Major Environmental Drivers Research Articles

Critical predictors of functional, phylogenetic and taxonomic diversity are geographically structured in lichen epiphytic communities

Abstract Assessing the response of biological communities to contrasting environmental conditions is crucial to predict the effects of global change drivers. The influence of multiple environmental factors may differ depending on the diversity facet considered, which emphasizes the need to simultaneously evaluate the functional (FD), phylogenetic (PD) and taxonomic (TD) diversity. To examine how these facets of biodiversity respond to environmental changes, we studied lichen epiphytic communities across 47 beech forest fragments from two biogeographic regions. We applied structural equation modelling to relate habitat fragmentation, climate and habitat quality with FD, PD and TD. We compared the community response to contrasting climatic conditions by analysing independently Atlantic and Mediterranean communities. We found different major drivers of biodiversity patterns across biogeographic regions. Habitat fragmentation performed the highest effect on lichen communities, with a reduction of FD, PD and TD at both regions. However, the influence of climate was stronger in the Atlantic region than in the Mediterranean region, where the effect of habitat quality was superior. The effect of the environmental predictors over PD and TD was both direct and indirect through the different components of FD, and their intensity and sign differed across regions. Changes in PD were not related to changes in TD. Synthesis. Our results evidenced that the major environmental drivers affecting epiphytic communities were geographically structured. These drivers modified the diversity of the epiphytic community directly but also indirectly through changes in FD, which emerged as a causal but not unique determinant of PD and TD. Our findings also showed the difficulty for inferring TD through PD. These results emphasize the essential role of FD predicting part of the response of lichen communities to global change drivers but also highlight the importance of considering multiple biodiversity facets to understand the effects of environmental change on community structure.

Unraveling the diversity of sedimentary sulfate-reducing prokaryotes (SRP) across Tibetan saline lakes using epicPCR

Sulfate reduction is an important biogeochemical process in the ecosphere; however, the major taxa of sulfate reducers have not been fully identified. Here, we used epicPCR (Emulsion, Paired Isolation, and Concatenation PCR) technology to identify the phylogeny of sulfate-reducing prokaryotes (SRP) in sediments from Tibetan Plateau saline lakes. A total of 12,519 OTUs and 883 SRP-OTUs were detected in ten lakes by sequencing of 16S rRNA gene PCR amplicons and epicPCR products of fused 16S rRNA plus dsrB gene, respectively, with Proteobacteria, Firmicutes, and Bacteroidetes being the dominant phyla in both datasets. The 120 highly abundant SRP-OTUs (> 1% in at least one sample) were affiliated with 17 described phyla, only 7 of which are widely recognized as SRP phyla. The majority of OTUs from both the whole microbial communities and the SRPs were not detected in more than one specific lake, suggesting high levels of endemism. The α-diversity of the entire microbial community and SRP sub-community showed significant positive correlations. The pH value and mean water temperature of the month prior to sampling were the environmental determinants for the whole microbial community, while the mean water temperature and total nitrogen were the major environmental drivers for the SRP sub-community. This study revealed there are still many undocumented SRP in Tibetan saline lakes, many of which could be endemic and adapted to specific environmental conditions.

Carbon forms, nutrients and water velocity filter hydrophyte and riverbank species differently: A trait‐based study

AbstractQuestionsThe majority of theories of trait‐based plant community assembly have been developed and tested predominantly in terrestrial ecosystems. Studies investigating the functional trait composition of aquatic plant communities and their relation to environmental determinants remain scarce. Macrophytes are essential components of aquatic ecosystems, and a more detailed knowledge of their trait‐based assembly is crucial for their management. We identified how plant functional traits respond to environmental gradients in streams and rivers.LocationDanube River Catchment, Hungary.MethodsWe studied the processes governing community assembly along major environmental gradients related to carbon‐ and nutrient‐limiting factors as well as physical strain. We used six continuous traits (leaf area, specific leaf area, leaf dry matter content, seed weight, seed shape, woodiness) and calculated community‐weighted mean and standardised effect size of functional diversity for each community. We then used stepwise regression analyses for each trait along the environmental gradients to test which environmental factors explain the changes in community‐weighted mean and functional diversity. All analyses were conducted for aquatic (hydato‐helophyte) and riverbank species separately.ResultsWe found that the effect of environmental filtering significantly increased toward higher pH, indicating the response of functional traits to carbon limitation. Our results showed trait convergence among riverbank species in rivers with higher productivity. Larger functional diversity (i.e., trait divergence) among hydato‐helophyte species suggests an increase in the diversity of resource acquisition strategies under higher productivity.ConclusionsHere, we have shown that the functional trait distribution of aquatic and riverbank plant communities responds to major environmental drivers related to nutrient and carbon availability. The understanding of how community assembly mechanisms varied along environmental gradients might be useful when proposing future management and restoration plans and actions towards the conservation of the aquatic vegetation in streams and rivers.

Economic Analysis and Environmental Impact Assessment of Heat Pump-Assisted Distillation in a Gas Fractionation Unit

The depletion of fossil fuels and environmental pollution (e.g., greenhouse gas emissions) through the combustion of fossil fuels have stimulated studies on new technologies able to curtail the energy consumption of existing fractionation units. In this regard, heat pumps have garnered substantial attention due to their potential to improve the process energy efficiency. This study aims to provide extensive economic analysis and environmental impact assessment of the application of heat pumps under different conditions and scenarios. For this purpose, we first selected three important conditions: feed composition, plant capacity, and fuel price. Then, we performed a range of analyses to identify the major costs and environmental drivers. The economics and environmental impact of heat pump-assisted distillation was investigated and compared with those of conventional distillation.

Successional trajectories and rates of change in sub-tropical Quercus forests in west-central Mexico: evidences from a permanent plot network

Forest succession was studied in sub-tropical high-altitude, Quercus-dominated forest in west-central Mexico in order to address the following research questions: (1) How do successional trajectories progress in three contrasting floristic zones? (2) Which is the magnitude of successional rate of change at different time-scales? (3) What are the major environmental drivers contributing to the observed patterns of forest succession? Data was derived from 86 non-managed permanent plots, 500 m2 each, established along a 10 km floristic gradient, ranging from xeric to mesic sites. In portraying successional trajectories over time and to measure the magnitude of rate of change in three floristic zones, Detrended Correspondence Analysis (DCA) was developed. In order to represent the most significant environmental drivers on patterns of successional trajectories and successional rate of change, we used generalized linear models with gaussian error. Results showed that successional trajectories were not deterministic in each of the floristic zones over the different time-scales analysed; instead we observed four successional trajectories i) plots with an outstanding displacement between time periods, accompanied by an erratic migration over the DCA diagram; ii) plots with a moderate rate of change and uniform movement across the ordination space; iii) a small number of plots with slight change and; iv) few plots with no changes. Soil related variables such as pH, P, N, Mg and Mn, together with slope and catena, were predicted as important contributing factors related to successional processes.

Characterization of Environmental Drivers Controlling the Baseline of Soil Surface CO2 Flux using Wavelet-based Multiresolution State-Space Model and Wavelet Denoising

Multivariate environmental time series including soil surface CO2 flux (FCO2) have non-stationarity and mutual interdependence, and thus the i.i.d assumption-based conventional regression techniques inevitably lead to spurious regression or lose the dynamic characteristics in the process of variable transformation. In this paper, we adopted a wavelet threshold technique for our newly developed wavelet-based multiresolution state-space model (MRSSM) to overcome such limitations and to quantitatively evaluate the environmental drivers (EDs) controlling the baseline of FCO2. First, the structural characteristics and the potential EDs (PEDs) of FCO2 were explored by wavelet denoised (threshold) SSM for complex environmental observation data. Then, the major EDs (MEDs) were identified using the scale localized correlation and the wavelet coherence analysis between PEDs and observation data. Next, the contribution of MEDs to FCO2 was quantitatively evaluated by calculating the effective dynamic efficiency using the wavelet energy ratio of the maximum-correlation time-frequency bands. Finally, the effectiveness of the wavelet threshold method for MRSSM was discussed. The proposed wavelet denoising method is expected to improve the performance of MRSSM which is effective to identify, evaluate and predict the main environmental factors inherent in the observation data from complex environmental systems where physicochemical and biological processes of various spatio-temporal scales occur simultaneously.

Environmental drivers of the geographical distribution of methanotrophs: Insights from a national survey

There is considerable evidence that environmental properties are important for microbial niche partitioning in general. However, little is known about the environmental factors explaining this for soil methane-oxidising bacteria (or methanotrophs), which play an essential role in ecosystem functioning and climate regulation through mitigation of net CH4 emissions worldwide. This knowledge gap limits the inclusion of taxon-based information to improve predictions of climate change-simulation models. In this study, 697 soil samples were collected across Scotland and 62 climo-edaphic properties were analysed. Combined with a set of hybrid geostatistical modelling approaches, the aim of this study was to investigate the biogeographical distribution (pmoA gene relative abundance) of key methanotrophic operational taxonomic units named Terminal-Restriction Fragments (T-RFs) and of methanotrophic community structure. The main objectives were to: 1) identify major environmental drivers influencing the distribution and composition of methanotrophs; and 2) perform spatial modelling and mapping of soil methanotrophic community assemblage and distribution of those dominant T-RFs. Herein, it was hypothesised that the assemblage of methanotrophic community and distribution of key populations across various landscapes could be predicted using a range of climo-edaphic factors optimised for spatial, climate and terrain attributes. The findings presented here suggest that the distribution of methanotrophs is strongly linked to land use and some edaphic properties, predominantly soil moisture/rainfall, nutrients and metal ions. The hybrid geostatistical approach allowed for spatial prediction of methanotrophic T-RFs and community, and demonstrated a clear niche partitioning between dominant T-RFs. Overall, these results provide novel evidence that the distribution of methanotrophs could be explained and mapped in terms of niche partitioning and predicted at the regional scale. The findings of the present study have significance for the sustainable management of ecosystems and improvement of simulation models for better prediction of ecosystem functions under predicted global changes.

Community and functional shifts in ammonia oxidizers across terrestrial and marine (soil/sediment) boundaries in two coastal Bay ecosystems.

Terrestrial-marine boundaries are significant sites of biogeochemical activity with delineated gradients from land to sea. While niche differentiation of ammonia-oxidizing archaea (AOA) and bacteria (AOB) driven by pH and nitrogen is well known, the patterns and environmental drivers of AOA and AOB community structure and activity across soil-sediment boundaries have not yet been determined. In this study, nitrification potential rate, community composition and transcriptional activity of AOA and AOB in soil, soil/sediment interface and sediments of two coastal Bays were characterized using a combination of field investigations and microcosm incubations. At DNA level, amoA gene abundances of AOA were significantly greater than AOB in soil, while in sediments AOB were significantly more abundant than AOA, but at the soil/sediment interface there were equal numbers of AOA and AOB amoA genes. Microcosm incubations provided further evidence, through qPCR and DGGE-sequencing analysis of amoA transcripts, that AOA were active in soil, AOB in sediment and both AOA and AOB were active at the soil/sediment interface. The AOA and AOB community composition shifted across the coastal soil-interface-sediment gradient with salinity and pH identified as major environmental drivers.

Distribution of fragrances and PAHs in the surface seawater of the Sicily Channel, Central Mediterranean

The Mediterranean Sea is highly influenced by several anthropic pressures, including different kinds of organic pollutants. Fragrance Materials (FMs) and Polycyclic Aromatic Hydrocarbons (PAHs) were investigated in the surface seawater of the Sicily Channel in offshore and coastal areas. Total concentrations of FMs and PAHs resulted respectively up to 112ngL−1 and 43ngL−1, with similar distributions of both classes of analytes. Low values were detected in some coastal samples, due to the upwelling of deep and unpolluted waters, while the presence of gyres probably accumulates contaminants in offshore areas. Confirming previous works, the allergenic and oestrogenic Salicylates generally resulted the most abundant FMs and diagnostic ratios indicated combustion processes as the sources of PAHs. The coupling of the well-known PAHs with a new class of Personal Care Products (PCPs) helped the identification of the major environmental drivers: the results highlighted the role of mesoscale hydrodynamics and suggested long-range atmospheric transport as key factors. The first detection of the selected FMs in open sea areas supports the hypothesis of their environmental persistence.

Ecological drivers of soil microbial diversity and soil biological networks in the Southern Hemisphere.

The ecological drivers of soil biodiversity in the Southern Hemisphere remain underexplored. Here, in a continental survey comprising 647 sites, across 58 degrees of latitude between tropical Australia and Antarctica, we evaluated the major ecological patterns in soil biodiversity and relative abundance of ecological clusters within a co-occurrence network of soil bacteria, archaea and eukaryotes. Six major ecological clusters (modules) of co-occurring soil taxa were identified. These clusters exhibited strong shifts in their relative abundances with increasing distance from the equator. Temperature was the major environmental driver of the relative abundance of ecological clusters when Australia and Antarctica are analyzed together. Temperature, aridity, soil properties and vegetation types were the major drivers of the relative abundance of different ecological clusters within Australia. Our data supports significant reductions in the diversity of bacteria, archaea and eukaryotes in Antarctica vs. Australia linked to strong reductions in temperature. However, we only detected small latitudinal variations in soil biodiversity within Australia. Different environmental drivers regulate the diversity of soil archaea (temperature and soil carbon), bacteria (aridity, vegetation attributes and pH) and eukaryotes (vegetation type and soil carbon) across Australia. Together, our findings provide new insights into the mechanisms driving soil biodiversity in the Southern Hemisphere.

Distribution of pines in the Iberian Peninsula agrees with species differences in foliage frost tolerance, not with vulnerability to freezing-induced xylem embolism.

Drought and frosts are major determinants of plant functioning and distribution. Both stresses can cause xylem embolism and foliage damage. The objective of this study was to analyse if the distribution of six common pine species along latitudinal and altitudinal gradients in Europe is related to their interspecific differences in frost tolerance and to the physiological mechanisms underlying species-specific frost tolerance. We also evaluate if frost tolerance depends on plant water status. We studied survival to a range of freezing temperatures in 2-year-old plants and assessed the percentage loss of hydraulic conductivity (PLC) due xylem embolism formation and foliage damage determined by needle electrolyte leakage (EL) after a single frost cycle to -15 °C and over a range of predawn water potential (ψpd) values. Species experiencing cold winters in their range (Pinus nigra J.F. Arnold, Pinus sylvestris L. and Pinus uncinata Raymond ex A. DC.) had the highest frost survival rates and lowest needle EL and soluble sugar (SS) concentration. In contrast, the pines inhabiting mild or cool winter locations (especially Pinus halepensis Mill. and Pinus pinea L. and, to a lesser extent, Pinus pinaster Ait.) had the lowest frost survival and highest needle EL and SS values. Freezing-induced PLC was very low and differences among species were not related to frost damage. Reduction in ψpd decreased leaf frost damage in P. pinea and P. sylvestris, increased it in P. uncinata and had a neutral effect on the rest of the species. This study demonstrates that freezing temperatures are a major environmental driver for pine distribution and suggests that interspecific differences in leaf frost sensitivity rather than vulnerability to freezing-induced embolism or SS explain pine juvenile frost survival.

Space and time matter in social-ecological vulnerability assessments

Fostering sustainable local social–ecological interactions playing out against a backdrop of larger-scale dynamics are ubiquitous challenges to natural resource management and biodiversity conservation. Social-ecological vulnerability assessments are highly relevant for place-based management and can help target and prioritize management actions. However, an understanding of how linked social-ecological vulnerabilities respond to external drivers is still lacking. This paper presents an approach that integrates the spatial and temporal dimensions into social-ecological vulnerability assessments, where social and ecological vulnerabilities are linked by a feedback loop. The approach is applied to the Moorea coral reef social-ecological system, which has been significantly influenced by major environmental and social drivers over the last decade. Temporal changes in linked social-ecological vulnerabilities are mapped before and after exposure to the multiple drivers. Nearly 23% of households and 13% of the reef area show low and decreasing vulnerability despite exposure. However, high and increasing levels of vulnerability were detected in 6% of households and associated reefs after exposure to the drivers, providing early warnings of potentially unsustainable situations. Importantly, changes in ecological vulnerability did not propagate linearly to changes in social vulnerability. Similarly, hot spots of social vulnerability were not necessarily associated with hot spots of ecological vulnerability, highlighting the need to specifically adapt management interventions to local social-ecological settings. Mapping social-ecological dependencies in space and time provides communities and decision-makers with the information required to identify and prioritize management interventions while accounting for the effects of large-scale or external drivers.

Determinants of stream bryophyte community structure: bringing ecology into conservation

Summary Bryophytes play an important role in headwater stream ecosystems sensitive to human pressures. The high number of bryophyte species listed as threatened in Europe suggests that further efforts to conserve fluvial bryophyte diversity are needed. Investigations of the spatial ecology of bryophyte diversity should help identifying priority areas for conservation of fluvial bryophytes and their habitats. Seasonal temperate headwater streams were sampled at their southern edge distribution in Portugal, within and outside protected areas, at two spatial scales: stream segments and microhabitats. The environmental variables best explaining richness and diversity patterns, as well as the number of threatened species, were identified by partial least square regression. The selection of the best sites for conservation was achieved through the development of a new Index of Fluvial Bryological and Hydrogeomorphological Signature (IFBHS). At the stream segment scale, bryophyte community structure was highly influenced by hydrogeomorphological variables, in particular by hydrological features. At the microhabitat scale, high current velocity constrained bryophyte richness and diversity. The prioritised sites identified through the application of the IFBHS exhibited exceptional bryological richness, high levels of endemism and red‐listed species, as well as unique fluvial microhabitats. Hydrological regime was identified as a major environmental driver of bryophyte community structure in seasonal headwater streams of southern temperate Europe, and this is of particular concern given projected scenarios of climate change and human‐induced flow regime alterations. Prioritised stream segments for fluvial bryophyte and habitat conservation were not only located within protected areas, reinforcing the need to enhance the effectiveness of Natura 2000 Network and national protection areas.

Green practices and financial performance: A global outlook

Companies around the world adopt green practices with the aim to reduce their environmental impacts and improve their financial performance. The present study theorizes about and empirically examines the impacts of corporate green practices on financial performance. Indexes of pollution prevention, green supply management, green product development and ISO 14001 adoption are obtained for each firm in a panel of 3490 publicly-traded companies from 58 countries over 13 years. Results show that internal green practices (pollution prevention and green supply chain management) are the major environmental drivers of financial performance, while external green practices (green product development) play a secondary role in determining financial performance. The adoption of ISO 14001 appears to have a negative impact on financial performance. This study provides empirical support for policy-makers promoting environmental practices that may lead to sustainable economic growth.

Regional variations in the diversity and predicted metabolic potential of benthic prokaryotes in coastal northern Zhejiang, East China Sea.

Knowledge about the drivers of benthic prokaryotic diversity and metabolic potential in interconnected coastal sediments at regional scales is limited. We collected surface sediments across six zones covering ~200 km in coastal northern Zhejiang, East China Sea and combined 16 S rRNA gene sequencing, community-level metabolic prediction, and sediment physicochemical measurements to investigate variations in prokaryotic diversity and metabolic gene composition with geographic distance and under local environmental conditions. Geographic distance was the most influential factor in prokaryotic β-diversity compared with major environmental drivers, including temperature, sediment texture, acid-volatile sulfide, and water depth, but a large unexplained variation in community composition suggested the potential effects of unmeasured abiotic/biotic factors and stochastic processes. Moreover, prokaryotic assemblages showed a biogeographic provincialism across the zones. The predicted metabolic gene composition similarly shifted as taxonomic composition did. Acid-volatile sulfide was strongly correlated with variation in metabolic gene composition. The enrichments in the relative abundance of sulfate-reducing bacteria and genes relevant with dissimilatory sulfate reduction were observed and predicted, respectively, in the Yushan area. These results provide insights into the relative importance of geographic distance and environmental condition in driving benthic prokaryotic diversity in coastal areas and predict specific biogeochemically-relevant genes for future studies.

Disentangling the drivers of taxonomic and phylogenetic beta diversities in disturbed and undisturbed subtropical forests.

Understanding the relative importance of dispersal limitation and environmental filtering processes in structuring the beta diversities of subtropical forests in human disturbed landscapes is still limited. Here we used taxonomic (TBD) and phylogenetic (PBD), including terminal PBD (PBDt) and basal PBD (PBDb), beta diversity indices to quantify the taxonomic and phylogenetic turnovers at different depths of evolutionary history in disturbed and undisturbed subtropical forests. Multiple linear regression model and distance-based redundancy analysis were used to disentangle the relative importance of environmental and spatial variables. Environmental variables were significantly correlated with TBD and PBDt metrics. Temperature and precipitation were major environmental drivers of beta diversity patterns, which explained 7–27% of the variance in TBD and PBDt, whereas the spatial variables independently explained less than 1% of the variation for all forests. The relative importance of environmental and spatial variables differed between disturbed and undisturbed forests (e.g., when Bray-Curtis was used as a beta diversity metric, environmental variable had a significant effect on beta diversity for disturbed forests but had no effect on undisturbed forests). We conclude that environmental filtering plays a more important role than geographical limitation and disturbance history in driving taxonomic and terminal phylogenetic beta diversity.

High spatiotemporal variability in meiofaunal assemblages in Blanes Canyon (NW Mediterranean) subject to anthropogenic and natural disturbances

We investigated the natural and anthropogenic drivers controlling the spatiotemporal distribution of the meiofauna in the submarine Blanes Canyon, and its adjacent western slope (NW Mediterranean margin of the Iberian Peninsula). We analyzed the relationships between the main sedimentary environmental variables (i.e. grain size, Chl-a, Chl-a: phaeopigments, CPE, organic carbon and total nitrogen) and the density and structure of the meiofaunal assemblages along a bathymetric gradient (from 500 to 2000m depth) in spring and autumn of 2012 and 2013.Twenty-one and 16 major taxa were identified for respectively the canyon and slope, where the assemblages were always dominated by nematodes. The gradual decreasing meiofaunal densities with increasing depth at the slope showed little variability among stations and corresponded with a uniform pattern of food availability. The canyon was environmentally much more variable and sediments contained greater amounts of food resources (Chl-a and CPE) throughout, leading not only to increased meiofaunal densities compared to the slope, but also different assemblages in terms of composition and structure. This variability in the canyon is only partly explained by seasonal food inputs. The high densities found at 900m and 1200m depth coincided with significant increases in food availability compared to shallower and deeper stations in the canyon. Our results suggest that the disruption in expected bathymetric decrease in densities at 900–1200m water depth coincided with noticeable changes in the environmental variables typical for disturbance and deposition events (e.g., higher sand content and CPE), evoking the hypothesis of an anthropogenic effect at these depths in the canyon. The increased downward particle fluxes at 900–1200m depth caused by bottom trawling along canyon flanks, as reported in previous studies, support our hypothesis and allude to a substantial anthropogenic factor influencing benthic assemblages at these depths. The possible relationships of the observed patterns and some major natural environmental (e.g., surface productivity or dense shelf water cascading) and anthropogenic (e.g. the lateral advection and downward transport of food-enriched sediments resuspended by the daily canyon-flank trawling activities) drivers are discussed.

Ecological response to hydrological variability and catchment development: Insights from a shallow oxbow lake in Lower Mississippi Valley, Arkansas

The ecological response of shallow oxbow lakes to variability in hydrology and catchment development in large river floodplain ecosystems (RFE) in Arkansas remains largely unknown. Investigating these responses will advance our understanding of ecological evolution of oxbow lakes in response to the major environmental drivers, which will establish baseline conditions required to develop effective management practices for RFE.In this pilot study, we examined the potential of using a dated surface sediment core from Adams Bayou, a floodplain lake located within the Cache-Lower White River Ramsar site in SE Arkansas. Stratigraphic records of diatoms and sediment geochemistry were used to ascertain variation in Adams Bayou's ecological condition. During 1968–2008, in response to hydrological and anthropogenic changes, Adams Bayou's diatom assemblages progressed from predominantly benthic (Gomphonema parvulum and Meridion circulare) to primarily planktonic assemblage (Aulacoseira granulata and Cyclotella meneghiniana), along with a decrease in magnetic susceptibility (k) and % silt. Statistical analyses reveled that during 1968–2000, higher hydrological connectivity and catchment alterations drove Adams Bayou's ecosystem. After 2000, lower hydrological connectivity and increase in cultivation were the major drivers. The potential impact of increasing air temperature was also noted.The shift in Adams Bayou from a connected, clear, mesotrophic state to a relatively isolated, turbid and nutrient enriched state is consistent with regime shift models and highlights its sensitivity to a combination of environmental stresses prevalent in the catchment. Although fluvial systems pose challenges in establishing clear chronologies, oxbow lake sediments can be a effective paleoecological archives. Our work provides clear evidence for the change in the ecological character of this wetland of international significance and flags the need for a wider assessment of water bodies across this site under obligations to the Ramsar Convention.

Hierarchical spatial segregation of two Mediterranean vole species: the role of patch-network structure and matrix composition

According to ecological theory, the coexistence of competitors in patchy environments may be facilitated by hierarchical spatial segregation along axes of environmental variation, but empirical evidence is limited. Cabrera and water voles show a metapopulation-like structure in Mediterranean farmland, where they are known to segregate along space, habitat, and time axes within habitat patches. Here, we assess whether segregation also occurs among and within landscapes, and how this is influenced by patch-network and matrix composition. We surveyed 75 landscapes, each covering 78ha, where we mapped all habitat patches potentially suitable for Cabrera and water voles, and the area effectively occupied by each species (extent of occupancy). The relatively large water vole tended to be the sole occupant of landscapes with high habitat amount but relatively low patch density (i.e., with a few large patches), and with a predominantly agricultural matrix, whereas landscapes with high patch density (i.e., many small patches) and low agricultural cover, tended to be occupied exclusively by the small Cabrera vole. The two species tended to co-occur in landscapes with intermediate patch-network and matrix characteristics, though their extents of occurrence were negatively correlated after controlling for environmental effects. In combination with our previous studies on the Cabrera-water vole system, these findings illustrated empirically the occurrence of hierarchical spatial segregation, ranging from within-patches to among-landscapes. Overall, our study suggests that recognizing the hierarchical nature of spatial segregation patterns and their major environmental drivers should enhance our understanding of species coexistence in patchy environments.

Variability in foraging behaviour of red-footed boobies nesting on Europa Island

Seabirds are considered to be good indicators of the marine environment. However, little is known about the effects of environmental variability on the foraging behaviour of tropical seabirds. Red-footed boobies (RFB) nesting on Europa Island (Mozambique Channel) were fitted with GPS devices over four years and different breeding stages. We first show that the durations of foraging trips vary extensively according to the stage of the breeding, being short during brooding, intermediate during incubation and long during fledging. This result highlights the importance of considering breeding stage when conducting comparisons of foraging between sites or years. In addition, we show that RFB adjusted their foraging behaviour between years (2003, 2011, 2012 and 2013) according to the prevailing environmental conditions. During 2011, RFB made longer foraging trips with larger area-restricted search (ARS) zones over a larger total surface area, suggesting that the foraging conditions were probably poor. This year was characterized by a decrease of the major environmental drivers of the Mozambique Channel system, i.e. particularly low chlorophyll concentrations in the northern part of the Mozambique Channel, as well as a weak eddy activity. This observation suggests that environmental conditions may have altered the southward transport and concentration processes structuring the trophic chain, leading to adverse conditions for a central-place forager like the RFB. Our results emphasize that environmental and breeding stage variation should be taken into account to better understand the distribution of these predators in marine tropical ecosystems.