Biology subjects

Lewis, O. T.

Publications and source records attributed to Lewis, O. T..

At least 19 recordsLinked to original sources

bioRxiv2025

Butterfly host plant use driven by microclimate not nutritional quality

O_LIAbundance of insect herbivores often depends on host plant suitability for their specialised immature stages. Suitability can be strongly influenced by both microclimate and the nutritional quality of the plants themselves. Where soil nitrogen is high, host plants tend to have high nutritional quality, but vigorous growth of surrounding vegetation reduces microclimatic temperatures. Thus, thermophilous insects may face a choice between host plants with optimal microclimates and those with optimal nutritional quality. C_LIO_LIWe investigated how microclimate and nitrogen content influence oviposition choices by the declining Small Copper butterfly, Lycaena phlaeas, on its host plant, Rumex acetosa. We predicted that warmer plants would have lower nitrogen content, and that butterflies would choose cooler, high-nitrogen plants during warmer ambient conditions. C_LIO_LIAlthough warmer R. acetosa plants had lower nitrogen content, L. phlaeas consistently chose to lay eggs on plants in warm microclimates, implying a trade-off between temperature and the nutritional quality of host plants. C_LIO_LIPatches of bare ground created by Talpa europaea (European Mole) near R. acetosa plants increased microclimatic temperatures and decoupled the negative correlation between nutritional quality and thermal suitability. C_LIO_LIOur results have implications for the conservation of thermophilous insect herbivores, especially close to their range margins and in the context of climate change. Rather than maximising host plant abundance or nutritional quality, management that creates suitable microclimatic conditions is likely to be critical. Our findings also suggest that, while nitrogen pollution may increase host plant nutritional quality, its negative impacts on microclimate will likely further reduce breeding habitat for L. phlaeas and other insects in grassland habitats. C_LI

ecology↗

bioRxiv2025

Characterising a species-rich and understudied tropical insect fauna using DNA barcoding

BackgroundWest Africa has high biodiversity that is relatively understudied, especially for insects. Studies of West African arthropod diversity can therefore help address important questions regarding conservation, ecosystem services, and insecticide use and other species-control interventions in agriculture and disease management. We intensively sampled arthropods in Ghana using complementary trapping methods, generated DNA barcodes, and classified sequences by Barcode Index Numbers (BINs, a species proxy). Using this dataset, we investigate assemblage composition, temporal activity patterns, and the state of regional biodiversity sampling. ResultsSequencing DNA from 95,996 individuals captured using Malaise, yellow pan, pitfall, Heath and Centre for Disease Control (CDC) traps, we identified 10,120 unique BINs. The rate of species accumulation did not approach an asymptote for any taxonomic group or trap type, indicating high biodiversity. The different trap types sampled different subsets of the local community, with greatest similarity between yellow pan and pitfall traps. More insects and species (BINs) were trapped during the day than at night. Our dataset shared more BINs in the Barcode of Life Database with South Africa than with any other country, although this predominantly reflects the limited sampling and DNA sequencing campaigns in Africa. ConclusionsThis study more than doubles the published BINs for West Africa, offering insights into the biodiversity of an ecologically important but understudied taxon and region. Using multiple trap types allowed a more complete assessment of the local arthropod assemblage. The public release of these data will support and stimulate further taxonomic and ecological work in the region.

ecology↗

bioRxiv2025

Early outcomes of England's new biodiversity offset market

Nature markets are increasingly being operationalised as a tool for filling the biodiversity finance gap to achieve global biodiversity targets. One example is the off-site market underpinning the requirement for construction projects to achieve Biodiversity Net Gain (BNG) in England. Here, we quantify the outcomes of the market after 16 months of operation, collecting data from Englands offset register and planning portals. We evaluate the habitat diversity being delivered and how it aligns with environmental targets and existing efforts to achieve goals such as 30x30. Current habitat delivery is skewed toward a few habitat types, with other neutral grassland constituting 44% of planned habitat. There is very limited delivery of new wetland and woodland habitats, with most commitments being to improve the condition of existing habitats. Perhaps more importantly, only around 2% of the registered offset area has been sold. Our results demonstrate how the design of the statutory biodiversity metric used to measure BNG is shaping the market through incentives within the metric. The results also give insight into the demand for off-site BNG units in England and the role which government regulation plays in setting demand and therefore scaling the market.

ecology↗

bioRxiv2024

Metrics based on habitat area and condition are poor proxies for invertebrate biodiversity

There is increasing demand for standardised, easy-to-use metrics to assess progress towards achieving biodiversity targets and the effectiveness of ecological compensation schemes. Biodiversity metrics based on combining habitat area and habitat condition scores are proliferating rapidly, but there is limited evidence on how they relate to ecological outcomes. Here, we test the relationship between the statutory biodiversity metric used for Biodiversity Net Gain (BNG) in England -- and as the basis for new biodiversity credit systems around the world -- and invertebrate richness, abundance, and community composition. We find that the combined area-condition BNG metric does not capture the value of arable farmland and grassland sites for invertebrate biodiversity: invertebrate communities were highly variable across sites that had the same type and condition under the BNG metric. We found no reliable relationship between scores under the metric and either invertebrate abundance or species richness, with the risk of the metric undervaluing sites of high invertebrate value. Our results highlight the need to incorporate factors beyond habitat type and condition into site evaluations, and to complement metric use with species-based surveys.

ecology↗

bioRxiv2023

Opsin gene duplication in Lepidoptera: retrotransposition, sex linkage, and gene expression

Colour vision in insects is determined by signalling cascades, central to which are opsin proteins, resulting in sensitivity to light at different wavelengths. In certain insect groups, lineage specific evolution of opsin genes, in terms of copy number, shifts in expression patterns, and functional amino acid substitutions, has resulted in changes in colour vision with subsequent behavioural and niche adaptations. Lepidoptera are a fascinating model to address whether evolutionary change in opsin content and sequence evolution are associated with changes in vision phenotype. Until recently, the lack of high quality genome data representing broad sampling across the lepidopteran phylogeny has greatly limited our ability to accurately address this question. Here, we annotate opsin genes in 219 lepidopteran genomes representing 33 families, reconstruct their evolutionary history, and analyse shifts in selective pressures and expression between genes and species. We discover 44 duplication events in opsin genes across [~]300 million years of lepidopteran evolution. While many duplication events are species or family specific, we find retention of an ancient long-wavelength sensitive (LW) opsin duplication derived by retrotransposition within the speciose superfamily Noctuoidea (in the families Nolidae, Erebidae, and Noctuidae). This conserved LW retrogene shows life stage specific expression suggesting visual sensitivities or other sensory functions specific to the early larval stage. This study provides a comprehensive order-wide view of opsin evolution across Lepidoptera, showcasing high rates of opsin duplications and changes in expression patterns.

evolutionary biology↗

bioRxiv2022

Logging alters tropical forest structure, while conversion reduces biodiversity and functioning

The impacts of degradation and deforestation on tropical forests are poorly understood, particularly at landscape scales. We present an extensive ecosystem analysis of the impacts of logging and conversion of tropical forest to oil palm from a large-scale study in Borneo, synthesizing responses from 82 variables categorized into four ecological levels spanning a broad suite of ecosystem properties: 1) structure and environment, 2) species traits, 3) biodiversity, and 4) ecosystem functions. Responses were highly heterogeneous and often complex and non-linear. Variables that were directly impacted by the physical process of timber extraction, such as soil structure, were sensitive to even moderate amounts of logging, whereas measures of biodiversity and ecosystem functioning were generally resilient to logging but more affected by conversion to oil palm plantation. One-Sentence SummaryLogging tropical forest mostly impacts structure while biodiversity and functions are more vulnerable to habitat conversion.

ecology↗

bioRxiv2022

Altered litter and cellulose decomposition across an anthropogenic habitat modification gradient in Sulawesi, Indonesia

O_LIMany tropical regions in Southeast Asia have experienced extensive habitat modification, creating a mosaic of forested and agricultural land. The capacity of these human-modified tropical landscapes to support biodiversity and ecosystem functions and services is of considerable practical interest. C_LIO_LIDecomposition of plant material is a key process maintaining the nutrient cycle in both natural and agro-ecosystems, but few studies have documented the relative contributions of different guilds of decomposers, acting on different plant substrates, across different tropical land-uses. C_LIO_LIWe measured decomposition of leaf litter and cellulose across a gradient of anthropogenic habitat modification (forest, shrubland, and corn farmland) within Panua Nature Reserve, Sulawesi, Indonesia. The influence of fungi and the litter invertebrate community were investigated experimentally. C_LIO_LIDecomposition of both substrates was significantly lower in corn plantations than in forest sites. Partial exclusion of litter invertebrates, but not fungi, significantly reduced decomposition, but the feeding guild composition of the litter invertebrate community did not differ significantly across habitat types. C_LIO_LIOur results confirm that even small-scale agricultural areas adjacent to forest fragments can experience impaired ecosystem functions. These changes can be linked to reduced invertebrate activity, apparently independent of the functional structure of the litter invertebrate community. Effective management of human-modified landscapes will be needed to maintain nutrient cycling, even in areas where agroecosystems and tropical forests occur in close proximity. C_LI HighlightsO_LIHabitat modification alters litter and cellulose decomposition C_LIO_LISmall-scale agriculture near forest fragments can impair ecosystem functions. C_LIO_LIExclusion of litter invertebrates, but not fungi, significantly reduced decomposition. C_LIO_LIMaintaining nutrient cycling requires effective management of human-altered landscapes. C_LI

ecology↗

bioRxiv2022

Higher aboveground carbon stocks in mixed-species planted forests than monocultures - a meta-analysis

Natural forest is declining globally as the area of planted forest increases. Planted forests are often monocultures, despite results suggesting that higher species richness improves ecosystem functioning and stability. To test if this is generally the case, we performed a meta-analysis of available results. We assessed aboveground carbon stocks in mixed-species planted forests vs (a) the average of constituent species monocultures, (b) the best constituent species monoculture, and (c) commercial species monocultures. We investigated whether any advantage of mixtures over monocultures was positively related to species richness, as well as potential mechanisms driving differences in carbon stocks between mixtures and monocultures. The meta-analysis dataset included 79 comparisons from 21 sites. Carbon stocks in mixed planted forests were higher than the average of stocks in monocultures of their constituent species, containing on average 70% more carbon. Mixed planted forests also out-performed commercial monocultures, containing on average 77% more carbon. There was c.25% more carbon in mixed planted forests relative to the best performing monocultures, although this difference was not statistically significant. Overyielding was highest in four-species mixtures (richness range 2-6 species). More data providing better coverage of richness and age gradients (study sites aged 3.5-28 years) is needed to increase confidence in these results. None of the potential mechanisms we examined (nitrogen-fixer present vs absent; native vs non-native/mixed origin; tree diversity experiment vs forestry plantation) consistently explained variation in the diversity effects. This suggests that our findings are driven by a combination of small (statistically insignificant) effects from these sources or further unidentified mechanisms or some combination of the two. We conclude that increasing tree species richness in planted forests can increase carbon stocks while bringing other potential benefits associated with diversification. However, implementation will depend on the balance of these benefits relative to the operational challenges and costs of diversification.

ecology↗

bioRxiv2021

Selective logging shows no impact on the dietary breadth of the fawn leaf-nosed bat (Hipposideros cervinus)

Logging activities degrade forest habitats across large areas of the tropics, but the impacts on trophic interactions that underpin forest ecosystems are poorly understood. DNA metabarcoding provides an invaluable tool to investigate such interactions, allowing analysis at a far greater scale and resolution than has previously been possible. We analysed the diet of the insectivorous fawn leaf-nosed bat Hipposideros cervinus across a forest disturbance gradient in Borneo, using a dataset of ecological interactions from an unprecedented number of bat-derived faecal samples. Bats predominantly consumed insects from the orders Lepidoptera, Blattodea, Diptera and Coleoptera, and the taxonomic composition of their diet remained relatively consistent across sites regardless of logging disturbance. There was little difference in the richness of prey consumed in each logging treatment, indicating potential resilience of this species to habitat degradation. In fact, bats consumed a high richness of prey items, and intensive sampling is needed to reliably compare feeding ecology over multiple sites regardless of the bioinformatic procedures used.

ecology↗

bioRxiv2021

Microbiome structure of a wild Drosophila community along tropical elevational gradients and comparison to laboratory lines

Variation along environmental gradients in host-associated microbial communities is not well understood, compared to free-living microbial communities. Because elevational gradients may serve as natural proxies for climate change, understanding patterns along these gradients can inform our understanding of the threats hosts and their symbiotic microbes face in a warming world. In this study, we analysed bacterial microbiomes from pupae and adults of four Drosophila species native to Australian tropical rainforests. We sampled wild individuals at high and low elevation along two mountain gradients, to determine natural diversity patterns. Further, we sampled laboratory-reared individuals from isofemale lines established from the same localities, to see if any natural patterns are retained in the lab. In both environments, we controlled for diet to help elucidate other deterministic patterns of microbiome composition. We found small but significant differences in Drosophila bacterial community composition across elevation, with some notable taxonomic differences between different Drosophila species and sites. Further, we found that field-collected fly pupae had significantly richer microbiomes than laboratory-reared pupae. We also found similar microbiome composition in both types of provided diet, suggesting that the significant differences found among Drosophila microbiomes are the product of surrounding environments with different bacterial species pools, possibly bound to elevational differences in temperature. Our results suggest that comparative studies between lab and field specimens help reveal the true variability in microbiome communities that can exist within a single species. ImportanceBacteria form microbial communities inside most higher-level organisms, but we know little about how the microbiome varies along environmental gradients and between natural host populations and laboratory colonies. To explore such effects on insect-associated microbiomes, we studied gut microbiome in four Drosophila species over two mountain gradients in tropical Australia. We also compared these data to individuals kept in the laboratory to understand how different settings changed microbiome communities. We found that field sampled individuals had significantly higher microbiome diversity than those from the lab. In wild Drosophila populations, elevation explains a small but significant amount of the variation in their microbial communities. Our study highlights the importance of environmental bacterial sources for Drosophila microbiome composition across elevational gradients, and shows how comparative studies help reveal the true flexibility in microbiome communities that can exist within a species.

ecology↗

bioRxiv2021

Opposing effects of competitive exclusion determine invasion outcomes and structure ant assemblages

Understanding how species phenotypic differences affect competition is key to explaining community assembly and predicting biodiversity responses. Many studies overlook the variable effects that species trait differences can have on the direction of competitive exclusion, which reverses depending on the specific mechanism at play. We performed a comprehensive trait-based study of an ant invasion integrating morphological, dietary, physiological and behavioral analyses. We found that trait differences between invasive and resident species were not only associated with niche differences which promoted the coexistence of dissimilar species, but also competitive ability differences which acted in the opposite fashion. Furthermore, competition along separate trait axes led to complex and contrasting patterns in the invaded assemblages, where species were at once similar (clustered) in some traits but also dissimilar (overdispersed) in others. Our results reveal that different aspects of phenotype may distinctly modulate the effect of competition in structuring ecological communities and functional diversity.

ecology↗

bioRxiv2020

Experimental warming influences species abundances in a Drosophila host community through direct effects on species performance rather than altered competition and parasitism

Current global warming trends are expected to have direct effects on species through their sensitivity to temperature, as well as on their biotic interactions, with cascading indirect effects on species, communities, and entire ecosystems. To predict the community-level consequences of global change we need to understand the relative roles of both the direct and indirect effects of warming. We used a laboratory experiment to investigate how warming affects a tropical community of three species of Drosophila hosts interacting with two species of parasitoids over a single generation. Our experimental design allowed us to distinguish between the direct effects of temperature on host species performance, and indirect effects through altered biotic interactions (competition among hosts and parasitism by parasitoid wasps). Although experimental warming significantly decreased parasitism for all host-parasitoid pairs, the effects of parasitism and competition on host communities did not vary across temperatures. Instead, effects on host relative abundances were species-specific, with one host species dominating the community at warmer temperatures, independently of parasitism and competition treatments. Our results show that temperature shaped a Drosophila host community directly through differences in species thermal performance, and not via its influences on biotic interactions.

ecology↗

bioRxiv2020

The effect of natural enemies on the coexistence of competing species - an empirical test using Bayesian modern coexistence theory

O_LIThe role of natural enemies in promoting coexistence of competing species has generated substantial debate. Modern coexistence theory provides a detailed framework to investigate this topic, but there have been remarkably few empirical applications to the impact of natural enemies. C_LIO_LIWe tested experimentally the capacity for a generalist enemy to promote coexistence of competing insect species, and the extent to which any impact can be predicted by trade-offs between reproductive rate and susceptibility to natural enemies. C_LIO_LIWe used experimental mesocosms to conduct a fully-factorial pairwise competition experiment for six rainforest Drosophila species, with and without a generalist pupal parasitoid. We then parameterised models of competition and examined the coexistence of each pair of Drosophila species within the framework of modern coexistence theory. C_LIO_LIWe found idiosyncratic impacts of parasitism on pairwise coexistence, mediated through changes in fitness differences, not niche differences. There was no evidence of an overall reproductive rate - susceptibility trade-off. Pairwise reproductive rate - susceptibility relationships were not useful shortcuts for predicting the impact of parasitism on coexistence. C_LIO_LIOur results exemplify the value of modern coexistence theory in multi-trophic contexts and the importance of contextualising the impact of natural enemies. In the set of species investigated, competition was affected by the higher trophic level, but the overall impact on coexistence cannot be easily predicted just from knowledge of relative susceptibility. Methodologically, our Bayesian approach highlights issues with the separability of model parameters within modern coexistence theory and shows how using the full posterior parameter distribution improves inferences. This method should be widely applicable for understanding species coexistence in a range of systems. C_LI

ecology↗

bioRxiv2020

Molecular analyses reveal consistent food web structure with elevation in rainforest Drosophila - parasitoid communities

The analysis of interaction networks across spatial environmental gradients is a powerful approach to investigate the responses of communities to global change. Using a combination of DNA metabarcoding and traditional molecular methods we built bipartite Drosophila-parasitoid food webs from six Australian rainforest sites across gradients spanning 850 m in elevation and 5{degrees} Celsius in mean temperature. Our cost-effective hierarchical approach to network reconstruction separated the determination of host frequencies from the detection and quantification of interactions. The food webs comprised 5-9 host and 5-11 parasitoid species at each site, and showed a lower incidence of parasitism at high elevation. Despite considerable turnover in the relative abundance of host Drosophila species, and contrary to some previous results, we did not detect significant changes to fundamental metrics of network structure including nestedness and specialisation with elevation. Advances in community ecology depend on data from a combination of methodological approaches. It is therefore especially valuable to develop model study systems for sets of closely-interacting species that are diverse enough to be representative, yet still amenable to field and laboratory experiments.

ecology↗

bioRxiv2020

Altered structure and stability of bat-prey interaction networks in logged tropical forests revealed by metabarcoding

O_LIHabitat degradation is pervasive across the tropics and is particularly acute in Southeast Asia, with major implications for biodiversity. Much research has addressed the impact of degradation on species diversity; however, little is known about how ecological interactions are altered, including those that constitute important ecosystem functions such as pest consumption. C_LIO_LIWe examined how rainforest degradation alters trophic interaction networks linking insectivorous bats and their prey. We used DNA metabarcoding to study the diets of forest-dwelling insectivorous bat species, and compared bat-prey interaction networks between old growth forest and forest degraded by logging in Sabah, Borneo. C_LIO_LIWe predicted that rainforest degradation would cause measurable reductions in the numbers of prey consumed by individual bats, and that this degradation would yield networks in logged forest with lower functional complementarity, modularity and nestedness than those in old growth forest. C_LIO_LICompared to bats in old growth rainforest, bats in logged sites consumed a lower diversity of prey. Their interaction networks were less nested and had a more modular structure in which bat species had lower closeness centrality scores than in old growth forest. These network structures were associated with reduced network redundancy and thus increased vulnerability to perturbations in logged forests. C_LIO_LIOur results show how ecological interactions change between old growth and logged forests, with potentially negative implications for ecosystem function and network stability. We also highlight the potential importance of insectivorous bats in consuming invertebrate pests. C_LI Malay abstractO_LIDegradasi habitat merupakan suatu fenomena yang berleluasa dikawasan tropika, terutamanya di Asia Tenggara dengan implikasi yang besar ke atas biodiversiti. Banyak kajian telahpun meneliti impak degradasi habitat atas kepelbagaian spesis. Walau bagaimanapun, dari segi mana interaksi ekologi diubah suai kurang diselidik, termasuk interaksi yang membentuk fungsi ekosistem yang penting seperti pemakanan binatang perosak. C_LIO_LIKami telah memeriksa bagaimana degradasi hutan hujan tropika dapat mengubah suai interaksi antara tahap trofik yang menghubungkan kelawar yang memakan serangga dan mangsa mereka. Kami telah menggunakan "DNA metabarcoding" untuk mengenal pasti kandungan artropod dalam sampel najis kelawar and membandingkan jaringan interaksi kelawar dan mangsa mereka diantara hutan dara dan hutan yang telah dibalak di Sabah, Borneo. C_LIO_LIKami meramalkan bahawa degradasi hutan hujan akan menyebabkan kekurangan dalam bilangan nod mangsa yang dimakan oleh setiap individu kelawar yang dapat diukur. Degradasi ini pula boleh menghasilkan jaringan yang mempunyai fungsi saling melengkapi dan modulariti yang rendah, dan lebih berkelompok atau "mempunyai "nestedness" yang lebih tinggi di hutan yang dibalak berbanding hutan dara. C_LIO_LIKelawar di kawasan hutan yang dibalak memakan diversiti mangsa yang lebih rendah dengan kelawar di habitat hutan hujan dara. Jaringan-jaringan interaksi mereka kurang berkelompok dan mempunyai stuktur yang lebih modular dimana spesis kelawar mempunyai pemarkahan kerapatan berpusat yang lebih rendah daripada sepesis kelawar di hutan dara. Struktur-struktur jaringan ini berkait dengan lebihan jaringan atau "network redundancy" yang lebih rendah and ini membawa kepada kerentantan yang meningkat terhadap gangguan luar di hutan yang telah dibalak. C_LIO_LIKeputusan kami menunjukkan bagaimana interaksi ekologi berubah diantara hutan dara dan hutan yang dibalak, dengan potensi implikasi negatif untuk fungsi ekosistem dan kestabilan jaringan. Kami juga telah menunjukkan potensi kepentingan kelawar yang memakan serangga dalam fungsi mereka untuk makan perosak invertebrat. C_LI Data Accessibility StatementData are currently archived at the Centre for Ecology and Hydrology Environmental Information Data Centre (https://doi.org/10.5285/8b106445-d8e0-482c-b517-5a372a09dc91) and will be released from embargo following publication. Specific analysis scripts are available on GitHub with links given in the manuscript and will be archived on Zenodo prior to publication. Statement of authorshipSR, EC, DHB, MS and OTL conceived the project, DHB, VK and JB undertook field collections and laboratory work, DHB analysed the data with input from EC, and DHB wrote the manuscript with input from all authors.

ecology↗

bioRxiv2020

Trait-similarity and trait-hierarchy jointly determine co-occurrences of resident and invasive ant species

Interspecific competition, a dominant process structuring ecological communities, acts on species phenotypic differences. Species with similar traits should compete intensely (trait-similarity), while those with traits that confer competitive ability should outcompete others (trait-hierarchy). Either or both of these mechanisms may drive competitive exclusion within a community, but their relative importance and interacting effects are rarely studied. We show empirically that spatial associations (pairwise co-occurrences) between an invasive ant Solenopsis invicta and 28 other ant species across a relatively homogenous landscape are explained largely by an interaction of trait-similarity and trait-hierarchy in one morphological trait. We find that increasing trait-hierarchy leads to more negative associations; however these effects are counteracted when species are sufficiently dissimilar (by 37-95%) in their trait ranges. We also show that a model of species co-occurrences integrating trait-similarity and trait-hierarchy consolidates predictions of different theoretical assembly rules. This highlights the explanatory potential of the trait-based co-occurrence approach.

ecology↗

bioRxiv2019

The cryptic impacts of invasion: functional homogenization of tropical ant communities by invasive fire ants

Invasive insects represent major threats to ecosystems worldwide. Yet their effects on the functional dimension of biodiversity, measured as the diversity and distribution of traits, are overlooked. Such measures often determine the resilience of ecological communities and the ecosystem processes they modulate. The fire ant Solenopsis invicta is a highly problematic invasive species occurring on five continents. Its impacts on the taxonomic diversity of native ant communities have been studied but its impacts on their functional diversity are unknown. Comparing invaded and uninvaded plots in tropical grasslands of Hong Kong, we investigated how the presence of S. invicta affects the diversity and distribution of ant species and traits within and across communities, the functional identities of communities, and functionally unique species. We calculated the functional diversity of individual species, including the trait variation from intraspecific polymorphisms, and scaled up these values to calculate functional diversity at the community level. Invasion had only limited effects on species richness and functional richness, which were 13% and 8.5% lower in invaded communities respectively. In contrast, invasion had pronounced effects on taxonomic and functional composition due to turnover in species and trait values. Furthermore, invaded communities were functionally more homogeneous, displaying 23% less turnover and 56% more redundancy than uninvaded communities, as well as greater clustering and lower divergence in trait values. Invaded communities had fewer functionally-unique individuals and were characterized by ant species with narrower heads and bodies and shorter mandibles. Our results suggest that studies based only on taxonomic measures of diversity or indices describing trait variety risk underestimating the full ramifications of invasions. Investigating the diversity and distributions of traits at species, community and landscape levels can reveal the cryptic impacts of alien species which, despite causing little taxonomic change, may substantially modify the structure and functioning of ecological communities.

ecology↗

bioRxiv2018

Interacting effects of the abiotic and biotic environment on fitness of rainforest Drosophila

Competition within and between species can have large effects on fitness and may therefore drive local adaptation. However, these effects are rarely tested systematically, or considered when predicting species responses to environmental change. We used a field transplant experiment to test the effects of intra and interspecific competition on fitness across the ecological niches of two rainforest Drosophila species that replace each other along an elevation gradient. For the species with the broader elevational range, we also tested for adaptation to the local abiotic and biotic environment. In both species, intraspecific competition reduced productivity more than interspecific competition at the centre of its elevational range, while interspecific competition had a stronger effect at the range edge, where the competing species is more abundant. Local adaptation was detected in the centre of the range of the more widespread species, but only in the presence of intraspecific competition. This study is the first to demonstrate that fitness effects of inter-specific competition increase at ecological margins, while intra-specific competition has more pervasive effects at range centres. This is a key assumption of "tangled bank" models of community evolution and has important implications for predicting the resilience of ecological networks to global change.

evolutionary biology↗