Biology subjects

Craven, D.

Publications and source records attributed to Craven, D..

17 recordsLinked to original sources

bioRxiv2026

Bridging the gaps between field-based ecology and remote sensing to estimate plant functional diversity: a systematic review

Understanding plant functional diversity across scales requires integrating field-based ecology and remote sensing, yet these disciplines differ in how traits are studied. We evaluated the conceptual and methodological convergence between these disciplines. Our results reveal that field-based ecology has undergone longer conceptual development and covers a broader range of traits, while remote sensing has experienced rapid growth driven by technological advances. Both disciplines are increasingly converging on similar concepts. However, major gaps in empirical coverage persist across biomes in both disciplines. Although plant-dominated ecosystems have been extensively studied, extreme ecosystems remain undersampled. While there is considerable diversity in the definition "functional traits", both disciplines converge on using a similar set of traits, reflecting their central role in plant strategies and spectral detectability. Our synthesis underscores the potential for methodological synergy. Harmonizing trait definitions, scaling assumptions, and computational steps involved in estimating plant functional diversity are crucial for building a unified, multiscale framework for biodiversity monitoring in ecosystems undergoing biodiversity loss and climate change. TeaserA synthesis of how field ecology and remote sensing can be aligned to monitor plant functional diversity across scales.

ecology↗

bioRxiv2026

Temporal span of biodiversity monitoring mediates the effects of area and environment

The scale at which diversity is observed shapes the patterns we find. While spatial scale is known to influence biodiversity patterns, the effects of temporal scale, namely the average duration of sampling (known as temporal span), have been mostly overlooked. Here, we investigate how temporal span affects species richness patterns, their environmental drivers, and species richness hotspots. We used species richness data from several large bird datasets from Czechia, with over 7000 observations, a spatial grain ranging from 0.03 to 100 km2, and a temporal span ranging from 1 to 36 years (1985-2017). Using Random Forests, we modelled species richness as a response to temporal span, while also including area, geographic location, time, and environmental and land-cover predictors. We found that the temporal span is consistently among the most important predictors of bird species richness. Moreover, temporal span interacts with key environmental conditions, particularly precipitation and water bodies, modulating their effects on species richness and revealing processes that differ from those traditionally attributed solely to spatial grain. We also found that using different time spans can shift the predicted locations of biodiversity hotspots. Our results provide empirical evidence that temporal span should be included in studies about biodiversity and conservation planning, given the urgent challenges arising from ongoing biodiversity change and the complexity of its drivers.

ecology↗

bioRxiv2025

Climatic niche conservatism in non-native plants depends on introduction history and biogeographic context

Many tools informing preventive invasion management build on the assumption that introduced species will conserve their climatic niches outside their native ranges. Previous research testing the validity of this assumption found contradictory results regarding niche conservatism vs. niche switching for non-native species. An open question is in how far these contradictions reflect context dependency, yet only few studies compared the niche dynamics of species introduced to multiple regions. Here, we used an ordination-based approach to quantify the climatic niche changes (stability, unfilling, expansion) of 316 plant species introduced to eight different regions across the world, including the Pacific region with extreme isolation between island groups. We then performed multiple phylogenetic regressions to assess how the regional context and species characteristics affect niche dynamics. Niche conservatism varied across regions, even within species. While niche expansion into previously unoccupied climates was generally low, niche unfilling varied strongly between regions. Generally, region-specific introduction history and species biogeographic attributes were more important for explaining niche changes than ecological traits. Niche expansion was consistently higher for species with small native range sizes, and niche stability increased. In contrast, niche unfilling decreased with time since introduction which could suggest that the lack of niche conservatism observed in many regions might be transient and potentially related to dispersal limitations. Overall, our results shed light on the context dependency of climatic niche changes when species are introduced to new regions, highlighting that the species and region-specific context should be accounted for when assessing the potential for niche changes. Significance StatementAs non-native species are introduced to new regions by humans, they may occupy the same climatic conditions as in their native ranges, leave parts of their native niche unfilled or expanding into previously unoccupied conditions. Knowing to which extent these niche dynamics generally occur is essential for understanding and managing biological invasions. Here, we evaluate regional differences in the climatic niche dynamics of non-native plants that were introduced to multiple regions across the world. We found marked variation across regions, influenced by factors such as the time that has passed since species were introduced, or biogeographic attributes of both the native and non-native ranges. These findings indicate that a lack of apparent niche changes is likely a temporary phenomenon.

ecology↗

bioRxiv2024

Uncertainty in blacklisting potential Pacific plant invaders using species distribution models

O_LIInvasive alien species pose a growing threat to global biodiversity, underscoring the need for evidence-based prevention strategies. Species distribution models (SDMs) are a widely used tool to estimate the potential distribution of alien species and to inform blacklists based on establishment risk. Yet, data limitations and modelling decisions can introduce uncertainty in these predictions. Here, we aim to quantify the contribution of four key sources of uncertainty in SDM-based blacklists: species occurrence data, environmental predictors, SDM algorithms, and thresholding methods for binarising predictions. C_LIO_LIFocusing on 82 of the most invasive plant species on the Hawaiian Islands, we built SDMs to quantify their establishment potential in the Pacific region. To assess uncertainty, we systematically varied four modelling components: species occurrence data (native vs. global), environmental predictors (climatic vs. edapho-climatic), four SDM algorithms, and three thresholding methods. From these models, we derived blacklists using three alternative blacklisting definitions and quantified the variance in establishment risk scores and resulting species rankings attributable to each source of uncertainty. C_LIO_LISDMs showed fair predictive performance overall. Among the sources of uncertainty, thresholding method had the strongest and most consistent influence on risk scores across all three blacklist definitions but resulted in only minor changes in blacklist rankings. In contrast, algorithm choice had the most pronounced effect on blacklist rankings, followed by smaller but important effects of species occurrence data and environmental predictors. Notably, models based only on native occurrences often underestimated establishment potential. C_LIO_LISDMs can provide valuable support for planning the preventive management of alien species. However, our findings show that blacklist outcomes are highly sensitive to modelling decisions. While ensemble modelling across multiple algorithms is a recommended best practice, our results reinforce the importance of incorporating global occurrence data when available and carefully evaluating the trade-offs of including additional environmental predictors. Given the strong influence of thresholding on risk scores, we emphasise the need for transparent, context-specific threshold selection. More broadly, explicitly assessing uncertainty in SDM outputs can improve the robustness of blacklists and support scientifically informed, precautionary decision-making, particularly in data-limited situations where pragmatic modelling choices must be taken. C_LI

ecology↗

bioRxiv2024

GLOBAL BIOGEOGRAPHY AND EVOLUTIONARY DRIVERS OF FERNS WITH CHLOROPHYLLOUS SPORES

About 14% of all fern species have chlorophyllous spores. Unlike their counterparts, chlorophyllous spores lack dormancy and have a shorter viability (i.e. only a few days in some species). Such spores should limit long-distance dispersal and be more susceptible to harsher climatic conditions raising questions about the evolutionary and ecological advantages of this trait. This study aims to assess the global biogeography of chlorophyllous-spored ferns evaluating their underlying environmental and evolutionary drivers. We studied the global distribution of 10,995 fern taxa across 556 geographical regions, and assessed the association of the proportional representation of 1387 chlorophyllous-spored species (CSS) with environmental variables using generalized linear mixed models. To assess the influence of phylogenetic relationships on the distribution of this trait across the phylogeny and across geographic regions, we calculated the phylogenetic signal and phylogenetic distances among species in different assemblages. Species richness of chlorophyllous-spored ferns peaked in the tropics while their proportional representation was highest in temperate and island floras. The proportion of CSS was positively influenced by water availability, but negatively by variables associated with temperature. Spore type was strongly conserved phylogenetically, and CSS assemblages were phylogenetically clustered towards higher latitudes. Our study provides strong evidence that chlorophyllous spores do not limit the geographical distribution of fern species. Their latitudinal distribution patterns can be explain both for environmental and phylogenetic drives.

ecology↗

bioRxiv2024

Unraveling the inverse latitudinal gradient: Environmental and geographic influences on plant diversity in South American coastal lomas

AbstractWater availability is widely recognized for its importance in shaping plant diversity gradients globally. However, even in arid ecosystems such as drylands, a remarkable diversity of plant species can persist. Yet, the environmental, topographic, and geographic drivers that have structured plant diversity gradients within drylands over evolutionary time, and their relative importance, are poorly understood, particularly for understudied ecosystems such as coastal lomas. Here, we evaluated the geographic distribution and drivers of taxonomic and phylogenetic diversity of plants across the coastal lomas of South America, which are isolated fog-fed vegetation oases within the Peruvian and Chilean coastal desert. We collated the most comprehensive data set to date of 72 coastal lomas, and used generalised linear models to assess latitudinal diversity gradients, and evaluated the relative importance of environmental, topographic, and geographic drivers of plant taxonomic and phylogenetic diversity. Notably, we found that both plant species richness and standardized mean nearest taxon distance (MNTD) decreased linearly towards the Equator, while standardized phylogenetic diversity (PD) and mean phylogenetic distance (MPD) exhibited non-linear relationships with latitude, peaking in the hyper-arid core of the Atacama Desert. Our results suggest that current climate, environmental heterogeneity, and geographical factors are the primary drivers of plant diversity. Plant species richness increased with cloud cover, slope, and area, and decreased with soil pH, while standardized PD increased with aridity, elevation, and the human footprint and decreased with distance to the coast. Standardized MNTD increased with elevation, and decreased with increasing area and temperature; standardized MPD increased with slope, and decreased with increasing aridity and distance to the coast. Our results suggest that environmental filtering is not the only macroecological process acting on plant diversity across coastal lomas, and has often been counterbalanced at different points in evolutionary time by factors associated with environmental heterogeneity, possibly reflecting the presence of climate refugia and diverse habitats that promote species coexistence. Also, our results offer empirical evidence supporting an inverse latitudinal gradient in plant diversity across coastal lomas, which emerges as a consequence of multiple factors that influence water availability, both directly and indirectly. Over evolutionary time, these factors may have significantly contributed to shaping the current structure and composition of coastal lomas.

ecology↗

bioRxiv2024

WITHIN AND ACROSS SPECIES VARIATION IN PLANT TRAITS IN RESPONSE TO LONG-TERM EXPERIMENTAL HERBIVORE EXCLUSION IN A SEMI-ARID SHRUBLAND

1) Herbivores shape multiple facets of biodiversity patterns and ecosystem processes, yet are increasingly threatened by habitat loss and climate change. Here, we use a long-term experiment to examine how excluding herbivores, a proxy for biodiversity loss, restructures dominant plant ecological strategies within and across species. 2) We measured twelve functional traits of four dominant annual plant species in the semi-arid shrublands of Chile. We evaluated changes in trait distributions within and across species and changes in the coordination between above- and below-ground strategies in response to vertebrate herbivore exclusion. 3) Our study reveals three dominant ecological strategies characterizing trait variation within and across species, with an increase in the coordination between above- and below-ground strategies in the presence of herbivores. Our results show that herbivores induce shifts in ecological strategies, leading to conservative resource use, increased herbivore tolerance, reduced collaboration with soil microorganisms, and greater intraspecific diversity, facilitating species coexistence. 4) We empirically demonstrate how herbivores shape ecological strategies within and across species, and demonstrate that the absence of herbivores alters the diversity of adaptation strategies of plants and leads to a decoupling of resource acquisition strategies above- and below-ground. These results advance understanding of annual plant responses to herbivore loss.

ecology↗

bioRxiv2023

Biogeographic context mediates multifaceted diversity-productivity relationships in island and mainland forests

AimGrowing evidence suggests that impacts of biodiversity loss on ecosystem functioning and natures contributions to people are usually negative, yet the magnitude and direction of these impacts can be variable across naturally-assembled ecosystems. A potential driver of variation in diversity-productivity relationships is the biogeographical context, which may alter these relationships via processes acting on the size and composition of the species pool like dispersal limitation, environmental filtering, speciation, and invasibility. However, the extent to which the relationships between biodiversity facets and forest productivity are shaped by the biogeographic context remains uncertain. Here, we examine the effects of taxonomic, phylogenetic, and functional tree diversity on aboveground productivity in climatically similar forests on islands and mainland. LocationContinental and insular Spain. Time period1997-2018. Major taxa studiedTrees. MethodsUsing plot data from a national forest inventory, we assessed the influence of taxonomic, phylogenetic, and functional diversity on aboveground productivity using linear models and structural equation models, while accounting for environmental conditions, non-native species, and the number of trees. ResultsWe find that drier environmental conditions lead to a decrease in productivity and in the number of trees in both island and mainland forests. In island forests, non-native species increased productivity directly and via their effects on phylogenetic diversity. Main conclusionsOur results suggest that multifaceted diversity, by capturing the diversity of evolutionary history, contributes to elucidating diversity-productivity relationships in island forests that could not be detected otherwise by taxonomic diversity alone. By filling empty niches in island forests, we find that non-native species are fundamentally altering ecosystem functioning on islands.

ecology↗

bioRxiv2023

Tree demographic strategies largely overlap across succession in Neotropical wet and dry forest communities

Secondary tropical forests play an increasingly important role for carbon budgets and biodiversity conservation. Understanding successional trajectories is therefore imperative for guiding forest restoration and climate change mitigation efforts. Forest succession is driven by the demographic strategies - combinations of growth, mortality and recruitment rates - of the tree species in the community. However, our understanding of demographic diversity in tropical tree species stems almost exclusively from old-growth forests. Here, we assembled demographic information from repeated forest inventories along chronosequences in two wet (Costa Rica, Panama) and two dry (Mexico) Neotropical forests to assess whether the range of demographic strategies present in a community shifts across succession. We calculated demographic rates for >500 tree species while controlling for canopy status to compare demographic diversity in early successional (0-30 years), late successional (30-120 years) and old-growth forests. We quantified demographic diversity using two-dimensional hypervolumes of pairs of demographic rates and assessed whether shifts in demographic strategies were caused by intra-specific changes in demographic rates across succession or by species turnover. We expected that demographic strategies would shift from faster life-histories (fast growth, high mortality, high recruitment) in early successional forests to slower life histories (slow growth, low mortality, low recruitment) in old-growth forests and that shifts would be stronger in wet than in dry forests due to more pronounced differences in environmental conditions between early successional and old-growth forests. We also expected that demographic diversity would increase with succession. We found that demographic strategies largely overlapped across successional stages and that early successional stages already covered the full spectrum of demographic strategies found in old-growth forests. An exception was a group of species characterized by exceptionally high mortality rates that was confined to early successional stages in the two wet forests. Demographic diversity did not increase with succession. Our results suggest that current understanding of demographic strategies of tropical tree species, which has been generated mostly from long-term forest monitoring plots in old-growth forests, is largely representative of demographic diversity in general, and that demographic diversity recovers quickly during succession.

ecology↗

bioRxiv2022

Latitude influences stability via stabilizing mechanisms in naturally-assembled forest ecosystems at different spatial grains

Ecosystem stability reveals how ecosystems respond to global change over time. Yet, the focus of past research on small spatial grains and extents overlooks scale dependence and how broad-scale environmental gradients shape stability. Here, we use forest inventory data covering a broad latitudinal gradient from the temperate to the tropical zone to examine cross-scale variation in stability of aboveground biomass and underlying stabilizing mechanisms. While stability did not shift systematically with latitude at either spatial grain, we found evidence that species asynchrony increased towards the tropics at the small spatial grain while species stability decreased at both spatial grains. Moreover, latitude stabilized forest communities via its effects on both stabilizing mechanisms, which compensated for the weak and destabilizing effects of species richness. Yet, the trade-off in the relative importance of species stability and species asynchrony for stability was not mediated by latitude, suggesting that context-dependent factors - to a greater extent than macroecological ones - underlie large-scale patterns of stability. Our results highlight the crucial role of species asynchrony and species stability in determining ecosystem stability across broad-scale environmental gradients, suggesting that conserving biodiversity alone may not be sufficient for stabilizing naturally-assembled forest ecosystems.

ecology↗

bioRxiv2022

Interacting abiotic and biotic drivers shape woody invasions across Hawaiian forests

The same features that generate native biodiversity patterns across and within oceanic islands over evolutionary time - climate, soil age, topography, and biotic interactions - also influence their vulnerability to biological invasions. Here, we identify the factors that shape the richness and abundance of alien woody species in forest communities across the Hawaiian archipelago, and assess the relative importance of abiotic, biotic, and anthropogenic factors and their interactions on the establishment and dominance of woody alien species. Using a database of 460 forest plots distributed across the six major Hawaiian islands, we examine variation in i) relative alien species richness and abundance as a function of abiotic and anthropogenic factors (e.g., temperature, aridity, soil age, and the human influence index) and ii) establishment and dominance of alien species as a function of the same abiotic and anthropogenic factors, as well as phylogenetic and trait distinctiveness. We found that relative alien species richness and abundance were higher in areas where temperature was high and aridity low. Gradients in temperature, aridity, soil age, and human influence also modulated the importance of biotic factors in determining establishment of alien species. In contrast, whether these alien species could become locally dominant was not strongly influenced by abiotic or biotic factors, or their interactions. Our results suggest that environmental filtering mediates the strength of biotic filtering in determining where woody aliens are able to colonize and establish on these oceanic islands, but not whether they become dominant. The context dependence of multi-species invasions highlights the complexity of developing management strategies to mitigate the biodiversity and ecosystem impacts of biological invasions.

ecology↗

bioRxiv2022

Assembly of functional diversity in an oceanic island flora

Oceanic island floras are well-known for their morphological peculiarities and exhibit striking examples of trait evolution1,2. These morphological shifts are commonly attributed to insularity and thought to be shaped by biogeographical processes and evolutionary histories of oceanic islands1,3. However, the mechanisms through which biogeography and evolution have shaped the distribution and diversity of plant functional traits remain unclear. Here, we describe the functional trait space of an oceanic island flora (Tenerife, Canary Islands, Spain) using extensive field and laboratory measurements, and relate it to global trade-offs in ecological strategies. We find that the island trait space is concentrated around a functional hotspot dominated by shrubs with a conservative life-history strategy. By dividing the island flora into species groups with distinct biogeographical distributions and diversification histories, our results reveal that long-distance dispersal, and the interplay between inter-island dispersal and archipelago-level speciation processes drive functional divergence and expand trait space. Conversely, speciation via cladogenesis has overall led to functional convergence, densely packing trait space around shrubbiness. Our approach combines ecology, biogeography and evolution and opens avenues for new trait-based insights into how dispersal and speciation shape the assembly of native island floras.

ecology↗

bioRxiv2021

Trash-basket epiphytes as secondary foundation species: a review of their distribution and effects on biodiversity and ecosystem functions

BackgroundSecondary foundation species (FS) are organisms that inhabit ecosystems structurally defined by a primary foundation species, providing additional structure to habitats and communities. Trash-basket epiphytes (TBE) are secondary FS that enhance arboreal soil accumulation, providing shelter to animals, and rooting sites for plants. While their importance may vary across biomes, TBE have been overlooked as drivers of biodiversity and ecosystem functions. Here, we discuss the prevalence of TBE across biomes, their effects on biodiversity and ecosystem functions, and future research directions. MethodsWe performed a systematic literature review of articles, books and theses and collated and synthesised information about the taxonomic distribution of TBE, their effects on ecosystem functions, and reports of plant-animal and plant-plant interactions. Then, we analysed the global distribution of TBE using a generalized linear model and summarised two studies to assess their effects on soil invertebrates. ResultsWe identified 120 publications describing 209 species of TBE. Most TBE belong to Araceae (43%), Polypodiaceae (23%), and Orchidaceae (14%) and occur in all tropical and southern temperate forests. TBE richness peaks in the South-American Pacific mangroves, Eastern Cordillera Real, and the Napo moist forests. TBE effects on ecosystem functions include arboreal soil accumulation, water retention and temperature regulation in the canopy, and nutrient leaching through stem-flow. TBE provide shelter to species in more than 97 animal families, including from invertebrates to mammals, while 72 vascular plants have been reported to root in arboreal soil of TBE. ConclusionsTBE are a compelling group of model organisms that can be used to study ecological processes such as facilitation cascades, niche construction, extended phenotypes, or the effects of secondary FS on biodiversity and ecosystem functioning. TBE should also be included in forest management plans to enhance the availability of microhabitats in the canopy supporting its associated flora and fauna.

ecology↗

bioRxiv2021

Non-structural carbohydrate concentrations in woody organs, but not leaves, of temperate and tropical tree angiosperms are independent of the "fast-slow" plant economic spectrum

Background and AimsCarbohydrate reserves play a vital role in plant survival during periods of negative carbon balance. Considering active storage of reserves, there is a trade-off between carbon allocation to growth and to reserves and defense. A resulting hypothesis is that allocation to reserves exhibits a coordinated variation with functional traits associated with the fast-slow plant economics spectrum. MethodsWe tested the relationship between non-structural carbohydrates (NSC) of tree organs and functional traits using 61 angiosperm tree species from temperate and tropical forests with phylogenetic hierarchical Bayesian models. Key ResultsOur results provide evidence that NSC concentrations in woody organs and plant functional traits are largely decoupled, meaning that species resilience is unrelated to their position on the fast-slow plant economics spectrum. In contrast, we found that variation between NSC concentrations in leaves and the fast-slow continuum was coordinated, as species with higher leaf NSC had traits values associated with resource conservative species such as lower SLA, lower Amax, and high wood density. We did not detect an influence of leaf habit on the variation of NSC concentrations in tree organs. ConclusionsEfforts to predict the response of ecosystems to global change will need to integrate a suite of plant traits, such as NSC concentrations in woody organs, that are independent of the fast-slow spectrum and that capture how species respond to a broad range of global change factors.

plant biology↗

bioRxiv2020

Biotic and abiotic drivers of soil microbial functions across tree diversity experiments

AimSoil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions may be linked to the tree species composition and diversity of forests, there has been no comprehensive study of how general potential relationships are and if these are context-dependent. A global network of tree diversity experiments (TreeDivNet) allows for a first examination of tree diversity-soil microbial function relationships across environmental gradients. LocationGlobal Major Taxa StudiedSoil microorganisms MethodsSoil samples collected from eleven tree diversity experiments in four biomes across four continents were used to measure soil basal respiration, microbial biomass, and carbon use efficiency using the substrate-induced respiration method. All samples were measured using the same analytical device in the same laboratory to prevent measurement bias. We used linear mixed-effects models to examine the effects of tree species diversity, environmental conditions, and their interactions on soil microbial functions. ResultsAcross biodiversity experiments, abiotic drivers, mainly soil water content, significantly increased soil microbial functions. Potential evapotranspiration (PET) increased, whereas soil C-to-N ratio (CN) decreased soil microbial functions under dry soil conditions, but high soil water content reduced the importance of other abiotic drivers. Tree species richness and phylogenetic diversity had overall similar, but weak and context-dependent (climate, soil abiotic variables) effects on soil microbial respiration. Positive tree diversity effects on soil microbial respiration were most pronounced at low PET, low soil CN, and high tree density. Soil microbial functions increased with the age of the experiment. Main conclusionsOur results point at the importance of soil water content for maintaining high levels of soil microbial functions and modulating effects of other environmental drivers. Moreover, overall tree diversity effects on soil microbial functions seem to be negligible in the short term (experiments were 1-18 years old). However, context-dependent tree diversity effects (climate, soil abiotic variables) have greater importance at high tree density, and significant effects of experimental age call for longer-term studies. Such systematic insights are key to better integrate soil carbon dynamics into the management of afforestation projects across environmental contexts, as todays reforestation efforts remain focused largely on aboveground carbon storage and are still dominated by less diverse forests stands of commercial species.

ecology↗

bioRxiv2019

A cross-scale assessment of productivity-diversity relationships

AimBiodiversity and ecosystem productivity vary across the globe and considerable effort has been made to describe their relationships. Biodiversity-ecosystem functioning research has traditionally focused on how experimentally controlled species richness affects net primary productivity (S[->]NPP) at small spatial grains. In contrast, the influence of productivity on richness (NPP[->]S) has been explored at many grains in naturally assembled communities. Mismatches in spatial scale between approaches have fostered debate about the strength and direction of biodiversity-productivity relationships. Here we examine the direction and strength of productivitys influence on diversity (NPP[->]S) and of diversitys influence on productivity (S[->]NPP), and how this varies across spatial grains. Locationcontiguous USA Time period1999 - 2015 Major taxa studiedwoody species (angiosperms and gymnosperms) MethodsUsing data from North American forests at grains from local (672 m2) to coarse spatial units (median area = 35,677 km2), we assess relationships between diversity and productivity using structural equation and random forest models, while accounting for variation in climate, environmental heterogeneity, management, and forest age. ResultsWe show that relationships between S and NPP strengthen with spatial grain. Within each grain, S[->]NPP and NPP[->]S have similar magnitudes, meaning that processes underlying S[->]NPP and NPP[->]S either operate simultaneously, or that one of them is real and the other is an artifact. At all spatial grains, S was one of the weakest predictors of forest productivity, which was largely driven by biomass, temperature, and forest management and age. Main conclusionsWe conclude that spatial grain mediates relationships between biodiversity and productivity in real-world ecosystems and that results supporting predictions from each approach (NPP[->]S and S[->]NPP) serve as an impetus for future studies testing underlying mechanisms. Productivity-diversity relationships emerge at multiple spatial grains, which should widen the focus of national and global policy and research to larger spatial grains.

ecology↗

bioRxiv2018

A framework for dissecting ecological mechanisms underlying the island species-area relationship

The relationship between an islands size and the number of species on that island--the island species-area relationship (ISAR)--is one of the most well-known patterns in biogeography, and forms the basis for understanding biodiversity loss in response to habitat loss and fragmentation. Nevertheless, there is contention about exactly how to estimate the ISAR, and the influence of the three primary ecological mechanisms--random sampling, disproportionate effects, and heterogeneity-- that drive it. Key to this contention is that estimates of the ISAR are often confounded by sampling and estimates of measures (i.e., island-level species richness) that are not diagnostic of potential mechanisms. Here, we advocate a sampling-explicit approach for disentangling the possible ecological mechanisms underlying the ISAR using parameters derived from individual-based rarefaction curves estimated across spatial scales. If the parameters derived from rarefaction curves at each spatial scale show no relationship with island area, we cannot reject the hypothesis that ISARs result only from random sampling. However, if the derived metrics change with island area, we can reject random sampling as the only operating mechanism, and infer that effects beyond sampling (i.e., disproportionate effects and/or heterogeneity) are also operating. Finally, if parameters indicative of within-island spatial variation in species composition (i.e., {beta}-diversity) increase with island area, we can conclude that intra-island compositional heterogeneity plays a role in driving the ISAR. We illustrate this approach using representative case studies, including oceanic islands, natural island-like patches, and habitat fragments from formerly continuous habitat, illustrating several combinations of underlying mechanisms. This approach will offer insight into the role of sampling and other processes that underpin the ISAR, providing a more complete understanding of how, and some indication of why, patterns of biodiversity respond to gradients in island area.

ecology↗