Find research datasets worth reusing

Data from: Genetic diversity and population structure of Varronia curassavica: a medicinal polyploid species in a threatened ecosystem

Varronia curassavica is an important medicinal species associated with the restinga, one of the most threatened coastal ecosystems of the Atlantic Forest. These circumstances call for studies aimed at estimating effective population size and gene flow to improve conservation efforts. Hence, the present study aimed to characterize the genetic diversity, ploidy level and population structure of this species in different areas of restinga using microsatellites. Varronia curassavica was characterized as an autotetraploid, with high genetic variability, low divergence, and no significant fixation indices, indicating the absence of, or reduced, inbreeding and genetic drift in the study area. About 44 % of the alleles occurred at low frequency in adults of all populations and 41 % in the progenies evaluated. Gene flow was high, consistent with outcrossing species with high dispersal capacity (Nm = 4.87). The results showed no tendency toward isolation by distance. The estimated effective size indicates that the populations studied have the potential to ensure conservation of the species in the long term. The genetic variability and population structure of V. curassavica, as determined in this study, could form the foundation for activities directed toward the sustainable use of this resource and its conservation. Even though the restinga ecosystem has suffered dramatic reductions in area, this study provides evidence that this species is resilient to anthropogenic threats to its genetic integrity, since it is a polyploid with self-incompatibility mechanisms that contribute to maintaining high genetic diversity in an panmictic meta-population along the coast of Santa Catarina.

Data from: Origin matters: diversity affects the performance of alien invasive species but not of native species

At local scales, it has often been found that invasibility declines with increasing resident plant diversity. However, whether resident community diversity similarly resists invasion by alien versus native species is seldom compared. We examined this issue by invading constructed native plant assemblages that varied in species and functional richness with invasive alien or native Asteraceae species. Assemblages were also invaded with spotted knapweed, Centaurea stoebe, a native European Aster that has been previously used in diversity-invasibility experiments in North America. We also conducted a field survey to explore the generality of the patterns generated from our experimental study. Both experimental and observational work revealed that increasing diversity reduced the performance of alien but not native invaders. Centaurea stoebe invading its native community performed poorly regardless of resident diversity whereas in a parallel previously published study in North America, C. stoebe easily invaded low but not high diversity assemblages. Our results suggest that diversity is an attribute of resident communities that makes them more or less susceptible to invasion by novel invasive alien but not native plant species. 19 pages, 2 tables, 3 figures; Appendix

opencc-zeroDec 2012View details →

Data from: Water level fluctuations and metapopulation dynamics as drivers of genetic diversity in populations of three Tanganyikan cichlid fish species

Understanding how genetic variation is generated and maintained in natural populations, and how this process unfolds in a changing environment, remains a central issue in biological research. In this work, we analyzed patterns of genetic diversity from several populations of three cichlid species from Lake Tanganyika in parallel, using the mitochondrial DNA control region. We sampled populations inhabiting the littoral rocky habitats in both very deep, and very shallow areas of the lake. We hypothesized that the former would constitute relatively older, more stable and genetically more diverse populations, because they should have been less severely affected by the well-documented episodes of dramatic water level fluctuations. In agreement with our predictions, populations of all three species sampled in very shallow shorelines showed traces of stronger population growth than populations of the same species inhabiting deep shorelines. However, contrary to our working hypothesis, we found a significant trend towards increased genetic diversity in the younger, demographically less stable populations inhabiting shallow areas, in comparison to the older and more stable populations inhabiting the deep shorelines. We interpret this finding as the result of the establishment of metapopulation dynamics in the former shorelines, by the frequent perturbation and reshuffling of individuals between populations due to the lake level fluctuations. The repeated succession of periods of allopatric separation and secondary contact is likely to have further increased the rapid pace of speciation in lacustrine cichlids.

Data from: Intraspecific haplotype diversity in Cherleria sedoides L. (Caryophyllaceae) is best explained by chloroplast capture from an extinct species

Cherleria sedoides, a plant species widespread in alpine areas of the major European mountain ranges and in Scotland, contains two highly divergent chloroplast haplotype groups, one widespread (WH) and one present only in some populations in the Alps (AH). We investigated whether this haplotype diversity is the result of (1) intraspecific differentiation, (2) retention of an ancestral polymorphism or (3) hybridisation. For this purpose, 106 matK sequences from throughout the Caryophyllaceae and 80 trnQ-rps16 and psbD-trnT sequences of C. sedoides (51) and other species of Cherleria (29) were used for the construction of phylogenies and haplotype networks. As the two haplotype groups were never each other's closest relatives, haplotype diversity as a result of intraspecific differentiation is unlikely. Patterns of genetic differentiation within the WH and AH groups are very different. Whereas WH shows a radial pattern typical of rapid expansion, AH is divided into two divergent subgroups each containing more variation than the WH group. This suggests that the two haplotype groups have dissimilar histories and are therefore unlikely to represent an ancestral polymorphism. Instead, we conclude that the polymorphism is best interpreted as the result of hybridisation. As the WH and AH haplotype groups fall into Cherleria, but do not group with any extant species, we conclude that the rare AH group represents the original C. sedoides, and that the WH group was captured from another, now extinct, species of Cherleria.

Data from: Multiple strong postmating and intrinsic postzygotic reproductive barriers isolate florally diverse species of Jaltomata (Solanaceae)

Divergence in phenotypic traits often contributes to premating isolation between lineages, but could also promote isolation at postmating stages. Phenotypic differences could directly result in mechanical isolation or hybrids with maladapted traits; alternatively, when alleles controlling these trait differences pleiotropically affect other components of development, differentiation could indirectly produce genetic incompatibilities in hybrids. Here, we determined the strength of 9 postmating and intrinsic postzygotic reproductive barriers among 10 species of Jaltomata (Solanaceae), including species with highly divergent floral traits. To evaluate the relative importance of floral trait diversification on the strength of these postmating barriers, we assessed their relationship to floral divergence, genetic distance, geographical context, and ecological differences, using conventional tests and a new linear mixed modeling approach. Despite close evolutionary relationships, all species pairs showed moderate to strong isolation. Nonetheless, floral trait divergence was not a consistent predictor of the strength of isolation; instead this was best explained by genetic distance, although we found evidence for mechanical isolation in one species, and an overall positive relationship between floral trait divergence and fruit set isolation across species pairs. Overall, our data indicate that intrinsic postzygotic isolation is more strongly associated with genome-wide genetic differentiation, rather than floral divergence.

Data from: Species patch size at seeding affects diversity and productivity responses in establishing grasslands

1. Species interactions in diverse plant communities affect community-scale functions such as above-ground biomass production, diversity and invasion resistance. While the strength of these formative interactions can be affected by the balance of inter- and intraspecific interactions among the resident species, it is unclear over what distances individuals typically interact in grasslands and whether or not species interactions at seeding can be effectively manipulated to improve these responses. 2. In a three-year study, we tested whether manipulating the size of seeded species patches affected above-ground biomass, diversity and invasion resistance in experimentally restored grassland plots (16 m2). Plots were divided into patches that were 1, 0.5, 0.25 or 0.125 m on a side, and the equivalent of 1 m2 in each plot was seeded with one of 16 grassland species (1728 seeds/m2). A final treatment involved mixing and broadcasting all seeds into an undivided plot to mimic typical restoration approaches. 3. Using successively smaller initial seed patches resulted in plots that were less diverse and initially more productive (~25% difference in second-year biomass production) than larger patch counterparts. Smaller patch plots also had a greater selection effect and experienced increases in resident species connectivity, suggesting that diversity declines and productivity gains resulted from the enhanced establishment and spread of more productive seeded species. 4. Plots seeded with larger patches of the resident species were initially more invaded than those seeded with smaller patches, but this effect diminished over time. This likely reflects the ability of the non-seeded species to more effectively colonize larger patches with poor seeded species establishment. 5. Mixed seeding plots were most similar to the smallest patch plots in their metrics of resident species spatial pattern, diversity and invasion resistance. However, these plots were initially less productive and had a weaker selection effect, which reflects a different compositional outcome, than the structured seeding plots. 6. Synthesis: Species interact over sub-metre scales in establishing tallgrass prairie and, once established, their patterns may change over time. Given these dynamics, structured seeding approaches may be used over traditional mixed seeding approaches to control species dominance and preserve seeded species diversity within grassland systems.

Data from: Linking functional diversity and ecosystem processes: a framework for using functional diversity metrics to predict the ecosystem impact of functionally unique species

1.Functional diversity (FD) metrics are widely used to assess invasion ecosystem impacts, but we have limited theory to predict how FD should respond to invasion. A key challenge to effectively using FD metrics is the complexity of conceptualizing alterations to multi-dimensional trait space, making it difficult to select a priori the most appropriate metric for specific ecological questions. 2.Here, we provide expectations on how invasion should change four commonly used FD metrics—functional richness (FRic), evenness (FEve), divergence (FDiv), and dispersion (FDis)—and then test these expectations in a lab decomposition experiment. We simulate invasion of a forest by understory plants by adding leaf litter from 18 natives and nonnatives to a representative canopy tree litter mixture to test changes in FD and decomposition. 3.All four metrics changed predictably with invasion. Species that were more functionally unique or when added at greater proportions had larger impacts on FD. Overall, FRic, FEve, and FDiv were poor choices for understanding impacts of nonnative species. FDis was the only metric that both changed predictably with addition of understory litter and correlated intuitively with changes in carbon mineralization. Furthermore, ranking species based upon how much they changed FDis of the litter mixture provided a fair assessment of which species had the largest impact on decomposition. As such, functional dispersion may be a key tool for predicting a priori which nonnatives will have the greatest impact on ecosystem processes. 4.Synthesis: We highlight the need to assess the suitability of each FD metric for the specific ecological question at hand. Our work reveals the pitfalls of considering multiple metrics or randomly choosing a single metric without suitability assessments. At the same time, it suggests a framework for metric assessment that should help lead to selection of a metric or metrics that provide robust a priori insights into how invasion by nonnative species can impact ecosystem processes.

Data from: Tree species diversity alters plant defence investment in an experimental forest plantation in Southern Mexico

The effects of plant species diversity on plant traits conferring herbivore resistance (e.g., chemical defences), as well as the mechanisms underlying such effects, have received little attention. One potential mechanism for diversity effects on plant defences is that increased plant growth at high diversity could lead to reduced investment in defences via growth-defence trade-offs. We measured tree growth (diameter at breast height) and collected leaves for quantification of total phenolics on 2.5-year old plants of six tropical tree species (N = 597 plants) in a young experimental plantation in southern Mexico. Selected plants were distributed across 23 plots (21 x 21 m each) classified as monocultures of one species (N = 13, 2-3 plots per species) or polycultures (N = 10) represented by mixtures of four out of the six species. We found a significant negative effect of tree species diversity on total phenolics, where polycultures exhibited a 13 percent lower mean concentration than monocultures. However, there was marked variation among tree species in diversity effects on defences, where some species exhibited strong reductions in phenolics in mixtures, whereas others were unresponsive. Further, we found no effect of tree species diversity on growth and results indicated that the negative effect of diversity on chemical defences was not mediated by a growth-defence trade-off. These results demonstrate that tree diversity can alter investment in chemical defences in long-lived tree species, which has important implications for predicting effects on consumers and ecosystem function.

opencc-zeroDec 2010View details →

Data from: Contracting patterns of diversity and population differentiation at the innate immunity gene Toll-like receptor 2 (TLR2) in two sympatric rodent species

Comparing patterns of diversity and divergence between populations at immune genes and neutral markers can give insights into the nature and geographic scale of parasite-mediated selection. To date, studies investigating such patterns of selection in vertebrates have primarily focused on the acquired branch of the immune system, whereas it remains largely unknown how parasite-mediated selection shapes innate immune genes both within and across vertebrate populations. Here, we present a study on the diversity and population differentiation at the innate immune gene Toll-like receptor 2 (TLR2) across nine populations of yellow-necked mice (Apodemus flavicollis) and bank voles (Myodes glareolus) in southern Sweden. In yellow-necked mice, TLR2 diversity was very low, as was TLR2 population differentiation compared to neutral loci. In contrast, several TLR2 haplotypes co-occurred at intermediate frequencies within and across bank vole populations, and pronounced isolation by distance between populations was observed. The diversity and differentiation at neutral loci was similar in the two species. These results indicate that parasite-mediated selection has been acting in dramatically different ways on a given immune gene in ecologically similar and sympatric species. Furthermore, the finding of TLR2 population differentiation at a small geographical scale in bank voles highlights that vertebrate innate immune defence may be evolutionarily more dynamic than has previously been appreciated.

opencc-zeroDec 2017View details →

Data from: Ascogrammitis lehnertii (Polypodiaceae): A new and dominant understory-species from a diverse community of grammitid ferns in the Andes of Ecuador

In the scope of pantropical studies aimed at understanding how the diversity of grammitid ferns (Polypodiaceae) has evolved and is maintained, we studied a diverse grammitid community in treeline elfin forests in eight study plots of 400 m2 each at 3200 m on Cerro Toledo, Loja, southern Ecuador. We recorded a total of 7986 individuals of 16 grammitid species. Ascogrammitis lehnertii is here described as a new species. We also recorded Mycopteris leucosticta, a species previously believed to be restricted to the Chocó region of Ecuador. We found that the grammitid species were segregated by habitat into trunk-base and trunk specialists, which suggests that species coexistence in these diverse epiphytic communities is at least partly linked to habitat segregation. Ascogrammitis lehnertii and M. leucosticta were the second and third most abundant species, respectively, and both were mostly trunk-base species. The new species A. lehnertii differs from its congeners by the combination of its relatively broad lamina, (2‐)3‐4 cm wide, fertile leaves bearing 2 mm long reddish setae in and near the sori, and by bearing proliferous roots from which new plants emerge. Phylogenetic analyses of atpß, rbcL, rps4, trnG-trnR, and trnL-trnF DNA molecular sequences, using maximum likelihood, place A. lehnertii as sister to A. cuencana with strong support. Despite previous intensive collection efforts in Loja for the past 30 yr, all but one of the collections of this new species were made in the last three years. The discovery of A. lehnertii and the new record of M. leucosticta highlight the patchy distribution of some species in the Andes and the value of surveying habitats that potentially host unrecognized plant diversity. In order to facilitate further discovery, we provide a key to all species of Ascogrammitis.

opencc-zeroDec 2010View details →

Data from: Testing the species–genetic diversity correlation in the Aegean archipelago: towards a haplotype-based macroecology?

A positive correlation between species and genetic diversity (SGDC) has been proposed, consistent with neutral predictions in macroecology. We assessed the SGDC in tenebrionid beetle communities of the Aegean archipelago on fifteen islands of different sizes, distances to mainland, and ages of isolation. Alpha- and beta-diversity of species and haplotypes were assessed using sequences of >1000 individuals (mitochondrial Cytochrome Oxidase I and nuclear Muscular Protein 20) to test the SGDC. We show that: (i) there is a strong species-area and haplotype-area relationship; (ii) species richness in island communities is correlated with intraspecific genetic diversity in the constituent species except when island size or distance to mainland are factored out in partial correlations; (iii) community similarity declines exponentially at an increasing rate when calculated based on species, nuclear and mtDNA haplotypes; and (iv) distance decay of community similarity is slower in dispersive sand-dwelling lineages compared to less dispersive lineages that are not sand-obligate. Taken together, these correlated patterns at the species and haplotype level are consistent with individual-based stochastic dispersal proposed by neutral theories of biodiversity. The results also demonstrate the utility of haplotype data for exploring macroecological patterns in poorly known biota and predicting large-scale biodiversity patterns based on genetic inventories of local samples.

opencc-zeroDec 2015View details →

Data from: Capturing neutral and adaptive genetic diversity for conservation in a highly structured tree species

Preserving intraspecific genetic diversity is essential for long-term forest sustainability in a climate change scenario. Despite that, genetic information is largely neglected in conservation planning, and how conservation units should be defined is still heatedly debated. Here, we use maritime pine (Pinus pinaster Ait.), an outcrossing long lived tree with a highly fragmented distribution in the Mediterranean biodiversity hotspot, to prove the importance of accounting for genetic variation - at both neutral molecular markers and quantitative traits - to define useful conservation units. Six gene pools associated to distinct evolutionary histories were identified within the species using 12 microsatellites and 266 Single Nucleotide Polymorphisms (SNPs). In addition, height and survival standing variation, their genetic control and plasticity were assessed in a multisite clonal common garden experiment (16,544 trees). We found high levels of quantitative genetic differentiation within previously defined neutral gene pools. Subsequent cluster analysis and post-hoc trait distribution comparisons allowed us to define ten genetically homogeneous population groups with high evolutionary potential. They constitute the minimum number of units to be represented in a maritime pine dynamic conservation program. Our results uphold that the identification of conservation units below the species level should account for key neutral and adaptive components of genetic diversity, especially in species with strong population structure and complex evolutionary histories. The environmental zonation approach currently used by the pan-European genetic conservation strategy for forest trees would be largely improved by gradually integrating molecular and quantitative trait information, as data become available.

opencc-zeroDec 2011View details →

Data from: The contribution of rare species to community phylogenetic diversity across a global network of forest plots

Niche differentiation has been proposed as an explanation for rarity in species assemblages. Testing this hypothesis requires quantifying the ecological similarity of species. This similarity can potentially be estimated by using phylogenetic relatedness. In this study, we predicted that if niche differentiation does explain the co-occurrence of rare and common species, then rare species should contribute greatly to the overall community phylogenetic diversity (PD), abundance will have phylogenetic signal and that common and rare species will be phylogenetically dissimilar. We tested these predictions by developing a novel method that integrates species rank abundance distributions with phylogenetic trees and trend analyses to examine the relative contribution of individual species to the overall community PD. We then supplement this approach with analyses of phylogenetic signal in abundances and measures of phylogenetic similarity within and between rare and common species groups. We applied this analytical approach to 15 long-term temperate and tropical forest dynamics plots from around the world. We show that the niche differentiation hypothesis is supported in six forests but is rejected in nine forests, and that the three metrics utilized in this study each provide unique but corroborating information regarding the phylogenetic distribution of rarity in communities.

opencc-zeroDec 2010View details →

Data from: Genetic diversity, population structure and sex-biased dispersal in three co-evolving species

Genetic diversity and spatial structure of populations are important for antagonistic coevolution. We investigated genetic variation and population structure of three closely related European ant species: the social parasite Harpagoxenus sublaevis and its two host species Leptothorax acervorum and Leptothorax muscorum. We sampled populations in 12 countries and analyzed eight microsatellite loci and an mtDNA sequence. We found high levels of genetic variation in all three species, only slightly less variation in the host L. muscorum. Using a newly introduced measure of differentiation (Jost's DEST), we detected strong population structuring in all species and less male-biased dispersal than previously thought. We found no phylogeographic patterns that could give information on post-glacial colonization routes - northern populations are as variable as more southern populations. We conclude that conditions for Thompson's geographic mosaic of coevolution are ideal in this system: all three species show ample genetic variation and strong population structure.

opencc-zeroDec 2015View details →

Data from: Positive species diversity and above-ground biomass relationships are ubiquitous across forest strata despite interference from overstorey trees

There is growing concern over rates of global species diversity loss and its implications on healthy ecosystem functioning. While positive relationships between tree species diversity and forest biomass production have been observed, forests are structurally complex, consisting of understorey vegetation layers that also contribute to ecosystem functioning as they often account for the majority of species richness. However, relationships between understorey vegetation diversity and function are largely unexplored. Further, few studies have simultaneously assessed how both overstorey and understory vegetation interact and contribute to overall ecosystem function. By analysing Canada's National Forest Inventory data base using structural equation modelling, we explored the relationships between species richness and above-ground biomass production across forest vegetation strata while accounting for potentially confounding factors, including climate, physical site characteristics and forest ageing. We found positive relationships between species richness and biomass production across all forest vegetation layers, but the relationship was strongest for the overstorey layer. Species richness of the understorey tree, shrub and herb layers was positively related to overstorey species richness. However, overstorey biomass had a negative effect on the biomass production of all understorey layers. Our results suggest that resource filtering by overstorey trees might have reduced the strength of the positive diversity–productivity relationships in the forest understorey, supporting previous hypotheses that the magnitude and direction of diversity–productivity relationships is context specific and dependent on the conditions of the surrounding environment. Further, heterogeneity in understory resources, as affected by the overstorey, may promote niche complementarity as the main mechanism driving diversity–productivity relationships in understorey vegetation.

opencc-zeroDec 2013View details →

Data from: Direct evidence that density-dependent regulation underpins the temporal stability of abundant species in a diverse animal community

To understand how ecosystems are structured and stabilized, and to identify when communities are at risk of damage or collapse, we need to know how the abundances of the taxa in the entire assemblage vary over ecologically meaningful timescales. Here, we present an analysis of species temporal variability within a single large vertebrate community. Using an exceptionally complete 33-year monthly time series following the dynamics of 81 species of fishes, we show that the most abundant species are least variable in terms of temporal biomass, because they are under density-dependent (negative feedback) regulation. At the other extreme, a relatively large number of low abundance transient species exhibit the greatest population variability. The high stability of the consistently common high abundance species—a result of density-dependence—is reflected in the observation that they consistently represent over 98% of total fish biomass. This leads to steady ecosystem nutrient and energy flux irrespective of the changes in species number and abundance among the large number of low abundance transient species. While the density-dependence of the core species ensures stability under the existing environmental regime, the pool of transient species may support long-term stability by replacing core species should environmental conditions change.

Data from: Evaluating multilocus Bayesian species delimitation for discovery of cryptic mycorrhizal diversity

The increasing availability of DNA sequence data enables exciting new opportunities for fungal ecology. However, it amplifies the challenge of how to objectively classify the diversity of fungal sequences into meaningful units, often in the absence of morphological characters. Here, we test the utility of modern multilocus Bayesian coalescent-based methods for delimiting cryptic fungal diversity in the orchid mycorrhiza morphospecies Serendipita vermifera. We obtained 147 fungal isolates from Caladenia, a speciose clade of Australian orchids known to associate with Serendipita fungi. DNA sequence data for 7 nuclear and mtDNA loci were used to erect competing species hypotheses by clustering isolates based on: (a) ITS sequence divergence, (b) Bayesian admixture analysis, and (c) mtDNA variation. We implemented two coalescent-based Bayesian methods to determine which species hypothesis best fitted our data. Both methods found strong support for eight species of Serendipita among our isolates, supporting species boundaries reflected in ITS divergence. Patterns of host plant association showed evidence for both generalist and specialist associations within the host genus Caladenia. Our findings demonstrate the utility of Bayesian species delimitation methods and suggest that wider application of these techniques will readily uncover new species in other cryptic fungal lineages.

Data from: Species mtDNA genetic diversity explained by infrapopulation size in a host-symbiont system

Understanding what shapes variation in genetic diversity among species remains a major challenge in evolutionary ecology, and it has been seldom studied in parasites and other host-symbiont systems. Here, we studied mtDNA variation in a host-symbiont non-model system: 418 individual feather mites from 17 feather mite species living on 17 different passerine bird species. We explored how a surrogate of census size, the median infrapopulation size (i.e., the median number of individual parasites per infected host individual), explains mtDNA genetic diversity. Feather mite species genetic diversity was positively correlated with mean infrapopulation size, explaining 34% of the variation. As expected from the biology of feather mites, we found bottleneck signatures for most of the species studied but, in particular, three species presented extremely low mtDNA diversity values given their infrapopulation size. Their star-like haplotype networks (in contrast with more reticulated networks for the other species) suggested that their low genetic diversity was the consequence of severe bottlenecks or selective sweeps. Our study shows for the first time that mtDNA diversity can be explained by infrapopulation sizes, and suggests that departures from this relationship could be informative of underlying ecological and evolutionary processes.

opencc-zeroDec 2015View details →

Data from: One species for one island? Unexpected diversity and weak connectivity in a widely distributed tropical hydrozoan

Isolation by distance (IBD) is one of the main modes of differentiation in marine species, above all in species presenting low dispersal capacities. This study reports the genetic structuring in the tropical hydrozoan Lytocarpia brevirostris α (sensu Postaire et al, 2016b), a brooding species, from 13 populations in the Western Indian Ocean (WIO) and one from New Caledonia (Tropical Southwestern Pacific). At the local scale, populations rely on asexual propagation at short distance, which was not found at larger scales; identical genotypes were restricted to single populations. After the removal of repeated genotypes, all populations presented significant positive FIS values (between 0.094*** and 0.335***). Gene flow was extremely low at all spatial scales, between sites within islands (<10 km distance) and among islands (100 to>11 000 km distance), with significant pairwise FST values (between 0.012*** and 0.560***). A general pattern of IBD was found at the Indo-Pacific scale, but also within sampled ecoregions of the WIO province. Clustering analyses identified each sampled island as an independent population, whereas analysis of molecular variance indicated that population genetic differentiation was significant at small (within island) and intermediate (among islands within province) spatial scales. The high population differentiation might reflect the life cycle of this brooding hydrozoan, possibly preventing regular dispersal at distances more than a few kilometres and probably leading to high cryptic diversity, each island housing an independent evolutionary lineage.

Data from: Are tree species diversity and genotypic diversity effects on insect herbivores mediated by ants?

Plant diversity can influence predators and omnivores and such effects may in turn influence herbivores and plants. However, evidence for these ecological feedbacks is rare. We evaluated if the effects of tree species (SD) and genotypic diversity (GD) on the abundance of different guilds of insect herbivores associated with big-leaf mahogany (Swietenia macrophylla) were contingent upon the protective effects of ants tending extra-floral nectaries of this species. This study was conducted within a larger experiment consisting of mahogany monocultures and species polycultures of four species and –within each of these two plot types– mahogany was represented by either one or four maternal families. We selected 24 plots spanning these treatment combinations, 10 mahogany plants/plot, and within each plot experimentally reduced ant abundance on half of the selected plants, and surveyed ant and herbivore abundance. There were positive effects of SD on generalist leaf-chewers and sap-feeders, but for the latter group this effect depended on the ant reduction treatment: SD positively influenced sap-feeders under ambient ant abundance but had no effect when ant abundance was reduced; at the same time, ants had negative effects on sap feeders in monoculture but no effect in polyculture. In contrast, SD did not influence specialist stem-borers or leaf-miners and this effect was not contingent upon ant reduction. Finally, GD did not influence any of the herbivore guilds studied, and such effects did not depend on the ant treatment. Overall, we show that tree species diversity influenced interactions between a focal plant species (mahogany) and ants, and that such effects in turn mediated plant diversity effects on some (sap-feeders) but not all the herbivores guilds studied. Our results suggest that the observed patterns are dependent on the combined effects of herbivore identity, diet breadth, and the source of plant diversity.