Imperial College London

ProfessorRobertEwers

Faculty of Natural SciencesDepartment of Life Sciences (Silwood Park)

Professor of Ecology
 
 
 
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Contact

 

+44 (0)20 7594 2223r.ewers

 
 
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Location

 

1.4Centre for Population BiologySilwood Park

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Summary

 

Publications

Publication Type
Year
to

141 results found

Sethi S, Ewers R, Jones N, Signorelli A, Picinali L, Orme CDLet al., 2020, SAFE Acoustics: an open-source, real-time eco-acoustic monitoring network in the tropical rainforests of Borneo, Methods in Ecology and Evolution, Vol: 11, Pages: 1182-1185, ISSN: 2041-210X

1. Automated monitoring approaches offer an avenue to unlocking large‐scale insight into how ecosystems respond to human pressures. However, since data collection and data analyses are often treated independently, there are currently no open‐source examples of end‐to‐end, real‐time ecological monitoring networks. 2. Here, we present the complete implementation of an autonomous acoustic monitoring network deployed in the tropical rainforests of Borneo. Real‐time audio is uploaded remotely from the field, indexed by a central database, and delivered via an API to a public‐facing website.3. We provide the open‐source code and design of our monitoring devices, the central web2py database, and the ReactJS website. Furthermore, we demonstrate an extension of this infrastructure to deliver real‐time analyses of the eco‐acoustic data. 4. By detailing a fully functional, open source, and extensively tested design, our work will accelerate the rate at which fully autonomous monitoring networks mature from technological curiosities, and towards genuinely impactful tools in ecology.

Journal article

Sethi SS, Ewers RM, Jones NS, Sleutel J, Shabrani A, Zulkifli N, Picinali Let al., 2020, Soundscapes predict species occurrence in tropical forests, Publisher: Cold Spring Harbor Laboratory

Accurate occurrence data is necessary for the conservation of keystone or endangered species, but acquiring it is usually slow, laborious, and costly. Automated acoustic monitoring offers a scalable alternative to manual surveys, but identifying species vocalisations requires large manually annotated training datasets, and is not always possible (e.g., for silent species). A new, intermediate approach is needed that rapidly predicts species occurrence without requiring extensive labelled data.We investigated whether local soundscapes could be used to infer the presence of 32 avifaunal and seven herpetofaunal species across a tropical forest degradation gradient in Sabah, Malaysia. We developed a machine-learning based approach to characterise species indicative soundscapes, training our models on a coarsely labelled manual point-count dataset.Soundscapes successfully predicted the occurrence of 34 out of the 39 species across the two taxonomic groups, with area under the curve (AUC) metrics of up to 0.87 (Bold-striped Tit-babbler Macronus bornensis). The highest accuracies were achieved for common species with strong temporal occurrence patterns.Soundscapes were a better predictor of species occurrence than above-ground biomass – a metric often used to quantify habitat quality across forest degradation gradients.Synthesis and applications: Our results demonstrate that soundscapes can be used to efficiently predict the occurrence of a wide variety of species. This provides a new direction for audio data to deliver large-scale, accurate assessments of habitat suitability using cheap and easily obtained field datasets.

Working paper

Wilkinson CL, Chua KWJ, Fiala R, Liew JH, Kemp V, Hadi Fikri A, Ewers RM, Kratina P, Yeo DCJet al., 2020, Forest conversion to oil palm compresses food chain length in tropical streams., Ecology, ISSN: 0012-9658

In Southeast Asia, biodiversity-rich forests are being extensively logged and converted to oil palm monocultures. Although the impacts of these changes on biodiversity are largely well documented, we know little about how these large-scale impacts affect freshwater trophic ecology. We used stable isotope analyses (SIA) to determine the impacts of land-use changes on the relative contribution of allochthonous and autochthonous basal resources in 19 stream food webs. We also applied compound-specific SIA and bulk-SIA to determine the trophic position of fish apex predators and meso-predators (invertivores and omnivores). There was no difference in the contribution of autochthonous resources in either consumer group (70-82%) among streams with different land-use type. There was no change in trophic position for meso-predators, but trophic position decreased significantly for apex predators in oil palm plantation streams compared to forest streams. This change in maximum food chain length was due to turnover in identity of the apex predator among land-use types. Disruption of aquatic trophic ecology, through reduction in food chain length and shift in basal resources, may cause significant changes in biodiversity as well as ecosystem functions and services. Understanding this change can help develop more focused priorities for mediating the negative impacts of human activities on freshwater ecosystems.

Journal article

Wiederkehr F, Wilkinson CL, Zeng Y, Yeo DCJ, Ewers RM, O'Gorman EJet al., 2020, Urbanisation affects ecosystem functioning more than structure in tropical streams, Biological Conservation, Vol: 249, Pages: 1-19, ISSN: 0006-3207

Urbanisation poses a clear threat to tropical freshwater streams, yet fundamental knowledge gaps hinder our ability to effectively conserve stream biodiversity and preserve ecosystem functioning. Here, we studied the impact of urbanisation on structural and functional ecosystem responses in low-order streams in Singapore, a tropical city with a mosaic landscape of protected natural forests, managed buffer zones (between forest and open-country habitats), and built-up urban areas. We quantified an urbanisation gradient based on landscape, in-stream, and riparian conditions, and found an association between urbanisation and pollution-tolerant macroinvertebrates (e.g. freshwater snail and worm species) in litter bags. We also found greater macroinvertebrate abundance (mean individuals bag−1; forest: 30.3, buffer: 70.1, urban: 109.0) and richness (mean taxa bag−1; forest: 4.53, buffer: 4.75, urban: 7.50) in urban streams, but similar diversity across habitats. Higher levels of primary productivity (measured from algal accrual on ceramic tiles) and microbial decomposition (measured from litter-mass loss in mesh bags) at urban sites indicate rapid microbial activity at higher light, temperature, and nutrient levels. We found that urbanisation affected function 32% more than structure in the studied tropical streams, likely driven by greater algal growth in urban streams. These changes in ecological processes (i.e. ecosystem functioning) possibly lead to a loss of ecosystem services, which would negatively affect ecology, society, and economy. Our results point to possible management strategies (e.g. increasing vegetation density through buffer park creation) to reduce the impacts of urbanisation, restore vital ecosystem functions in tropical streams, and create habitat niches for native species.

Journal article

Muscarella R, Emilio T, Phillips OL, Lewis SL, Slik F, Baker WJ, Couvreur TLP, Eiserhardt WL, Svenning J, AffumBaffoe K, Aiba S, Almeida EC, Almeida SS, Oliveira EA, ÁlvarezDávila E, Alves LF, AlvezValles CM, Carvalho FA, Guarin FA, Andrade A, Aragão LEOC, Murakami AA, Arroyo L, Ashton PS, Corredor GAA, Baker TR, Camargo PB, Barlow J, Bastin J, Bengone NN, Berenguer E, Berry N, Blanc L, BöhningGaese K, Bonal D, Bongers F, Bradford M, Brambach F, Brearley FQ, Brewer SW, Camargo JLC, Campbell DG, Castilho CV, Castro W, Catchpole D, Cerón Martínez CE, Chen S, Chhang P, Cho P, Chutipong W, Clark C, Collins M, Comiskey JA, Medina MNC, Costa FRC, Culmsee H, DavidHiguita H, Davidar P, AguilaPasquel J, Derroire G, Di Fiore A, Van Do T, Doucet J, Dourdain A, Drake DR, Ensslin A, Erwin T, Ewango CEN, Ewers RM, Fauset S, Feldpausch TR, Ferreira J, Ferreira LV, Fischer M, Franklin J, Fredriksson GM, Gillespie TW, Gilpin M, Gonmadje C, Gunatilleke AUN, Hakeem KR, Hall JS, Hamer KC, Harris DJ, Harrison RD, Hector A, Hemp A, Herault B, Pizango CGH, Coronado ENH, Hubau W, Hussain MS, Ibrahim F, Imai N, Joly CA, Joseph S K A, Kartawinata K, Kassi J, Killeen TJ, Kitayama K, Klitgård BB, Kooyman R, Labrière N, Larney E, Laumonier Y, Laurance SG, Laurance WF, Lawes MJ, Levesley A, Lisingo J, Lovejoy T, Lovett JC, Lu X, Lykke AM, Magnusson WE, Mahayani NPD, Malhi Y, Mansor A, Peña JLM, MarimonJunior BH, Marshall AR, Melgaco K, Bautista CM, Mihindou V, Millet J, Milliken W, Mohandass D, Mendoza ALM, Mugerwa B, Nagamasu H, Nagy L, Seuaturien N, Nascimento MT, Neill DA, Neto LM, Nilus R, Vargas MPN, Nurtjahya E, Araújo RNO, Onrizal O, Palacios WA, PalaciosRamos S, Parren M, Paudel E, Morandi PS, Pennington RT, Pickavance G, Pipoly JJ, Pitman NCA, Poedjirahajoe E, Poorter L, Poulsen JR, Rama Chandra Prasad P, Prieto A, Puyravaud J, Qie L, Quesada CA, RamírezAngulo H, Razafimahaimodison JC, Reitsma JM, RequenaRojas EJ, Correa ZR, Rodriguez CR, Roopsind A, Rovero F, Rozak A, Lleraset al., 2020, The global abundance of tree palms, Global Ecology and Biogeography, Vol: 29, Pages: 1495-1514, ISSN: 1466-822X

AimPalms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change.LocationTropical and subtropical moist forests.Time periodCurrent.Major taxa studiedPalms (Arecaceae).MethodsWe assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure.ResultsOn average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work.ConclusionsTree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Futur

Journal article

Sethi S, Jones NS, Fulcher B, Picinali L, Clink DJ, Klinck H, Orme CDLO, Wrege P, Ewers Ret al., 2020, Characterising soundscapes across diverse ecosystems using a universal acoustic feature-set, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 17049-17055, ISSN: 0027-8424

Natural habitats are being impacted by human pressures at an alarming rate. Monitoring these ecosystem-level changes often requires labor-intensive surveys that are unable to detect rapid or unanticipated environmental changes. Here we have developed a generalizable, data-driven solution to this challenge using eco-acoustic data. We exploited a convolutional neural network to embed soundscapes from a variety of ecosystems into a common acoustic space. In both supervised and unsupervised modes, this allowed us to accurately quantify variation in habitat quality across space and in biodiversity through time. On the scale of seconds, we learned a typical soundscape model that allowed automatic identification of anomalous sounds in playback experiments, providing a potential route for real-time automated detection of irregular environmental behavior including illegal logging and hunting. Our highly generalizable approach, and the common set of features, will enable scientists to unlock previously hidden insights from acoustic data and offers promise as a backbone technology for global collaborative autonomous ecosystem monitoring efforts.

Journal article

Gregory N, 2020, Vectorial capacity across an environmental gradient

Disease transmitted by mosquitoes present some of the most pressing challenges facing human health today. Land-use change is a key driver of disease emergence, however the mechanisms linking environmental covariates of change, such as temperature, to the transmission potential of mosquitoes is poorly understood. Studies exploring these relationships have largely been correlative in nature, and thus have limited capacity to predict dynamics through space and time. Mechanistic approaches provide a valuable framework for understanding the processes underlying transmission, however they suffer from a dearth of field data on fundamental mosquito ecology. In both approaches, the environmental data used is typically coarse in scale and interpolated from weather stations located in open areas. In reality, local climatic conditions can vary considerably over fine spatial and temporal scales, particularly in dynamic working landscapes. Wild mosquitoes experience and respond to this highly dynamic environment, and failing to account for this variation may have significant implications for the accuracy of epidemiological models. This thesis uses an established epidemiological framework to explore the effects of tropical forest conversion to oil palm plantation on the potential for Ae. albopictus mosquitoes to transmit disease. Using field-derived microclimate data and published thermal responses of mosquito traits, I first examine how the scale of environmental data affects predictions of mosquito demography under land-use change. Next, I conduct field experiments to investigate whether microclimate heterogeneity across a land-use gradient drives variation in the rates of larval development. By pairing fine-scale microclimate data with temperature-dependent trait estimates, I find that forest conversion significantly increases the potential of Ae. albopictus to transmit disease. Together, these findings advance our understanding of Ae. albopictus ecology, and highlight the impo

Thesis dissertation

Gregory N, 2020, Vectorial capacity across an environmental gradient

Disease transmitted by mosquitoes present some of the most pressing challenges facing human health today. Land-use change is a key driver of disease emergence, however the mechanisms linking environmental covariates of change, such as temperature, to the transmission potential of mosquitoes is poorly understood. Studies exploring these relationships have largely been correlative in nature, and thus have limited capacity to predict dynamics through space and time. Mechanistic approaches provide a valuable framework for understanding the processes underlying transmission, however they suffer from a dearth of field data on fundamental mosquito ecology. In both approaches, the environmental data used is typically coarse in scale and interpolated from weather stations located in open areas. In reality, local climatic conditions can vary considerably over fine spatial and temporal scales, particularly in dynamic working landscapes. Wild mosquitoes experience and respond to this highly dynamic environment, and failing to account for this variation may have significant implications for the accuracy of epidemiological models. This thesis uses an established epidemiological framework to explore the effects of tropical forest conversion to oil palm plantation on the potential for Ae. albopictus mosquitoes to transmit disease. Using field-derived microclimate data and published thermal responses of mosquito traits, I first examine how the scale of environmental data affects predictions of mosquito demography under land-use change. Next, I conduct field experiments to investigate whether microclimate heterogeneity across a land-use gradient drives variation in the rates of larval development. By pairing fine-scale microclimate data with temperature-dependent trait estimates, I find that forest conversion significantly increases the potential of Ae. albopictus to transmit disease. Together, these findings advance our understanding of Ae. albopictus ecology, and highlight the impo

Thesis dissertation

Swinfield T, Both S, Riutta T, Bongalov B, Elias D, Majalap-Lee N, Ostle N, Svatek M, Kvasnica J, Milodowski D, Jucker T, Ewers RM, Zhang Y, Johnson D, Teh YA, Burslem DFRP, Malhi Y, Coomes Det al., 2019, Imaging spectroscopy reveals the effects of topography and logging on the leaf chemistry of tropical forest canopy trees, Global Change Biology, Vol: 26, Pages: 989-1002, ISSN: 1354-1013

Logging, pervasive across the lowland tropics, affects millions of hectares of forest, yet its influence on nutrient cycling remains poorly understood. One hypothesis is that logging influences phosphorus (P) cycling, because this scarce nutrient is removed in extracted timber and eroded soil, leading to shifts in ecosystem functioning and community composition. However, testing this is challenging because P varies within landscapes as a function of geology, topography and climate. Superimposed upon these trends are compositional changes in logged forests, with species with more acquisitive traits, characterized by higher foliar P concentrations, more dominant. It is difficult to resolve these patterns using traditional field approaches alone. Here, we use airborne light detection and ranging‐guided hyperspectral imagery to map foliar nutrient (i.e. P, nitrogen [N]) concentrations, calibrated using field measured traits, over 400 km2 of northeastern Borneo, including a landscape‐level disturbance gradient spanning old‐growth to repeatedly logged forests. The maps reveal that canopy foliar P and N concentrations decrease with elevation. These relationships were not identified using traditional field measurements of leaf and soil nutrients. After controlling for topography, canopy foliar nutrient concentrations were lower in logged forest than in old‐growth areas, reflecting decreased nutrient availability. However, foliar nutrient concentrations and specific leaf area were greatest in relatively short patches in logged areas, reflecting a shift in composition to pioneer species with acquisitive traits. N:P ratio increased in logged forest, suggesting reduced soil P availability through disturbance. Through the first landscape scale assessment of how functional leaf traits change in response to logging, we find that differences from old‐growth forest become more pronounced as logged forests increase in stature over time, suggesting exacerbated phosphorus limitation as

Journal article

Betts MG, Wolf C, Pfeifer M, Banks-Leite C, Arroyo-Rodríguez V, Ribeiro DB, Barlow J, Eigenbrod F, Faria D, Fletcher RJ, Hadley AS, Hawes JE, Holt RD, Klingbeil B, Kormann U, Lens L, Levi T, Medina-Rangel GF, Melles SL, Mezger D, Morante-Filho JC, Orme CDL, Peres CA, Phalan BT, Pidgeon A, Possingham H, Ripple WJ, Slade EM, Somarriba E, Tobias JA, Tylianakis JM, Urbina-Cardona JN, Valente JJ, Watling JI, Wells K, Wearn OR, Wood E, Young R, Ewers RMet al., 2019, Extinction filters mediate the global effects of habitat fragmentation on animals, Science, Vol: 366, Pages: 1236-1239, ISSN: 0036-8075

Habitat loss is the primary driver of biodiversity decline worldwide, but the effects of fragmentation (the spatial arrangement of remaining habitat) are debated. We tested the hypothesis that forest fragmentation sensitivity-affected by avoidance of habitat edges-should be driven by historical exposure to, and therefore species' evolutionary responses to disturbance. Using a database containing 73 datasets collected worldwide (encompassing 4489 animal species), we found that the proportion of fragmentation-sensitive species was nearly three times as high in regions with low rates of historical disturbance compared with regions with high rates of disturbance (i.e., fires, glaciation, hurricanes, and deforestation). These disturbances coincide with a latitudinal gradient in which sensitivity increases sixfold at low versus high latitudes. We conclude that conservation efforts to limit edges created by fragmentation will be most important in the world's tropical forests.

Journal article

Sethi S, Jones N, Fulcher B, Picinali L, Clink D, Klinck H, Orme D, Wrege P, Ewers Ret al., 2019, Combining machine learning and a universal acoustic feature-set yields efficient automated monitoring of ecosystems, Publisher: bioRxiv

Natural habitats are being impacted by human pressures at an alarming rate. Monitoring these ecosystem-level changes often requires labour-intensive surveys that are unable to detect rapid or unanticipated environmental changes. Here we developed a generalisable, data-driven solution to this challenge using eco-acoustic data. We exploited a convolutional neural network to embed ecosystem soundscapes from a wide variety of biomes into a common acoustic space. In both supervised and unsupervised modes, this allowed us to accurately quantify variation in habitat quality across space and in biodiversity through time. On the scale of seconds, we learned a typical soundscape model that allowed automatic identification of anomalous sounds in playback experiments, paving the way for real-time detection of irregular environmental behaviour including illegal activity. Our highly generalisable approach, and the common set of features, will enable scientists to unlock previously hidden insights from eco-acoustic data and offers promise as a backbone technology for global collaborative autonomous ecosystem monitoring efforts.

Working paper

Ewers RM, Barlow J, Banks-Leite C, Rahbek Cet al., 2019, Separate authorship categories to recognize data collectors and code developers, NATURE ECOLOGY & EVOLUTION, Vol: 3, Pages: 1610-1610, ISSN: 2397-334X

Journal article

Davison CW, Chapman PM, Wearn OR, Bernard H, Ewers RMet al., 2019, Shifts in the demographics and behavior of bearded pigs (Sus barbatus) across a land-use gradient, Biotropica, Vol: 51, Pages: 938-948, ISSN: 0006-3606

Beyond broad‐scale investigations of species diversity and abundance, there is little information on how land conversion in the tropics is affecting the behavior and demographics of surviving species. To fill these knowledge gaps, we explored the effects of land‐use change on the ecologically important and threatened bearded pig (Sus barbatus) over seven years in Borneo. Random placement of camera traps across a land‐use gradient of primary forest, logged forest, and oil palm plantations (32,542 trap nights) resulted in 2,303 independent capture events. Land‐use was associated with changes in the age structure and activity patterns of photographed individuals, alongside large changes in abundance shown previously. The proportion of adults recorded declined from 92% in primary forests to 76% in logged forests, and 67% in plantations, likely indicating increased fecundity in secondary forests. Activity level (capture rate) did not vary, but activity patterns changed markedly, from diurnal in primary forests, crepuscular in logged forests, to nocturnal in plantations. These changes corresponded with avoidance of diurnal human activity and may also protect bearded pigs from increased thermal stress in warmer degraded forests. The percentage of adult captures that were groups rather than individuals increased five‐fold from primary forests (4%) to logged forests (20%), possibly due to increased mating or in response to perceived threats from indirect human disturbance. We recommend further investigation of the demographic and behavioral effects of land‐use change on keystone species as altered population structure, activity patterns, and social behavior may have knock‐on effects for entire ecosystems.

Journal article

Sharp AC, Barclay MVL, Chung AYC, Ewers RMet al., 2019, Tropical logging and deforestation impacts multiple scales of weevil beta-diversity, Biological Conservation, Vol: 234, Pages: 172-179, ISSN: 0006-3207

Half of Borneo's forest has been logged and oil palm plantations have replaced millions of hectares of forest since the 1970's. While this extensive land-use change has been shown to reduce species richness across landscapes, there is limited current knowledge on how deforestation affects the spatial arrangement of ecological communities. Identifying responses of beta-diversity to land-use change may reveal processes which could mitigate total biodiversity loss. We sampled weevils (superfamily: Curculionoidea) at multiple spatial scales across a land-use gradient at the Stability of Altered Forest Ecosystems (SAFE) Project in Sabah, Malaysia, in 2011–2012. We caught 160 taxa of weevil and calculated the response of alpha-diversity (1-ha scale) and beta-diversity (10-, 100-, and 1000-ha scales) to disturbance. Alpha-diversity of weevils was greatest in unlogged forest but landscape-level beta-diversity (100- and 1000-ha scale) was maintained across logged and unlogged due to high rates of spatial turnover. Turnover at smallest spatial scales (10-ha) in unlogged forest was highest in rough, flat terrain but smooth, sloping terrain had highest turnover in logged forest. Logging of flat terrain at small spatial scales has potential to decrease beta-diversity at greater scales. Beta-diversity at landscape-level in oil palm plantation remained high but was propagated by abundance shifts of few species instead of spatial turnover of many species. High temporal beta-diversity in unlogged forest was evident through periodic fluxes in abundance of many weevil species. We conclude that unlogged forest is irreplaceable for high beetle biodiversity but increased spatial turnover in some terrains may help conserve beetle communities in heavily-degraded landscapes.

Journal article

Heon SP, Chapman PM, Bernard H, Ewers RMet al., 2019, Small logging roads do not restrict movements of forest rats in Bornean logged forests, Biotropica, Vol: 51, Pages: 412-420, ISSN: 0006-3606

Selective logging is driving the proliferation of roads throughout tropical rain forests, particularly narrow, unpaved logging roads. However, little is known about the extent of road edge effects or their influence on the movements of tropical understory animal species. Here, we used forest rats to address the following questions: (a) Does the occupancy of rats differ from road edges to forest interior within logged forests? (b) Do roads inhibit the movements of rats within these forests? We established trapping grids along a road edge‐to‐forest interior gradient at four roads and in three control sites within a logged forest in Sabah, Malaysia. To quantify the probability of road crossing, rats were captured, translocated across a road, and then recaptured on subsequent nights. We caught 216 individuals of eight species on 3,024 trap nights. Rat occupancy did not differ across the gradient from road edge to interior, and 48 percent of the 105 translocated individuals crossed the roads and were recaptured. This proportion was not significantly different from that of rats returning in control sites (38% of 60 individuals), suggesting that small roads were not barriers to rat movements within logged forests. Subadults were significantly more likely to return from translocation than adults in both road and control sites. Our results are encouraging for the ecology of small mammal communities in heavily logged forests, because small logging roads do not restrict the movements of rats and therefore are unlikely to create an edge effect or influence habitat selection.

Journal article

Qie L, Telford E, Massam MR, Tangki H, Nilus R, Hector A, Ewers Ret al., 2019, Drought cuts back regeneration in logged tropical forests, Environmental Research Letters, Vol: 14, ISSN: 1748-9326

Logged tropical forests represent a major opportunity for preserving biodiversity and sequestering carbon, playing a large role in meeting global forest restoration targets. Left alone, these ecosystems have been expected to undergo natural regeneration and succession towards old growth forests, but extreme drought events may challenge this process. While old growth forests possess a certain level of resilience, we lack understanding as to how logging may affect forest responses to drought. This study examines the drought–logging interaction in seedling dynamics within a landscape of logged and unlogged forests in Sabah Malaysia, based on 73 plots monitored before and after the 2015-16 El Niño drought. Drought increased seedling mortality in all forests, but the magnitude of this impact was modulated by logging intensity, with forests with lower canopy leaf area index (LAI) and above ground biomass (AGB) experiencing greater drought induced mortality. Moreover, community traits in more heavily logged forests shifted towards being more ruderal after drought, suggesting that the trajectory of forest succession had been reversed. These results indicate that with reoccurring strong droughts under a changing climate, logged forests that have had over half of their biomass removed may suffer permanently arrested succession. Targeted management interventions may therefore be necessary to lift the vulnerable forests above the biomass threshold.

Journal article

Wilkinson CL, Yeo DCJ, Tan HH, Hadi Fikri A, Ewers RMet al., 2019, Resilience of tropical, freshwater fish (Nematabramis everetti) populations to severe drought over a land-use gradient in Borneo, Environmental Research Letters, Vol: 14, ISSN: 1748-9326

Biodiversity-rich forests in tropical Southeast Asia are being extensively logged and converted to oil-palm monocultures. In addition, extreme climatic events such as droughts are becoming more common. Land-use change and extreme climatic events are thought to have synergistic impacts on aquatic biodiversity, but few studies have directly tested this. A severe El Niño drought in Southeast Asia in early 2016 caused 16 low-order hill streams across a land-use gradient encompassing primary forest, logged forest and oil palm plantations in Sabah, Malaysia, to dry up into series of disconnected pools. The resulting disturbance (specifically, increased water temperature and decreased dissolved oxygen concentration) tolerated by the fish during the drought exceeded any worst-case scenario for climate change-induced warming. We quantified the biomass, density and movement of the dominant freshwater fish species, Nematabramis everetti (Cyprinidae), in these streams across this land-use gradient before, during, and after the 2016 El Niño drought period. Density of N. everetti was significantly lower in logged forest streams than primary forest or oil palm streams, and the biomass of individuals captured was lower during drought than prior to the drought; however, there was no change in the biomass density of individuals during drought. The distance moved by N. everetti was significantly lower during and after the drought compared to before the drought. We detected a significant antagonistic interaction on biomass of captured fish, with the magnitude of the drought impact reduced according to land-use. Populations of N. everetti were surprisingly resilient to drought and seem most affected instead by land-use. Despite this resilience, it is important to monitor how this widespread and abundant species, which provides an important ecosystem service to local human communities, is affected by future land-use and climate change, as logging, deforestation and conversi

Journal article

Chapman P, Loveridge R, Rowcliffe JM, Carbone C, Bernard H, Davison CW, Ewers RMet al., 2019, Minimal spillover of native small mammals from Bornean tropical forests into adjacent oil palm plantations, Frontiers in Forests and Global Change, Vol: 2, ISSN: 2624-893X

In the face of rapid tropical agricultural expansion, preservation of tropical forest remnants is crucially important. Forest remnants often abut the edges of new or established plantations, so landscape-level conservation requires an understanding of the balance between ecosystem services and disservices provided by forest, including potential crop yield reductions caused by species such as rodents, an important pest group in oil palm plantations. However, very little is known about the scale of any spillover of native species which inhabit forest into adjacent agricultural areas. We examined the distribution and behaviour of small mammals across an edge separating logged tropical forest and oil palm plantations in Sabah, Malaysian Borneo, using a dual approach. We used a trapping grid to reveal patterns of species relative abundance across the forest-plantation edge, and tracked individuals of forest species using a spool-and-line. We uncovered little evidence that the native forest small mammal community crosses the edge and uses the plantation, although two invasive small mammal species were found across the whole edge gradient. Of 10 forest species detected, we found only the adaptable murid Maxomys whiteheadi in the plantation, where it persisted at low abundances across all sampling points, including in the plantation interior control site. This pattern is more consistent with persistence of M. whiteheadi throughout plantations than with spill-over from forest fragments. On the forest side, observed species richness of small mammals increased with distance into the interior, suggesting a negative edge effect may exist within forest remnants. Of 23 successfully tracked small mammals, only one M. whiteheadi crossed the forest-plantation edge, and overall, this species was significantly repelled from crossing into plantation habitat. Our results suggest that spillover of native small mammals contributes little to oil palm damage close to forest-plantation edges

Journal article

Gregory N, Ewers RM, Chung AYC, Cator LJet al., 2019, El Niño drought and tropical forest conversion synergistically determine mosquito development rate, Environmental Research Letters, Vol: 14, ISSN: 1748-9326

Extreme warming events can profoundly alter the transmission dynamics of mosquito–borne diseases by affecting the physiology of mosquito vectors. At local scales, temperatures are determined largely by vegetation structure and can be dramatically altered by drivers of land-use change (e.g. forest conversion). Disturbance activities can also hinder the buffering capacity of natural habitats, making them more susceptible to seasonal climate variation and extreme weather events (e.g. droughts). Using experiments spanning three years, we demonstrate that variation in microclimates due to forest conversion dramatically increases development rates in Aedes albopictus mosquitoes. However, this effect was mediated by an El Niño Southern Oscillation (ENSO) drought event. In normal years, mean temperatures did not differ between land-use types, however mosquitoes reared in oil palm plantations typically emerged 2-3 days faster than in logged forests. During an ENSO drought, mean temperatures did differ between land-use types, but surprisingly this did not result in different mosquito development rates. Driving this idiosyncratic response may be the differences in daily temperature fluctuations between the land-use types that either push mosquito larvae towards optimal development, or over the thermal optimum, thereby reducing fitness. This work highlights the importance of considering the synergistic effects of land-use and seasonal climate variations for predicting a key disease transmission-relevant mosquito trait.

Journal article

Woon JS, Boyle MJW, Ewers RM, Chung A, Eggleton Pet al., 2019, Termite environmental tolerances are more linked to desiccation than temperature in modified tropical forests, Insectes Sociaux, Vol: 66, Pages: 57-64, ISSN: 0020-1812

Termites are vital members of old-growth tropical forests, being perhaps the main decomposers of dead plant material at all stages of humification (decay). Termite abundance and diversity drop in selectively logged forest, and it has been hypothesised that this drop is due to a low tolerance to changing micro-climatic conditions. Specifically, the thermal adaptation hypothesis suggests that tropical species are operating at, or close to, their thermal optimum, and therefore, small temperature increases can have drastic effects on abundance, however, other climatic variables such as humidity might also cause termite abundance to drop. We tested termite tolerance to these two climatic variables (temperature and humidity). We found that termites had a higher CTmax than expected, and that three traits, feeding group, body sclerotisation, and nesting type, were significantly correlated with CTmax. We found that termite desiccation tolerance was low, however, and that all termite genera lost significantly more water in a desiccated environment than in a control. Body sclerotisation, the only trait that was tested, was surprisingly not significantly correlated with desiccation tolerance. Our results suggest that desiccation, rather than ambient temperature, may be the determining factor in dictating termite distributions in modified forests. Should climate change lead to reduced humidity within tropical rainforests, termite abundances and the rates of the functions they perform could be severely reduced.

Journal article

Galan-Acedo C, Arroyo-Rodriguez V, Andresen E, Verde Arregoitia L, Vega E, Peres CA, Ewers RMet al., 2019, The conservation value of human-modified landscapes for the world's primates, Nature Communications, Vol: 10, ISSN: 2041-1723

Land-use change pushes biodiversity into human-modified landscapes, where native ecosystems are surrounded by anthropic land covers (ALCs). Yet, the ability of species to use these emerging covers remains poorly understood. We quantified the use of ALCs by primates worldwide, and analyzed species’ attributes that predict such use. Most species use secondary forests and tree plantations, while only few use human settlements. ALCs are used for foraging by at least 86 species with an important conservation outcome: those that tolerate heavily modified ALCs are 26% more likely to have stable or increasing populations than the global average for all primates. There is no phylogenetic signal in ALCs use. Compared to all primates on Earth, species using ALCs are less often threatened with extinction, but more often diurnal, medium or large-bodied, not strictly arboreal, and habitat generalists. These findings provide valuable quantitative information for improving management practices for primate conservation worldwide.

Journal article

Qie L, Elsy A, Stumvoll A, Kwasnicka M, Peel A, Sullivan JA, Ettinger MS, Robertson AJ, Brisbane JK, Sawyer AL, Lui YN, Ow SN, Sebastianelli M, Majcher B, Duan M, Vigus H, Pounsin G, Nilus R, Ewers Ret al., 2019, Impending regeneration failure of the IUCN vulnerable Borneo ironwood (Eusideroxylon zwageri), Tropical Conservation Science, Vol: 12, Pages: 1-6, ISSN: 1940-0829

The regeneration of many climax species in tropical forest critically depends on adequate seed dispersal and seedling establishment. Here, we report the decreased abundance and increased spatial aggregation of younger trees of the Borneo ironwood (Eusideroxylon zwageri) in a protected forest in Sabah Malaysia. We observed a high level of seedling herbivory with strong density dependence, likely exacerbated by local aggregation and contributing to the progressively shrinking size distribution. We also note the largely undocumented selective herbivory by sambar deer on E. zwageri seedlings. This study highlights the combined impact of altered megafauna community on a tree population through interlinked ecological processes and the need for targeted conservation intervention for this iconic tropical tree species.

Journal article

Wearn OR, Carbone C, Rowcliffe JM, Pfeifer M, Bernard H, Ewers RMet al., 2019, Land-use change alters the mechanisms assembling rainforest mammal communities in Borneo, Journal of Animal Ecology, Vol: 88, Pages: 125-137, ISSN: 0021-8790

1.The assembly of species communities at local scales is thought to be driven by environmental filtering, species interactions, and spatial processes such as dispersal limitation. Little is known about how the relative balance of these drivers of community assembly changes along environmental gradients, especially man-made environmental gradients associated with land-use change. 2.Using concurrent camera- and live-trapping, we investigated the local-scale assembly of mammal communities along a gradient of land-use intensity (old-growth forest, logged forest and oil palm plantations) in Borneo. We hypothesised that increasing land-use intensity would lead to an increasing dominance of environmental control over spatial processes in community assembly. Additionally, we hypothesised that competitive interactions among species might reduce in concert with declines in α-diversity (previously documented) along the land-use gradient. 3.To test our first hypothesis, we partitioned community variance into the fractions explained by environmental and spatial variables. To test our second hypothesis, we used probabilistic models of expected species co-occurrence patterns, in particular focussing on the prevalence of spatial avoidance between species. Spatial avoidance might indicate competition, but might also be due to divergent habitat preferences. 4.We found patterns that are consistent with a shift in the fundamental mechanics governing local community assembly. In support of our first hypothesis, the importance of spatial processes (dispersal limitation and fine-scale patterns of home-ranging) appeared to decrease from low to high intensity land-uses, whilst environmental control increased in importance (in particular due to fine-scale habitat structure). Support for our second hypothesis was weak: whilst we found that the prevalence of spatial avoidance decreased along the land-use gradient, in particular between congeneric species pairs most likely to be in compet

Journal article

Sethi S, Ewers R, Jones N, Orme D, Picinali Let al., 2018, Robust, real-time and autonomous monitoring of ecosystems with an open, low-cost, networked device, Methods in Ecology and Evolution, Vol: 9, Pages: 2383-2387, ISSN: 2041-210X

1. Automated methods of monitoring ecosystems provide a cost-effective way to track changes in natural system's dynamics across temporal and spatial scales. However, methods of recording and storing data captured from the field still require significant manual effort. 2. Here we introduce an open source, inexpensive, fully autonomous ecosystem monitoring unit for capturing and remotely transmitting continuous data streams from field sites over long time-periods. We provide a modular software framework for deploying various sensors, together with implementations to demonstrate proof of concept for continuous audio monitoring and time-lapse photography. 3. We show how our system can outperform comparable technologies for fractions of the cost, provided a local mobile network link is available. The system is robust to unreliable network signals and has been shown to function in extreme environmental conditions, such as in the tropical rainforests of Sabah, Borneo. 4. We provide full details on how to assemble the hardware, and the open-source software. Paired with appropriate automated analysis techniques, this system could provide spatially dense, near real-time, continuous insights into ecosystem and biodiversity dynamics at a low cost.

Journal article

Nainar A, Tanaka N, Bidin K, Annammala KV, Ewers RM, Reynolds G, Walsh RPDet al., 2018, Hydrological dynamics of tropical streams on a gradient of land-use disturbance and recovery: A multi-catchment experiment, Journal of Hydrology, Vol: 566, Pages: 581-594, ISSN: 0022-1694

Although erosional impacts of rainforest logging are well established, changes in hydrological dynamics have been less explored especially in the post-logging recovery phase following repeat-logging cycles and mature phase of oil palm plantation cycles. This study addresses this gap by comparing hydrological characteristics of five catchments in a steep land area of Sabah, Malaysian Borneo on a gradient of disturbance and recovery – twice-logged forest, 22 years recovery (LF2); multiple-logged forest, 8 years recovery (LF3); mature oil palm, 20 years old (OP); and two primary forests (PF and VJR) as controls. Each catchment was instrumented with water depth (converted to discharge), conductivity, temperature, and turbidity sensors, and a raingauge connected to a solar-powered datalogger recording data at 5-minute intervals from November 2011 to August 2013. Data were analysed via the flow-duration curve (FDC) supplemented by the runoff coefficient (RR) and coefficient of variation in discharge (QVAR) for aggregated characteristics, as well as via a combination of the Dunn's test and multiple-regression at the storm event scale for focused hydrological dynamics. Results show that OP is characterised by a relatively low RR (0.357) but with high responsiveness during storm events and very low baseflow (38.4% of total discharge). Discharge in the LF3 (RR = 0.796) is always the highest while having an intermediate level of responsiveness. LF2 with longer-term recovery shown a reduction in terms of discharge (RR = 0.640). Being the benchmark, the undisturbed forest (PF) has the most buffered storm response with the highest baseflow (67.9% of total discharge). Stormflow and baseflow are anomalously high and low respectively in the near-primary VJR catchment, but this probably reflects the shallow soils and short-stature rainforest associated with its igneous and metamorphic lithology. From a management aspect, although hydrological recovery is more advanced in the 22

Journal article

Jucker T, Hardwick SR, Both S, Elias DMO, Ewers RM, Milodowski DT, Swinfield T, Coomes DAet al., 2018, Canopy structure and topography jointly constrain the microclimate of human-modified tropical landscapes, Global Change Biology, Vol: 24, Pages: 5243-5258, ISSN: 1354-1013

Local-scale microclimatic conditions in forest understoreys play a key role in shaping the composition, diversity and function of these ecosystems. Consequently, understanding what drives variation in forest microclimate is critical to forecasting ecosystem responses to global change, particularly in the tropics where many species already operate close to their thermal limits and rapid land-use transformation is profoundly altering local environments. Yet our ability to characterize forest microclimate at ecologically meaningful scales remains limited, as understorey conditions cannot be directly measured from outside the canopy. To address this challenge, we established a network of microclimate sensors across a land-use intensity gradient spanning from old-growth forests to oil-palm plantations in Borneo. We then combined these observations with high-resolution airborne laser scanning data to characterize how topography and canopy structure shape variation in microclimate both locally and across the landscape. In the processes, we generated high-resolution microclimate surfaces spanning over 350 km2 , which we used to explore the potential impacts of habitat degradation on forest regeneration under both current and future climate scenarios. We found that topography and vegetation structure were strong predictors of local microclimate, with elevation and terrain curvature primarily constraining daily mean temperatures and vapour pressure deficit (VPD), whereas canopy height had a clear dampening effect on microclimate extremes. This buffering effect was particularly pronounced on wind-exposed slopes but tended to saturate once canopy height exceeded 20 m-suggesting that despite intensive logging, secondary forests remain largely thermally buffered. Nonetheless, at a landscape-scale microclimate was highly heterogeneous, with maximum daily temperatures ranging between 24.2 and 37.2°C and VPD spanning two orders of magnitude. Based on this, we estimate that

Journal article

Banks-Leite C, Fletcher R, Didham R, Barlow J, Ewers RM, Rosindell JL, Holt RD, Gonzalez A, Pardini R, Damschen E, Melo FPL, Ries L, Prevedello JA, Tscharntke WF, Laurance WF, Lovejoy T, Haddad NMet al., 2018, Is habitat fragmentation good for biodiversity?, Biological Conservation, Vol: 226, Pages: 9-15, ISSN: 0006-3207

Habitat loss is a primary threat to biodiversity across the planet, yet contentious debate has ensued on the importance of habitat fragmentation ‘per se’ (i.e., altered spatial configuration of habitat for a given amount of habitat loss). Based on a review of landscape-scale investigations, Fahrig (2017; Ecological responses to habitat fragmentation per se. Annual Review of Ecology, Evolution, and Systematics 48:1-23) reports that biodiversity responses to habitat fragmentation ‘per se’ are more often positive rather than negative and concludes that the widespread belief in negative fragmentation effects is a ‘zombie idea’. We show that Fahrig's conclusions are drawn from a narrow and potentially biased subset of available evidence, which ignore much of the observational, experimental and theoretical evidence for negative effects of altered habitat configuration. We therefore argue that Fahrig's conclusions should be interpreted cautiously as they could be misconstrued by policy makers and managers, and we provide six arguments why they should not be applied in conservation decision-making. Reconciling the scientific disagreement, and informing conservation more effectively, will require research that goes beyond statistical and correlative approaches. This includes a more prudent use of data and conceptual models that appropriately partition direct vs indirect influences of habitat loss and altered spatial configuration, and more clearly discriminate the mechanisms underpinning any changes. Incorporating these issues will deliver greater mechanistic understanding and more predictive power to address the conservation issues arising from habitat loss and fragmentation.

Journal article

Wilkinson CL, Yeo DCJ, Tan HH, Fikri AH, Ewers RMet al., 2018, The availability of freshwater fish resources is maintained across a land-use gradient in Sabah, Borneo, AQUATIC CONSERVATION-MARINE AND FRESHWATER ECOSYSTEMS, Vol: 28, Pages: 1044-1054, ISSN: 1052-7613

Freshwater fish are a vital resource for local communities across the rural tropics. In Southeast Asia, biodiversity‐rich forests are being logged and converted to extensive oil palm monocultures. This clearly has impacts on associated freshwater ecosystems, but the impact on their biodiversity remains largely understudied and poorly understood, despite the important provisioning service that freshwater fishes provide for human well‐being. This study quantifies the biomass stocks of freshwater fish across a land‐use gradient encompassing primary forest, twice‐logged forest, and oil palm plantations in Sabah, Malaysia, in an area where local communities are known to harvest freshwater fish. Stream fish were sampled using a cast net, the dominant technique used by local fishermen, in 200‐m‐long transects in 16 streams over three sampling years (2011, 2013, and 2015). Unexpectedly, no impact from land use on total fish availability was detected. There were no significant differences in fish species richness or, most importantly, biomass per unit fishing effort across the land‐use gradient. There was variation in the responses of five known food species (Tor tambra, Hampala sabana, Barbodes sealei, Barbonymus balleroides, and Gastromyzon lepidogaster), and these small differences are attributed to variation in species habitat selection that co‐vary with land‐use change. Despite evidence to suggest that freshwater fish communities are resilient to land‐use change, they still face risks associated with disturbance, such as invasion by alien species; furthermore, several of the more stenotopic species were only present in primary forest catchments. Nonetheless, freshwater fish in small headwater streams appear to represent a sustainable food resource for villages established in human‐modified forests or in developed oil palm plantations.

Journal article

Chapman P, Wearn OR, Riutta T, Carbone C, Rowcliffe M, Bernard H, Ewers RMet al., 2018, Inter-annual dynamics and persistence of small mammal communities in a selectively logged tropical forest in Borneo, Biodiversity and Conservation, Vol: 27, Pages: 3155-3169, ISSN: 1572-9710

Understanding temporal change and long-term persistence of species and communities is vital if we are to accurately assess the relative values of human-modified habitats for biodiversity. Despite a large literature and emerging consensus demonstrating a high conservation value of selectively logged tropical rainforests, few studies have taken a long-term perspective. We resampled small mammals (≤1kg) in a heavily logged landscape in Sabah, Borneo between 2011 and 2016 to investigate temporal patterns of species-level changes in population density. We found that small mammal population density in heavily logged forest was highly variable among years, consistent with patterns previously observed in unlogged forest, and uncovered evidence suggesting that one species is potentially declining towards local extinction. Across nine species, population densities varied almost sevenfold during our six-year study period, highlighting the extremely dynamic nature of small mammal communities in this ecosystem. Strictly terrestrial murid species tended to exhibit strong temporal dynamics, whereas semi-arboreal foraging species such as treeshrews had more stable dynamics. We found no relationships between population density and fruit/seed mass, and therefore no evidence that our patterns represent responses to inter-annual mast fruiting of the dominant canopy dipterocarp trees. This may be due to the removal of most of the canopy during logging, and hence the dipterocarp seed resource, although it possibly also reflects spatiotemporal limitations of our data. Our results underline the importance of understanding long-term variability in animal communities before developing conservation and management recommendations for human-altered ecosystems.

Journal article

Ewers RM, 2018, Boring speakers talk for longer, NATURE, Vol: 561, Pages: 464-464, ISSN: 0028-0836

Journal article

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