大亚湾鱼类群落嵌套分布格局

为保护大亚湾渔业资源,2015年4月(春季)、8月(夏季)、10月(秋季)和12月(冬季)对大亚湾进行了4航次底拖网渔业资源调查,结合距最近大陆距离、距最近大岛距离、水深、水温、盐度、叶绿素a、总氮、总磷、鱼类的最大体长和捕捞努力量(CPUE)这些参数,研究了大亚湾鱼类的群聚特征。结果表明,大亚湾鱼类呈嵌套分布格局,鱼类最大体长对嵌套格局的形成具有显著影响;大亚湾鱼类群落嵌套格局的形成支持选择性迁入假说;大亚湾鱼类全年与四季的嵌套最友好位点均在湾口杨梅坑和大辣甲北部海域,此两海域为大亚湾鱼类的主要群聚区,大辣甲北部海域是鱼类的产卵场繁殖区,杨梅坑海域是鱼类的主要育肥区,均应优先进行保护和管理,是开展大亚湾鱼类增殖放流的最适宜海域。     

Floodplain lake fish assemblages in the Amazon River: directions in conservation biology

The Neotropical region is renowned for its high biodiversity, and the Amazon River basin contains the highest number of fish species of any river system in the world. In recent years, habitat fragmentation and exploitation of biotic resources have threatened biological integrity and provoked to need for sustainable management and conservation of the Amazon River system. We studied 36 floodplain lakes along 2000 km of the Amazon River. The fish assemblages associated with flood forests are moderately diverse, with low species dominance and reduced populations. To detect nestedness of fish assemblage composition in floodplain lakes, a nested subset analysis was performed on species presence–absence. The incidence matrix (species × lakes) was maximally packed using the Nestedness Temperature Calculator software. The results of ranking lakes and species allow us to establish targets for conservation. Such strategy for sustainable management should be focused on maintaining the Amazonian biodiversity.     

Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Nestedness of faunal assemblages is a multi-scale phenomenon, potentially influenced by a variety of factors. Prior small-scale studies have found freshwater fish species assemblages to be nested along stream courses as a result of either selective colonization or extinction. However, within-stream gradients in temperature and other factors are correlated with the distributions of many fish species and may also contribute to nestedness. At a regional level, strongly nested patterns would require a consistent set of structuring mechanisms across streams, and correlation among species tolerances of the environmental factors that influence distribution. Thus, nestedness should be negatively associated with the spatial extent of the region analyzed and positively associated with elevational gradients (a correlate of temperature and other environmental factors). We examined these relationships for the freshwater fishes of Virginia. Regions were defined within a spatial hierarchy and included whole river drainages, portions of drainages within physiographic provinces, and smaller subdrainages. In most cases, nestedness was significantly stronger in regions of smaller spatial extent and in regions characterized by greater topographic relief. Analysis of hydrologic variability and patterns of faunal turnover provided no evidence that inter-annual colonization/extinction dynamics contributed to elevational differences in nestedness. These results suggest that, at regional scales, nestedness is influenced by interactions between biotic and abiotic factors, and that the strongest nestedness is likely to occur where a small number of organizational processes predominate, i.e., over small spatial extents and regions exhibiting strong environmental gradients.The Virginia Cooperate Fish and Wildlife Research Unit is jointly sponsored by United States Geological Survey, Virginia Polytechnic Institute and State University, and Virginia Department of Game and Inland Fisheries.     

Nested structure acquired through simple evolutionary process

Nested structure, which is non-random, controls cooperation dynamics and biodiversity in plant-animal mutualistic networks. This structural pattern has been explained in a static (non-growth) network models. However, evolutionary processes might also influence the formation of such a structural pattern. We thereby propose an evolving network model for plant-animal interactions and show that non-random patterns such as nested structure and heterogeneous connectivity are both qualitatively and quantitatively predicted through simple evolutionary processes. This finding implies that network models can be simplified by considering evolutionary processes, and also that another explanation exists for the emergence of non-random patterns and might provide more comprehensible insights into the formation of plant-animal mutualistic networks from the evolutionary perspective.     

Occurrence patterns of butterflies (Rhopalocera) in semi-natural pastures in southeastern Sweden

Occurrence patterns of butterflies (Rhopalocera) were analysed in relation to locality characteristics, and nested patterns were evaluated, based on a survey of 100 semi-natural pastures in the county of Östergötland, southeastern Sweden. Species richness of butterflies was positively related with locality-size, but not with the density of pastures in the surroundings. Species richness was lower in heavily grazed pastures compared with localities with a low or intermediate grazing pressure. This suggests that a uniformed, heavy grazing pressure should be avoided if butterflies are to be protected, even though such a management is favourable for many vascular plants. Out of 45 analysed species, 73% exhibited a significantly nested pattern, and species regarded to be sedentary had generally a more nested pattern. Several butterflies (such as Erynnis tages, Mellicta athalia and Pyrgus malvae) are possible to use as indicators of a relatively intact butterfly community. In a short-term perspective, the great bulk of butterflies confined to semi-natural pastures would be saved if management were adapted to the requirements of butterflies only at the localities richest in species. However, for conservation strategies to be successful over a longer time, whole landscapes harbouring the majority of the species and with a high density of semi-natural pastures should be selected and be given priority for conservation.     

Patterns and processes of nestedness in a Great Basin butterfly community

We examined nestedness and potential mechanisms causing that distributional pattern in resident butterfly communities of the Toiyabe Range, a mountain range in the central Great Basin of western North America. We tested whether life history characteristics, including habitat use and vagility, affected the relative degree of nestedness or mean species incidence. We also tested whether nestedness at the level of individual species was independent of life history. Relationships between distributional patterns and habitat use, particularly in ecologically sensitive riparian areas, are relevant to ongoing conservation planning in the Great Basin. The distributional pattern of the 68 resident butterfly species in 19 Toiyabe Range canyons was significantly nested, as was the distribution of all functional subgroups that we tested. Life history affected neither relative nestedness of species groups nor mean species incidence. More than 80% of the individual butterfly species that inhabit the Toiyabe Range had distributions that were more nested than expected. Colonization does not appear to have played an important role in determining the composition of butterfly communities in Toiyabe Range canyons. Likewise, selective dispersal has probably played a minor role in producing nested distributions of Toiyabe Range butterflies. Our results suggest either that impacts to riparian areas are not jeopardizing species viability, or that highly sensitive butterfly species have already been extirpated from the Toiyabe Range. Received: 15 February 1998 / Accepted: 19 December 1998     

Biological invasion into the nested assemblage of tree–beetle associations on the oceanic Ogasawara Islands

Invasion by alien organisms is a common worldwide phenomenon, and many alien species invade native communities. Invasion by alien species is especially likely to occur on oceanic islands. To determine how alien species become integrated into island plant–insect associations, we analyzed the structure of tree–beetle associations using host plant records for larval feeding by wood-feeding beetles (Coleoptera: Cerambycidae) on the oceanic Ogasawara Islands in the northwestern Pacific Ocean. The host plant records comprised 109 associations among 28 tree (including 8 alien) and 26 cerambycid (including 5 alien) species. Of these associations, 41.3% involved at least one alien species. Most native cerambycid species feed on host trees that have recently died. Alien trees were used by as many native cerambycid species (but by significantly more alien cerambycid species) as were native trees. Native cerambycid species used as many alien tree species (but significantly more native tree species) as did alien cerambycids. Thus, we observed many types of interactions among native and alien species. A network analysis revealed a significant nested structure in tree–cerambycid associations regardless of whether alien species were excluded from the analysis. The original nested associations on the Ogasawara Islands may thus have accepted alien species.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.     

Disentangling patch and landscape constraints of nested assemblages

The role of the matrix for the functionality of residual patches and therefore for species persistence has been recently recognised. However its influence on assemblage structure and composition is still unclear. We studied the effect of both patch and matrix attributes on community assemblage structure and composition in a fragmented landscape of central Italy. We used bird assemblages as a study model. Birds were sampled in 24 wood patches and distribution patterns were analysed considering both assemblage and guild-level responses. Patch composition and structure together with landscape patterns quantified with GIS were used as explanatory variables. The assemblages appeared to be strongly influenced by the landscape context, both in terms of composition and configuration. The functional connectivity of the patches, in terms of amount of neighbouring borders between woods and hedgerows, the shape of the woods in the matrix, together with the age of the patches, expressed as tree diameter, acted as the essential determinants, and even if the assemblages presented a significant nested structure, seven out of 40 species showed an idiosyncratic distribution. The study of the association between functional guilds and environmental parameters highlighted the influence of ecological constraints on the occurrence of unexpected presences and absences, suggesting the ability of some species to perceive and exploit matrix habitats. The matrix holds the capability to at least mitigate the effects of isolation and habitat loss, and the semi-natural elements of the mosaic may represent a biodiversity reservoir in an otherwise deprived landscape.     

From species to individuals: does the variation in ant–plant networks scale result in structural and functional changes?

Predicting the outcomes of any mutualistic interaction between ants and plants can be a very difficult task, since these outcomes are often determined by the ecological context in which the interacting species are embedded. Network theory has been an important tool to improve our understanding about the organizational patterns of animal–plant interactions. Nevertheless, traditionally, network studies have focused mainly on species-based differences and ignoring the importance of individual differences within populations. In this study, we evaluated if downscaling an ant–plant network from species to the individual level results in structural and functional changes in a network involving different-sized plant individuals. For this, we studied the extrafloral-nectar producing-tree Caryocar brasiliense (Caryocaraceae) and their associated ants in a Neotropical savanna. We observed 254 interactions involving 43 individuals of C. brasiliense and 47 ant species. The individual-based ant–plant network exhibited a nested pattern of interactions, with all developmental stages contributing equally to structuring this non-random pattern. We also found that plants with greater centrality within the network were better protected by their ant partners. However, plants with higher levels of individual specialization were not necessarily better protected by ants. Overall, we presented empirical evidence that intra-population variations are important for shaping ant–plant networks, since they can change the level of protection against herbivores conferred by the ants. These results highlight the importance of individual-based analyses of ecological networks, opening new research venues in the eco-evolutionary dynamics of ant–plant interactions.