BIODIVERSITY RESEARCH: Nestedness for different reasons: the distributions of birds,lizards and small mammals on islands of an inundated lake

Aim We examined whether the community compositions of birds, lizards and small mammals were nested in a fragmented landscape in the Thousand Island Lake, China. We also assessed whether the mechanisms influencing nestedness differed among these taxonomic groups. Location Thousand Island Lake, China. Methods Presence/absence matrices were compiled for birds (42 islands) and lizards (42 islands) using line‐transect methods, and for small mammals (14 islands) using live‐trapping methods from 2006 to 2009. Nestedness was analysed using BINMATNEST, and statistical significance was assessed using the conservative null model 3. We used Spearman rank correlations and partial Spearman rank correlations to examine associations of nestedness and habitat variables (area, isolation, habitat diversity and plant richness) as well as life‐history traits (body size, habitat specificity, geographical range size and area requirement) related to species extinction and immigration tendencies. Results The community compositions of birds, lizards and small mammals were all significantly nested, but the causal factors underlying nestedness differed among taxonomic groups. For birds, island area, habitat specificity and area requirement were significantly correlated with nestedness after controlling for other independent variables. For lizards, habitat heterogeneity was the single best correlate of nestedness. For small mammals, island area, habitat heterogeneity and habitat specificity were significantly correlated with nestedness. The nested patterns of birds, lizards and small mammals were not attributable to passive sampling or selective colonization. Main conclusions The processes influencing nested patterns differed among taxonomic groups. Nestedness of bird assemblages was driven by selective extinction, and lizard assemblage was caused by habitat nestedness, while nestedness of small mammals resulted from both selective extinction and habitat nestedness. Therefore, we should take taxonomic differences into account when analysing nestedness to develop conservation guidelines and refrain from using single taxa as surrogates for others.     

Testing multiple assembly rule models in avian communities on islands of an inundated lake,Zhejiang Province,China

Aim A fundamental question in community ecology is whether general assembly rules determine the structure of natural communities. Although many types of assembly rules have been described, including Diamond’s assembly rules, constant body‐size ratios, favoured states, and nestedness, few studies have tested multiple assembly rule models simultaneously. Therefore, little is known about the relative importance of potential underlying factors such as interspecific competition, inter‐guild competition, selective extinction and habitat nestedness in structuring community composition. Here, we test the above four assembly rule models and examine the causal basis for the observed patterns using bird data collected on islands of an inundated lake. Location Thousand Island Lake, China. Methods  We collected data on presence–absence matrices, body size and functional groups for bird assemblages on 42 islands from 2007 to 2009. To test the above four assembly rule models, we used null model analyses to compare observed species co‐occurrence patterns, body‐size distributions and functional group distributions with randomly generated assemblages. To ensure that the results were not biased by the inclusion of species with extremely different ecologies, we conducted separate analyses for the entire assemblage and for various subset matrices classified according to foraging guilds. Results The bird assemblages did not support predictions by several competitively structured assembly rule models, including Diamond’s assembly rules, constant body‐size ratios, and favoured states. In contrast, bird assemblages were highly significantly nested and were apparently shaped by extinction processes mediated through area effects and habitat nestedness. The nestedness of bird assemblages was not a result of passive sampling or selective colonization. These results were very consistent, regardless of whether the entire assemblage or the subset matrices were analysed. Main conclusions Our results suggest that bird assemblages were shaped by extinction processes mediated through area effects and habitat nestedness, rather than by interspecific or inter‐guild competition. From a conservation point of view, our results indicate that we should protect both the largest islands with the most species‐rich communities and habitat‐rich islands in order to maximize the number of species preserved.     

千岛湖陆桥岛屿繁殖鸟类的扩散能力差异 对群落动态的影响

岛屿生物地理学理论的核心过程是岛屿物种的周转, 包括迁入与灭绝。本研究旨在探讨扩散能力差异对岛屿繁殖鸟类群落动态的影响。2007年4月至2013年6月, 采用样线法调查了千岛湖36个陆桥岛屿的繁殖鸟类, 依据扩散能力强弱将其划分为两类, 结合陆桥岛屿参数, 并运用逻辑斯蒂回归模型和最大似然法, 来研究鸟类扩散能力的不同对其周转率的影响。结果表明, 千岛湖繁殖鸟类扩散能力强的物种具有较高周转率且受岛屿参数约束较小, 而扩散能力弱的物种周转率较低且对岛屿参数变化更敏感。因此, 千岛湖陆桥岛屿繁殖鸟类的扩散能力显著影响其群落动态。     

Small island biogeography in the Gulf of California: lizards, the subsidized island biogeography hypothesis, and the small island effect

Aim We used insular lizard communities to test the predictions of two hypotheses that attempt to explain patterns of species richness on small islands. We first address the subsidized island biogeography (SIB) hypothesis, which predicts that spatial subsidies may cause insular species richness to deviate from species–area predictions, especially on small islands. Next, we examine the small island effect (SIE), which suggests small islands may not fit the traditional log‐linear species–area curve. Location Islands with arthropodivorous lizard communities throughout the Gulf of California. Methods To evaluate the SIB hypothesis, we first identified subsidized and unsubsidized islands based on surrogate measures of allochthonous productivity (i.e. island size and bird presence). Subsequently, we created species–area curves from previously published lizard species richness and island area data. We used the residuals and slopes from these analyses to compare species richness on subsidized and unsubsidized islands. To test for an SIE, we used breakpoint regression to model the relationship between lizard species richness and island area. We compared results from this model to results from the log‐linear regression model. Results Subsidized islands had a lower slope than unsubsidized islands, and the difference between these groups was significant when small islands were defined as < 1 km². In addition to comparing slopes, we tested for differences in the magnitude of the residuals (from the species–area regression of all islands) for subsidized vs. unsubsidized islands. We found no significant patterns in the residual values for small vs. large islands, or between islands with and without seabirds. The SIE was found to be a slightly better predictor of lizard species richness than the traditional log‐linear model. Main conclusions Predictions of the SIB hypothesis were partially supported by the data. The absence of a significant SIE may be a result of spatial subsidies as explained by the SIB hypothesis and data presented here. We conclude by suggesting potential scenarios to test for interactions between these two small island hypotheses. Future studies considering factors affecting species richness should examine the possible role of spatial subsidies, an SIE, or a synergistic effect of the two in data sets with small islands.     

Richness and composition of plants and birds on land‐bridge islands: effects of island attributes and differential responses of species groups

Aim To test relationships between the richness and composition of vascular plants and birds and attributes of habitat fragments using a model land‐bridge island system, and to investigate whether the effects of fragmentation differ depending on species natural history traits. Location Thousand Island Lake, China. Methods We compiled presence/absence data of vascular plant and bird species through exhaustive surveys of 41 islands. Plant species were assigned to two categories: shade‐intolerant and shade‐tolerant species; bird species were assigned to three categories: edge, interior, and generalist species. We analysed the relationships between island attributes (area, isolation, elevation, shape complexity, and perimeter to area ratio) and species richness using generalized linear models (GLMs). We also investigated patterns of composition in relation to island attributes using ordination (redundancy analysis). Results We found that island area explained a high degree of variation in the species richness of all species groups. The slope of the species–area relationship (z) was 0.16 for all plant species and 0.11 for all bird species. The lowest z‐value was for generalist birds (0.04). The species richness of the three plant species groups was associated with island area per se, while that of all, generalist, and interior birds was explained mainly by elevation, and that of edge bird species was associated primarily with island shape. Patterns of species composition were most strongly related to elevation, island shape complexity, and perimeter to area ratio rather than to island area per se. Species richness had no significant relationship with isolation, but species composition did. We also found differential responses among the species groups to changes in island attributes. Main conclusions Within the Thousand Island Lake system, the effects of fragmentation on both bird and plant species appear to be scale‐dependent and taxon‐specific. The number of plant species occurring on an island is strongly correlated with island area, and the richness of birds and the species composition of plants and birds are associated with variables related to habitat heterogeneity. We conclude that the effects of fragmentation on species diversity and composition depend not only on the degree of habitat loss but also on the specific patterns of habitat fragmentation.     

Patterns of species richness on very small islands: the plants of the Aegean archipelago

Aim To investigate the species–area relationship (SAR) of plants on very small islands, to examine the effect of other factors on species richness, and to check for a possible Small Island Effect (SIE). Location The study used data on the floral composition of 86 very small islands (all < 0.050 km²) of the Aegean archipelago (Greece). Methods We used standard techniques for linear and nonlinear regression in order to check several models of the SAR, and stepwise multiple regression to check for the effects of factors other than area on species richness (‘habitat diversity’, elevation, and distance from nearest large island), as well as the performance of the Choros model. We also checked for the SAR of certain taxonomic and ecological plant groups that are of special importance in eastern Mediterranean islands, such as halophytes, therophytes, Leguminosae and Gramineae. We used one‐way anova to check for differences in richness between grazed and non‐grazed islands, and we explored possible effects of nesting seabirds on the islands’ flora. Results Area explained a small percentage of total species richness variance in all cases. The linearized power model of the SAR provided the best fit for the total species list and several subgroups of species, while the semi‐log model provided better fits for grazed islands, grasses and therophytes. None of the nonlinear models explained more variance. The slope of the SAR was very high, mainly due to the contribution of non‐grazed islands. No significant SIE could be detected. The Choros model explained more variance than all SARs, although a large amount of variance of species richness still remained unexplained. Elevation was found to be the only important factor, other than area, to influence species richness. Habitat diversity did not seem important, although there were serious methodological problems in properly defining it, especially for plants. Grazing was an important factor influencing the flora of small islands. Grazed islands were richer than non‐grazed, but the response of their species richness to area was particularly low, indicating decreased floral heterogeneity among islands. We did not detect any important effects of the presence of nesting seabird colonies. Main conclusions Species richness on small islands may behave idiosyncratically, but this does not always lead to a typical SIE. Plants of Aegean islets conform to the classical Arrhenius model of the SAR, a result mainly due to the contribution of non‐grazed islands. At the same time, the factors examined explain a small portion of total variance in species richness, indicating the possible contribution of other, non‐standard factors, or even of stochastic effects. The proper definition of habitat diversity as pertaining to the taxon examined in each case is a recurrent problem in such studies. Nevertheless, the combined effect of area and a proxy for environmental heterogeneity is once again superior to area alone in explaining species richness.     

Island biogeography of the Mediterranean sea: the species–area relationship for terrestrial isopods

Aim We looked at the biogeographical patterns of Oniscidean fauna from the small islands of the Mediterranean Sea in order to investigate the species–area relationship and to test for area‐range effects. Location The Mediterranean Sea. Methods We compiled from the literature a data set of 176 species of Oniscidea (terrestrial isopods) distributed over 124 Mediterranean islands. Jaccard's index was used as input for a UPGMA cluster analysis. The species–area relationship was investigated by applying linear, semi‐logarithmic, logarithmic and sigmoid models. We also investigated a possible ‘small island effect’ (SIE) by performing breakpoint regression. We used a cumulative and a sliding‐window approach to evaluate scale‐dependent area‐range effects on the log S/log A regression parameters. Results Based on similarity indexes, results indicated that small islands of the Mediterranean Sea can be divided into two major groups: eastern and western. In general, islands from eastern archipelagos were linked together at similarity values higher than those observed for western Mediterranean islands. This is consistent with a more even distribution of species in the eastern Mediterranean islands. Separate archipelagos in the western Mediterranean could be discriminated, with the exception of islets, which tended to group together at the lowest similarity values regardless of the archipelago to which they belong. Islets were characterized by a few common species with large ranges. The species–area logarithmic model did not always provide the best fit. Most continental archipelagos showed very similar intercepts, higher than the intercept for the Canary island oceanic archipelago. Sigmoid regression returned convex curves. Evidence for a SIE was found, whereas area‐range effects that are dependent on larger scale analyses were not unambiguously supported. Main conclusions The Oniscidea fauna from small islands of the Mediterranean Sea is highly structured, with major and minor geographical patterns being identifiable. Some but not all of the biogeographical complexity can be explained by interpreting the different shapes of species–area curves. Despite its flexibility, the sigmoid model tested did not always provide the best fit. Moreover, when the model did provide a good fit the curves looked convex, not sigmoid. We found evidence for a SIE, and minor support for scale‐dependent area‐range effects.     

Detecting the small island effect and nestedness of herpetofauna of the West Indies

To detect the small island effect (SIE) and nestedness patterns of herpetofauna of the West Indies, we derived and updated data on the presence/absence of herpetofauna in this region from recently published reviews. We applied regression‐based analyses, including linear regression and piecewise regressions with two and three segments, to detect the SIE and then used the Akaike's information criterion (AIC) as a criterion to select the best model. We used the NODF (a nestedness metric based on overlap and decreasing fill) to quantify nestedness and employed two null models to determine significance. Moreover, a random sampling effort was made to infer about the degree of nestedness at portions of the entire community. We found piecewise regression with three segments performed best, suggesting the species–area relationships possess three different patterns that resulted from two area thresholds: a first one, delimiting the SIE, and a second one, delimiting evolutionary processes. We also found that taxa with lower resource requirement, higher dispersal ability, and stronger adaptation to the environment generally displayed lower corresponding threshold values, indicating superior taxonomic groups could earlier end the SIE period and start in situ speciation as the increase of island size. Moreover, the traditional two‐segment piecewise regression method may cause poor estimations for both slope and threshold value of the SIE. Therefore, we suggest previous SIE detection works that conducted by two‐segment piecewise regression method, ignoring the possibility of three segments, need to be reanalyzed. Antinestedness occurred in the entire system, whereas high degree of nestedness could still occur in portions within the region. Nestedness may still be applicable to conservation planning at portions even if it is antinested at the regional scale. However, nestedness may not be applicable to conservation planning at the regional scale even if nestedness does exist among sampling islands from a portion.     

Island,archipelago and taxon effects: mixed models as a means of dealing with the imperfect design of nature's experiments

A major aim of island biogeography has been to describe general patterns of species richness across islands and to identify the processes responsible. Data are often collected across many islands; with larger datasets providing increased statistical power and more accurate parameter estimates. However, there is often structure in observational data, violating an assumption of linear models that each datum is independent. In island biogeography this structure may take the form of an island, archipelago or taxon being represented by multiple data points. We survey recent papers in this field and find that these forms of non‐independence are a common feature. Most authors addressed this problem by conducting separate analyses for each archipelago, taxon or combination of the two, but a better tool for dealing with non‐independence and structure in data, the mixed model, already exists. We demonstrate the advantages of a mixed model approach by applying it to a well‐known dataset that spans 134 observations of single island endemic (SIE) richness across 39 islands, four archipelagos and four taxa. Taking island area and age into account, SIE richness varies substantially more among archipelagos than it does among islands or taxa. We find that SIE richness rises with island age on the Azores and Galapagos, while on the Canaries and Hawaii SIE richness initially rises with age but later declines on older islands. Our analyses demonstrate three advantages to island biogeography of applying a mixed modelling approach: 1) structure in the data is controlled for; 2) the variance among islands, archipelagos and taxa is estimated; 3) all the data can be included in a single model, making it possible to test whether trends are general across all archipelagos and taxa or are idiosyncratic.     

Ant communities on small tropical islands: effects of island size and isolation are obscured by habitat disturbance and ‘tramp’ ant species

Aim Comparisons among islands offer an opportunity to study the effects of biotic and abiotic factors on small, replicated biological communities. Smaller population sizes on islands accelerate some ecological processes, which may decrease the time needed for perturbations to affect community composition. We surveyed ants on 18 small tropical islands to determine the effects of island size, isolation from the mainland, and habitat disturbance on ant community composition. Location Thousand Islands Archipelago (Indonesian name: Kepulauan Seribu) off Jakarta, West Java, Indonesia. Methods Ants were sampled from the soil surface, leaf litter and vegetation in all habitat types on each island. Island size, isolation from the mainland, and land‐use patterns were quantified using GIS software. The presence of settlements and of boat docks were used as indicators of anthropogenic disturbance. The richness of ant communities and non‐tramp ant species on each island were analysed in relation to the islands’ physical characteristics and indicators of human disturbance. Results Forty‐eight ant species from 5 subfamilies and 28 genera were recorded from the archipelago, and approximately 20% of the ant species were well‐known human‐commensal ‘tramp’ species. Islands with boat docks or human settlements had significantly more tramp species than did islands lacking these indicators of anthropogenic disturbance, and the diversity of non‐tramp species decreased with habitat disturbance. Main conclusions Human disturbance on islands in the Thousand Islands Archipelago promotes the introduction and/or establishment of tramp species. Tramp species affect the composition of insular ant communities, and expected biogeographical patterns of ant richness are masked. The island with the greatest estimated species richness and the greatest number of unique ant species, Rambut Island, is a forested bird sanctuary, highlighting the importance of protected areas in preserving the diversity of species‐rich invertebrate faunas.     

千岛湖库区岛屿面积对植物分布的影响及植物物种多样性保护研究

修建大坝形成水库蓄水是造成景观破碎化的原因和形式之一.本研究选取了浙江千岛湖库区景观破碎化的典型区域小金山林场,调查了74个大小不一的岛屿,研究了面积对植物物种分布的影响,并比较了使物种多样性最大化的几种植物物种保护方案:小岛组合、中岛组合、大岛组合、大中小组合岛.调查共记录到乔木物种56种,灌木物种79种.将岛屿按照面积由大到小排序,将相对应分布的乔木、灌木绘制成植物物种分布表.结果显示:乔木中分布不受面积影响的物种有15种,受面积影响的有11种,介于两者之间的有30种;灌木物种中不受面积影响的有24种,受面积影响的有16种,介于两者之间的有39种.将乔木、灌木和总物种数分别累加,同时将相对应的岛屿面积按不同组合累加,绘制累加物种和面积关系图,发现在特定的相同累加面积下,组合岛的累加乔木、灌木、总物种数最多,小岛组合次之,大岛组合最少.因此,建立相同面积的保护区时,组合岛有利于保护更多的物种.     

Dung beetle assemblages on tropical land‐bridge islands: small island effect and vulnerable species

Aim Using dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in a tropical land‐bridge island system, we test for the small island effect (SIE) in the species–area relationship and evaluate its effects on species richness and community composition. We also examine the determinants of species richness across island size and investigate the traits of dung beetle species in relation to their local extinction vulnerability following forest fragmentation. Location Lake Kenyir, a hydroelectric reservoir in north‐eastern Peninsular Malaysia. Methods We sampled dung beetles using human dung baited pitfall traps on 24 land‐bridge islands and three mainland sites. We used regression tree analyses to test for the SIE, as well as species traits related to local rarity, as an indication of extinction vulnerability. We employed generalized linear models (GLMs) to examine determinants for species richness at different scales and compared the results with those from conventional linear and breakpoint regressions. Community analyses included non‐metric multidimensional scaling, partial Mantel tests, nestedness analysis and abundance spectra. Results Regression tree analysis revealed an area threshold at 35.8 ha indicating an SIE. Tree basal area was the most important predictor of species richness on small islands (<35.8 ha). Results from GLMs supported these findings, with isolation and edge index also being important for small islands. The SIE also manifested in patterns of dung beetle community composition where communities on small islands (<35.8 ha) departed from those on the mainland and larger islands, and were highly variable with no significant nestedness, probably as a result of unexpected species occurrences on several small islands. The communities exhibited a low degree of spatial autocorrelation, suggesting that dispersal limitation plays a part in structuring dung beetle assemblages. Species with lower baseline density and an inability to forage on the forest edge were found to be rarer among sites and hence more prone to local extinction. Main conclusions We highlight the stochastic nature of dung beetle community composition on small islands and argue that this results in reduced ecosystem functionality. A better understanding of the minimum fragment size required for retaining functional ecological communities will be important for effective conservation management and the maintenance of tropical forest ecosystem stability.     

千岛湖陆桥岛屿鸟类集团对栖息地片段化的敏感性及其季节变化

为探究千岛湖陆桥岛屿不同鸟类集团对栖息地片段化敏感性的差异和季节变化,于2009年4月—2012年1月鸟类繁殖季(4、5、6月)和冬季(11、12、1月)对千岛湖41个陆桥岛屿鸟类集团进行了研究。结果表明,冬季杂食鸟对片段化敏感性高于食虫鸟,繁殖季时二者无显著差异,繁殖季和冬季时下层鸟对片段化敏感性均高于林冠鸟,冬季留鸟对片段化敏感性高于候鸟,繁殖季则无显著差异。杂食鸟和留鸟对片段化敏感性存在季节差异,而食虫鸟、林冠鸟、下层鸟和候鸟对片段化敏感性均无季节差异。不同鸟类集团对栖息地片段化敏感性的差异和季节变化规律,有助于人们在栖息地管理和保护区设计时采取更有针对性的鸟类保护措施。     

Slaying dragons: limited evidence for unusual body size evolution on islands

Aim Island taxa often attain forms outside the range achieved by mainland relatives. Body size evolution of vertebrates on islands has therefore received much attention, with two seemingly conflicting patterns thought to prevail: (1) islands harbour animals of extreme size, and (2) islands promote evolution towards medium body size (‘the island rule’). We test both hypotheses using body size distributions of mammal, lizard and bird species. Location World‐wide. Methods We assembled body size and insularity datasets for the world’s lizards, birds and mammals. We compared the frequencies with which the largest or smallest member of a group is insular with the frequencies expected if insularity is randomly assigned within groups. We tested whether size extremes on islands considered across mammalian phylogeny depart from a null expectation under a Brownian motion model. We tested the island rule by comparing insular and mainland members of (1) a taxonomic level and (2) mammalian sister species, to determine if large insular animals tend to evolve smaller body sizes while small ones evolve larger sizes. Results The smallest species in a taxon (order, family or genus) are insular no more often than would be expected by chance in all groups. The largest species within lizard families and bird genera (but no other taxonomic levels) are insular more often than expected. The incidence of extreme sizes in insular mammals never departs from the null, except among extant genera, where gigantism is marginally less common than expected under a Brownian motion null. Mammals follow the island rule at the genus level and when comparing sister species and clades. This appears to be driven mainly by insular dwarfing in large‐bodied lineages. A similar pattern in birds is apparent for species within orders. However, lizards follow the converse pattern. Main conclusions The popular misconception that islands have more than their fair share of size extremes may stem from a greater tendency to notice gigantism and dwarfism when they occur on islands. There is compelling evidence for insular dwarfing in large mammals, but not in other taxa, and little evidence for the second component of the island rule – gigantism in small‐bodied taxa.     

千岛湖栖息地片段化对大山雀营巢资源利用的影响

为了解栖息地片段化对次级洞巢鸟营巢资源利用的影响, 我们于2008年2-8月, 在千岛湖地区选取21个岛屿, 采用悬挂人工巢箱方法进行大山雀(Parus major)招引实验。通过测定岛屿面积、岛屿隔离度、捕食者活动率、人工巢箱周围植被盖度和人工巢箱巢向等5种参数, 分析大山雀人工巢箱利用与上述参数间的关系。实验期间, 共悬挂443个人工巢箱, 其中有72个(16.3%)被大山雀利用。大山雀倾向于选择捕食者活动率低、植被盖度低、巢口向东或向南的人工巢箱; 岛屿面积和隔离度对大山雀利用人工巢箱不存在显著的直接影响, 但岛屿面积可通过影响捕食者的活动率, 对大山雀利用人工巢箱产生间接影响。因此, 我们认为在栖息地片段化后, 应更多关注对洞巢鸟营巢资源利用有直接影响的栖息地特征因素, 以及片段化效应的间接影响。     

Robust methods for detecting a small island effect

Aim The small island effect (SIE), i.e. the hypothesis that species richness below a certain threshold area varies independently of island size, has become a widely accepted part of the theory of island biogeography. However, there are doubts whether the findings of SIEs were based on appropriate methods. The aim of this study was thus to provide a statistically sound methodology for the detection of SIEs and to show this by re‐analysing data in which an SIE has recently been claimed ( Sfenthourakis & Triantis, 2009 , Diversity and Distributions, 15 , 131–140). Location Ninety islands of the Aegean Sea (Greece). Methods First, I reviewed publications on SIEs and evaluated their methodology. Then, I fitted different species–area models to the published data of area (A) and species richness (S) of terrestrial isopods (Oniscidea), with log A as predictor and both S (logarithm function) and log S (power function) as response variables: (i) linear; (ii) quadratic; (iii) cubic; (iv) breakpoint with zero slope to the left (SIE model); (v) breakpoint with zero slope to the right; (vi) two‐slope model. I used non‐linear regression with R²_adj., AIC_c and BIC as goodness‐of‐fit measures. Results Many different methods have been applied for detecting SIEs, all of them with serious shortcomings. Contrary to the claim of the original study, no SIE occurs in this particular dataset as the two‐slope variants performed better than the SIE variants for both the logarithm and power functions. Main conclusions For the unambiguous detection of SIEs, one needs to (i) include islands with no species; (ii) compare all relevant models; and (iii) account for different model complexities. As none of the reviewed SIE studies met all these criteria, their findings are dubious and SIEs may be less common than reported. Thus, conservation‐related predictions based on the assumption of SIEs may be unreliable.     

Wallacea and its nectarivorous birds: nestedness and modules

Aim Wallacea, the vast oceanic boundary between the Oriental and Australian regions, contains 122 true nectarivorous bird species. It is the contact zone of the Oriental sunbirds and the Australian honeyeaters, and at least three more true nectarivorous families are resident in the region. An island–bird matrix for Wallacea was tested for the presence of two patterns, nestedness and modularity. If the matrix is modular, it consists of a number of densely linked subgroups or modules of islands and birds, which are weakly interconnected. These modules are used as a new tool in analysing biogeographical boundaries in Wallacea. Location Wallacea, Indonesia. Methods We constructed an island–bird matrix for Wallacea and used two algorithms, aninhado and sa , to test it for nestedness and modularity, respectively. aninhado calculates the matrix temperature and provides a null model, and sa is a module‐detecting program based on simulated annealing. The results of the sa were compared with those from a hierarchical cluster analysis. Results The matrix had a nested pattern, as is commonly the case for island–species matrices. The SA detected four modules in Wallacea, each consisting of a group of islands sharing a group of nectarivorous birds. The sa algorithm produced a more detailed pattern of the area than did the hierarchical cluster analysis. Main conclusions Modularity and nestedness do not preclude each other as biogeographical patterns. The boundaries of the modules detected by sa compared well with major boundaries from the existing literature and showed a clear division of Wallacea into modules of birds and islands closely linked together. Thus modules are biogeographical units of islands sharing a specific nectarivorous fauna. For some research questions, we suggest that modules may be more appropriate biogeographical units than single islands or traditionally perceived archipelagos. The nectarivorous families showed distinctly different distributions, indicating variation in their colonization history and speciation processes. We recommend sa as a tool for detecting fine‐grained biogeographical patterns.     

Habitat diversity, ecological requirements of species and the Small Island Effect

Aim  To explore the causal factors leading to a significant Small Island Effect (SIE), that is, the absence of the commonly found species–area relationships below an island size, on the terrestrial isopod communities from a large number of islands.
Location  Ninety islands of the Aegean Sea (Greece).
Methods  The detection of a significant SIE is assessed through the application of all three methods available in the literature. Species are divided into generalists and specialists. We tested if the minimum area and the area range of each species' occurrences differ between generalists and specialists. Next, we searched for differences in the ratios of specialists to generalists above and below the SIE threshold, and tested their cumulative ratios when islands are arranged according to increasing area, altitude or habitat diversity in order to identify the threshold where they become statistically indistinguishable from the ratio of the total set of islands.
Results  Our results indicate a strong effect of habitat availability on the SIE. Communities of islands within the SIE range, host a higher percentage of generalists. An analysis of the specific habitat requirements shows that, for isopods, the crucial factor is the lack of habitats related to inland waters from small islands.
Main conclusions  The distribution of habitats on islands of different size is of major importance for the occurrence of a SIE. The relative representation of specialist and generalist species on islands of different size plays an important role in shaping SIE-related patterns. Conservation efforts should pay special attention on freshwater habitats, especially on small Aegean islands. Identifying the causal factors of SIE, combined with a thorough knowledge of the ecological requirements of species can offer insights into identifying habitat types and groups of species that are more vulnerable to alterations of the environment.     

千岛湖栖息地片段化效应对鸟类巢捕食风险的影响

为了解栖息地片段化对鸟类巢捕食风险的影响,我们于2010年4-8月,在千岛湖地区选取16个岛屿,分别在岛屿边缘和内部区域用放置鸡蛋(大型卵)和鹌鹑(Coturnix japonica)蛋(小型卵)的方法进行人工模拟地面巢试验,研究不同体积大小鸟卵的巢捕食率及其差异,分析巢捕食率与岛屿面积、隔离度、形状指数和植物物种丰富...     

千岛湖陆桥岛屿地表蚂蚁群落物种多样性空间格局及其影响因素

为了探讨千岛湖岛屿景观参数对地表蚂蚁群落物种α和β多样性空间格局的影响, 作者分别于2017和2018年的5-8月, 采用陷阱法、凋落物分拣法和手捡法调查了千岛湖33个岛屿上的地表蚂蚁群落, 并依据食性将其划分为捕食性蚂蚁和杂食性蚂蚁。利用回归模型分析了全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁群落α和β多样性与岛屿景观参数的关系。结果表明, 岛屿面积对全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁的物种丰富度均有显著的正向影响, 而隔离度则无显著作用。蚂蚁群落的β多样性由空间周转组分主导。岛屿面积差对全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁群落β多样性的嵌套组分有正向影响, 隔离度差只对杂食性蚂蚁的总体β多样性有正向影响。因此, 岛屿面积是影响千岛湖地表蚂蚁群落物种丰富度的主要因素, 并且岛屿面积通过嵌套组分来影响蚂蚁群落的β多样性, 表现出选择性灭绝过程。此外, 不同食性蚂蚁可能因为扩散能力的差异对岛屿景观参数产生不同的响应。