Land-use Gradient Research Articles

A protocol for a longitudinal, observational cohort study of infection and exposure to zoonotic and vector-borne diseases across a land-use gradient in Sabah, Malaysian Borneo: a socio-ecological systems approach

Introduction. Landscape changes disrupt environmental, social and biological systems, altering pathogen spillover and transmission risks. This study aims to quantify the impact of specific land management practices on spillover and transmission rates of zoonotic and vector-borne diseases within Malaysian Borneo. This protocol describes a cohort study with integrated ecological sampling to assess how deforestation and agricultural practices impact pathogen flow from wildlife and vector populations to human infection and detection by health facilities. This will focus on malaria, dengue and emerging arboviruses (Chikungunya and Zika), vector-borne diseases with varying contributions of simian reservoirs within this setting. Methods. A prospective longitudinal observational cohort study will be established in communities residing or working within the vicinity of the Stability of Altered Forest Ecosystems (SAFE) Project, a landscape gradient within Malaysian Borneo encompassing different plantation and forest types. The primary outcome of this study will be transmission intensity of selected zoonotic and vector-borne diseases, as quantified by changes in pathogen-specific antibody levels. Exposure will be measured using paired population-based serological surveys conducted at the beginning and end of the two-year cohort study. Secondary outcomes will include the distribution and infection rates of Aedes and Anopheles mosquito vectors, human risk behaviours and clinical cases reported to health facilities. Longitudinal data on human behaviour, contact with wildlife and GPS tracking of mobility patterns will be collected throughout the study period. This will be integrated with entomological surveillance to monitor densities and pathogen infection rates of Aedes and Anopheles mosquitoes relative to land cover. Within surrounding health clinics, continuous health facility surveillance will be used to monitor reported infections and febrile illnesses. Models will be developed to assess spillover and transmission rates relative to specific land management practices and evaluate abilities of surveillance systems to capture these risks.

A protocol for a longitudinal, observational cohort study of infection and exposure to zoonotic and vector-borne diseases across a land-use gradient in Sabah, Malaysian Borneo: a socio-ecological systems approach.

Introduction. Landscape changes disrupt environmental, social and biological systems, altering pathogen spillover and transmission risks. This study aims to quantify the impact of specific land management practices on spillover and transmission rates of zoonotic and vector-borne diseases within Malaysian Borneo. This protocol describes a cohort study with integrated ecological sampling to assess how deforestation and agricultural practices impact pathogen flow from wildlife and vector populations to human infection and detection by health facilities. This will focus on malaria, dengue and emerging arboviruses (Chikungunya and Zika), vector-borne diseases with varying contributions of simian reservoirs within this setting. Methods. A prospective longitudinal observational cohort study will be established in communities residing or working within the vicinity of the Stability of Altered Forest Ecosystems (SAFE) Project, a landscape gradient within Malaysian Borneo encompassing different plantation and forest types. The primary outcome of this study will be transmission intensity of selected zoonotic and vector-borne diseases, as quantified by changes in pathogen-specific antibody levels. Exposure will be measured using paired population-based serological surveys conducted at the beginning and end of the two-year cohort study. Secondary outcomes will include the distribution and infection rates of Aedes and Anopheles mosquito vectors, human risk behaviours and clinical cases reported to health facilities. Longitudinal data on human behaviour, contact with wildlife and GPS tracking of mobility patterns will be collected throughout the study period. This will be integrated with entomological surveillance to monitor densities and pathogen infection rates of Aedes and Anopheles mosquitoes relative to land cover. Within surrounding health clinics, continuous health facility surveillance will be used to monitor reported infections and febrile illnesses. Models will be developed to assess spillover and transmission rates relative to specific land management practices and evaluate abilities of surveillance systems to capture these risks.

Modelling the Relative Abundance of Roe Deer (Capreolus capreolus L.) along a Climate and Land-Use Gradient.

Simple SummaryThe European roe deer is the most abundant ungulate in Europe. Information on the number of animals and the factors that influence this are essential for the effective management of this species. We developed a model to estimate the pellet group density using transect surveys of dung pellets in the federal state of Bavaria, south-eastern Germany. We used the pellet group density as a proxy for roe deer relative abundance. Our results show that climate, habitat type and wildlife management approach determine the relative number of roe deer. Influential factors differed between seasons and were expected due to changes in food and shelter availability. Although recognized as a woodland species, the majority of roe deer are expected in agriculture-dominated landscapes, which shows their ability to adapt to a wide range of landscape types, especially those with high food availability. Higher numbers were also predicted in regions with intermediate temperatures. Estimates of relative number do not give the actual absolute number of animals but are useful in determining which conditions will have more or fewer animals and can provide information for broad-scale management recommendations. Our results also provide insights into possible future changes in the distribution of relative numbers of roe deer due to climate and land-use change.European roe deer (Capreolus capreolus L.) are important given their economic, recreational and ecological value. However, uncontrolled roe deer numbers can result in negative impacts on forest regeneration and agricultural crops, disease transmission and occurrences of deer-vehicle collisions. Information on the abundance and distribution is needed for effective management. We combined distance sampling (DS) of roe deer dung pellet groups with multiple variables to develop a density surface model (DSM) in the federal state of Bavaria in south-eastern Germany. We used the estimates of pellet group density as a proxy for roe deer relative abundance. We extrapolated our best DSM, conducted a quantitative evaluation and contrasted relative abundance along climate and land-use gradients. Relative abundance of roe deer was influenced by a combination of habitat type, climate and wildlife management variables, which differed between seasons and which reflected changes in food and shelter availability. At the landscape scale, the highest abundance was observed in agriculture-dominated areas and the lowest in urban areas. Higher abundance was also observed in areas with intermediate temperatures compared to the warmest areas. Our results provide information on possible future changes in the distribution of relative abundance due to changes in climate and land-use.

Honey bee-collected pollen richness and protein content across an agricultural land-use gradient

Higher protein content and greater taxonomic richness of pollen have been noted as beneficial for bee health, but the relationship between pollen protein content and richness as well as how pollen protein content varies across landscape gradients remain understudied. We assessed correlations between pollen protein content and plant species richness and species composition in pollen collected from honey bee colonies across three states over 2 years. We selected sites along an agricultural-grassland gradient to investigate how pollen protein content and species composition varied with land-use. We observed a weak, negative relationship between pollen protein content and taxonomic richness, although we found no evidence of relationships between land-use and either pollen richness or species composition. Results suggest that the richness of pollen collected by honey bees can, albeit weakly, correlate with the pollen protein content in agroecosystems of the Upper Midwest, and that in some systems, land use may have minimal influence on the species collected by honey bees.

Response of aquatic insects to an environmental gradient in Amazonian streams

The increasing land use in the Amazon region has resulted in the widespread substitution of forest areas with pasture and bauxite mining. These land uses reduce the forest cover of streams and modify their characteristics, reducing the diversity of aquatic insect assemblages. In the present study, we aimed to identify the threshold of the assemblages of the larvae of insects of the orders Ephemeroptera, Plecoptera, and Trichoptera (collectively known as EPT), and adults of the order Odonata, along an environmental gradient of land use and land cover (LULC). We sampled 30 streams along an environmental gradient determined by the proportion of forest, pasture, and bauxite mining observed within the catchment of each stream. We identified 12 taxa associated with forest (nine positively and three negatively) and four negativelyassociated with pasture. However, no taxa were associated explicitly with the bauxite mining gradient. As forest is converted to pasture, the abundance and frequency of occurrence of the taxa sensitive to pasture are reduced, reflecting their environmental sensitivity and their potential as sentinels of preserved streams. The identification of the thresholds of the EPT and odonates taxa allowed us to determine which of these organisms are positively or negatively associated with the environmental gradient of LULC in Amazonian streams. We hope that the results of the present study can be applied in future biomonitoring programs, particularly for monitoring the response of aquatic insects to the degradation of streams.

How index selection, compression, and recording schedule impact the description of ecological soundscapes.

Acoustic indices derived from environmental soundscape recordings are being used to monitor ecosystem health and vocal animal biodiversity. Soundscape data can quickly become very expensive and difficult to manage, so data compression or temporal down‐sampling are sometimes employed to reduce data storage and transmission costs. These parameters vary widely between experiments, with the consequences of this variation remaining mostly unknown.We analyse field recordings from North‐Eastern Borneo across a gradient of historical land use. We quantify the impact of experimental parameters (MP3 compression, recording length and temporal subsetting) on soundscape descriptors (Analytical Indices and a convolutional neural net derived AudioSet Fingerprint). Both descriptor types were tested for their robustness to parameter alteration and their usability in a soundscape classification task.We find that compression and recording length both drive considerable variation in calculated index values. However, we find that the effects of this variation and temporal subsetting on the performance of classification models is minor: performance is much more strongly determined by acoustic index choice, with Audioset fingerprinting offering substantially greater (12%–16%) levels of classifier accuracy, precision and recall.We advise using the AudioSet Fingerprint in soundscape analysis, finding superior and consistent performance even on small pools of data. If data storage is a bottleneck to a study, we recommend Variable Bit Rate encoded compression (quality = 0) to reduce file size to 23% file size without affecting most Analytical Index values. The AudioSet Fingerprint can be compressed further to a Constant Bit Rate encoding of 64 kb/s (8% file size) without any detectable effect. These recommendations allow the efficient use of restricted data storage whilst permitting comparability of results between different studies.

Assembly of the amphibian microbiome is influenced by the effects of land-use change on environmental reservoirs.

A growing focus in microbial ecology is understanding how beneficial microbiome function is created and maintained through various assembly mechanisms. This study explores the role of both the environment and disease in regulating the composition of microbial species in the soil and on amphibian hosts. We compared the microbial communities of Plethodon cinereus salamanders along a land-use gradient in the New York metropolitan area and paired these with associated soil cores. Additionally, we characterized the diversity of bacterial and fungal symbionts that putatively inhibit the pathogenic fungus Batrachochytrium dendrobatidis. We predicted that variation in skin microbial community composition would correlate with changes seen in the soil which functions as the regional species pool. We found that salamanders and soil share many microbial taxa but that these two communities exhibit differences in the relative abundances of the bacterial phyla Acidobacteria, Actinobacteria, and Proteobacteria and the fungal phyla Ascomycota and genus Basidiobolus. Microbial community composition varies with changes in land-use associated factors creating site-specific compositions. By employing a quantitative, null-based assembly model, we identified that dispersal limitation, variable selection, and drift guide assembly of microbes onto their skin, creating high dissimilarity between individuals with likely consequences in disease preventative function.

Agricultural land use changes stream dissolved organic matter via altering soil inputs to streams

Agricultural land use leads to significant changes in both the quality (e.g., sources and compositions) and quantity of dissolved organic matter (DOM) exported from terrestrial to aquatic ecosystems. However, the effect of agricultural activities often interacts with those of hydroclimatic drivers, making it difficult to delineate agriculture-induced changes and identify associated mechanisms. Using partial least square path modeling (PLS-PM), we examined the relative importance of agricultural land use, stream order, precipitation, and temperature in mediating allochthonous versus autochthonous sources and pathways that influenced stream DOM quality and quantity. We analyzed stream water DOM from 15 small streams draining watersheds across a gradient of agricultural land use in Southeast USA for about one year. For DOM quantity, agricultural land use increased the export of DOC and various DOM pools (terrestrial humic, microbial humic, and protein-like DOM) from land to streams, and for DOM quality, agricultural streams showed greater proportions of microbial humic compounds than forested streams. The PLS-PM model for DOM quantity accounted for 75.5% of total variance and identified that agricultural land use increased stream water DOM quantity primarily through increasing allochthonous inputs, which can be attributed to shallower flow paths in agricultural watersheds that enabled the export of organic materials from the upper, organic-rich soil horizon. PLS-PM models for DOM quality only explained ~13% of the total variance, highlighting the complex dynamics between environmental drivers and stream water DOM. Relative to commonly used multivariate statistic modeling (e.g., redundancy analysis (RDA)), PLS-PM models offer the advantages of identifying the primary pathway by which agricultural lands alter freshwater DOM and quantifying the relative importance of interactive effects of agriculture and hydroclimatic drivers. Therefore, structural equation modeling is a powerful tool that should be more widely adopted to distinguish among multiple drivers and mechanisms regulating freshwater biogeochemistry.

Plant-plant co-occurrences under a complex land-use gradient in a temperate forest.

Land-use generates multiple stress factors, and we need to understand their effects on plant-plant interactions to predict the consequences of land-use intensification. The stress-gradient hypothesis predicts that the relative strength of positive and negative interactions changes inversely under increasing environmental stress. However, the outcome of interactions also depends on stress factor's complexity, the scale of analysis, and the role of functional traits in structuring the community. We evaluated plant-plant co-occurrences in a temperate forest, aiming to identify changes in pairwise and network metrics under increasing silvopastoral use intensity. Proportionally, positive co-occurrences were more frequent under high than low use, while negative co-occurrences were more frequent under low than high. Networks of negative co-occurrences showed higher centralization under low use, while networks of positive co-occurrences showed lower modularity and higher centralization under high use. We found a partial relationship between co-occurrences and key functional traits expected to mediate facilitation and competition processes. Our results shows that the stress-gradient hypothesis predicts changes in spatial co-occurrences even when two stress factors interact in a complex way. Networks of negative co-occurrences showed a hierarchical effect of dominant species under low use intensity. But positive co-occurrence network structure partially presented the characteristics expected if the facilitation was an important mechanism characterizing the community under high disturbance intensity. The partial relationship between functional traits and co-occurrences may indicate that other factors besides biotic interactions may be structuring the observed negative spatial associations in temperate Patagonian forests.

Land use and elevation interact to shape bird functional and phylogenetic diversity and structure: Implications for designing optimal agriculture landscapes

Abstract The conversion of rainforests into agriculture resulted in massive changes in species diversity and community structure. Although the conservation of the remaining rainforests is of utmost importance, identifying and creating a biodiversity‐friendly agriculture landscape is vital for preserving biodiversity and their functions. Biodiversity studies in agriculture have often been conducted at low elevations. In this study, we compared the functional diversity (FD), phylogenetic diversity (PD) and community structure of birds along an interacting gradient of land use (protected rainforest, reserve buffer and agriculture) and elevation (low, middle and high) in Sri Lanka. Then, we measured the compositional change by identifying how ecological traits (dietary guild, vertical strata, body mass and dispersal ability) and conservation characteristics (forest dependence and threatened status) responded to land use types. Elevation and land use interacted with each other to shape bird FD. Depending on the elevation, FD in agriculture was either higher or similar to forest. However, PD was similar across all elevation and land use types. Bird community structure in forest was functionally and phylogenetically clustered in comparison to agriculture. Insectivorous birds declined from forest to agriculture, and so did understorey and middle‐storey birds. But frugivorous and canopy birds did not change across land use types, while nectarivores, granivores and carnivores proliferated in agriculture. Forests were dominated by birds with low dispersal abilities, but birds in agriculture had more evenly distributed dispersal abilities. About half of all the individuals in agriculture were composed of forest species, several of which were threatened. Synthesis and applications. Most farmers in Sri Lanka practice agriculture on small farms (c. 2 ha) and rely on services (e.g. pest control and pollination) provided by biodiversity for their livelihoods. Our results underline the important role of these heterogeneous agriculture landscapes in maintaining high functional diversity (FD) and harbouring several threatened species. While FD in agriculture was comparatively high, conservation decisions based on land use alone cannot be reliable, because land use effects were elevation dependent. Thus, priority setting exercises aimed at designing optimal agriculture landscapes should consider landscape features, in combination with elevation, to benefit both people and wildlife outside protected areas.

Effects of Different Land Use Types on Active Autotrophic Ammonia and Nitrite Oxidizers in Cinnamon Soils.

Land use types with different disturbance gradients show many variations in soil properties, but the effects of different land use types on soil nitrifying communities and their ecological implications remain poorly understood. Using 13CO2-DNA-based stable isotope probing (DNA-SIP), we examined the relative importance and active community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in soils under three land use types, forest, cropland, and greenhouse vegetable soil, representing three interference gradients. Soil net nitrification rate was in the order forest soil > cropland soil > greenhouse vegetable soil. DNA-SIP showed that active AOA outcompeted AOB in the forest soil, whereas AOB outperformed AOA in the cropland and greenhouse vegetable soils. Cropland soil was richer in NOB than in AOA and AOB. Phylogenetic analysis revealed that ammonia oxidation in the forest soil was predominantly catalyzed by the AOA Nitrosocosmicus franklandus cluster within the group 1.1b lineage. The 13C-labeled AOB were overwhelmingly dominated by Nitrosospira cluster 3 in the cropland soil. The active AOB Nitrosococcus watsonii lineage was observed in the greenhouse vegetable soil, and it played an important role in nitrification. Active NOB communities were closely affiliated with Nitrospira in the forest and cropland soils, and with Nitrolancea and Nitrococcus in the greenhouse vegetable soil. Canonical correlation analysis showed that soil pH and organic matter content significantly affected the active nitrifier community composition. These results suggest that land use types with different disturbance gradients alter the distribution of active nitrifier communities by affecting soil physicochemical properties. IMPORTANCE Nitrification plays an important role in the soil N cycle, and land use management has a profound effect on soil nitrifiers. It is unclear how different gradients of land use affect active ammonia-oxidizing archaea and bacteria and nitrite-oxidizing bacteria. Our research is significant because we determined the response of nitrifiers to human disturbance, which will greatly improve our understanding of the niche of nitrifiers and the differences in their physiology.

An Online Survey of Community Perceptions of Mammalian Mesocarnivores Across a Land-Use Gradient in KwaZulu-Natal, South Africa

Globally, anthropogenic land conversion has resulted in reduced natural land available for free-roaming wildlife, and a shift in species composition. Certain mesocarnivores exhibit an ability to adapt and expand distribution ranges under differing anthropogenic pressures. Our study addressed the socio-ecological attitudes and general perspectives towards mammalian mesocarnivores across a land-use gradient (rural–urban) from the uMgungundlovu to eThekwini municipalities of KwaZulu-Natal, South Africa. We determined threats, conflicts and attitudes towards mammalian mesocarnivores using an online questionnaire survey. The public held a range of opinions on mesocarnivores. Participants from both land-use types generally regarded mesocarnivores as non-threatening and vital for the environment. However, not all mesocarnivores were regarded with equal benevolence. Black-backed jackals, Canis mesomelas, were consistently singled out as a problematic species by rural inhabitants and this intensified reactions when a confrontation occurred. Smaller and more behaviourally flexible mesocarnivores (mongoose spp. and Cape genets, Genetta tigrina) were the most observed species in both land-use types, indicating potential population increases. Vehicle collision was the leading cause of mesocarnivore fatalities. Overall, perceived impacts and threats of mesocarnivores differed across the land-use gradients. Our study illustrates the importance of citizen science and community engagement across a land-use gradient in wildlife conservation efforts.

Effects of rainforest transformation to monoculture cash crops on soil living ants (Formicidae) in Jambi Province, Sumatra, Indonesia

Ants (Formicidae) are fundamental components of almost every terrestrial ecosystem, especially in the tropics. While epigaeic ants are extensively studied, hypogaeic, soil living ants are still neglected to a large extent. To remedy this, in this paper we explore the effects of rainforest transformation cash crop monocultures on abundance, richness and community composition of soil living ants (Formicidae). Ants in this study were procured as a by-product of extensive sampling of soil meso- and macrofauna along a land-use gradient from lowland rainforest via jungle rubber to monocultures of rubber and oil palm in Jami Province, Sumatra, Indonesia. Sampled in 32 plots of 50 * 50 m each, with three 16 cm * 16 cm * 5 cm soil cores each, we collected 2.079 worker ant individuals, belonging to 90 morphospecies from 37 genera and six subfamilies. Land use had a significant effect on abundance and richness, while distance-based community composition was not affected. Cumulatively, lowland rainforest had the highest number of ant species exclusively living in it, and the highest average ant abundance, although multiple comparison tests did not detect significant differences. We also found highest species richness in the lowland rainforest in one of the two investigated landscapes, while not significantly different from the agricultural systems in the other. High abundance variances among the sample sites suggest inadequacy of the sampling method, however. Despite that, our study provides a first glimpse into hypogaeic ant community responses to rainforest conversion to cash crop monocultures in Sumatra, Indonesia.

Taxonomic and functional threshold responses of vertebrate communities in the Atlantic Forest Hotspot

Ecological thresholds are an indicator of rapid and non-linear changes along both natural habitat and land-use gradients. Thus, they can be used to quantify biodiversity responses to human-induced environmental change. We investigated multiple thresholds by analyzing eight environmental predictors of both taxonomic and functional composition of amphibian and bird communities in 47 independent sample units, located within a heterogeneous land use matrix of the megadiverse Atlantic Forest hotspot. We demonstrate that current land use practices alter both the taxonomic and functional composition and promote the establishment of non-native taxa resulting in novel assemblages. Whereas anuran communities experienced dramatic compositional shifts as a result of the transformation of closed forest habitats into Eucalyptus monocultures (at less than 10% land cover), bird communities were mainly altered through the loss of old-growth forest (at 20% forest cover loss). In both groups, observed thresholds were lower than previously reported and much lower than the 20% forest set-aside requirement defined by current land-use legislation. We argue that the strategy of halting forest loss through rapid afforestation with non-native trees has converse and potentially detrimental effects on the conservation of native forest biodiversity. Future studies need to investigate how including novel assemblages in current conservation management strategies can enhance biodiversity protection in human-impacted forest landscapes. The identification of taxon-specific thresholds for both taxonomic and functional community shifts is indispensable when formulating common land use practices and designing mitigation measures. Threshold analyses can guide these actions by providing clear and quantifiable break-points for conservation practitioners.

Multi-trophic level responses to environmental stressors over the past ~150 years: Insights from a lake-rich region of the world

Multiple stressors affect water quality and biodiversity in lakes worldwide. However, our understanding of which combinations of stressors are of greatest impact and how lakes have shifted from their pre-industrial baselines is fragmented. Questions remain regarding how multiple trophic groups are affected by global change stressors and whether region-specific differences need to be considered. Here, we apply multiple factor analyses together with latent variable modeling to quantify potential interactions within and among taxa that span multiple trophic levels (i.e. diatoms, cladocerans and chironomids) to improve our understanding of paleo-environmental dynamics from a suite of Canadian lakes spanning four ecozones: the Boreal Shield, the Mixedwood Plains, the Atlantic Highlands, and the Atlantic Maritimes. Across all ecozones, multi-trophic assemblages were distinguished in a multiple factor analysis along a land-use gradient, with mesotrophic/eutrophic diatoms and profundal chironomids tolerant of low bottom-water oxygen concentrations recorded in more disturbed sites. Functional units across three indicator groups formed distinct networks of co-responses to key environmental and land-use gradients, although cladocerans seemed to be driven by additional (i.e., residual) gradients. Applying a temporal beta-diversity approach between modern and pre-industrial assemblages, we detected significantly greater turnover of diatom functional groups in high versus low human impact sites (p = 0.03, n = 57), with similar but non-significant trends apparent with the chironomid and cladoceran groups. Ecozonal differences in temporal turnover were also evident in diatom (p = 0.003, n = 57) and chironomid functional groups (p = 0.04, n = 41). The ecozonal differences may be partially due to differential sensitivities of the pre-industrial assemblages and may also be driven by historical disturbances. Our work highlights how the magnitude and direction of ecological change vary across ecozones and can modify responses to human impacts, with a general trend of higher species turnover in sites with greater human disturbance.

Environmental and biological factors are joint drivers of mercury biomagnification in subarctic lake food webs along a climate and productivity gradient

Subarctic lakes are getting warmer and more productive due to the joint effects of climate change and intensive land-use practices (e.g. forest clear-cutting and peatland ditching), processes that potentially increase leaching of peat- and soil-stored mercury into lake ecosystems. We sampled biotic communities from primary producers (algae) to top consumers (piscivorous fish), in 19 subarctic lakes situated on a latitudinal (69.0–66.5° N), climatic (+3.2 °C temperature and +30% precipitation from north to south) and catchment land-use (pristine to intensive forestry areas) gradient. We first tested how the joint effects of climate and productivity influence mercury biomagnification in food webs focusing on the trophic magnification slope (TMS) and mercury baseline (THg baseline) level, both derived from linear regression between total mercury (log10THg) and organism trophic level (TL). We examined a suite of environmental and biotic variables thought to explain THg baseline and TMS with stepwise generalized multiple regression models. Finally, we assessed how climate and lake productivity affect the THg content of top predators in subarctic lakes. We found biomagnification of mercury in all studied lakes, but with variable TMS and THg baseline values. In stepwise multiple regression models, TMS was best explained by negative relationships with food chain length, climate-productivity gradient, catchment properties, and elemental C:N ratio of the top predator (full model R2 = 0.90, p < 0.001). The model examining variation in THg baseline values included the same variables with positive relationships (R2 = 0.69, p = 0.014). Mass-standardized THg content of a common top predator (1 kg northern pike, Esox lucius) increased towards warmer and more productive lakes. Results indicate that increasing eutrophication via forestry-related land-use activities increase the THg levels at the base of the food web and in top predators, suggesting that the sources of nutrients and mercury should be considered in future bioaccumulation and biomagnification studies.

Changes in diversity and community assembly of jumping spiders (Araneae: Salticidae) after rainforest conversion to rubber and oil palm plantations.

Rainforest conversion into monoculture plantations results in species loss and community shifts across animal taxa. The effect of such conversion on the role of ecophysiological properties influencing communities, and conversion effects on phylogenetic diversity and community assembly mechanisms, however, are rarely studied in the same context. Here, we compare salticid spider (Araneae: Salticidae) communities between canopies of lowland rainforest, rubber agroforest (“jungle rubber”) and monoculture plantations of rubber or oil palm, sampled in a replicated plot design in Jambi Province, Sumatra, Indonesia. Overall, we collected 912 salticid spider individuals and sorted them to 70 morphospecies from 21 genera. Salticid richness was highest in jungle rubber, followed by rainforest, oil palm and rubber, but abundance of salticids did not differ between land-use systems. Community composition was similar in jungle rubber and rainforest but different from oil palm and rubber, which in turn were different from each other. The four investigated land-use systems differed in aboveground plant biomass, canopy openness and land use intensity, which explained 12% of the observed variation in canopy salticid communities. Phylogenetic diversity based on ~850 bp 28S rDNA fragments showed similar patterns as richness, that is, highest in jungle rubber, intermediate in rainforest, and lowest in the two monoculture plantations. Additionally, we found evidence for phylogenetic clustering of salticids in oil palm, suggesting that habitat filtering is an important factor shaping salticid spider communities in monoculture plantations. Overall, our study offers a comprehensive insight into the mechanisms shaping communities of arthropod top predators in canopies of tropical forest ecosystems and plantations, combining community ecology, environmental variables and phylogenetics across a land-use gradient in tropical Asia.

Organic carbon burial in a large, deep alpine lake (southwest China) in response to changes in climate, land use and nutrient supply over the past ~100 years

Inland waterbodies play an important role in the global carbon cycle, acting both as carbon sources with organic carbon (OC) mineralization and as sinks with OC burial in sediments. Under recent impacts of global warming, anthropogenic land-use change and nutrient supply, however, there is a limited knowledge regarding OC dynamics in sediments of large, deep lakes especially in subtropical alpine regions. Here, we studied the patterns of OC burial and the potential regulating factors using multiple sedimentary proxies and observational records in Lugu Lake (southwest China) over the past ~100 years. Comparisons of 15 sediment cores in different areas of the lake reveal similar temporal trends in OC content and other sediment parameters, indicating coherent patterns of whole-lake sedimentary environmental change dominated by watershed human perturbation. Based on C/N ratios and δ13Corg analyses, the sediment OC has primarily been autochthonous in source. OC accumulation rates (OCAR) increased during 1880–1980, from ~14 to 43 g C m−2 yr−1 in a central core (LGS), mainly resulting from elevated primary production under increased phosphorus input and soil erosion. Subsequently, OCAR decreased considerably to ~15 g C m−2 yr−1, although the phosphorus supply and lake primary productivity remained high. We infer the OCAR decline likely resulted from increased organic matter decomposition and OC mineralization in the water column because of climate warming and lake-water thermal stratification. This phenomenon might mask the positive contribution of primary production to OC burial. Our findings suggest that the commonly observed synergistically positive effects of warming and eutrophication on sediment OC burial may be impaired in deep lakes, which needs further investigations across ecological, climatic and land-use gradients.

Landscape controls on riverine export of dissolved organic carbon from Great Britain

The dissolved organic carbon (DOC) export from land to ocean via rivers is a significant term in the global C cycle, and has been modified in many areas by human activity. DOC exports from large global rivers are fairly well quantified, but those from smaller river systems, including those draining oceanic regions, are generally under-represented in global syntheses. Given that these regions typically have high runoff and high peat cover, they may exert a disproportionate influence on the global land–ocean DOC export. Here we describe a comprehensive new assessment of the annual riverine DOC export to estuaries across the island of Great Britain (GB), which spans the latitude range 50–60° N with strong spatial gradients of topography, soils, rainfall, land use and population density. DOC yields (export per unit area) were positively related to and best predicted by rainfall, peat extent and forest cover, but relatively insensitive to population density or agricultural development. Based on an empirical relationship with land use and rainfall we estimate that the DOC export from the GB land area to the freshwater-seawater interface was 1.15 Tg C year−1 in 2017. The average yield for GB rivers is 5.04 g C m−2 year−1, higher than most of the world’s major rivers, including those of the humid tropics and Arctic, supporting the conclusion that under-representation of smaller river systems draining peat-rich areas could lead to under-estimation of the global land–ocean DOC export. The main anthropogenic factor influencing the spatial distribution of GB DOC exports appears to be upland conifer plantation forestry, which is estimated to have raised the overall DOC export by 0.168 Tg C year−1. This is equivalent to 15% of the estimated current rate of net CO2 uptake by British forests. With the UK and many other countries seeking to expand plantation forest cover for climate change mitigation, this ‘leak in the ecosystem’ should be incorporated in future assessments of the CO2 sequestration potential of forest planting strategies.

Stream sediment bacterial communities exhibit temporally-consistent and distinct thresholds to land use change in a mixed-use watershed.

Freshwater ecosystems are susceptible to biodiversity losses due to land conversion. This is particularly true for the conversion of land from forests for agriculture and urban development. Freshwater sediments harbor microorganisms that provide vital ecosystem services. In dynamic habitats like freshwater sediments, microbial communities can be shaped by many processes, although the relative contributions of environmental factors to microbial community dynamics remain unclear. Given the future projected increase in land use change, it is important to ascertain how associated changes in stream physico-chemistry will influence sediment microbiomes. Here, we characterized stream chemistry and sediment bacterial community composition along a mixed land-use gradient in West Virginia, USA across one growing season. Sediment bacterial community richness was unaffected by increasing anthropogenic land use, though microbial communities were compositionally distinct across sites. Community threshold analysis revealed greater community resilience to agricultural land use than urban land use. Further, predicted metagenomes suggest differences in potential microbial function across changes in land use. The results of this study suggest that low levels of urban land use change can alter sediment bacterial community composition and predicted functional capacity in a mixed-use watershed, which could impact stream ecosystem services in the face of global land use change.