Species richness and structure of ant communities in a dynamic archipelago: effects of island area and age

Aim To assess how ant species richness and structure of ant communities are influenced by island age (disturbance history) in a dynamic archipelago. Location Cabra Corral dam, Salta Province, north‐west Argentina (25°08′ S, 65°20′ W). Methods Ant species richness on remaining fragments (islands) of a flooded forest was determined, as well as island area, isolation and age. Simple linear regressions were performed to assess relationships between ant species richness and those insular variables. Furthermore, a stepwise multiple linear regression analysis was conducted in order to determine the relative influence of each insular variable on ant species richness. Islands were categorized in two age classes (old and young) and co‐occurrence analyses were applied within each class to evaluate changes in community structure because of interspecific competition. Results Simple regression analyses indicated a moderate, positive effect of island area on ant species richness. Weak, marginally non‐significant relationships were found between ant species richness and both island isolation and island age, showing the tendency for there to be a decrease in ant species richness with island isolation and that ant species richness might be higher in old islands. The multiple regression analysis indicated that island isolation and age had no significant effects on the number of ant species, island area being the only independent variable retained in the analysis. On the contrary, whereas a random pattern of species co‐occurrence was found on young islands, ant communities in old islands showed a significantly negative pattern of species co‐occurrence, suggesting that the effect of competition on community structure was stronger on older islands than on younger islands. Main conclusions Island area was the most important variable explaining ant species richness on the islands of Cabra Corral dam. However, both island isolation and island age (or disturbance history) might also contribute to shape the observed community patterns. The present study also shows that island age significantly affects the strength with which interspecific interactions structure ant communities on islands.     

The environmental determinants of the insular butterfly faunas of the British Isles

A multiple regression analysis was performed upon selected environmental variables for a series of islands in the British Isles, to establish their effects upon the size of the butterfly fauna, measured as he number of species regularly breeding, S_B .
So that the data be normally distributed, the regression analyses were performed upon log₁₀ transformed data only, with the data for outliers, mainland Britain and Ireland, the two largest islands, excluded.
Most highly correlated with the number of butterfly species breeding upon an island is the number breeding within a 25 km radius of the nearest point of the mainland, r ²=0.5941, followed by the correlations with the latitude of the mid-point of the island, r ²=0.5541, the number of plant species comprising the island Hora, r ²=0.5225, and the distance separating the island from the mainland, r ²=0.4514.
A partial correlation analysis confirms the importance of the parameters distance separating the island from the mainland, D ₁, and the size of the faunal source S _F , and rejects the importance of the size of the flora and the latitude of the island. This is further confirmed by the results of a step-wise regression analysis, the two variables D ₁ and S_F accounting for 66% of the variation of the butterfly fauna.
If an alternative measure of isolation, D ₂, which allows for the geographical clumping of islands, is combined with the variable S_F , then 69% of the variation of the butterfly fauna is accounted for.     

Evolutionary assembly of island faunas reverses the classic island–mainland richness difference in Anolis lizards

Aim Islands are widely considered to be species depauperate relative to mainlands but, somewhat paradoxically, are also host to many striking adaptive radiations. Here, focusing on Anolis lizards, we investigate if cladogenetic processes can reconcile these observations by determining if in situ speciation can reduce, or even reverse, the classical island–mainland richness discrepancy. Location Caribbean islands and the Neotropical mainland. Methods We constructed range maps for 203 mainland anoles from museum records and evaluated whether geographical area could account for differences in species richness between island and mainland anole faunas. We compared the island species–area relationship with total mainland anole diversity and with the richness of island‐sized mainland areas. We evaluated the role of climate in the observed differences by using Bayesian model averaging to predict island richness based on the mainland climate–richness relationship. Lastly, we used a published phylogeny and stochastic mapping of ancestral states to determine if speciation rate was greater on islands, after accounting for differences in geographical area. Results Islands dominated by in situ speciation had, on average, significantly more species than similarly sized mainland regions, but islands where in situ speciation has not occurred were species depauperate relative to mainland areas. Results were similar at the scale of the entire mainland, although marginally non‐significant. These findings held even after accounting for climate. Speciation has not been faster on islands; instead, when extinction was assumed to be low, speciation rate varied consistently with geographical area. When extinction was high, there was some evidence that mainland speciation was faster than expected based on area. Main conclusions Our results indicate that evolutionary assembly of island faunas can reverse the general pattern of reduced species richness on islands relative to mainlands.     

The role of introduced species in shaping the distribution and abundance of island reptiles

Summary Species interactions, as revealed by historical introductions of predators and competitors, affect population densities and sometimes result in extinctions of island reptiles. Mongoose introductions to Pacific islands have diminished the abundance of diurnal lizards and in some cases have led to extinctions. Through these population level effects, biogeographic patterns are produced, such as the reciprocal co-occurrence pattern seen with the tuatara and its predator, the Polynesian rat, and with the tropical gecko competitorsHemidactylus frenatus andLepidodactylus lugubris in urban habitats in the Pacific. Although competition has led to changes in abundance and has caused habitat displacement and reduced colonization success, extinctions of established reptile populations usually occur only as a result of predation.These introductions, along with many manipulative experiments, demonstrate that present day competition and predation are potent forces shaping community structure and geographic distributions. The human introduction of species to islands can be viewed as an acceleration of the natural processes of range expansion and colonization. The immediate biotic consequences of these natural processes should be of the same intensity as those of the human introductions. Coevolution may subsequently act to ameliorate these interactions and reduce the dynamical response of one species to the other. The role played by coevolution in mediating interactions between competitors and predator and prey is highlighted by the susceptibility of predator-naive endemic species to introduced predators and the invalidity of species-poor communities.     

Composition and structure of Caribbean bat (Chiroptera) assemblages: effects of inter‐island distance,area, elevation and hurricane‐induced disturbance

Aim Although bats of the Caribbean have been studied extensively, previous work is largely restricted to zoogeography, phylogeography or the effects of island characteristics on species richness. Variation among islands in species composition that is related to geographical or environmental variation remains poorly understood for much of the Caribbean. Location Caribbean islands, including the Bahamas, Greater Antilles and Lesser Antilles. Methods Using presence–absence data, we assessed the extent to which island area, maximum island elevation, inter‐island distance and hurricane‐induced disturbance affected patterns of composition and nestedness for bats in the Bahamas, Greater Antilles and Lesser Antilles. Analyses were conducted for all species, as well as for two broadly defined guilds: carnivores and herbivores. Results For the Bahamas, only inter‐island distance accounted for variation in species composition between islands. For the Greater and Lesser Antilles, differences in island area and inter‐island distance accounted for differences in species composition between islands. Variation in species composition was not related significantly to differences in elevation or hurricane‐related disturbance. In general, results of analyses restricted to a particular broad guild (i.e. carnivores or herbivores) mirrored those for all bats. Bat species composition was nested significantly in each island group. Nestedness was stronger in the Greater Antilles and in the Lesser Antilles than in the Bahamas. Carnivore assemblages were nested significantly in the Greater and in the Lesser Antilles, but not in the Bahamas. In contrast, herbivore assemblages were nested significantly in each island group. Main conclusions Inter‐island distance had a greater effect on compositional similarity of Caribbean bat assemblages than did island area, elevation or disturbance related to hurricanes. Differential immigration and hierarchical habitat distributions associated with elevational relief are likely to be primary causes for nestedness of Caribbean bat assemblages.     

A model-independent test for the presence of regulatory equilibrium and non-random structure in island species trajectories

Aims To test a key prevision of the dynamic equilibrium theory of island biogeography, namely that changes in species numbers on islands over time (hereafter, species trajectories) are equilibrial, and to characterize aspects of the dynamical properties of species change over time using a model‐independent test. Methods We tested for regulatory equilibrium and non‐random structure in species numbers through time by comparing observed correlation coefficients at lag‐k for species trajectories from four true islands and two habitat islands. First, we estimated the shape of the autocorrelation function for each observed species trajectory by calculating correlation coefficients of the observed data between pairs of values N_t?k and N_t separated by lag‐k (k = 1, 2, …, N ? 1). Second, we tested the observed correlation coefficients at each lag against a distribution of correlation coefficients generated by randomly ordering observed numbers in the species trajectories. Results The patterns of autocorrelation functions for all but one of the observed species trajectories did not exhibit evidence of regulatory equilibrium, and, in fact, closely matched what would be expected from a non‐stationary or ‘random walk’ process. The majority of the correlation coefficients generated from the observed species trajectories did not deviate significantly from correlation coefficients produced by the randomized trajectories. However, there was strong evidence of unusual positive autocorrelation at small time lags for birds on islands measured annually (2‐ to 4‐year lags) and for arthropods on islands measured weekly (7‐ to 8‐week lags), suggesting some degree of structure in change in species richness over time. Main conclusions The autocorrelation function patterns for all but one of the observed species trajectories showed various forms of non‐stationarity. These types of patterns suggest that the numbers of species through time gradually wandered away from their initial sizes. Our model‐independent test of individual correlation coefficients revealed significant structure in the observed species trajectories. These trajectories appear to be non‐random at relatively short lag intervals, indicating a process with short memory.     

Macro‐scale bird species richness patterns of the East Asian mainland and islands: energy,area and isolation

Aim To create a map of bird species richness (BSR) in East Asia and to examine the effect of area, isolation, primary productivity, topographic heterogeneity, and human population density on BSR. Location East Asia (from 70° E to 180° E longitude), including the eastern half of the Palaearctic Region, the entire Oriental Region, and the entire Wallacea Subregion. Methods The breeding ranges of 2406 terrestrial bird species were mapped and overlaid to create a species richness map. The BSR map was transformed into a 100 × 100 km quadrat system, and BSR was analysed in relation to land area, average normalized difference vegetation index (NDVI), elevation range, and average population density. Results In general, BSR declined from the Tropics to the Arctic. In mainland East Asia, however, BSR was highest around the Tropic of Cancer, and fluctuated between 30° and 50° N. Islands had lower BSR than adjacent mainland areas. The NDVI was strongly positively correlated with BSR in mainland areas and on islands. For mainland areas, NDVI explained 65% of the BSR variation, and topographic heterogeneity explained an additional 6% in ordinary least‐squares regression. On islands, NDVI explained 66% of BSR variation, island area explained 13%, and distance to mainland accounted for 1%. Main conclusions In East Asia, we suggest that primary productivity is the key factor underpinning patterns of BSR. Primary productivity sets the upper limits of the capacity of habitats to support bird species. In isolated areas such as islands and peninsulas, however, BSR might not reach the richness limits set by primary productivity because the degree of isolation and area size also can affect species richness. Other factors, such as spatial heterogeneity, biotic interactions, and perturbations, may also affect species richness. However, their effects are secondary and are not as strong as primary productivity, isolation, and area size.     

Alien herbivores and native parasitoids: rapid developments and structure of the parasitoid and inquiline complex in an invading gall wasp Andricus quercuscalicis (Hymenoptera: Cynipidae)

Abstract.

• 1 Rapid and substantial changes have occurred in the parasitoid and inquiline community associated with the agamic galls of Andricus quercuscalicis since it invaded Britain in the late 1950s. The number of parasitoid and inquiline species has risen from one to thirteen over a 15-year period. Although the number of species has been relatively consistent over the last 8 years, the species composition has changed considerably and in a highly characteristic way during this period.
• 2 The parasitoid complex can be divided into two broadly distinct sets of parasitoid species; one set attacks only the gall former whereas the other set concentrates on the inquilines living in the wall of the gall.
• 3 The most dramatic change, however, is in the abundance of inquilines which were reported to be virtually absent in earlier studies on this community in Britain. Over a period of only 5 years, between 1988 and 1993, inquiline attack rose from less than 0.01 to an average of 0.26 inquilines per gall. The intensity of inquiline attack is geographically heterogenous, with high inquiline numbers restricted to south-east England. Because of the relatively high specificity of the parasitoids, high inquiline abundance is positively correlated with parasitoid species richness in knopper galls.
• 4 Parasitism rates, particularly on the gall former, were generally low (<10%). Over the last 5 years, however, seven parasitoid species have been consistently recorded and the mortality caused by these species has increased continuously. The species composition of the community associated with this alien gall wasp in Britain has quickly converged to the community known from its native range in continental Europe. Parasitoid species known to attack the galls of A.quercuscalisis on the continent have been recorded from it in Britain for the first time mainly in areas where inquilines have recently become abundant.
• 5 Since rates of parasitism of the gall former are still low, parasitoids are unlikely to play a major role in the population dynamics of this invading gall wasp at present, but the rapidly increasing inquiline and parasitoid attack could be a source of increased mortality for native cynipid species which are the alternative hosts of those parasitoid species.

     

Tree diversity on islands: assembly rules,passive sampling and the theory of island biogeography

Aim Species diversity is distributed heterogeneously through space, for reasons that are poorly understood. We tested three hypotheses to account for spatial variation in coniferous tree species diversity in a temperate island archipelago. The theory of island biogeography (ToIB) predicts that island area affects species diversity both directly (by increasing habitat diversity) and indirectly (by increasing abundances, which in turn reduce extinction rates). The ToIB also predicts that island isolation directly affects species diversity by reducing immigration rates. The passive sampling hypothesis predicts that island area and isolation both affect species diversity indirectly, by increasing and decreasing abundances, respectively. Community assembly rules (i.e. even partitioning of conifer abundances among islands) might also reduce tree species diversity beyond the core predictions of ToIB and the passive sampling hypothesis. Location Barkley Sound, British Columbia, Canada. Methods The abundances of eight coniferous tree species were quantified on 34 islands and two (1 ha) mainland plots. The predictions of the ToIB and the passive sampling hypothesis were tested using path analysis, and null models were used to test for abundance‐based assembly rules and to further test the passive sampling hypothesis. Results Path analysis showed that island area and isolation did not have direct, statistical effects on tree species diversity. Instead, both geographic variables had direct statistical effects on total tree abundances, which in turn predicted tree diversity. Results from several passive sampling null models were correlated with observed patterns in species diversity, but they consistently overestimated the number of tree species inhabiting most islands. A different suite of null models showed support for community assembly rules, or that tree species often reached higher abundances on islands that housed fewer heterospecific trees. Main conclusions Results were inconsistent with the ToIB. Instead, patterns in tree diversity were best explained by a combination of stochastic (passive sampling) and deterministic (assembly rules) processes. Stochastic and deterministic processes are commonly considered to be exclusive explanations for island community structure, but results from this study suggest that they can work synergistically to structure island tree communities.     

Islands within an island: Population genetic structure of the endemic Sardinian newt,Euproctus platycephalus

The identification of historic and contemporary barriers to dispersal is central to the conservation of endangered amphibians, but may be hindered by their complex life history and elusive nature. The complementary information generated by mitochondrial (mtDNA) and microsatellite markers generates a valuable tool in elucidating population structure and the impact of habitat fragmentation. We applied this approach to the study of an endangered montane newt, Euproctus platycephalus. Endemic to the Mediterranean island of Sardinia, it is threatened by anthropogenic activity, disease, and climate change. We have demonstrated a clear hierarchy of structure across genetically divergent and spatially distinct subpopulations. Divergence between three main mountain regions dominated genetic partitioning with both markers. Mitochondrial phylogeography revealed a deep division dating to ca. 1 million years ago (Mya), isolating the northern region, and further differentiation between the central and southern regions ca. 0.5 Mya, suggesting an association with Pleistocene severe glacial oscillations. Our findings are consistent with a model of southward range expansion during glacial periods, with postglacial range retraction to montane habitat and subsequent genetic isolation. Microsatellite markers revealed further strong population structure, demonstrating significant divergence within the central region, and partial differentiation within the south. The northern population showed reduced genetic diversity. Discordance between mitochondrial and microsatellite markers at this scale indicated a further complexity of population structure, in keeping with male‐biased dispersal and female philopatry. Our study underscores the need to elucidate cryptic population structure in the ecology and conservation strategies for endangered island‐restricted amphibians, especially in the context of disease and climate change.     

Species diversity and structure of phytophagous beetle assemblages along a latitudinal gradient: predicting the potential impacts of climate change

Abstract.  1. Assemblages of phytophagous beetles on Acacia were examined along a 1150 km latitudinal gradient in eastern Australia to investigate the potential effects of climate change on insect communities. The latitudinal gradient was used as a surrogate for differences in temperature. Several possible confounding variables were held constant by selecting comparable sites and emphasising a single host-plant species.
2. Total species richness increased towards the tropics, but there were no significant differences among latitudes for average species density, species richness, Fisher's α , or average Chao-1 index.
3. Beetles sampled along the gradient were classified into four climate change response groups, depending on their latitudinal range and apparent host specificity: cosmopolitan species, generalist feeders , climate generalists , and specialists . These four groups might respond differently to shifting climate zones. Cosmopolitan species (22% of community, found at more than one latitude and on more than one host plant) may be resilient to climate change. Generalist feeders (16%, found only at one latitude but found on more than one Acacia species) may well feed on several species but will have to move with their climatic envelope. Climate generalists (6%, found only on Acacia falcata but found at more than one latitude) may be constrained by the host species' ability to either cope with the changing climate or move with it. Finally, specialists (55%, found only on A. falcata and at only one latitude) may be forced to move poleward concurrently with their host species, or go extinct.
4. The analyses indicate that community structure may be fairly resilient to temperature change. The displacement or local extinction of species, especially the species that are found at only one latitude and on only one host plant, however, may lead to significant changes in community composition.     

宁夏中部干旱带不同作物根际土壤真菌群落多样性及群落结构

【背景】宁夏中部干旱带常年缺水,植被稀疏,土地沙漠化严重,生态环境十分脆弱。土地沙漠化导致土地生产力下降,制约着该区农业的发展,因此,改善宁夏中部干旱带农田生态环境具有重要意义。【目的】为该区土地资源的合理利用开发及干旱区土壤真菌多样性的深入研究提供基础数据和理论依据。【方法】运用IlluminaMiSeq高通量测序技术对宁夏中部干旱带农田作物土壤真菌种类进行预测,并对其进行真菌多样性和群落结构的分析。【结果】5个处理中真菌种类均较为丰富,丰富度指数无差异;真菌多样性指数分别以‘张杂谷5号’谷子最高,藜麦的多样性最低,且存在极显著差异。不同作物根际土壤中,子囊菌门(Ascomycota)为最优势菌门,相对丰度为73.00%-89.14%,且远远大于次优势菌门——担子菌门(Basidiomycota,3.9%-16.5%),表现出非常明显的优势;支顶孢属(Acremonium)和裂壳菌属(Schizothecium)为共有的优势菌属。土壤速效磷和土壤碱解氮会对土壤真菌群落结构和功能多样性产生影响,土壤微生物群落结构、功能多样性的变化是土壤理化性质与微生物相互作用的结果。【结论】休闲和种植作物的农田土壤养分均可不同程度的提高,土壤pH降低,真菌群落结构和多样性发生变化。说明合理的土地利用有利于丰富农田土壤微生物群落结构和多样性,改良土壤特性,进而促进该区域土壤生态系统的稳定,提高农田土地资源的合理利用。     

Changes in community structure of active protistan assemblages from the lower Pearl River to coastal Waters of the South China Sea

Protists make up an important component of aquatic ecosystems, playing crucial roles in biogeochemical processes on local and global scales. To reveal the changes of diversity and community structure of protists along the salinity gradients, community compositions of active protistan assemblages were characterized along a transect from the lower Pearl River estuary to the open waters of the South China Sea (SCS), using high-throughput sequencing of the hyper-variable V9 regions of 18S rRNA. This study showed that the alpha diversity of protists, both in the freshwater and in the coastal SCS stations was higher than that in the estuary. The protist community structure also changed along the salinity gradient. The relative sequence abundance of Stramenopiles was highest at stations with lower salinity and decreased with the increasing of salinity. By contrast, the contributions of Alveolata, Hacrobia and Rhizaria to the protistan communities generally increased with the increasing of salinity. The composition of the active protistan community was strongly correlated with salinity, indicating that salinity was the dominant factor among measured environmental parameters affecting protistan community composition and structure.     

Spatial genetic structure of Aquilegia taxa endemic to the island of Sardinia

Background and Aims

The Mediterranean Basin is one of the most important regions for the Earth''s plant biodiversity; however, the scarcity of studies on fine scale patterns of genetic variation in this region is striking. Here, an assessment is made of the spatial genetic structure of all known locations of the three Sardinian endemic species of Aquilegia in order to determine the relative roles of gene flow and genetic drift as underlying evolutionary forces canalizing the divergence of Sardinian Aquilegia taxa, and to see if the spatial genetic structure found fits the current taxonomic differentiation of these taxa.

Methods

DNA from 89 individuals from all known locations of Aquilegia across Sardinia was analysed by means of amplified fragment length polymorphism (AFLP) markers. Both principal co-ordinates analysis (PCoA) and Bayesian clustering analyses were used to determine the spatial genetic structure irrespective of any taxonomic affiliation. Historical effects of gene flow and genetic drift were assessed by checking for the existence of isolation-by-distance patterns.

Key Results

STRUCTURE and PCoA analyses revealed a pattern of genetic variation geographically structured into four spatial genetic groups. No migration–drift equilibrium was detected for Aquilegia in Sardinia, when analysed either as a whole or in individual groups. The scenario approached a Case III pattern sensu Hutchinson and Templeton, which is associated with extreme isolation conditions where genetic drift has historically played a dominant role over gene flow.

Conclusions

The pattern of genetic variation of Sardinian taxa of Aquilegia indicates that genetic drift has been historically more influential than gene flow on population structure of Sardinian species of Aquilegia. Limited seed dispersal and divergent selection imposed by habitat conditions have been probably the main causes reinforcing post-Pleistocene geographical isolation of Aquilegia populations. The spatial genetic structure found here is not fully compatible with current taxonomic affiliations of Sardinian Aquilegia taxa. This is probably a consequence of the uncoupling between morphological and genetic patterns of differentiation frequently found in recently radiated taxa.