The contribution of insects to global forest deadwood decomposition.

The amount of carbon stored in deadwood is equivalent to about 8 per cent of the global forest carbon stocks1. The decomposition of deadwood is largely governed by climate2-5 with decomposer groups-such as microorganisms and insects-contributing to variations in the decomposition rates2,6,7. At the global scale, the contribution of insects to the decomposition of deadwood and carbon release remains poorly understood7. Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effect-including the direct consumption by insects and indirect effects through interactions with microorganisms-insects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9 per cent and -0.1 per cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9 ± 3.2 petagram of carbon per year released from deadwood globally, with 93 per cent originating from tropical forests. Globally, the net effect of insects may account for 29 per cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle.

Climate-land-use interactions shape tropical mountain biodiversity and ecosystem functions.

Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem functioning are largely unknown1-3. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use4,5. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa's largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained-on average-54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions.

Nature 4.0: A networked sensor system for integrated biodiversity monitoring.

Ecosystem functions and services are severely threatened by unprecedented global loss in biodiversity. To counteract these trends, it is essential to develop systems to monitor changes in biodiversity for planning, evaluating, and implementing conservation and mitigation actions. However, the implementation of monitoring systems suffers from a trade-off between grain (i.e., the level of detail), extent (i.e., the number of study sites), and temporal repetition. Here, we present an applied and realized networked sensor system for integrated biodiversity monitoring in the Nature 4.0 project as a solution to these challenges, which considers plants and animals not only as targets of investigation, but also as parts of the modular sensor network by carrying sensors. Our networked sensor system consists of three main closely interlinked components with a modular structure: sensors, data transmission, and data storage, which are integrated into pipelines for automated biodiversity monitoring. We present our own real-world examples of applications, share our experiences in operating them, and provide our collected open data. Our flexible, low-cost, and open-source solutions can be applied for monitoring individual and multiple terrestrial plants and animals as well as their interactions. Ultimately, our system can also be applied to area-wide ecosystem mapping tasks, thereby providing an exemplary cost-efficient and powerful solution for biodiversity monitoring. Building upon our experiences in the Nature 4.0 project, we identified ten key challenges that need to be addressed to better understand and counteract the ongoing loss of biodiversity using networked sensor systems. To tackle these challenges, interdisciplinary collaboration, additional research, and practical solutions are necessary to enhance the capability and applicability of networked sensor systems for researchers and practitioners, ultimately further helping to ensure the sustainable management of ecosystems and the provision of ecosystem services.

Beetle diversity is higher in sunny forests due to higher microclimatic heterogeneity in deadwood.

Microclimate is a crucial driver of saproxylic beetle assemblages, with more species often found in sunny forests than in shady ones. Whether this pattern is caused by a higher detectability due to increased beetle activity under sunny conditions or a greater diversity of beetles emerging from sun-exposed deadwood remains unclear. This study examined whether sun exposure leads to higher microclimatic heterogeneity in deadwood and whether this drives beetle diversity in deadwood logs and at forest stand scale. Saproxylic beetles were sampled at the stand scale using flight-interception traps and at object scale using stem-emergence traps on deadwood logs at the same site. The variability in wood surface temperature was measured on single logs and between logs as a proxy for microclimatic heterogeneity in deadwood. Abundance in sunny forests was higher at the stand scale, and in shady forests at the object scale. The estimated number of species was higher in sunny forests at both scales and correlated positively with temperature variability on single logs and between logs at the stand scale and, albeit weakly, with temperature variability on single logs at the object scale. Gamma-diversity, and thus beta-diversity, across logs at the object scale was higher in sunny forests. These findings indicate that sun exposure promotes saproxylic beetle diversity due to higher microclimatic heterogeneity within and between deadwood logs. Our study therefore corroborates previous research demonstrating the importance of canopy cover and microclimate for forest biodiversity.

Global analysis reveals an environmentally driven latitudinal pattern in mushroom size across fungal species.

Although macroecology is a well-established field, much remains to be learned about the large-scale variation of fungal traits. We conducted a global analysis of mean fruit body size of 59 geographical regions worldwide, comprising 5340 fungal species exploring the response of fruit body size to latitude, resource availability and temperature. The results showed a hump-shaped relationship between mean fruit body size and distance to the equator. Areas with large fruit bodies were characterised by a high seasonality and an intermediate mean temperature. The responses of mutualistic species and saprotrophs were similar. These findings support the resource availability hypothesis, predicting large fruit bodies due to a seasonal resource surplus, and the thermoregulation hypothesis, according to which small fruit bodies offer a strategy to avoid heat and cold stress and therefore occur at temperature extremes. Fruit body size may thus be an adaptive trait driving the large-scale distribution of fungal species.

A research framework for projecting ecosystem change in highly diverse tropical mountain ecosystems.

Tropical mountain ecosystems are threatened by climate and land-use changes. Their diversity and complexity make projections how they respond to environmental changes challenging. A suitable way are trait-based approaches, by distinguishing between response traits that determine the resistance of species to environmental changes and effect traits that are relevant for species' interactions, biotic processes, and ecosystem functions. The combination of those approaches with land surface models (LSM) linking the functional community composition to ecosystem functions provides new ways to project the response of ecosystems to environmental changes. With the interdisciplinary project RESPECT, we propose a research framework that uses a trait-based response-effect-framework (REF) to quantify relationships between abiotic conditions, the diversity of functional traits in communities, and associated biotic processes, informing a biodiversity-LSM. We apply the framework to a megadiverse tropical mountain forest. We use a plot design along an elevation and a land-use gradient to collect data on abiotic drivers, functional traits, and biotic processes. We integrate these data to build the biodiversity-LSM and illustrate how to test the model. REF results show that aboveground biomass production is not directly related to changing climatic conditions, but indirectly through associated changes in functional traits. Herbivory is directly related to changing abiotic conditions. The biodiversity-LSM informed by local functional trait and soil data improved the simulation of biomass production substantially. We conclude that local data, also derived from previous projects (platform Ecuador), are key elements of the research framework. We specify essential datasets to apply this framework to other mountain ecosystems.

Tree Response to Herbivory Is Affected by Endogenous Rhythmic Growth and Attenuated by Cotreatment With a Mycorrhizal Fungus.

Herbivores and mycorrhizal fungi interactively influence growth, resource utilization, and plant defense responses. We studied these interactions in a tritrophic system comprising Quercus robur, the herbivore Lymantria dispar, and the ectomycorrhizal fungus Piloderma croceum under controlled laboratory conditions at the levels of gene expression and carbon and nitrogen (C/N) allocation. Taking advantage of the endogenous rhythmic growth displayed by oak, we thereby compared gene transcript abundances and resource shifts during shoot growth with those during the alternating root growth flushes. During root flush, herbivore feeding on oak leaves led to an increased expression of genes related to plant growth and enriched gene ontology terms related to cell wall, DNA replication, and defense. C/N-allocation analyses indicated an increased export of resources from aboveground plant parts to belowground. Accordingly, the expression of genes related to the transport of carbohydrates increased upon herbivore attack in leaves during the root flush stage. Inoculation with an ectomycorrhizal fungus attenuated these effects but, instead, caused an increased expression of genes related to the production of volatile organic compounds. We conclude that oak defense response against herbivory is strong in root flush at the transcriptomic level but this response is strongly inhibited by inoculation with ectomycorrhizal fungi and it is extremely weak at shoot flush.

Leaf traits mediate changes in invertebrate herbivory along broad environmental gradients on Mt. Kilimanjaro, Tanzania.

Temperature, primary productivity, plant functional traits, and herbivore abundances are considered key predictors of leaf herbivory but their direct and indirect contributions to community-level herbivory are not well understood along broad climatic gradients. Here, we determined elevational herbivory patterns and used a path analytical approach to disentangle the direct and indirect effects of climate, land use, net primary productivity (NPP), herbivore abundance, and plant functional traits on community-level invertebrate herbivory along the extensive elevational and land use gradients at Mt. Kilimanjaro, Tanzania. We recorded standing leaf herbivory caused by leaf chewers, leaf miners and leaf gallers on 55 study sites distributed in natural and anthropogenic habitats along a 3,060 m elevation gradient. We related the total community-level herbivory to climate (temperature and precipitation), NPP, plant functional traits (specific leaf area, leaf carbon-to-nitrogen [CN] ratio and leaf nitrogen-to-phosphorus [NP] ratio) and herbivore abundances. Leaf herbivory ranged from 5% to 11% along the elevation gradient. Total leaf herbivory showed unimodal pattern in natural habitats but a strongly contrasting bimodal pattern in anthropogenic habitats. We also detected some variation in the patterns of leaf herbivory along environmental gradients across feeding guilds with leaf chewers being responsible for a disproportionally large part of herbivory. Path analyses indicated that the variation in leaf herbivory was mainly driven by changes in leaf CN and NP ratios which were closely linked to changes in NPP in natural habitats. Similarly, patterns of leaf herbivory in anthropogenic habitats were best explained by variation in leaf CN ratios and a negative effect of land use. Our study elucidates the strong role of leaf nutrient stoichiometry and its linkages to climate and NPP for explaining the variation in leaf herbivory along broad climatic gradients. Furthermore, the study suggests that climatic changes and nutrient inputs in the course of land use change may alter leaf herbivory and consequently energy and nutrient fluxes in terrestrial habitats.

Beyond body size: consistent decrease of traits within orthopteran assemblages with elevation.

Morphological traits provide the interface between species and their environment. For example, body size affects the fitness of individuals in various ways. Yet especially for ectotherms, the applicability of general rules of interspecific clines of body size and even more so of other morphological traits is still under debate. Here we tested relationships between elevation (as a proxy for temperature) and productivity with four ecologically relevant morphological traits of orthopteran assemblages that are related to fecundity (body size), dispersal (wing length), jumping ability (hind femur length), and predator detection (eye size). We measured traits of 160 orthopteran species that were sampled along an extensive environmental gradient at Mt. Kilimanjaro (Tanzania), spanning elevations from 790 to 4,410 m above sea level (a.s.l.) with different levels of plant productivity. For traits other than body size, we calculated the residuals from a regression on body length to estimate the variation of traits irrespective of body size. Bayesian analyses revealed that mean body size of assemblages, as well as the means of relative wing length, hind femur length, and eye size, decreased with increasing elevation. Body size and relative eye size also decreased with increasing productivity. Both phylogenetic relationships, as well as species-specific adaptations, contributed to these patterns. Our results suggest that orthopteran assemblages had higher fecundity and better dispersal and escape abilities, as well as better predator detection at higher temperatures (low elevations) than at low temperatures (high elevations). Large body sizes might be advantageous in habitats with low productivity because of a reduced risk of starvation. Likewise, large eye size might be advantageous because of the ability to detect predators in habitats with low vegetation cover, where hiding possibilities are scarce. Our study highlights that changes in temperature and productivity not only lead to interspecific changes in body size but are also related to independent changes of other morphological traits that influence the ecological fit of organisms in their environment.

Habitat availability drives the distribution-abundance relationship in phytophagous true bugs in managed grasslands.

The nearly universal positive relationship between the distribution and abundance of species has been explained by several hypotheses but hitherto no consensus has been reached. Here, we used monitoring data of 105 phytophagous true bug species (Heteroptera) from 150 grassland sites over six years to test how (1) range position, (2) resource use, (3) resource availability, (4) density-dependent habitat selection, (5) metapopulation dynamics, and (6) habitat dispersal affect the distribution-abundance relationship. For the use in a confirmatory path analysis, we constructed causal pathways representing the hypothesized relationships and tested them separately and in a combined analysis. Our results show that the distribution-abundance relationship in phytophagous true bugs is driven by habitat-availability. An increasing local density of the host-plants increases the distribution of the species in the landscape, which in turn increases their local abundance. Thereby habitat availability facilitates dispersal success. We conclude that local abundance of herbivores facing habitat destruction could decline owing to a decrease in population dynamics between sites at the landscape scale. Finally, our results underline the potential of confirmatory path analysis for testing competing hypotheses.

An experimental test of the habitat-amount hypothesis for saproxylic beetles in a forested region.

The habitat-amount hypothesis challenges traditional concepts that explain species richness within habitats, such as the habitat-patch hypothesis, where species number is a function of patch size and patch isolation. It posits that effects of patch size and patch isolation are driven by effects of sample area, and thus that the number of species at a site is basically a function of the total habitat amount surrounding this site. We tested the habitat-amount hypothesis for saproxylic beetles and their habitat of dead wood by using an experiment comprising 190 plots with manipulated patch sizes situated in a forested region with a high variation in habitat amount (i.e., density of dead trees in the surrounding landscape). Although dead wood is a spatio-temporally dynamic habitat, saproxylic insects have life cycles shorter than the time needed for habitat turnover and they closely track their resource. Patch size was manipulated by adding various amounts of downed dead wood to the plots (~800 m³ in total); dead trees in the surrounding landscape (~240 km2 ) were identified using airborne laser scanning (light detection and ranging). Over 3 yr, 477 saproxylic species (101,416 individuals) were recorded. Considering 20-1,000 m radii around the patches, local landscapes were identified as having a radius of 40-120 m. Both patch size and habitat amount in the local landscapes independently affected species numbers without a significant interaction effect, hence refuting the island effect. Species accumulation curves relative to cumulative patch size were not consistent with either the habitat-patch hypothesis or the habitat-amount hypothesis: several small dead-wood patches held more species than a single large patch with an amount of dead wood equal to the sum of that of the small patches. Our results indicate that conservation of saproxylic beetles in forested regions should primarily focus on increasing the overall amount of dead wood without considering its spatial arrangement. This means dead wood should be added wherever possible including in local landscapes with low or high dead-wood amounts. For species that have disappeared from most forests owing to anthropogenic habitat degradation, this should, however, be complemented by specific conservation measures pursued within their extant distributional ranges.

Association of extinction risk of saproxylic beetles with ecological degradation of forests in Europe.

To reduce future loss of biodiversity and to allocate conservation funds effectively, the major drivers behind large-scale extinction processes must be identified. A promising approach is to link the red-list status of species and specific traits that connect species of functionally important taxa or guilds to resources they rely on. Such traits can be used to detect the influence of anthropogenic ecosystem changes and conservation efforts on species, which allows for practical recommendations for conservation. We modeled the German Red List categories as an ordinal index of extinction risk of 1025 saproxylic beetles with a proportional-odds linear mixed-effects model for ordered categorical responses. In this model, we estimated fixed effects for intrinsic traits characterizing species biology, required resources, and distribution with phylogenetically correlated random intercepts. The model also allowed predictions of extinction risk for species with no red-list category. Our model revealed a higher extinction risk for lowland and large species as well as for species that rely on wood of large diameter, broad-leaved trees, or open canopy. These results mirror well the ecological degradation of European forests over the last centuries caused by modern forestry, that is the conversion of natural broad-leaved forests to dense conifer-dominated forests and the loss of old growth and dead wood. Therefore, conservation activities aimed at saproxylic beetles in all types of forests in Central and Western Europe should focus on lowlands, and habitat management of forest stands should aim at increasing the amount of dead wood of large diameter, dead wood of broad-leaved trees, and dead wood in sunny areas.

Decomposition rate of carrion is dependent on composition not abundance of the assemblages of insect scavengers.

Environmental factors and biodiversity affect ecosystem processes. As environmental change modifies also biodiversity it is unclear whether direct effects of environmental factors on ecosystem processes are more important than indirect effects mediated by changes in biodiversity. High-quality resources like carrion occur as heterogeneous pulses of energy and nutrients. Consequently, the distribution of scavenging insects is related to resource availability. Therefore, carrion decomposition represents a suitable process from which to unravel direct effects of environmental change from indirect biodiversity-related effects on ecosystem processes. During three field seasons in 2010 we exposed traps baited with small-mammal carrion at 21 sites along a temperature gradient to explore the insect carrion fauna and decomposition rate in the Bohemian Forest, Germany. The abundance component of beetle and fly assemblages decreased with decreasing temperature. Independently, the composition component of both taxa changed with temperature and season. The change in the composition component of beetles depicted a loss of larger species at higher temperatures. Decomposition rate did not change directly along the temperature gradient but was directly influenced by season. The composition component of beetles, and to a small extent of flies, but not their abundance component, directly affected carrion decomposition. Consequently, lower decomposition rates at lower temperatures can be explained by the absence of larger beetle species. Thus, we predict that future environmental change will modify carrion fauna composition and thereby indirectly decomposition rate. Moreover, reorganizations of the insect carrion composition will directly translate into modified decomposition rates, with potential consequences for nutrient availability and carbon storage.

Effects of experimental canopy openness on wood-inhabiting fungal fruiting diversity across succession.

While the succession of terrestrial plant communities is well studied, less is known about succession on dead wood, especially how it is affected by environmental factors. While temperate forests face increasing canopy mortality, which causes considerable changes in microclimates, it remains unclear how canopy openness affects fungal succession. Here, we used a large real-world experiment to study the effect of closed and opened canopy on treatment-based alpha and beta fungal fruiting diversity. We found increasing diversity in early and decreasing diversity at later stages of succession under both canopies, with a stronger decrease under open canopies. However, the slopes of the diversity versus time relationships did not differ significantly between canopy treatments. The community dissimilarity remained mainly stable between canopies at ca. 25% of species exclusively associated with either canopy treatment. Species exclusive in either canopy treatment showed very low number of occupied objects compared to species occurring in both treatments. Our study showed that canopy loss subtly affected fungal fruiting succession on dead wood, suggesting that most species in the local species pool are specialized or can tolerate variable conditions. Our study indicates that the fruiting of the fungal community on dead wood is resilient against the predicted increase in canopy loss in temperate forests.

OakContigDF159.1, a reference library for studying differential gene expression in Quercus robur during controlled biotic interactions: use for quantitative transcriptomic profiling of oak roots in ectomycorrhizal symbiosis.

Oaks (Quercus spp.), which are major forest trees in the northern hemisphere, host many biotic interactions, but molecular investigation of these interactions is limited by fragmentary genome data. To date, only 75 oak expressed sequence tags (ESTs) have been characterized in ectomycorrhizal (EM) symbioses. We synthesized seven beneficial and detrimental biotic interactions between microorganisms and animals and a clone (DF159) of Quercus robur. Sixteen 454 and eight Illumina cDNA libraries from leaves and roots were prepared and merged to establish a reference for RNA-Seq transcriptomic analysis of oak EMs with Piloderma croceum. Using the Mimicking Intelligent Read Assembly (MIRA) and Trinity assembler, the OakContigDF159.1 hybrid assembly, containing 65 712 contigs with a mean length of 1003 bp, was constructed, giving broad coverage of metabolic pathways. This allowed us to identify 3018 oak contigs that were differentially expressed in EMs, with genes encoding proline-rich cell wall proteins and ethylene signalling-related transcription factors showing up-regulation while auxin and defence-related genes were down-regulated. In addition to the first report of remorin expression in EMs, the extensive coverage provided by the study permitted detection of differential regulation within large gene families (nitrogen, phosphorus and sugar transporters, aquaporins). This might indicate specific mechanisms of genome regulation in oak EMs compared with other trees.

Community genetics in the time of next-generation molecular technologies.

Understanding the interactions of co-occurring species within and across trophic levels provides key information needed for understanding the ecological and evolutionary processes that underlie biological diversity. As genetics has only recently been integrated into the study of community-level interactions, the time is right for a critical evaluation of potential new, gene-based approaches to studying communities. Next-generation molecular techniques, used in parallel with field-based observations and manipulative experiments across spatio-temporal gradients, are key to expanding our understanding of community-level processes. Here, we introduce a variety of '-omics' tools, with recent studies of plant-insect herbivores and of ectomycorrhizal systems providing detailed examples of how next-generation approaches can revolutionize our understanding of interspecific interactions. We suggest ways that novel technologies may convert community genetics from a field that relies on correlative inference to one that reveals causal mechanisms of genetic co-variation and adaptations within communities.

Current near-to-nature forest management effects on functional trait composition of saproxylic beetles in beech forests.

With the aim of wood production with negligible negative effects on biodiversity and ecosystem processes, a silvicultural practice of selective logging with natural regeneration has been implemented in European beech forests (Fagus sylvatica) during the last decades. Despite this near-to-nature strategy, species richness of various taxa is lower in these forests than in unmanaged forests. To develop guidelines to minimize the fundamental weaknesses in the current practice, we linked functional traits of saproxylic beetle species to ecosystem characteristics. We used continental-scale data from 8 European countries and regional-scale data from a large forest in southern Germany and forest-stand variables that represented a gradient of intensity of forest use to evaluate the effect of current near-to-nature management strategies on the functional diversity of saproxylic beetles. Forest-stand variables did not have a statistically significant effect on overall functional diversity, but they did significantly affect community mean and diversity of single functional traits. As the amount of dead wood increased the composition of assemblages shifted toward dominance of larger species and species preferring dead wood of large diameter and in advanced stages of decay. The mean amount of dead wood across plots in which most species occurred was from 20 to 60 m(3) /ha. Species occurring in plots with mean dead wood >60 m(3) /ha were consistently those inhabiting dead wood of large diameter and in advanced stages of decay. On the basis of our results, to make current wood-production practices in beech forests throughout Europe more conservation oriented (i.e., promoting biodiversity and ecosystem functioning), we recommend increasing the amount of dead wood to >20 m(3) /ha; not removing dead wood of large diameter (50 cm) and allowing more dead wood in advanced stages of decomposition to develop; and designating strict forest reserves, with their exceptionally high amounts of dead wood, that would serve as refuges for and sources of saproxylic habitat specialists.

Seasonal variation in dragonfly assemblage colouration suggests a link between thermal melanism and phenology.

Phenology, the seasonal timing of life events, is an essential component of diversity patterns. However, the mechanisms involved are complex and understudied. Body colour may be an important factor, because dark-bodied species absorb more solar radiation, which is predicted by the Thermal Melanism Hypothesis to enable them to thermoregulate successfully in cooler temperatures. Here we show that colour lightness of dragonfly assemblages varies in response to seasonal changes in solar radiation, with darker early- and late-season assemblages and lighter mid-season assemblages. This finding suggests a link between colour-based thermoregulation and insect phenology. We also show that the phenological pattern of dragonfly colour lightness advanced over the last decades. We suggest that changing seasonal temperature patterns due to global warming together with the static nature of solar radiation may drive dragonfly flight periods to suboptimal seasonal conditions. Our findings open a research avenue for a more mechanistic understanding of phenology and spatio-phenological impacts of climate warming on insects.

The global importance and interplay of colour-based protective and thermoregulatory functions in frogs.

Small-scale studies have shown that colour lightness variation can have important physiological implications in ectotherms, with darker species having greater heating rates, as well as protection against pathogens and photooxidative damage. Using data for 41% (3059) of all known frog and toad species (Anura) from across the world, we reveal ubiquitous and strong clines of decreasing colour lightness towards colder regions and regions with higher pathogen pressure and UVB radiation. The relative importance of pathogen resistance is higher in the tropics and that of thermoregulation is higher in temperate regions. The results suggest that these functions influence colour lightness evolution in anurans and filtered for more similarly coloured species under climatic extremes, while their concurrent importance resulted in high within-assemblage variation in productive regions. Our findings indicate three important functions of colour lightness in anurans - thermoregulation, pathogen and UVB protection - and broaden support for colour lightness-environment relationships in ectotherms.

Effects of leaf traits of tropical trees on the abundance and body mass of herbivorous arthropod communities.

In tropical forests, herbivorous arthropods remove between 7% up to 48% of leaf area, which has forced plants to evolve defense strategies. These strategies influence the palatability of leaves. Palatability, which reflects a syndrome of leaf traits, in turn influences both the abundance and the mean body mass not only of particular arthropod taxa but also of the total communities. In this study, we tested two hypotheses: (H1) The abundance of two important chewer guilds ('leaf chewers' and 'rostrum chewers'), dominant components of arthropod communities, is positively related to the palatability of host trees. (H2) Lower palatability leads to an increased mean body mass of chewers (Jarman-Bell principle). Arthropods were collected by fogging the canopies of 90 tropical trees representing 31 species in three plots at 1000 m and three at 2000 m a.s.l. Palatability was assessed by measuring several 'leaf traits' of each host tree and by conducting a feeding trial with the generalist herbivore Gryllus assimilis (Orthoptera, Gryllidae). Leaf traits provided partial support for H1, as abundance of leaf chewers but not of rostrum chewers was positively affected by the experimentally estimated palatability. There was no support for H2 as neither leaf traits nor experimentally estimated palatability affected the mean body mass of leaf chewers. The mean body mass of rostrum chewers was positively related to palatability. Thus, leaf traits and experimentally estimated palatability influenced the abundance and mean body mass of chewing arthropods on the community level. However, the data were not consistent with the Jarman-Bell principle. Overall, our results suggest that the palatability of leaves is not among the dominant factors influencing abundance and mean body mass of the community of chewing arthropod herbivores. If other factors, such as the microclimate, predation or further (a-)biotic interactions are more important has to be analyzed in refined studies.