Behavior influences range limits and patterns of coexistence across an elevational gradient in tropical birds

Does competition influence patterns of coexistence between closely related taxa? Here we address this question by analyzing patterns of range overlap between related species of birds (‘sister pairs’) co‐occurring on a tropical elevational gradient. We explicitly contrast the behavioral dimension of interspecific competition (interference competition) with similarity in resource acquisition traits (exploitative competition). Specifically, we ask whether elevational range overlap in 118 sister pairs that live along the Manu Transect in southeastern Peru is predicted by proxies for competition (intraspecific territorial behavior) or niche divergence (beak divergence and divergence times, an estimate of evolutionary age). We find that close relatives that defend year‐round territories tend to live in non‐overlapping elevational distributions, while close relatives that do not defend territories tend to broadly overlap in elevational distribution. In contrast, neither beak divergence nor evolutionary age was associated with patterns of range limitation. We interpret these findings as evidence that behavioral interactions – particularly direct territorial aggression – can be important in setting elevational range limits and preventing coexistence of closely related species, though this depends upon the extent to which intraspecific territorial behavior can be extended to territorial interactions between species. Our results suggest that interference competition can be an important driver of species range limits in diverse assemblages, and thus highlight the importance of considering behavioral dimensions of the niche in macroecological studies.     

Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny,Functional Biogeography,and Environmental Gradients

To compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current‐day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and re‐colonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re‐expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).     

Neutral lipid fatty acid composition as trait and constraint in Collembola evolution

Functional traits determine the occurrence of species along environmental gradients and their coexistence with other species. Understanding how traits evolved among coexisting species helps to infer community assembly processes. We propose fatty acid composition in consumer tissue as a functional trait related to both food resources and physiological functions of species. We measured phylogenetic signal in fatty acid profiles of 13 field‐sampled Collembola (springtail) species and then combined the data with published fatty acid profiles of another 24 species. Collembola fatty acid profiles generally showed phylogenetic signal, with related species resembling each other. Long‐chain polyunsaturated fatty acids, related to physiological functions, demonstrated phylogenetic signal. In contrast, most food resource biomarker fatty acids and the ratios between bacterial, fungal, and plant biomarker fatty acids exhibited no phylogenetic signal. Presumably, fatty acids related to physiological functions have been constrained during Collembola evolutionary history: Species with close phylogenetic affinity experienced similar environments during divergence, while niche partitioning in food resources among closely related species favored species coexistence. Measuring phylogenetic signal in ecologically relevant traits of coexisting species provides an evolutionary perspective to contemporary assembly processes of ecological communities. Integrating phylogenetic comparative methods with community phylogenetic and trait‐based approaches may compensate for the limitations of each method when used alone and improve understanding of processes driving and maintaining assembly patterns.     

Niche evolution in Australian terrestrial mammals? Clarifying scale-dependencies in phylogenetic and functional drivers of co-occurrence

Interactive forces between competition and habitat filtering drive many biogeographic patterns over evolutionary time scales. However, the responsiveness of assemblages to these two forces is highly influenced by spatial scale, forming complex patterns of niche separation. We explored these spatial dependencies by quantifying the influence of phylogeny and functional traits in shaping present day native terrestrial mammal assemblages at multiple scales, principally by identifying the spatial scales at which niche evolution operates. We modelled the distribution of 53 native terrestrial mammal species across New South Wales, Australia. Using predicted distributions, we estimated the range overlap between each pair of species at increasing grain sizes (~0.8, 5.1, 20, 81, 506, 2,025, 8,100 km²). We employed a decision tree to identify how interactions among functional traits and phylogenetic relatedness translated to levels of sympatry at increasing spatial scales. We found that Australian terrestrial mammals displayed phylogenetic over-dispersion that was inversely related to spatial scale, suggesting that ecological processes were more influential than biogeographic sympatry patterns in defining assemblages of species. While the contribution of phylogenetic relatedness to patterns of co-occurrence decreased as spatial scale increased, the reverse was true for habitat preferences. At the same time, functional traits also operated at different scales, as dietary preferences dominated at local spatial scales (<10 km²) while body mass has a stronger effect at larger spatial scales. Our findings show that ecological and evolutionary processes operate at different scales and that Australian terrestrial mammals diverged slower along their micro-scale niche compared to their macro-scale niche. By combining phylogenetic and niche methods through the modelling of species distributions, we assessed whether specific traits were related to a particular niche. More importantly, conducting multi-scale spatial analysis avoids categorical assignment of traits-to-niches, providing a clearer relationship between traits and a species ecological niche and a more precise scaling for the axes of niche evolution.     

Disentangling the historical routes to community assembly in the global epicentre of biodiversity

Aim

The exceptional turnover in biota with elevation and number of species coexisting at any elevation makes tropical mountains hotspots of biodiversity. However, understanding the historical processes through which species arising in geographical isolation (i.e. allopatry) assemble along the same mountain slope (i.e. sympatry) remains a major challenge. Multiple models have been proposed including (1) the sorting of already elevationally divergent species, (2) the displacement of elevation upon secondary contact, potentially followed by convergence, or (3) elevational conservatism, in which ancestral elevational ranges are retained. However, the relative contribution of these processes to generating patterns of elevational overlap and turnover is unknown.

Location

Tropical mountains of Central- and South-America.

Time Period

The last 12 myr.

Major Taxa Studied

Birds.

Methods

We collate a dataset of 165 avian sister pairs containing estimates of phylogenetic age, geographical and regional elevational range overlap. We develop a framework based on continuous-time Markov models to infer the relative frequency of different historical pathways in explaining present-day overlap and turnover of sympatric species along elevational gradients.

Results

We show that turnover of closely related bird species across elevation can predominantly be explained by displacement of elevation ranges upon contact (81%) rather than elevational divergence in allopatry (19%). In contrast, overlap along elevation gradients is primarily (88%) explained by conservatism of elevational ranges rather than displacement followed by elevational expansion (12%).

Main Conclusions

Bird communities across elevation gradients are assembled through a mix of processes, including the sorting, displacement and conservatism of species elevation ranges. The dominant role of conservatism in explaining co-occurrence of species on mountain slopes rejects more complex scenarios requiring displacement followed by expansion. The ability of closely related species to coexist without elevational divergence provides a direct and faster pathway to sympatry and helps explain the exceptional species richness of tropical mountains.     

The roles of environment,space, and phylogeny in determining functional dispersion of rodents (Rodentia) in the Hengduan Mountains,China

The recently described trait‐based approach is becoming widely popular for a mechanistic understanding of species coexistence. However, the greatest challenge in functional analyses is decomposing the contributions of different ecological and evolutionary processes (e.g., niche‐based process, neutral process, and evolutionary process) in determining trait structure. Taking rodents (Rodentia) in the Hengduan Mountains as our study model, we aim to (1) quantify the vertical patterns of functional structure for head–body length (HL), tail/body ratio (TR), animal component in diet (ACD), and all traits; (2) disentangle the relative importance of different assembly processes (environment, space, and phylogeny) in structuring trait dispersion; and (3) assess the feasibility of Bergmann's rule and Allen's rule along elevational gradient. Our results have suggested that the vertical functional structure pattern varied across these three traits, indicating distinct functional roles in the community assembly process. These nonrandom vertical patterns of HL, TR, and terminal ACD have demonstrated these traits were dominated by different ecological process along environmental gradient. In variance partitioning, high proportion of the spatial variations in trait dispersion was explained by environmental and spatial models, which have provided supporting strong evidence for niche‐based and neutral processes in leading species coexistence. Although the three traits all exhibited apparent phylogenetic signals, phylogenetic relationship within community failed to predict the spatial variations of functional dispersion, confirming the enormous inference of phylogenetic signals in predicting trait structure. By assessing the vertical patterns of HL and TR at order and family levels, we argued that functional adaptation along an environmental gradient is a surrogate of series of complex processes (e.g., environmental filtering, interspecific interaction, and neutral dispersal) acting on multiple functional axes, which results in inconsistence with the empirical rules along elevational gradient.     

Phylogenetic and morphological relationships between nonvolant small mammals reveal assembly processes at different spatial scales

The relative roles of historical processes, environmental filtering, and ecological interactions in the organization of species assemblages vary depending on the spatial scale. We evaluated the phylogenetic and morphological relationships between species and individuals (i.e., inter‐ and intraspecific variability) of Neotropical nonvolant small mammals coexisting in grassland‐forest ecotones, in landscapes and in regions, that is, three different scales. We used a phylogenetic tree to infer evolutionary relationships, and morphological traits as indicators of performance and niche similarities between species and individuals. Subsequently, we applied phylogenetic and morphologic indexes of diversity and distance between species to evaluate small mammal assemblage structures on the three scales. The results indicated a repulsion pattern near forest edges, showing that phylogenetically similar species coexisted less often than expected by chance. The strategies for niche differentiation might explain the phylogenetic repulsion observed at the edge. Phylogenetic and morphological clustering in the grassland and at the forest interior indicated the coexistence of closely related and ecologically similar species and individuals. Coexistence patterns were similar whether species‐trait values or individual values were used. At the landscape and regional scales, assemblages showed a predominant pattern of phylogenetic and morphological clustering. Environmental filters influenced the coexistence patterns at three scales, showing the importance of phylogenetically conserved ecological tolerances in enabling taxa co‐occurrence. Evidence of phylogenetic repulsion in one region indicated that other processes beyond environmental filtering are important for community assembly at broad scales. Finally, ecological interactions and environmental filtering seemed important at the local scale, while environmental filtering and historical colonization seemed important for community assembly at broader scales.     

杜鹃花属植物的可育性研究进展

结合作者近年来的工作, 总结了国内外有关杜鹃花属(Rhododendron)植物可育性研究的成果和进展, 旨在为相关研究者和技术人员提供参考。(1)杜鹃花属的杜鹃亚属(subgen. Rhododendron)和羊踯躅亚属(subgen. Pentanthera)中存在多倍化现象, 甚至存在同一物种有多种倍性。(2)在自然授粉条件下, 除了常见种内杂交及自交情形外, 常绿杜鹃亚属(subgen. Hymenanthes)、杜鹃亚属和映山红亚属(subgen. Tsutsusi)内种间杂交十分普遍, 也有跨亚组之间的自然杂交案例。(3)杜鹃花属植物中自交亲和(self compatibility, SC)与自交不亲和(self incompatibility, SI)现象并存, 云锦杜鹃亚组(subsect. Fortunea)兼具自交败育到高可育性的所有类型, 而在映山红亚属与马银花亚属(subgen. Azaleastrum)中自交不亲和现象则更为常见。通常自交被认为是杜鹃花物种的被动适应, 但对于一些在极端气候条件下分布的局域种而言, 则可能是一种主动响应。(4)不同分类等级(亚属、组和亚组)间的人工杂交研究表明, 杂交亲和性或可育性与双亲的系统发育关系及染色体倍性具有明显的关联, 并反映在发育阶段和各项亲和力指标的变化之中。常绿杜鹃亚属与杜鹃亚属间的远缘杂交相对比较容易, 常绿杜鹃亚属与映山红亚属间、映山红亚属与杜鹃亚属的正反交、映山红亚属与羊踯躅亚属的正交以及常绿杜鹃亚属与羊踯躅亚属的正交、马银花亚属与杜鹃亚属正交等也有亲和的案例。(5)自交不亲和亲本的介入可大幅度增加种间杂交的不育比率, 并导致其由双向可育到单向不育再到双向不育方向发展。     

Contrasting Effects of Intraspecific Trait Variation on Trait-Based Niches and Performance of Legumes in Plant Mixtures

Niche differentiation, assumed to be a key mechanism of species coexistence, requires that species differ in their functional traits. So far it remains unclear to which extent trait plasticity leads to niche shifts of species at higher plant diversity, thereby increasing or decreasing niche overlap between species. To analyse this question it is convenient to measure niches indirectly via the variation in resource-uptake traits rather than directly via the resources used. We provisionally call these indirectly measured niches trait-based niches. We studied shoot- and leaf-morphological characteristics in seven legume species in monoculture and multi-species mixture in experimental grassland. Legume species varied in the extent of trait variation in response to plant diversity. Trait plasticity led to significant shifts in species niches in multiple dimensions. Single-species niches in several traits associated with height growth and filling of canopy space were expanded, while other niche dimensions were compressed or did not change with plant diversity. Niche separation among legumes decreased in dimensions related to height growth and space filling, but increased in dimensions related to leaf size and morphology. The total extent of occupied niche space was larger in mixture than in the combined monocultures for dimensions related to leaf morphology and smaller for dimensions related to whole-plant architecture. Taller growth, greater space filling and greater plasticity in shoot height were positively, while larger values and greater plasticity in specific leaf area were negatively related with increased performance of species in mixture. Our study shows that trait variation in response to plant diversity shifts species niches along trait axes. Plastically increased niche differentiation is restricted to niche dimensions that are apparently not related to size-dependent differences between species, but functional equivalence (convergence in height growth) rather than complementarity (divergence in traits associated with light acquisition) explains increased performance of legumes in mixture.     

Phylogenetic structure and phylogenetic diversity of angiosperm assemblages in forests along an elevational gradient in Changbaishan,China

Aims Understanding what drives the variation in species composition and diversity among local communities can provide insights into the mechanisms of community assembly. Because ecological traits are often thought to be phylogenetically conserved, there should be patterns in phylogenetic structure and phylogenetic diversity in local communities along ecological gradients. We investigate potential patterns in angiosperm assemblages along an elevational gradient with a steep ecological gradient in Changbaishan, China.Methods We used 13 angiosperm assemblages in forest plots (32×32 m) distributed along an elevational gradient from 720 to 1900 m above sea level. We used Faith's phylogenetic diversity metric to quantify the phylogenetic alpha diversity of each forest plot, used the net relatedness index to quantify the degree of phylogenetic relatedness among angiosperm species within each forest plot and used a phylogenetic dissimilarity index to quantify phylogenetic beta diversity among forest plots. We related the measures of phylogenetic structure and phylogenetic diversity to environmental (climatic and edaphic) factors.Important findings Our study showed that angiosperm assemblages tended to be more phylogenetically clustered at higher elevations in Changbaishan. This finding is consistent with the prediction of the phylogenetic niche conservatism hypothesis, which highlights the role of niche constraints in governing the phylogenetic structure of assemblages. Our study also showed that woody assemblages differ from herbaceous assemblages in several major aspects. First, phylogenetic clustering dominated in woody assemblages, whereas phylogenetic overdispersion dominated in herbaceous assemblages; second, patterns in phylogenetic relatedness along the elevational and temperature gradients of Changbaishan were stronger for woody assemblages than for herbaceous assemblages; third, environmental variables explained much more variations in phylogenetic relatedness, phylogenetic alpha diversity and phylogenetic beta diversity for woody assemblages than for herbaceous assemblages.     

Co-occurrence of tree species at fine spatial scale in a woodland cerrado,southeastern Brazil

Species co-occurrence at fine spatial scales is expected to be nonrandom in relation to species phylogenetic relatedness and functional similarity. On the one hand, closely related species that occur together and experience similar environmental conditions are likely to share phenotypic traits due to the process of environmental filtering. On the other hand, species that are too similar are unlikely to co-occur due to competitive exclusion. We surveyed a woodland cerrado, southeastern Brazil, to test whether co-occurrence in tree species shows functional or phylogenetic structuring at fine spatial scale. Searching for correlations between an index of species co-occurrence and both functional trait differences and phylogenetic distances, we provided evidence for a predominant role of environment filters in determining the co-occurrence of functionally similar tree species in cerrado. However, we did not find any effect of phylogenetic relatedness on tree species co-occurrence. We suggest that the phylogenetic relatedness of co-occurring cerrado tree species did not present a pattern, because the species functional traits were randomly distributed on the phylogeny. Thus, phylogenetic relatedness and functional similarity do not seem to limit the co-occurrence at fine spatial scale of cerrado tree species.     

Elevational differentiation accelerates trait evolution but not speciation rates in Amazonian birds

The importance of ecologically mediated divergent selection in accelerating trait evolution has been poorly studied in the most species‐rich biome of the planet, the continental Neotropics. We performed macroevolutionary analyses of trait divergence and diversification rates across closely related pairs of Andean and Amazonian passerine birds, to assess whether the difference in elevational range separating species pairs – a proxy for the degree of ecological divergence – influences the speed of trait evolution and diversification rates. We found that elevational differentiation is associated with faster divergence of song frequency, a trait important for pre‐mating isolation, and several morphological traits, which may contribute to extrinsic post‐mating isolation. However, elevational differentiation did not increase recent speciation rates, possibly due to early bursts of diversification during the uplift of the eastern Andes followed by a slow‐down in speciation rate. Our results suggest that ecological differentiation may speed up trait evolution, but not diversification of Neotropical birds.     

Both traits and phylogenetic history influence community structure in snakes over steep environmental gradients

Assemblages of closely related organisms are generated on axes of deep time diversification, biogeographic processes related to dispersal and habitat filtering, and competition. Using models that account for phylogeny, ecology, and traits, we examine how the interaction among biogeography, habitat filtering, and trait convergence influences community assemblage in Nearctic snakes. With 122 community surveys, environmental niche, trait data including size, diet, parity and habitat preference, and a nearly complete phylogeny of snakes from the United States, we ask 1) do phylogenetic species variability (PSV) and traits change in predictable and correlated ways given ecology and geographic distance, 2) are the measured traits variable within and across communities and how is this related to PSV at local scales, and 3) is there evidence of habitat filtering or trait divergence? Following a general trend of western to eastern North American origin and dispersal of major groups, we similarly show a significant decrease in PSV in this direction but unexpectedly with stable trait variance, showing that traits and phylogenetic variability are disconnected at the community level. We also demonstrate that trait variability and not PSV dominates local communities. Finally, regardless of phylogeny, we show that certain traits, such as reproductive mode (parity) frequency, change within communities in response to steep ecological gradients.     

Phylogenetic overdispersion in Floridian oak communities

Closely related species that occur together in communities and experience similar environmental conditions are likely to share phenotypic traits because of the process of environmental filtering. At the same time, species that are too similar are unlikely to co-occur because of competitive exclusion. In an effort to explain the coexistence of 17 oak species within forest communities in North Central Florida, we examined correlations between the phylogenetic relatedness of oak species, their degree of co-occurrence within communities and niche overlap across environmental gradients, and their similarity in ecophysiological and life-history traits. We show that the oaks are phylogenetically overdispersed because co-occurring species are more distantly related than expected by chance, and oaks within the same clade show less niche overlap than expected. Hence, communities are more likely to include members of both the red oak and the white + live oak clades than only members of one clade. This pattern of phylogenetic overdispersion arises because traits important for habitat specialization show evolutionary convergence. We hypothesize further that certain conserved traits permit coexistence of distantly related congeners. These results provide an explanation for how oak diversity is maintained at the community level in North Central Florida.     

Low levels of climate niche conservatism may explain clade diversity patterns in the South African genus Pelargonium (Geraniaceae)

? Premise of the study: Sharp climatic gradients in South Africa and in particular in the Cape Floristic Region (CFR) provide a diversity of niches over short distances that may have promoted ecological diversification in local clades. Here we measured the extent to which closely related species occupy divergent climates and test whether niche lability is correlated with higher species diversity in the genus. ? Method: We integrated phylogenetic information and environmental niche models (ENM) to assess the levels of climate niche conservatism. ENMs for 113 species of Pelargonium were calculated using maximum entropy. We used two tests, one assessing climate niche equivalency and the other testing niche similarity between sister species and within sections. We also examined whether niche similarity was correlated with phylogenetic relatedness across the genus. ? Key results: Niche similarity was mostly independent of phylogenetic relationships. Compared to random expectations, 23% of closely related species pairs had climate niches that were more similar, and only 6.5% were more disparate; the remaining 70% of comparisons had similarities that fell within random expectations. Similar trends were observed when analyses were restricted to only sister species pairs. Although the overall proportion of niche divergence was low, this was significantly related to sectional diversity. We also found a negative relationship between diversity and the proportion of random niches. ? Conclusions: Lack of widespread niche conservatism in a highly heterogeneous landscape and few instances of significant climate niche lability suggest that an adaptive divergence process was implicated in the Pelargonium radiation.     

Towards a trait-based quantification of species niche

Aims Although the niche concept is of prime importance in ecology, the quantification of plant species' niches remains difficult. Here we propose that plant functional traits, as determinants of species performance, may be useful tools for quantifying species niche parameters over environmental gradients.Important findings Under this framework, the mean trait values of a species determine its niche position along gradients, and intraspecific trait variability determines its niche breadth. This trait-based approach can provide an operational assessment of niche for a potentially large number of species, making it possible to understand and predict species niche shifts under environmental changes. We further advocate a promising method that recently appeared in the literature, which partitions trait diversity into among- and within-community components as a way to quantify the species niche in units of traits instead of environmental parameters. This approach allows the switch of the focus from ecological niches to trait niches, facilitating the examination of species coexistence along undefined environmental gradients. Altogether, the trait-based approach provides a promising toolkit for quantifying the species ecological niche and for understanding the evolution of species niche and traits.     

Trait adaptation promotes species coexistence in diverse predator and prey communities

Species can adjust their traits in response to selection which may strongly influence species coexistence. Nevertheless, current theory mainly assumes distinct and time‐invariant trait values. We examined the combined effects of the range and the speed of trait adaptation on species coexistence using an innovative multispecies predator–prey model. It allows for temporal trait changes of all predator and prey species and thus simultaneous coadaptation within and among trophic levels. We show that very small or slow trait adaptation did not facilitate coexistence because the stabilizing niche differences were not sufficient to offset the fitness differences. In contrast, sufficiently large and fast trait adaptation jointly promoted stable or neutrally stable species coexistence. Continuous trait adjustments in response to selection enabled a temporally variable convergence and divergence of species traits; that is, species became temporally more similar (neutral theory) or dissimilar (niche theory) depending on the selection pressure, resulting over time in a balance between niche differences stabilizing coexistence and fitness differences promoting competitive exclusion. Furthermore, coadaptation allowed prey and predator species to cluster into different functional groups. This equalized the fitness of similar species while maintaining sufficient niche differences among functionally different species delaying or preventing competitive exclusion. In contrast to previous studies, the emergent feedback between biomass and trait dynamics enabled supersaturated coexistence for a broad range of potential trait adaptation and parameters. We conclude that accounting for trait adaptation may explain stable and supersaturated species coexistence for a broad range of environmental conditions in natural systems when the absence of such adaptive changes would preclude it. Small trait changes, coincident with those that may occur within many natural populations, greatly enlarged the number of coexisting species.     

Phylogenetic limiting similarity and competitive exclusion

One of the oldest ecological hypotheses, proposed by Darwin, suggests that the struggle for existence is stronger between more closely related species. Despite its long history, the validity of this phylogenetic limiting similarity hypothesis has rarely been examined. Here we provided a formal experimental test of the hypothesis using pairs of bacterivorous protist species in a multigenerational experiment. Consistent with the hypothesis, both the frequency and tempo of competitive exclusion, and the reduction in the abundance of inferior competitors, increased with increasing phylogenetic relatedness of the competing species. These results were linked to protist mouth size, a trait potentially related to resource use, exhibiting a significant phylogenetic signal. The likelihood of coexistence, however, was better predicted by phylogenetic relatedness than trait similarity of the competing species. Our results support phylogenetic relatedness as a useful predictor of the outcomes of competitive interactions in ecological communities.     

南海北部近海头足类优势种及其生态位特征

为了解南海北部近海头足类优势种的种间关系,根据2014—2015年该海域4个季节底拖网渔业资源调查,应用相对重要性指数、生态位宽度和重叠指数从时空维度分析头足类优势种的生态位特征。结果表明: 该海域4个季节的头足类优势种共5种,分别为剑尖枪乌贼、中国枪乌贼、火枪乌贼、金乌贼和杜氏枪乌贼,前两种是4个季节的共同优势种。与历史数据相比,头足类优势种的种类组成已发生改变。头足类资源时空分布格局明显,海南岛南部至粤东海域资源密度高于北部湾,季节变化呈夏季高而冬季低特征。时空生态位分析表明,优势种的时间和空间生态位宽度没有一致位序,剑尖枪乌贼和中国枪乌贼分别占据最大的时间(1.32)和空间生态位宽度(3.90),而时间和空间生态位宽度最小的物种分别是金乌贼(0.98)和杜氏枪乌贼(2.04)。虽然时间生态位重叠在数值上显著高于空间生态位重叠,但二者均是在中国枪乌贼、剑尖枪乌贼、火枪乌贼等种对间有较高重叠,而杜氏枪乌贼与其余4个优势种的重叠较低。相关分析表明,在时空尺度上生态位宽度与丰度的变化均呈极显著负相关。生态位可反映物种资源量时空变化信息,丰富了传统渔业群落研究方法。     

Similarities between invaders and native species: Moving past Darwin's naturalization conundrum

Darwin's naturalization conundrum states that successful invaders must be closely related to native species to possess the traits to tolerate that environment, but distantly related enough to possess traits allowing exploitation of underutilized niches, thereby minimizing competition. Although influential, this hypothesis is based on several simplistic assumptions. In particular, the relationship among phylogenetic relatedness, similarity, and competition is more complex than assumed and changes with spatial and phylogenetic scale. Competitive interactions are determined by limiting similarity and trait hierarchies associated with separate traits. Successful invaders thus need to be similar to native species in some respects, but different in others. This combination of similarities and differences is unlikely to be conserved. Further, many invasive species are represented in their novel range by genotypes with extreme trait values or plasticity relative to the species mean. Selection for these genotypes may alter the similarity between invasive and native species, thus obscuring the relationship between competition and phylogenetic relatedness. As environmental filtering and competition often act on different spatial scales, approaches assessing how individual traits relate to invasion at these scales (species pools vs local community) may improve our understanding of the relationship between similarity and invasion.