studies have combined multiple factors to investigate the influences on bat trophic niches. In this study, we analyzed the summer diet and potential influencing factors of five sympatric rhinolophid bats in southwestern China: Rhinolophus macrotis, Rhinolophus osgoodi, Rhinolophus ferrumequinum, Rhinolophus affinis, and Rhinolophus pusillus. All five species mainly fed on Lepidopteran and Dipteran insects, with a large trophic niche breadth for each species and a low degree of dietary overlap. With the exception of R. affinis and R. pusillus, significant differences in diet composition were detected among species, which indicated relatively low interspecific competition. Canonical correspondence analysis showed that both echolocation calls and body size significantly affected interspecific diet differentiation, while wing morphology and bite force had relatively weak effects. This study suggests that the combined effects of multiple factors may drive trophic niche differentiation among five rhinolophid bat species in the study area.

Diversity of beetle species and functional traits along gradients of deadwood suggests weak environmental filtering

BackgroundGradients in local environmental characteristics may favour the abundance of species with particular traits, while other species decline, or favour species with different traits at the same time, without an increase in average species abundances. Therefore, we asked: do variations in species and traits differ along gradients of deadwood variables? Do species abundance and trait occurrence change with species richness within or between functional groups? Thus, we analysed the beetle assemblages of five forest sites located in Italy, along the Apennines mountains. MethodsFrom 2012 to 2018 we sampled beetles and five deadwood types in 193 plots to characterise the deadwood gradient: standing dead trees, snags, dead downed trees, coarse woody debris, and stumps. We modelled beetle species relative abundances and trophic traits occurrences against the deadwood variables using joint species distribution models. ResultsOut of 462 species, only 77 showed significant responses to at least one deadwood type, with a weak mean response across species. Trophic groups showed mostly negative responses to deadwood variables. Species abundance increased with species richness among sites only for phytophagous and saproxylophagous. Trait occurrence did not increase with species richness among sites, except for phytophagous and saproxylophagous. However, trait occurrence changed significantly with species richness of several trophic groups within some sites. We found that increases in species richness do not result in decreases in species abundance of a given trophic group, but rather null or positive relationships were found suggesting low interspecific competition. ConclusionsOur findings suggest that in Mediterranean mountain forests there is still room for increasing the level of naturalness, at least for what concerns deadwood management. On one side, our findings suggest that competition for deadwood substrates is still low, on the other side they indicate that increasing deadwood volume and types to improve overall beetle richness may increase also beetle abundances.

Competition in a Mixed-Species Planting with Four Contrasting Tree Species

Mixed-species systems are well-suited to smallholder and community forestry, but reliable evidence regarding and procedures to assess species performance in such systems is scarce. This field trial uses a pair of clinal plots with varying spacing and species composition to gain insights into competition between four species proposed for landscape rehabilitation in the Philippines. We examine the efficiency of this compact clinal trial in revealing growth traits of four species (Paraserianthes falcataria, Pterocarpus indicus, Shorea palosapis, Swietenia macrophylla) in mixed plantings. The use of a size-distance competition index allowed an assessment of the competitive and collaborative influences between four tree species. Within the expected general trend for diameter increment to decline with increasing competition, there were indications that Shorea palosapis is a benign competitor that may stimulate the growth of neighbouring individuals. Paraserianthes falcataria is a strong competitor that is also strongly impacted by competition, especially through antagonistic intraspecific competition. Paraserianthes falcataria appears well suited as a solitary tree in a field or village, whereas Shorea palosapis seems ideal for plantations, in both monoculture and mixed plantings. The clinal spacing and mixture trial, when examined using a size-distance competition index based on diameter increment, revealed useful insights into species performance. Pterocarpus indicus exhibits strong intraspecific, but low inter-specific competition, so appears well-suited for polyculture plantings. Of the four species trialled, Swietenia macrophylla appears to be best-suited as a monoculture species as it exhibits the lowest intraspecific competition.

Decreasing Defoliation Frequency Enhances Bromus valdivianus Phil. Growth under Low Soil Water Levels and Interspecific Competition

Bromus valdivianus Phil. (Bv) is a water stress-tolerant species, but its competitiveness in a diverse pasture may depend on defoliation management and soil moisture levels. This glasshouse study examined the effect of three defoliation frequencies, based on accumulated growing degree days (AGDD) (250, 500, and 1000 AGDD), and two soil water levels (80–85% of field capacity (FC) and 20–25% FC) on Bv growth as monoculture and as a mixture with Lolium perenne L. (Lp). The treatments were applied in a completely randomised block design with four blocks. The above-ground biomass of Bv was lower in the mixture than in the monoculture (p ≤ 0.001). The Bv plants in the mixture defoliated more infrequently (1000 AGDD) showed an increase in root biomass under 20–25% FC compared to 80–85% FC, with no differences measured between soil water levels in the monoculture. Total root length was highest in the mixture with the combination of infrequent defoliation and 20–25% FC. Conversely, frequent defoliation treatments resulted in reduced water-soluble carbohydrate reserves in the tiller bases of plants (p ≤ 0.001), as they allocated assimilates mainly to foliage growth. These results provide evidence that B. valdivianus can increase its competitiveness relative to Lp through the enhancement of the root growth and the energy reserve in the tiller base under drought conditions and infrequent defoliation in a mixture.

Influences of Forest Structure on the Density and Habitat Preference of Two Sympatric Gibbons (Symphalangus syndactylus and Hylobates lar)

Forest structure, defined as the three-dimensional vertical and horizontal distribution of canopy vegetation, has a great influence on the distribution patterns and abundance of forest primates. The complexity of this structural canopy produces a diverse range of microhabitats and distinct ecological niches, allowing ecologically similar species to coexist. Degradation of forests through anthropogenic factors significantly alters forest structure, and arboreal species such as gibbons are particularly vulnerable to these changes because of their reliance on canopy for survival. We investigated how forest structural variables influenced the density of two sympatric gibbon species (siamangs, Symphalangus syndactylus and lar gibbons, Hylobates lar) in Sikundur, a historically disturbed tropical lowland forest in north Sumatra. We used auditory sampling to establish group density in 10 locations and assessed structural characteristics of forest within 4–6 vegetation plots in each location. Lar gibbon group densities were 0.53–3.10 groups/km2 and siamang group densities were lower, with 0.0–1.0 groups/km2. The densities of both species were positively influenced by median height of first bole and the percentage of canopy connectivity. Lar gibbon group density was positively related to large (diameter at breast height 30–100 cm), tall (20–25 m) trees with a large crown area (100–300 m2), while siamang group density showed no significant relationships with these variables. These findings show canopy connectivity and height to first bole are significant structural variables for the continued presence of both gibbon species although, ecologically similar species can be influenced by different levels of structural disturbance. This canopy structural variation between sympatric species existing in the same ecosystem allows for home range overlap, low interspecific competition, and coexistence.

Population ecology, growth, and physico-chemical habitat of anadromous European perch Perca fluviatilis

Anadromous sub-populations of stenohaline freshwater fish are vastly understudied in the estuarine environment. The purpose of the present study was therefore to study the population ecology, growth rate, and physico-chemical environment of an anadromous sub-population of European perch (Perca fluviatilis) from the western Baltic Sea. Fish (301) were marked with external identification tags, and anglers and fishermen reported recaptures in a citizen science set-up over three years. In addition, scale samples were collected for population growth rate determination. Furthermore, water temperature, salinity, and oxygen concentration were monitored in the area. The fish showed a consistent annual migration pattern over the three years residing in a bay during summer while being in a delta during autumn, winter, and spring. The population had a high growth rate, but a meta-analysis showed that growth of European perch is not distinctly different between estuarine and freshwater populations. The average salinity measured in the area was around 10, but increased on multiple occasions to salinity levels known for being physiologically challenging for European perch. We argue that high growth rates of estuarine European perch is more likely due to high food availability and low interspecific competition in this environment, rather than due to physiologically optimal salinities. Furthermore, the European perch in the present study lived on the edge of the species salinity tolerance, and the migration into the delta during winter is likely a combination of avoiding high salinities at low temperatures and a spawning migration. These results are important knowledge for the management of estuaries and coastal areas, especially as climate change is locally altering these environments drastically, and calls for further studies on other anadromous sub-populations of stenohaline freshwater fish.

Pelagic-benthic resource polymorphism in Schizopygopsis thermalis Herzenstein 1891 (Pisces, Cyprinidae) in a headwater lake in the Salween River system on the Tibetan Plateau.

Resource polymorphism is a ubiquitous phenomenon in vertebrates and may represent a critical intermediate stage in speciation. Freshwater lakes in high‐altitude areas represent a natural system for understanding resource polymorphism in fishes benefiting from diverse lacustrine environments and species‐poor fish assemblages. We report resource polymorphism in a cyprinid fish, Schizopygopsis thermalis, in Lake Amdo Tsonak Co, a headwater lake in the upper Salween River system. Two discrete intraspecific morphs, planktivorous and benthivorous, were identified according to geometric morphometrics and traditional univariate linear measures. The planktivorous morph exhibits a longer head, longer upper and lower jaw, larger asymptotic standard length (L∞), lower growth rate (k), and higher growth performance index (φ) than the benthivorous morph. With respect to descriptive traits, the planktivorous morph possesses a large, terminal mouth and obvious mucus pores on the cheek and chin, while the benthivorous morph is characterized by a more inferior mouth with a sharpen horny edge on the lower jaw and unconspicuous mucus pores. The discrete pelagic–benthic resources and low interspecific competition in the lake system might drive the initial differentiation of the two morphs, and partial spatial reproductive isolation in breeding further maintains and reinforces the differences between them.

How does timing of flowering affect competition for pollinators, flower visitation and seed set in an early spring grassland plant?

Knowledge on how the timing of flowering is related to plant fitness and species interactions is crucial to understand consequences of phenological shifts as they occur under climate change. Early flowering plants may face advantages of low competition for pollinators and disadvantages of low pollinator abundances and unfavourable weather conditions. However, it is unknown how this trade-off changes over the season and how the timing affects reproductive success. On eight grasslands we recorded intra-seasonal changes in pollinators, co-flowering plants, weather conditions, flower visitation rates, floral longevity and seed set of Pulsatilla vulgaris. Although bee abundances and the number of pollinator-suitable hours were low at the beginning of the season, early flowers of P. vulgaris received higher flower visitation rates and estimated total number of bee visits than later flowers, which was positively related to seed set. Flower visitation rates decreased over time and with increasing number of co-flowering plants, which competed with P. vulgaris for pollinators. Low interspecific competition for pollinators seems to be a major driver for early flowering dates. Thus, non-synchronous temporal shifts of co-flowering plants as they may occur under climate warming can be expected to strongly affect plant-pollinator interactions and the fitness of the involved plants.

High growth potential of Ailanthus altissima in warm and dry weather conditions in novel forests of southern Switzerland

Our analysis of short-term growth responses to weather conditions provided evidence that the non-native tree species Ailanthus altissima may have a high growth potential in a warmer and drier environment, as predicted by global warming scenarios. Non-native tree species may alter ecosystem services in colonized forest communities. These novel forests represent a challenge for management, which is further accentuated by anthropogenic global change. Knowledge on the intra-annual growth performance and tree water relations of established and novel tree species is required to elucidate the drivers underlying forest dynamics. Here, we analysed intra-annual radial growth of the introduced tree species Ailanthus altissima (Mill.) Swingle and co-occurring Castanea sativa Mill. in novel forest communities in southern Switzerland. We used four years of continuously measured growth data in two sites to identify weather conditions in which the species achieved highest hourly growth and conditions in which largest proportions of seasonal growth occurred. While both species reached the largest proportion of seasonal growth and achieved the highest hourly growth under the most frequent weather conditions, A. altissima featured the highest growth rates in a wider range of weather conditions than C. sativa, particularly at high temperature and high vapour pressure deficit. We conclude that A. altissima has a greater potential than C. sativa to sustain growth in warm-dry conditions. Importantly, the advantages of A. altissima may be more accentuated in forest stands with low interspecific competition.

柏木低效林不同改造模式优势草本植物多样性及其生态位

PDF HTML阅读 XML下载 导出引用 引用提醒 柏木低效林不同改造模式优势草本植物多样性及其生态位 DOI: 10.5846/stxb201610202152 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家"十二五"科技支撑项目（2011BAC09B05）；德国政府贷款四川林业可持续经营管理项目（003H0602）；国家林业局中央财政林业科技推广示范（2010TK55）；四川省科技支撑计划（2010NZ0049） Study on plant diversity and niche characteristics of dominant herbaceous populations under different reconstruction patterns in low efficiency stands of Cupressus funebris Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:草本层对森林生态系统具有重要的作用，其对于环境的变化比乔木层和灌木层更为敏感，在较短的时间内更容易反映改造带来的影响。为了分析林分改造后草本植物多样性的变化和揭示草本群落间的关系，以川中丘陵区改造4 a后的11种模式：不同密度（株行距1.5 m×4 m与1.5 m×2 m）的桤木（Alnus cremastogyne）、香椿（Toona sinensis）、银木（Cinnamomum septentrionale）纯林模式和株行距为1.5 m×2 m的银木+桤木模式、香椿+银木模式、香椿+桤木模式、桤木+香椿+银木模式以及采伐迹地作为研究对象，柏木（Cupressus funebris）纯林为对照，对柏木低效林不同改造模式的优势草本植物多样性、生态位宽度及生态位重叠进行研究。结果表明：（1）除高低密度香椿模式、低密度银木模式和桤木+香椿+银木模式外，其他模式的草本植物多样性均优于柏木纯林，其中以香椿+银木模式（Shannon-Wiener指数、Simpson指数、均匀度和丰富度指数分别为（1.82、0.83、0.94和1.30），与香椿+桤木模式（1.83、0.83、0.93和1.33）的生物多样性显著高于柏木纯林（1.48、0.69、0.82和1.27），为最优的改造模式。（2）改造前铁线蕨（Adiantum capillus-veneris）生态位宽度最广为2.365，喜阴植物占有优势地位，改造后林下光照环境发生变化，喜阳植物五节芒（Miscanthus floridulus）在低密度的纯林模式中迅速占据林下生长空间，生态位宽度较大，随改造模式郁闭度的增加，薹草（Carex tristachya）、地果（Ficus tikoua）、竹叶草（Oplismenus compositus）等喜阴植物逐渐占据优势地位，喜阳植物逐渐被淘汰。生态位宽度的大小与重要值呈极显著正相关关系（r=0.916），但也与资源位呈极显著正相关关系（r=0.977）。（3）生态位宽度较大的物种间既有较大的生态位重叠，也有较小的生态位重叠，不能仅凭生态位宽度来判定生态位重叠值，而生态位宽度较小的鼠麴草（Gnaphalium affine）（0.647）与蛇莓（Duchesnea indica）（2.152）之间拥有最大的生态位重叠（0.123），可能是因为它们有相似的资源利用方式或相近的生态学特性。总体来说所有模式中草本植物物种间生态位重叠值都较低（ < 0.2），生态位分化明显，种间竞争并不激烈，这可能与改造时间较短有关系。 Abstract:Herbaceous layer plays a very important role in a forest ecosystem; it is more sensitive to environment than the arborous and shrub layers. Changes in herbaceous communities are more likely to reflect the effects of transformation in a relatively short period. To analyze the diversity of herbaceous plants after reconstruction and reveal the ecological relationships of herbaceous communities, pure forest plantations of Cinnamomum septentrionale, Alnus cremastogyne, and Toona sinensis and mixed plantations of C. septentrionale + A. cremastogyne, Cinnamomum septentrionale + T. sinensis, T. sinensis + A. cremastogyne, and C. septentrionale + A. cremastogyne + T. sinensis were studied The cutting-blank were selected as the research object, whereas the pure C. funebris forest was used as contrast. Pure forest plantations exhibit high and low planting densities, i.e. a spacing of 1.5 m×2 m and 1.5 m×4 m, respectively. Planting spacing in mixed plantations is 1.5 m×2 m. The results were as follows:(1) The Shannon-Wiener index, Simpson's index, Pielou's index and richness index of reconstruction plantation types were higher than those of the pure C. funebris forest (1.48, 0.69, 0.82, and 1.27, respectively), except low and high density pure T.sinensis plantation (1.19, 0.65, 0.86, and 0.66, respectively) (1.30, 0.65, 0.72, and 1.15, respectively), low density pure C. septentrionale plantation (1.48, 0.76, 0.92, and 0.85, respectively) and C. septentrionale + A. cremastogyne + T. sinensis plantation (1.44, 0.72, 0.81, and 1.12, respectively). Among all planting patterns, the biological diversity indices of mixed plantations of C. septentrionale + T. sinensis (1.83, 0.83, 0.94, and 1.30, respectively) and A. cremastogyne + T. sinensis (1.82, 0.83, 0.93, and 1.33, respectively) were significantly higher than those of the pure C. funebris forest; the two mixed plantation types were the relatively optimal reconstruction types. (2) The Adiantum capillus-veneris had the widest niche breadth (2.365) before the reconstruction and the ombrophytes were in the dominant position. After the reconstruction, the light condition and soil properties of the undergrowth changed, and heliophytes such as Miscanthus floridulus had rapidly occupied the living space in the low-density pure forest plantations. With increased forest canopy density, ombrophytes such as Carex tristachya, Ficus tikoua, Oplismenus compositus, and Duchesnea indica reoccupied the dominant position. The niche breadth values were significantly positively correlated with the importance values (r=0.916) and resource-niche values (r=0.977). (3) The niche overlap was not related niche breadth, species with wide niche breadths showed both high and low niche overlap values. The niche overlap values between D. indica and Gnaphalium affine were the highest (0.123), but these two species had low niche breadth (0.647 and 2.152, respectively) due to their similar environmental requirements and ecological characteristics. In general, the niche overlap values among the herbaceous communities were low ( < 0.2), which indicates obvious niche differentiation and low interspecific competition. This may be associated with the short reconstruction period. 参考文献 相似文献 引证文献

Spatial configuration drives complementary capture of light of the understory cotton in young jujube plantations

In intercropping systems (growing >1 species in a field), interactions between species affect the performance of plants and the overall yield. These interactions lead to plastic responses in plant traits due to the specific environmental conditions typical for intercrops, especially in agroforestry in which the understory crop is strongly shaded by the trees. To quantify the extent to how physiological plasticity is driven by inter-specific competition, field experiments with mixtures of cotton and jujube trees grown in strips were conducted in 2012 and 2013 in Hetian, Xinjiang, China. Cotton was grown at three levels of inter-specific competition, represented by the distance between the adjacent cotton and tree rows without change in plant density. The highest cotton yield was attained farthest away from the trees, i.e. at the lowest level of inter-specific competition, with a higher proportion of fiber in the bolls as well as a higher boll density compared to plants grown at higher inter-specific competition. Low inter-specific competition also increased maximum leaf area index (LAI), total light interception and dry matter accumulation. However, light-use efficiency was higher at high levels of inter-specific competition especially in the rows close to the tree line, associated with a higher fraction of diffuse radiation. These results aid in the optimization of the spatial pattern of crops in agroforestry system.

Microfungal oasis in an oligotrophic desert: diversity patterns and community structure in three freshwater systems of Cuatro Ciénegas, Mexico.

The Cuatro Ciénegas Basin (CCB) comprises several oligotrophic aquatic ecosystems limited by phosphorus. These aquatic systems are dominated by a high prokaryotic diversity, shaped by the stress of low nutrient supplies and interspecific competition. Although fungi constitute a diverse and important component of microbial diversity, the microfungal diversity in the CCB remains to be unveiled. With the aim to explore microfungal diversity and ecological patterns in this area, we present the first investigation analyzing cultivable taxa from sediment and water, as well as lignocellulolytic taxa obtained from incubated submerged plant debris, and wood panels in three contrasting freshwater systems in the CCB: Churince, Becerra and Pozas Rojas. We chose a culture-based approach to analyze sediment and water samples in order to obtain fungal cultures, providing opportunities for a posteriori studies, and the possibility of ex situ preservation of the diversity. We evaluated sequence data from the nuclear ribosomal internal transcribed spacer including the 5.8 rDNA region for 126 isolates, revealing 37 OTUs. These OTUs were phylogenetically affiliated to several genera in the fungal phyla: Zygomycota, Basidiomycota, and Ascomycota. We recorded two OTUs with saline affinity, agreeing with previous findings on the prokaryotic communities with ancestral marine resemblances. All the studied systems showed moderate diversity levels, however discrepancies among the diversity indexes were observed, due to the occurrence of abundant taxa in the samples. Our results indicated that lignocellulolytic microfungal communities are dominated by transient fungal taxa, as resident species were not recorded perhaps as a result of the long-term strong competition with the highly adapted prokaryotic community. Moreover, the obtained microfungal taxa occurred mostly on the resident plant debris, rather than submerged wood panels, perhaps as a result of the high adaptation to specific environmental conditions. In conclusion, the CCB possess a moderate taxonomical diversity compared to other arid environments, probably as a result of high selective pressures. Nonetheless, due to high spatial and temporal heterogeneity, the functional fungal diversity was considerable as predicted by the intermediate disturbance hypothesis. Decisively, the assessment of microfungal diversity freshwater systems is relevant, since this ecological group of microorganisms represents an important indicator of trophic complexity and biotic interactions among microbial communities, having important implications for understanding eukaryotic survival at the oligotrophic limit for life.

Diversity partitioning in Jurassic level-bottom communities

The analysis of diversity partitioning is a potential tool for detecting the factors that control taxonomic diversification in a given ecological context. Previously proposed models provide a theoretical framework that is herein applied to three sets of level-bottom communities representing different phases of the Jurassic diversification of marine life. The analysis shows that mean alpha-diversity remained surprisingly constant through most of the Jurassic, whereas beta-diversity increased by a factor of 2.6 during the same time interval. Diversification that is primarily driven by increasing beta-diversity is indicative of late diversification phases in ecosystems with low interspecific competition and/or high predation, as typical for marine level-bottom communities. Although generality of this conclusion is not claimed because of data limitations, the example demonstrates that the study of diversity partitioning provides a promising approach to the basic question about the factors that control the diversification of life.

Interactive effects of juvenile defoliation, light conditions, and interspecific competition on growth and ectomycorrhizal colonization of Fagus sylvatica and Pinus sylvestris seedlings.

Seedlings of forest tree species are exposed to a number of abiotic (organ loss or damage, light shortage) and biotic (interspecific competition) stress factors, which may lead to an inhibition of growth and reproduction and, eventually, to plant death. Growth of the host and its mycorrhizal symbiont is often closely linked, and hence, host damage may negatively affect the symbiont. We designed a pot experiment to study the response of light-demanding Pinus sylvestris and shade-tolerant Fagus sylvatica seedlings to a set of abiotic and biotic stresses and subsequent effects on ectomycorrhizal (ECM) root tip colonization, seedling biomass, and leaf nitrogen content. The light regime had a more pronounced effect on ECM colonization than did juvenile damage. The interspecific competition resulted in higher ECM root tip abundance for Pinus, but this effect was insignificant in Fagus. Low light and interspecific competition resulted in lower seedling biomass compared to high light, and the effect of the latter was partially masked by high light. Leaf nitrogen responded differently in Fagus and Pinus when they grew in interspecific competition. Our results indicated that for both light-demanding (Pinus) and shade-tolerant (Fagus) species, the light environment was a major factor affecting seedling growth and ECM root tip abundance. The light conditions favorable for the growth of seedlings may to some extent compensate for the harmful effects of juvenile organ loss or damage and interspecific competition.

Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals

The degree of individual specialization in resource use differs widely among wild populations where individuals range from fully generalized to highly specialized. This interindividual variation has profound implications in many ecological and evolutionary processes. A recent review proposed four main ecological causes of individual specialization: interspecific and intraspecific competition, ecological opportunity and predation. Using the isotopic signature of subsampled whiskers, we investigated to what degree three of these factors (interspecific and intraspecific competition and ecological opportunity) affect the population niche width and the level of individual foraging specialization in two fur seal species, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis), over several years. Population niche width was greater when the two seal species bred in allopatry (low interspecific competition) than in sympatry or when seals bred in high-density stabilized colonies (high intraspecific competition). In agreement with the niche variation hypothesis (NVH), higher population niche width was associated with higher interindividual niche variation. However, in contrast to the NVH, all Antarctic females increased their niche width during the interbreeding period when they had potential access to a wider diversity of foraging grounds and associated prey (high ecological opportunities), suggesting they all dispersed to a similar productive area. The degree of individual specialization varied among populations and within the annual cycle. Highest levels of interindividual variation were found in a context of lower interspecific or higher intraspecific competition. Contrasted results were found concerning the effect of ecological opportunity. Depending on seal species, females exhibited either a greater or lower degree of individual specialization during the interbreeding period, reflecting species-specific biological constraints during that period. These results suggest a significant impact of ecological interactions on the population niche width and degree of individual specialization. Such variation at the individual level may be an important factor in the species plasticity with significant consequences on how it may respond to environmental variability.

The effects of forest fragmentation on the population ecology and natural history of a funnel-web spider

Habitat fragmentation strongly affects the abundance, distribution, body size and population genetics of invertebrates. Urban growth in Brazil has led to severe fragmentation, especially in the Atlantic Forest and savannas. The effects of this fragmentation on the common funnel-web spider Aglaoctenus lagotis were examined in two forest fragments within the interior savanna: a smaller fragment within an urban environment and a larger fragment within a rural environment. The reproductive period occurred in October, coinciding with the beginning of the rainy season, when the species was aggregated in the two forest fragments. The smaller fragment contained a larger population, and the spiders had a larger average prosoma size and web area. The presence of a larger population in a smaller area within the urban centre may reflect a limited dispersal ability, reduced predator abundance or low interspecific competition. The larger prosoma length and web area in the smaller habitat fragment suggest greater resource availability and a higher probability of capturing prey in the urban environment. In both areas, a larger number of capture threads was positively correlated with the presence of inquiline spiders in the webs. The genetic data indicate close similarity between and within the two areas, indicating that the species has low genetic variability or that the areas studied, consistent with their proximity, have separated only recently. Most savannas and forests in midwestern Brazil have recently undergone severe fragmentation, and further studies of this nature are needed.

Mathematical analysis of a model for plant invasion mediated by allelopathy

Exotic plants threaten the biodiversity of natural habitats and the integrity of agricultural systems throughout the World. Therefore, understanding, predicting and controlling plant invasions became issues of great practical importance. In the present paper, a model for plant invasion based on allelopathic suppression is proposed and studied through analytical methods and numerical integration. Employing linear stability analysis the conditions for plant coexistence as well as one species extinction were determined for the spatially homogeneous system. These conditions demonstrate the advantage conferred to the alien plant by its phytotoxin. It was shown that the system exhibits bistability between two distinct fixed points, either associated to species coexistence or to the extinction of one species. Numerical simulation is also included to support such results. Further, the invasion spreading starting from a single, spatially localized initial focus was investigated by numerical integration of the model's equations. As obtained for the spatially homogeneous system, at strong interspecific competition the outcome is the extinction of one plant species. In contrast, at low interspecific competition, the rule is the coexistence between the invader and native plants. So, under weak competition alien species can invade, but genetic diversity can be sustained.

Niche Analysis of Pinus tabulaeformis Community Dominant Species in Wulu Mountain Nature Reserve

According to the data of 57 plots,Pinus tabulaeformis community from Wulu Mountain Nature Reserve was classified by TWINSPIN cluster analysis.Shannon-Wiener,Hurbert niche width and niche overlap of Morisita Index of the type of tree and shrub were calculated by utilizing the type of association as a resource axis.The results showed that P.tabulaeformis,Quercus wutainnesis and Acer ginnala had larger Shannon-Wiener values which were 1.656,1.404 and 1.047,respectively and Hurbert niche width values were 0.948,0.735 and 0.386,respectively,in the tree layer.Cotoneaster multiflorus,Spiraea pubescens,and Viburnum schensianum had larger Shannon-Wiener values which were 1.562,1.401 and 1.300,respectively and Hurbert niche breadth values were 0.512,0.447 and 0.389,respectively,in the shrub layer.The niche overlapping of tree layer included three degrees which consisted of high overlap,moderate overlap and low overlap,high overlap accounted for 6%(0.8),moderate overlap accounted for 10%(0.6-0.8) and low overlap accounted for 84%.Besides,the niche overlapping of shrub layer also included three degrees which consisted of high overlap,moderate overlap and low overlap,high degree overlap accounted for 7%(0.8),moderate overlap accounted for 10.39%(0.6-0.8),and low overlap accounted for 82.25%.As succession proceeding,P.tabuliformis had higher adaptability and the ability of using resources,and lower inter-specific competition in the local environment.However,the niches of some species obviously tended to specialize,the community was in the polled stage.

Biogeographical comparison of the invasive Lepidium draba in its native, expanded and introduced ranges

Invasive plants are expected to perform better and consequently be more abundant in their introduced compared to their native ranges. However, few studies have simultaneously compared plant and population traits along with biotic and abiotic environmental parameters for invasive and native plant populations. We compared 17 native Eastern European, 14 expanded Western European and 31 introduced US populations of the invasive Lepidium draba over 2 years. Most parameters were similar between the two European ranges, but differed for the US. Density, cover, and biomass of L. draba were greater in the US while cover of other vegetation was lower. Bare-ground and litter cover were greater for US populations in 1 year, as was L. draba shoot height and seed output. Availability of labile soil nitrogen was also greater in the US range. Endophagous shoot herbivory was greater in Western Europe compared to the US in 1 year. As expected, specialist herbivores were only found in Europe. Differences between ranges were not explained by varying environmental conditions (climate, altitude and latitude). In summary our results indicate that lower interspecific competition, higher resource availability and the lack of specialist natural enemies may all contribute to the increased performance of L. draba in its introduced US range. Additionally, L. draba is well adapted to disturbance events, which may further benefit its competitiveness at degraded sites. In general our results were consistent between years, which reinforces their validity. However, some of the differences were only significant in one of the 2 years, which, on the other hand, emphasizes the importance to ideally conduct biogeographic comparisons over multiple years.

Effects of damming a large lowland river on chironomids and fish assessed with the (multiplicative partitioning of) true/Hill biodiversity measure

AbstractThe impact of a large lowland temperate zone reservoir on chironomid and fish biodiversity was investigated in the same upstream (U) and downstream (D) sites on the same sampling occasions in spring and autumn of several post‐impoundment years. The true/Hill N1 diversity measure was used to construct diversity models of the impact, and partitioning of N1 to reveal the importance of ecological gradients. N1 is unique in being decomposable among multiple levels and easily comparable across ecosystems and animal groups.Chironomids were more diverse than fish in all community sets owing to their probably lower mobility, lower interspecific competition, opportunistic character and much shorter life spans than those of fish. Fish exerted consumption pressure on chironomids upstream by foraging mostly on benthic insects, but not downstream where they fed on microcrustaceans of reservoir origin or on epiphytic fauna (mainly Chironomidae).The reservoir impact on chironomids decreased their diversity in U and increased in D, while much the opposite was true in fish. In D in macroinvertebrates, the impact consisted in advancing over time intensification of seasonal development of submersed macrophytes, while in D in fish in a few species escaping from the reservoir after their populational explosions each year.Partitioning of diversity revealed that the spatial (upstream–downstream) gradient was the strongest factor of diversity change in chironomids as compared with season, and age of the impoundment. No gradient was dominant in fish. Comparisons of observed data with a null model testified to very strong intraspecific aggregation in both chironomids and fish. Copyright © 2010 John Wiley &amp; Sons, Ltd.