Gradient In Species Richness Research Articles

A Latitudinal Gradient of Reference Genomes.

Global inequality rooted in legacies of colonialism and uneven development can lead to systematic biases in scientific knowledge. In ecology and evolutionary biology, findings, funding and research effort are disproportionately concentrated at high latitudes, while biological diversity is concentrated at low latitudes. This discrepancy may have a particular influence in fields like phylogeography, molecular ecology and conservation genetics, where the rise of genomics has increased the cost and technical expertise required to apply state-of-the-art methods. Here, we ask whether a fundamental biogeographic pattern-the latitudinal gradient of species richness in tetrapods-is reflected in the available reference genomes, an important data resource for various applications of molecular tools for biodiversity research and conservation. We also ask whether sequencing approaches differ between the Global South and Global North, reviewing the last 5 years of conservation genetics research in four leading journals. We find that extant reference genomes are scarce relative to species richness at low latitudes and that reduced representation and whole-genome sequencing are disproportionately applied to taxa in the Global North. We conclude with recommendations to close this gap and improve international collaborations in biodiversity genomics.

Anomalous latitudinal gradients in parasitoid wasp diversity-Hotspots in regions with larger temperature range.

Knowledge of global patterns of genetic diversity is essential for biodiversity conservation as this parameter describes the ability of a species to respond to environmental changes. Ichneumonoids parasitoid wasps are among the few taxa showing an anomalous latitudinal diversity gradient. Using the largest georeferenced molecular dataset for this group, we used a macrogenetics approach to examine latitudinal patterns and predictors of intraspecific genetic diversity. We calculated the mean nucleotide diversity of mitochondrial DNA barcode sequences at three geographic levels: grid cells, latitudinal bands and climatic zones. Nucleotide diversity values were consistently higher at northern temperate latitudes, peaking at 50°. We found a positive but weak relationship between intraspecific diversity and the latitude, between intra- and interspecific diversity, and a positive effect of the temperature range. Examining the spatial relationship between different levels of biodiversity and its drivers is particularly relevant considering climate change and its impact on species distribution. Yet, in insects, it has been challenging to integrate ecological, evolutionary and geographical components when analysing the processes leading to species richness gradients.

The disruption of birds' double mutualistic interactions in novel ecosystems.

Non-native trees disrupt ecological processes vital to native plant communities. We studied how forests dominated by Acacia dealbata and Eucalyptus globulus affect the role of birds as dual pollinators and seed dispersers in a region heavily impacted by these two non-native species. We compared bird-plant interactions in the native and in the two non-native forest types. We constructed a multilayer regional network for each forest type and evaluated differences in network dissimilarity between networks. We also calculated the bird's importance in connecting processes and variables associated with module diversity. To determine how the networks react to changes in species richness, we did a simulation of species richness gradient and link percentage for each forest type. The number of birds acting both as pollinators and seed dispersers was higher in native than in non-native forests. However, birds in non-native forests still play a crucial role in maintaining the ecological services provided to native plant communities. However, the eucalyptus network exhibited a concerning simplification, forcing bird species to fully exploit the few remaining resources, leaving little room for structural adjustments and limiting the ecosystem's ability to withstand further species loss. These findings highlight how non-native trees may trigger cascading effects across trophic levels.

Spatial Distribution Patterns and Beta Diversity of Fish Communities in a Tropical River Basin of Deccan Plateau

ABSTRACTRiverine ecosystems exhibit significant spatial variations in their communities, and understanding of these variances is vital to comprehend the mechanisms that maintain biodiversity. This study was conducted to understand pattern of distribution and beta diversity of fish communities in the Bhima River basin in the Deccan Plateau region of India. Fish distribution data from 59 sites across 11 rivers of the Bhima River basin were collected, and pair‐wise βDissimilarity and site‐wise local contribution to beta diversity (LCβDSorensen) and its components (LCβDTurnover and LCβDNestedness) were calculated. Power function regression was analysed to understand the decay in community similarity with geographical and environmental distances. Redundancy analysis was performed to investigate the relationship between fish distribution and environmental variables. Results indicated that species richness declined with increasing longitude from west to east. A negative relationship was observed between species richness and LCβDSorensen. LCβDTurnover formed Ո‐shaped curve at both ends of the species richness gradient, while LCβDNestedness values exhibited Ս‐shaped curve. No significant difference between mean LCβDTurnover and mean LCβDNestedness across the sites was observed. The distance decay relationship between community similarity and both geographical and environmental distances follows the power law shape, and the slope of this relationship flattened with increasing distance. Precipitation, topography, temperature variation and dissolved oxygen played a pivotal role in shaping fish assemblages. This study provides insight into the spatial distribution of fish communities in the Bhima River basin, which will be helpful to comprehend the ordination of biodiversity in the riverine ecosystem of the Deccan Plateau region.

Tree species richness suppresses red imported fire ant invasion in a subtropical plantation forest

Abstract The ecological resistance to the invasion of alien species has been extensively researched at the within‐trophic level; however, the effect of cross‐trophic interactions remains largely unknown. The red imported fire ant (RIFA, Solenopsis invicta) is a globally invasive species, and a cross‐trophic interaction study between RIFAs and plants may provide a more comprehensive understanding and management of its invasion. We hypothesized that the diversity of trees, which are the primary producers supporting terrestrial ecosystems, could suppress the invasion of omnivorous RIFAs by regulating food resources (e.g. plants and arthropods) and the microenvironment (e.g. soil microclimate) as well as enhancing competition with other carnivorous ants. To test this hypothesis, we investigated RIFA abundance and mound numbers across tree species richness gradients in a subtropical plantation forest. Using structural equation models, we discovered that tree species richness had contrasting effects on RIFA abundance and mound numbers. RIFA abundance directly decreased with higher tree species richness because of the dilution effect (i.e. lower abundance of preferred tree species). In contrast, RIFA mound numbers indirectly increased with tree species richness via an increase in arthropod abundance (excluding ants) (i.e. more ample food resources for RIFA). Moreover, warmer soil temperatures decreased RIFA abundance, whereas other carnivorous ant species richness and abundance negatively affected RIFA abundance and mound numbers. Synthesis and applications: Our findings demonstrate that the ecological resistance to RIFA invasion is influenced by tree species richness in a complex manner; specifically, the relative strengths of the effects of tree species characteristics, native competitors and environmental conditions are likely to impact the power of ecological resistance. This highlights the importance of cross‐trophic interactions underlying the resistance of complex ecosystems to alien species invasion; therefore, maintaining diverse tree communities in controlled systems (e.g. suburban and urban green spaces) should be viewed as a potential strategy for controlling RIFA invasion.

Why are plant communities stable? Disentangling the role of dominance, asynchrony and averaging effect following realistic species loss scenario

Abstract A growing number of studies have demonstrated that biodiversity is a strong and positive predictor of ecosystem temporal stability by simultaneously affecting multiple underlying mechanisms of stability, that is dominance, asynchrony and averaging effects. However, to date, no study has disentangled the relative role of these key mechanisms of stability in biodiversity experiments. We created a species richness gradient by mimicking a loss of rare species and assessed the role of species richness on community stability and, more importantly, quantified the relative role of three stabilizing mechanisms, that is dominance (stabilization due to stable dominants compared to the rest of the species in the community), asynchrony (stabilization due to temporal asynchrony between species), and averaging effects (pure effect of diversity) on community stability across a species richness gradient. We found that extreme species loss negatively impacted community stability, but just three species were enough to stabilize biomass production to a level similar to highly diverse communities. However, the similar stability of communities resulted from differing contributions from each stabilizing mechanism, depending on the community diversity. Since less abundant species were more temporally variable, species loss stabilized the populations of the remaining species. The loss of rare and subordinate species reduced the dominance and averaging effects, but increased the asynchrony effect. Hence, the asynchrony effect played a major role in the stability of species poor communities, while the averaging effect drove most of the stability of species rich communities. Overall, dominance played only a minor role, accounting for 5%–15% of the stabilization, while asynchrony and averaging effects were dominating forces contributing to ~85%–95% of the total stabilization. Synthesis. This study highlights the importance of biodiversity and roles of dominant and rare species for long‐term community stability and, for the first time, disentangles relative roles of dominance effect, asynchrony and averaging effect on community stability in a real‐world biodiversity experiment.

The effect of successive summer drought periods on bacterial diversity along a plant species richness gradient.

Drought is a major stressor to soil microbial communities, and the intensification of climate change is predicted to increase hydric stress worldwide in the coming decades. As a possible mitigating factor for the consequences of prolonged drought periods, above and belowground biodiversity can increase ecosystem resistance and resilience by improving metabolic redundancy and complementarity as biodiversity increases. Here, we investigated the interaction effect between plant richness and successive, simulated summer drought on soil microbial communities during a period of 9 years.To do that, we made use of a well-established biodiversity experiment (The Jena Experiment) to investigate the response of microbial richness and community composition to successive drought periods alongside a plant richness gradient, which covers 1-, 2-, 4-, 8-, 16-, and 60-species plant communities. Plots were covered from natural precipitation by installing rain shelters 6 weeks every summer. Bulk soil samples were collected 1 year after the last summer drought was simulated. Our data indicate that bacterial richness increased after successive exposure to drought, with the increase being stable along the plant richness gradient. We identified a significant effect of plant species richness on the soil microbial community composition and determined the taxa significantly impacted by drought at each plant richness level. Our data successfully demonstrates that summer drought might have a legacy effect on soil bacterial communities.

Biogeographic isolation and climate shape the evolutionary heritage of Neotropical inselbergs

AbstractAimQuaternary climatic shifts can explain the current distribution of ancient ecosystems as well as the current distributions of gradients that hold species richness and diversity of several lineages in old, climatically buffered, infertile landscapes (OCBILs) as inselbergs. Thus, the combination of phylogenetic approaches and temporal landscape connectivity allows disentangling the mechanisms involved in the origin of the disjunct distribution of plant species and the evolutionary heritage of Neotropical inselbergs.LocationBrazilian Atlantic Forest and Caatinga.Time PeriodPliocene until the current period.Major TaxaAngiosperms.MethodsWe used a compiled data set of 42 inselbergs across the Atlantic Forest and Caatinga biomes in eastern Brazil to describe their structure and phylogenetic diversity and map the landscape resistance distances and the effects of resistance on their phylogenetic beta diversity. We also aimed to identify the effectiveness of protected areas and gaps in the conservation of plant species in Brazilian inselbergs.ResultsWe found evidence of dispersal limitation in the inselberg species pool and a latitudinal gradient in plant species richness and phylogenetic diversity across the Neotropical inselberg landscape, with greater isolation between the northeastern and southeastern core areas. Our findings indicate that inselbergs can lead to a high turnover of phylogenetic diversity, thus imposing distinctiveness on the evolutionary lineages of the inselberg flora.Main ConclusionsOur results suggest that the current distribution of inselberg's flora in isolated ecosystems may result from a more connected distribution of this flora in the past, as postulated by the Pleistocene habitat fluctuations. However, the patterns of diversity have probably been influenced by events much older than Quaternary climate shifts, due to inselbergs climate stability areas (refugia) since ancient periods. Conservation of mountain vegetation is a crucial strategy for maintaining biodiversity and distinct phylogenetic lineages in the current rapid global climate and land use change scenario.

Vegetation diversity and structure influence small‐mammal communities in native and restored northern mixed grasslands

AbstractCurrent grassland restoration strategies aim to recreate grassland vegetation communities, and often rely on high‐diversity native seeding to promote vegetation diversity. Questions remain concerning the influence of vegetation richness and diversity on grassland fauna. Small‐mammal communities are integral parts of grassland ecosystems, but their responses to restoration are often mixed or overlooked. During July 2014 to 2016, we used Sherman live traps to survey grassland small‐mammal communities of 24 study sites in northeastern South Dakota and southeastern North Dakota, USA, to better understand their responses to vegetation cover type, diversity, richness, and site‐specific vegetation structure. Sites represented a vegetation species richness gradient and 3 vegetation cover types including low‐diversity restorations planted with dense nesting cover (DNC) seed mix, high‐diversity seeded restorations, and unseeded reference grasslands. Small‐mammal abundance was highest at low‐diversity DNC restoration sites and lowest in reference grassland. Small‐mammal diversity was highest at high‐diversity restoration sites and lowest at low‐diversity DNC restoration sites. Models assessing the influence of vegetation structure on the abundance of focal taxa differed. Deer mice (Peromyscus spp.) were negatively influenced by percent native vegetation cover, and voles (Microtus spp.) showed yearly variation and were influenced positively by litter depth and negatively by vegetation richness. Small‐mammal communities of low‐diversity DNC restorations differed from reference sites, but high‐diversity restorations were not different from reference or low‐diversity DNC sites. Thirteen‐lined ground squirrel (Ictidomys tridecemlineatus) abundance was higher at reference and high‐diversity restored sites, while low‐diversity DNC sites had higher deer mice abundance. Results indicate small mammals are unlikely to respond uniformly to vegetation characteristics, and diversity of seed mixes used in grassland restoration is likely to influence grassland small‐mammal communities.

Both local stability and dispersal contribute to metacommunity sensitivity to asynchronous habitat availability

The stability of isolated communities depends on the complexity of their foodwebs. However, it remains unclear how local stability interacts with dispersal in multitrophic metacommunities to shape biodiversity patterns. This lack of understanding is deeper in the more realistic frame of landscapes that exhibit non-trivial and time-varying structures. Therefore, in this study, we aim to evaluate the influence of local stabilizing factors versus dispersal in determining the sensitivity of metacommunity biodiversity to increasing asynchrony of site availability. Additionally, we assess the role of foodweb complexity and landscape structure as modulating factors. To accomplish our goals we developed a model based on random matrices for local communities, which are linked by stochastic dispersal over explicit dynamic landscapes. We ran numerical simulations and computed the effect sizes of foodweb temperature, self-limitation, dispersal ability, and all pairwise combinations, on the sensitivity of biodiversity to landscape asynchrony. In our experiments we explored gradients of species richness, foodweb connectance, number of sites, and landscape modularity. Our results showed that asynchrony among site availability periods reduced α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}-diversity and increased β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document}-diversity. Asynchrony increased γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma$$\\end{document}-diversity at high dispersal rates. Both local and regional stabilizing factors determined the sensitivity of metacommunities to landscape asynchrony. Local factors were more influential in landscapes with fewer sites and lower modularity, as well as in metacommunities composed of complex foodwebs. This research offers insights into the dynamics of metacommunities in dynamic landscapes, providing valuable knowledge about the interplay between local and regional factors in shaping ecological stability and species persistence.

Trophic interactions in soil micro-food webs drive ecosystem multifunctionality along tree species richness.

Rapid biodiversity losses under global climate change threaten forest ecosystem functions. However, our understanding of the patterns and drivers of multiple ecosystem functions across biodiversity gradients remains equivocal. To address this important knowledge gap, we measured simultaneous responses of multiple ecosystem functions (nutrient cycling, soil carbon stocks, organic matter decomposition, plant productivity) to a tree species richness gradient of 1, 4, 8, 16, and 32 species in a young subtropical forest. We found that tree species richness had negligible effects on nutrient cycling, organic matter decomposition, and plant productivity, but soil carbon stocks and ecosystem multifunctionality significantly increased with tree species richness. Linear mixed-effect models showed that soil organisms, particularly arbuscular mycorrhizal fungi (AMF) and soil nematodes, elicited the greatest relative effects on ecosystem multifunctionality. Structural equation models revealed indirect effects of tree species richness on ecosystem multifunctionality mediated by trophic interactions in soil micro-food webs. Specifically, we found a significant negative effect of gram-positive bacteria on soil nematode abundance (a top-down effect), and a significant positive effect of AMF biomass on soil nematode abundance (a bottom-up effect). Overall, our study emphasizes the significance of a multitrophic perspective in elucidating biodiversity-multifunctionality relationships and highlights the conservation of functioning soil micro-food webs to maintain multiple ecosystem functions.

Body size and trophic structure explain global asymmetric response of tetrapod diversity to climate effects.

Although climate-based hypotheses are widely used to explain large-scale diversity patterns, they fall short of explaining the spatial variation among taxonomic groups. Integrating food web and metabolic theories into macroecology is a promising step forward, as they allow including explicit taxon-specific traits that can potentially mediate the relationship between climate and diversity. Our investigation focuses on the role of body size and trophic structure in mediating the influence of contemporary climate and historical climate change on global tetrapods species richness. We used piecewise structural equation modeling to assess the direct effects of contemporary climate and climate instability of species richness and the indirect effects of climate on tetrapod richness mediated by community-wide species traits. We found that birds and mammals are less sensitive to the direct effect of contemporary climate than amphibians and squamates. Contemporary climate and climate instability favored the species richness of mammals and amphibians. However, for birds and squamates, this link is only associated with contemporary climate. Moreover, we showed that community-wide traits are correlated with species richness gradients. However, we highlight that this relationship is dependent upon the specific traits and taxonomic groups. Specifically, bird communities with smaller bodies and bottom-heavy structures support higher species richness. Squamates also tend to be more diverse in communities with prevalence of smaller bodies, while mammals are correlated with top-heavy structures. Moreover, we showed that higher contemporary climate and climate instability reduce the species richness of birds and mammals through community-wide traits and indirectly increase squamate species richness. We also showed that body size and trophic structure are driving a global asymmetric response of tetrapod diversity to climate effects, which highlights the limitation to use the "typical" climate-based hypotheses. Furthermore, by combining multiple theories, our research contributes to a more realistic and mechanistic understanding of diversity patterns across taxonomic groups.

Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13 C responses to drought.

Mixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. In particular, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. Using tree cores from a large-scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; δ13 C) to changes in climate-induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases δ13 C and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterised the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance versus resource acquisition and stomatal control. Tree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods. The effects of neighbourhood species richness and climate on growth and δ13 C were modulated by the traits of focal trees and the traits of their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during dry and wet years. We show that species' drought-tolerance traits can explain the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress.

Latitudinal biodiversity gradients of rocky intertidal assemblages: Spatial scales and complex associations with environmental factors

AbstractLatitudinal biodiversity gradients vary across taxonomic groups and spatial scales, and various environmental factors have been associated with those patterns. However, it remains unknown whether taxonomic groups with strong ecological associations have similar or different latitudinal patterns. Macroalgae are foundation assemblages on rocky intertidal shores and are often inhabited by invertebrates, predominantly polychaetes. This study analysed latitudinal patterns of macroalgae and their associated polychaetes at different spatial scales and determined how environmental factors influenced those patterns. Macroalgae and polychaetes were collected from transects within 38 rocky intertidal shores of Western Australia at 14 latitudes between 18° S and 34° S. Latitudinal gradients in species richness, diversity (Simpson's diversity index) and abundance were evaluated at transect, site and latitudinal scales. Relationships between environmental factors and rocky intertidal assemblages were analysed using piecewise structural equation modelling based on direct, indirect and complex models. Macroalgae showed increases in species richness, diversity and abundance at transect and site scales towards high latitudes, but species richness and diversity patterns were unclear at the latitudinal scale where transect and site data were pooled. In contrast, polychaete diversity decreased towards high latitudes, although this pattern was unclear at the transect scale. Polychaete richness and abundance tended to follow parabolic patterns that peaked at 27° S. Relationships between environmental factors and rocky intertidal assemblages were best described by a complex model, with significant relationships more often at transect and site scales. Sea surface temperatures showed the strongest relationship with macroalgal and polychaete distributions.

Facets of functional diversity support niche‐based explanations for Australian biodiversity gradients

AbstractAimThere is widespread support that species richness increases with the available energy of an ecosystem, but the mechanisms underlying this driver of biodiversity patterns remain elusive. We evaluated gradients of functional diversity to test whether the higher species richness of productive, structurally diverse environments is due to a greater range of niches being supported by the abiotic conditions present (environmental filtering), greater availability of biotic resource and habitat niches (more niches) or increasing functional similarity of species (niche packing).LocationAustralia.TaxonBirds and mammals.MethodsWe used structural equation modelling to evaluate the relative contributions of climatic harshness (actual evapotranspiration, AET) and the availability of resource (gross primary productivity, GPP) and habitat (tree height) niches on taxonomic richness and functional richness, dispersion and evenness. We performed parallel analyses within 15 bioclimatic zones and continentally to evaluate the scaling of biodiversity gradients and the shifting balance between niche‐based mechanisms along environmental gradients.ResultsAll continental diversity gradients were primarily associated with energy variables, but while species richness of both taxa and all functional diversity measures of bird assemblages increased with AET, mammal functional diversity was more strongly associated with GPP gradients. Results were more variable at the regional scale, but species richness gradients along tree height (birds and mammals) and GPP (mammals) within bioclimatic zones tended not to be paralleled by increases in functional richness or dispersion.Main ConclusionsThe niche‐based explanations of biodiversity gradients varied in importance with scale, position on environmental gradients and taxonomic group. At the continental extent, bird biodiversity gradients were structured by environmental filtering by climatic harshness, while mammal biodiversity was related to the increasing availability of resource niches with increasing productivity. Niche packing was more prominent at the regional scale, especially in bioclimatic zones where productivity and vegetation height were less limiting, and in mammal assemblages, suggesting that biodiversity patterns scale differently for birds and mammals.

Latitudinal distributions of the species richness, phylogenetic diversity, and functional diversity of fleas and their small mammalian hosts in four geographic quadrants

We studied latitudinal patterns in the species richness (SR), the phylogenetic diversity (PD), and the functional diversity (FD) of fleas and their mammalian hosts. We asked whether these patterns in either fleas, hosts, or both 1) conform to a classical latitudinal gradient; 2) vary geographically; and 3) differ between fleas and hosts. We also asked whether the patterns of PD and FD follow those of SR. We collected data on the latitudinal distribution of 1022 flea and 900 mammal species from literature sources and calculated the SR, PD, and FD of both groups in 1° latitude bands. Then, we used broken‐stick regression models to analyse separately the latitudinal variation of 1) each diversity facet and 2) fleas and hosts in each geographic quadrant. The classical latitudinal gradient pattern was not found in either fleas or hosts across any facet of diversity or geographic quadrant, except for the PD of fleas in the southeastern quadrant and the FD of hosts in the southwestern quadrant. Latitudinal patterns of the SR, PD and FD of fleas and hosts differed substantially between geographic quadrants. Furthermore, the latitudinal distributions of flea and host SR were similar in three of four quadrants (except the northeastern quadrant), whereas the latitudinal distributions of flea and host PD were similar in the southwestern quadrant only. No similarity in flea versus host FD was revealed. The latitudinal patterns of flea and host PD and FD mostly did not follow those of their SR. We conclude that latitudinal gradients of species richness and phylogenetic and functional diversity appeared not to be universal phenomena. Instead, the latitudinal distributions of these diversity facets represent an interplay of ecological (current and past) and historical processes. For parasites, the processes acting on hosts add another layer of complexity underlying their latitudinal diversity patterns.

Variation in a Darwin Wasp (Hymenoptera: Ichneumonidae) Community along an Elevation Gradient in a Tropical Biodiversity Hotspot: Implications for Ecology and Conservation.

Understanding how biodiversity varies from place to place is a fundamental goal of ecology and an important tool for halting biodiversity loss. Parasitic wasps (Hymenoptera) are a diverse and functionally important animal group, but spatial variation in their diversity is poorly understood. We survey a community of parasitic wasps (Ichneumonidae: Pimplinae) using Malaise traps up a mountain in the Brazilian Atlantic Rainforest, and relate the catch to biotic and abiotic habitat characteristics. We find high species richness compared with previous similar studies, with abundance, richness, and diversity peaking at low to intermediate elevation. There is a marked change in community composition with elevation. Habitat factors strongly correlated with elevation also strongly predict changes in the pimpline community, including temperature as well as the density of bamboo, lianas, epiphytes, small trees, and herbs. These results identify several possible surrogates of pimpline communities in tropical forests, which could be used as a tool in conservation. They also contribute to the growing evidence for a typical latitudinal gradient in ichneumonid species richness, and suggest that low to medium elevations in tropical regions will sometimes conserve the greatest number of species locally, but to conserve maximal biodiversity, a wider range of elevations should also be targeted.

Global gradients in species richness of marine plankton functional groups

Abstract The patterns of species diversity of plankton functional groups (PFGs) remain poorly understood although they matter greatly for marine ecosystem functioning. Here, we use an ensemble of empirical species distribution models for 845 plankton species to estimate the global species richness of three phytoplankton and 11 zooplankton functional groups as a function of objectively selected environmental predictors. The annual mean species richness of all PFGs decreases from the low to the high latitudes, but the steepness and the shape of this decrease vary significantly across PFGs. Pteropods, small copepods (Oithonids and Poecilostomatoids) and Salps have the steepest latitudinal gradients, whereas Amphipods and the three phytoplankton groups have the weakest ones. Temperature, irradiance and nutrient concentration are the first-order control on the latitudinal richness patterns, whilst the environmental conditions associated to upwelling systems, boundary currents and oxygen minimum zones modulate the position of the peaks and troughs in richness. The species richness of all PFGs increases with net primary production but decreases with particles size and the efficiency of the biological carbon pump. Our study puts forward emergent biodiversity–ecosystem functioning relationships and hypotheses about their underlying drivers for future field-based and modelling research.

Tree communities and functional traits determine herbivore compositional turnover.

There are many factors known to drive species turnover, although the mechanisms by which these operate are less clear. Based on comprehensive datasets from the largest tree diversity experiment worldwide (BEF-China), we used shared herbivore species (zeta diversity) and multi-site generalized dissimilarity modelling to investigate the patterns and determinants of species turnover of Lepidoptera herbivores among study plots across a gradient in tree species richness. We found that zeta diversity declined sharply with an increasing number of study plots, with complete changes in caterpillar species composition observed even at the fine spatial scale of our study. Plant community characteristics rather than abiotic factors were found to play key roles in driving caterpillar compositional turnover, although these effects varied with an increasing number of study plots considered, due to the varying contributions of rare and common species to compositional turnover. Our study reveals details of the impact of phylogeny- and trait-mediated processes of trees on herbivore compositional turnover, which has implications for forest management and conservation and shows potential avenues for maintenance of heterogeneity in herbivore communities.

Predation pressure by arthropods, birds, and rodents is interactively shaped by tree species richness, vegetation structure, and season

Tree species richness, forest structure, and seasonal fluctuations between rainy and dry seasons can strongly affect trophic interactions in forest ecosystems, but the inter- and scale dependence of these variables remains unclear. Using artificial caterpillars (~18,000 replicates), we analyzed predation pressure by arthropods, birds, and rodents along a tree species richness gradient across seasons in a subtropical tree diversity experiment (BEF-China). The aim of the study was to test if forest structure, in addition to tree species richness, has an effect on predation pressure and to further specify which structural variables are important in driving predation. We assessed the effects of tree species richness and forest structure at the plot and local neighborhood levels. We also included fine-scale placement covariates, plot size, and topographical covariates of the study site. Forest structure and tree species richness independently and interactively affected predation pressure. The spatial scale was an important determinant for tree species richness and structural effects, extending from within plot scales to the overall heterogeneity of the plots’ surrounding environment. For example, the effect of branch density in the local neighborhood depended on both surrounding tree species richness and plot-level vegetation density. Similarly, visibility-enhancing factors increased attacks by arthropods (lack of branches in close surroundings) and by birds (open area), depending on the surrounding vegetation. A comparison of structural measures showed that predation pressure can be addressed in much greater detail with multiple specific structural features than with overall forest complexity. Seasonal change also affected predation pressure, with foliage being a stronger attractant in spring, but also by presumable topography-driven study plot differences in sun exposure and humidity between rainy and dry seasons. Our study demonstrates that predation pressure is not simply a function of tree species richness or structure but is shaped by the interplay of structural elements, spatial scale, and seasonal dynamics along gradients of tree species richness and forest structure. The structural and seasonal effects are important to take into account when addressing how current and future biodiversity loss may change top‐down control of herbivory and overall ecosystem functioning.