Spatial Environmental Gradients Research Articles

Characterising intertidal sediment temperature gradients in estuarine systems

Coastal marine ecosystems are under increasing threat from environmental shifts associated with climate change, particularly increasing temperatures, as temperature influences the physiology, distribution, and abundance of marine organisms. Sediment temperatures on soft sediment intertidal flats are highly variable in space and time due to intermittent exposure to air and seawater. Surface sediment layers may have greater temperature variation relative to deeper layers, and local physical and biological characteristics as well as oceanic and atmospheric temperature conditions are expected to influence the temperatures experienced by sediment dwelling fauna. However, there is little reporting of the dynamics of sediment temperatures in these ecosystems and the local conditions that drive them. We focused on measuring estuarine intertidal sediment temperatures to describe the conditions that resident intertidal macroinvertebrates, including infauna, are being exposed to. Monitoring of sediment temperatures in intertidal ecosystems during summer revealed that sandy intertidal flats had greater temperature fluctuations than muddy intertidal flats. Local weather conditions were important drivers of both low and high tide sediment temperatures, and satellite derived sea surface temperature (SST) data for the study area were sparse and poorly matched sediment temperatures, revealing limitations of satellite SST for predicting site-specific intertidal sediment temperatures in nearshore areas. This study demonstrates the need for long term monitoring of intertidal sediment temperatures across large spatial scales and environmental gradients to understand and predict the potential impacts of climate change.

Ecological patterns of benthic foraminiferal communities driven by seasonal and spatial environmental gradients in an Arctic fjord

AbstractArctic fjords, being transitional areas between glacier‐covered land and the ocean, are characterized by strong environmental gradients. The seasonal melting of glaciers generates strong turbidity and primary production antagonist gradients, which can affect benthic habitats. Two sampling campaigns were carried out in Kongsfjorden (Svalbard, Arctic Ocean) in May and August 2021 to investigate seasonal changes in benthic foraminifera spatial distribution and ecosystem functioning along a longitudinal transect of 10 km from the Kronebreen tidewater glacier front. Concurrently, organic matter quantity and biochemical composition, sediment grain size, and physical parameters of the water masses were investigated as possible driving factors of benthic ecosystem responses. In a previous study, three statistically determined foraminiferal biozonations (glacier proximal, medial, and distal) were observed on the basis of their species content within the closest 10 km from the glacier front, presenting similar assemblages in both seasons. Our results indicate that foraminiferal distribution at the local scale is mainly driven by physical and geochemical gradients induced by melting waters and sediment discharges from the tidewater glacier occurring during summer. Due to the climate change, the melting season is expected to last longer and increasing global temperature will much probably accelerate the melting processes. Our findings strongly support the use of foraminifera as bioindicators to monitor the effects of ongoing climate change on the benthic ecosystems of Arctic fjords and, accessorily, as proxies for reconstructing glacier front positions in the recent past.

Spatial patterns and variations in leaf traits of alpine plants on the interior Tibetan Plateau

Spatial patterns and environmental gradients in plant traits can elucidate the relationships between plant characteristics, environmental factors, and ecosystem functions and can be used to develop the next generation of vegetation models for predicting vegetation distribution and functions. Studies of Plant traits across spatial scales have advanced significantly worldwide, including on the Tibetan Plateau (TP), the highest and largest plateau globally. Previous research on plant traits on the TP has been limited to specific areas, leaving the overall trend across the plateau unclear. In this study, we examined seven leaf traits—leaf thickness (LT), leaf dry matter content (LDMC), leaf area (LA), specific leaf area (SLA), and leaf carbon (LCC), nitrogen (LNC), and phosphorus (LPC) contents—in 1314 individuals at 237 sites within the alpine vegetation region above 3000 m on the TP to determine their distribution patterns across three spatial dimensions and their relationships with environmental factors. Our results indicated that, compared with Chinese plants, TP plants exhibited significantly greater LT, LDMC, and LNC but lower LA, LCC, and LPC. Except for SLA and LCC, most leaf traits showed significant spatial variability. Climate and soil explained 29.23 % of the total variations in traits. Radiation had the most pronounced effect on LDMC, LA, LNC, and LPC, whereas soil pH primarily constrained LT and LCC. Precipitation influenced most traits both directly and indirectly, with substantial overall effects. Temperature and soil nutrient had minimal influence on the regulation of leaf traits across most of the TP. Our findings suggest that alpine plants typically employ a conservative strategy to cope with the harsh conditions on the TP, but this strategy varies at broader spatial scales and longer environmental gradients, particularly in extreme environments such as the highest alpine regions.

Facilitation cascades across space: Monitoring estuarine foundation species from satellites to the microscope

AbstractEstuaries are productive ecosystems that are vulnerable to human impacts and environmental disturbances. Estuaries are often inhabited by foundation species that facilitate other organisms by creating and modifying habitats. However, spatiotemporal variability and underpinning drivers of facilitation from estuarine foundation species are poorly studied, especially in the context of monitoring and conservation. Here, we combined the analyses of satellite, drone, and camera images, close‐up field sampling of quadrats and individuals, and laboratory microscopy, to quantify co‐occurrences between the cockle Austrovenus stutchburyi and green macroalga Ulva spp., and their associated invertebrate communities, across spatial resolutions and environmental gradients in a New Zealand estuary. We found higher abundance of Ulva in winter and higher abundance of Austrovenus at a site near the ocean. Furthermore, Ulva was, across space and time, often attached to Austrovenus, either live or dead shells, suggesting a hierarchy between a primary (cockle) and secondary (macroalgae) foundation species. Finally, Ulva provided a better habitat for mobile invertebrates than Austrovenus, and thereby increased estuarine diversity through a density‐dependent facilitation cascade, which also was consistent in space and time. Overall, our study showed that facilitation cascades can be indirectly inferred and monitored through remote sensing of foundation species using supplementary imaging methods, and that integration of data across scales allows researchers to better understand the drivers and consequences of facilitation from foundation species. These insights may aid in the development of efficient monitoring strategies and ultimately improve the management of estuarine ecosystems.

Changes in species richness with climate change in subalpine communities are dependent on regional environmental conditions and local functional composition

AbstractQuestionsClimate change may have different effects on species richness depending on regional climates, soil types and the functional composition of local communities.LocationSubalpine belt of the Grandes Rousses (Alps) and Sancy mountain ranges (the Massif Central), France.MethodsWe compared changes in species richness in response to recent climate change in communities from two mountain ranges subjected to contrasting environmental conditions, with a more continental climate and drier soils in the Alps than in the Massif Central. Vegetation composition of 189 and 157 plots was assessed in 1997 and 2017–2018 in the Alps and 1988–1989 and 2022 in the Massif Central, respectively. Five species traits (height, lateral spread, leaf area, specific leaf area and leaf dry matter content) were measured on 108 and 144 species, respectively. Changes in vegetation composition and species richness along spatial environmental gradients were analysed with correspondence analysis at the Sancy site and canonical correspondence analysis at the Alpe d'Huez site. Changes in functional composition across sites were analysed with principal components analysis. Changes in species richness with climate change were analysed with repeated‐measure ANOVAs.ResultsIn both mountain ranges summer temperatures increased and the hydric balance decreased over the past three decades, but snow cover duration decreased in the Alps only, whereas irradiance strongly increased in the Massif Central only. Functional composition was characterized by shorter and more conservative species in the Alps than in the Massif Central, which was dominated by tall exploitative species. Species richness overall decreased with climate change by ca 10% in the Alps but overall increased by ca 10% in the Massif Central. Species richness decreased in the Alps probably because of increasing competition induced by dwarf shrub encroachment due to decreasing snow cover duration, whereas species richness increased in the Massif Central probably due to increasing irradiance in a very nebulous climate.ConclusionThe opposite changes in species richness observed in the two mountain ranges with recent climate change were likely to be explained by their contrasting climate and soil conditions driving different functional compositions and diversity–environment relationships.

Using historical catch data to evaluate predicted changes in fish relative abundance in response to a warming climate

Using models to predict future changes in species distributions in response to projected climate change is a common tool to aid management and species conservation. However, the assumption underlying this approach, that ecological processes remain stationary through time, can be unreliable, and more empirical tests are needed to validate predictions of biotic outcomes of global change. The scarcity of reliable historical and long‐term datasets can make these tests difficult. Moreover, incorporating abundance and multiple sampling methods can improve model predictions and usability for management. Our study 1) provides insight into how well models can predict environmental change under a warming climate, 2) incorporates multiple sampling gears and abundance data in modeling to better capture changes in populations and 3) shows the value of historical datasets for improving predictive models of population change. We used contemporary (2003–2019) and historical (1936–1964) abundance datasets of the North American fish largemouth bass Micropterus salmoides in lakes across the state of Michigan, USA. We developed Bayesian hierarchical models that leverage the use of multiple gears in contemporary lake surveys to estimate the relative catchabilities of largemouth bass for each gear and hindcast the models to predict historical abundance. Our estimates of relative density change over time were correlated with temperature change over time; increasing surface water temperature led to increasing largemouth bass density. Hindcasting models to historical lake temperatures performed similarly in predicting historical density to models predicting contemporary density. Our results suggest that models built using spatial environmental gradients can reliably predict population changes through time. Understanding the sampling methods and the environmental context of observational datasets can help researchers test for potential sampling biases and identify confounding factors that will improve predictions of future impacts of environmental change.

Bryophyte assembly rules across scales

Abstract Understanding how species assemble into communities is a central issue in community ecology. So far, most studies have focused on the assembly mechanisms of vascular plant communities, while the role of deterministic (environmental filtering and biotic interactions) and stochastic (e.g. dispersal limitation) processes structuring bryophyte assemblages remains poorly understood. To evaluate how different assembly processes shape bryophyte communities in mountain streams, we examined functional trait patterns across spatial scales and along environmental gradients. To do so, we sampled 754 microhabitat plots (0.25 m2) nested within 165 sites (100‐m long stream segments) and 13 sub‐basins, located in the northwest and central‐west of Portugal. At each spatial scale, observed functional diversity indices (Functional Richness and Rao's quadratic entropy) were compared to random expectations derived from null models, followed by the analysis of changes in functional trait patterns along environmental gradients by fitting a series of generalized additive mixed models. At local scales (site and microhabitat plot), coexisting species tended to be more functionally similar than expected, suggesting the prevalence of environmental filtering effects. In contrast, no significant deviations from random expectations were detected at the broadest spatial scale (sub‐basin), indicating the prevalence of stochastic processes. We found contrasting assembly processes along environmental gradients: environmental filtering prevailed in stressful environments, while competitive interactions were more important in favourable conditions. Synthesis. Our results highlight the role of environmental filtering in bryophyte community assembly at fine spatial scales, emphasizing the importance of measuring environmental conditions at the same spatial scales where biotic interactions take place. In line with the stress‐dominance hypothesis, the relative importance of environmental filtering increased with abiotic stress. Thus, analysing functional trait patterns across different spatial scales and environmental gradients may contribute to a better understanding of the mechanisms underlying community assembly.

Forest stand-by-environment interaction invalidates the use of space-for-time substitution for site index modeling under climate change

Quantification and prediction of forest site productivity potential under climate changes are core issues of growth and yield modelling and crucial for the effective management of forest stands. Climatic factors typically enter these models as long-term baseline data of mean air temperature and sum of precipitation. Such models frequently are parameterized using spatially distributed data, an approach that can be considered as indirect space-for-time substitution (SFTS), which is based on the assumption that the growth response across spatial environmental gradients is equivalent to the dynamic growth response in time when site factors shift in situ due to environmental changes over time. In site index modelling this assumption has never been thoroughly tested. We applied procedures to test the validity of the SFTS approach using altitudinal transect analysis of data from long-term experimental plots with Norway spruce (Picea abies) in southwest Germany. The following procedures were applied 1. Partitioning of spatial and temporal variance components of site index and air temperature; 2. Test of the equivalence of spatial and temporal variation in models predicting site index from air temperature; 3. Bias analysis of the SFTS- and the altitudinal range-specific individual models. The results show that the response of site index to changes in growing season air temperature as estimated by the SFTS-based approach is significantly different from the observed temporal dynamics within the plots. The estimated sensitivity of site index to changes in growing season air temperature is significantly larger in the SFTS-model. Bias trends increase with increasing air temperature in all altitudinal ranges. We found significant effects of stand-by-environment interaction on site index responses to changing growing season air temperature. Possible reasons for the found differences are discussed. Furthermore, based on an independent data set from the German National Forestry Inventory (NFI), a SFTS-based climate-sensitive site index model was compared to a state-space modelling approach (SSM) which considers the dynamics of environmental changes over time. The results show that the SSM is statistically superior to the SFTS approach, corroborating the findings of the altitudinal transect analysis. Finally, future site index dynamics of Norway spruce were simulated on the basis of climate change scenarios using the SSM approach. We recommend for all climate sensitive forest growth and yield models based on spatially and temporally distributed data to properly account for within- and between-group effects to avoid erroneous model predictions under climate change.

Consistency and Variation in the Kelp Microbiota: Patterns of Bacterial Community Structure Across Spatial Scales.

Kelp species are distributed along ~ 25% of the world's coastlines and the forests they form represent some of the world's most productive and diverse ecosystems. Like other marine habitat-formers, the associated microbial community is fundamental for host and, in turn, wider ecosystem functioning. Given there are thousands of bacteria-host associations, determining which relationships are important remains a major challenge. We characterised the associated bacteria of two habitat-forming kelp species, Laminaria hyperborea and Saccharina latissima, from eight sites across a range of spatial scales (10s of metres to 100s of km) in the northeast Atlantic. We found no difference in diversity or community structure between the two kelps, but there was evidence of regional structuring (across 100skm) and considerable variation between individuals (10s of metres). Within sites, individuals shared few amplicon sequence variants (ASVs) and supported a very small proportion of diversity found across the wider study area. However, consistent characteristics between individuals were observed with individual host communities containing a small conserved "core" (8-11 ASVs comprising 25 and 32% of sample abundances for L. hyperborea and S. latissima, respectively). At a coarser taxonomic resolution, communities were dominated by four classes (Planctomycetes, Gammaproteobacteria, Alphaproteobacteria and Bacteroidia) that made up ~ 84% of sample abundances. Remaining taxa (47 classes) made up very little contribution to overall abundance but the majority of taxonomic diversity. Overall, our study demonstrates the consistent features of kelp bacterial communities across large spatial scales and environmental gradients and provides an ecologically meaningful baseline to track environmental change.

Increasing temporal variance leads to stable species range limits.

What prevents populations of a species from adapting to the novel environments outside the species' geographic distribution? Previous models highlighted how gene flow across spatial environmental gradients determines species expansion versus extinction and the location of species range limits. However, space is only one of two axes of environmental variation-environments also vary in time, and we know temporal environmental variation has important consequences for population demography and evolution. We used analytical and individual-based evolutionary models to explore how temporal variation in environmental conditions influences the spread of populations across a spatial environmental gradient. We find that temporal variation greatly alters our predictions for range dynamics compared to temporally static environments. When temporal variance is equal across the landscape, the fate of species (expansion versus extinction) is determined by the interaction between the degree of temporal autocorrelation in environmental fluctuations and the steepness of the spatial environmental gradient. When the magnitude of temporal variance changes across the landscape, stable range limits form where this variance increases maladaptation sufficiently to prevent local persistence. These results illustrate the pivotal influence of temporal variation on the likelihood of populations colonizing novel habitats and the location of species range limits.

Genetic differentiation and phylogeography of rotifer Polyarthra dolichoptera and P. vulgaris populations between Southeastern China and eastern North America: High intercontinental differences.

Genetic differentiations and phylogeographical patterns of small organisms may be shaped by spatial isolation, environmental gradients, and gene flow. However, knowledge about genetic differentiation of rotifers at the intercontinental scale is still limited. Polyarthra dolichoptera and P. vulgaris are cosmopolitan rotifers that are tolerant to environmental changes, offering an excellent model to address the research gap. Here, we investigated the populations in Southeastern China and eastern North America and evaluated the phylogeographical patterns from their geographical range sizes, geographic–genetic distance relationships and their responses to spatial‐environmental factors. Using the mitochondrial cytochrome c oxidase subunit I gene as the DNA marker, we analyzed a total of 170 individuals. Our results showed that some putative cryptic species, also known as entities were widely distributed, but most of them were limited to single areas. The divergence of P. dolichoptera and P. vulgaris indicated that gene flow between continents was limited while that within each continent was stronger. Oceanographic barriers do affect the phylogeographic pattern of rotifers in continental waters and serve to maintain genetic diversity in nature. The genetic distance of P. dolichoptera and P. vulgaris populations showed significant positive correlation with geographic distance. This might be due to the combined effects of habitat heterogeneity, long‐distance colonization, and oceanographic barriers. Furthermore, at the intercontinental scale, spatial distance had a stronger influence than environmental variables on the genetic differentiations of both populations. Wind‐ and animal‐mediated transport and even historical events of continental plate tectonics are potential factors for phylogeography of cosmopolitan rotifers.

More than What Meets the Eye: Differential Spatiotemporal Distribution of Cryptic Intertidal Bangiales.

Morphologically similar but genetically distinct species have been termed cryptic and most have been assumed to be ecologically similar. However, if these species co-occur at a certain spatial scale, some niche differences at finer scales should be expected to allow for coexistence. Here, we demonstrate the existence of a disjointed distribution of cryptic bladed Bangiales along spatial (intertidal elevations) and temporal (seasons) environmental gradients. Bladed Bangiales were identified and quantified across four intertidal elevations and four seasons for one year, at five rocky intertidal sites (between 39° S and 43° S) in southern Chile. Species determination was based on partial sequences of the mitochondrial cytochrome c oxidase 1 (COI) gene amplification. To assess species gross morphology, thallus shape, color, and maximum length and width were recorded. Hundreds of organisms were classified into nine Bangiales species belonging to three genera (i.e., Fuscifolium, Porphyra, and Pyropia), including five frequent (>97% of specimens) and four infrequent species. All species, except for Pyropia saldanhae, had been previously reported along the coasts of Chile. The thallus shape and color were very variable, and a large overlap of the maximum width and length supported the cryptic status of these species. Multivariate analyses showed that the main variable affecting species composition was intertidal elevation. Species such as Py. orbicularis were more abundant in low and mid intertidal zones, while others, such as Po. mumfordii and Po. sp. FIH, were principally observed in high and spray elevations. Despite all numerically dominant species being present all year long, a slight effect of seasonal variation on species composition was also detected. These results strongly support the existence of spatial niche partitioning in cryptic Bangiales along the Chilean rocky intertidal zone.

Spatial patterns in the cover and composition of macroalgal assemblages on fringing and nearshore coral reefs

Context Although increases in macroalgal cover on coral reefs are often reported alongside declines in coral, the composition of algal assemblages and their spatial dynamics are not commonly investigated. Aims To quantify changes in macroalgal assemblage composition over two spatial environmental gradients, depth and distance from shore, within a nearshore reef system in Kimbe Bay, Papua New Guinea, where coral cover has declined. Methods Benthic cover was quantified at three depths (reef flat, 10 and 15 m) on the windward reef slopes of six reefs located three distances from shore (fringing reefs, and platform reefs 100–200 m and 0.7−1 km offshore). Key results Macroalgal cover was highest on the reef flat, and assemblage composition varied among depths and distances from shore. Macroalgal cover was not correlated with coral cover except where macroalgal cover was greater than 20%, where a negative correlation occurred. There was no correlation between macroalgal cover and turf algal cover. All three benthic groups were negatively correlated with the combined total cover of sand and gravel. Conclusions These results indicated a fine-scale spatial structure of macroalgal assemblages on coral reefs over a narrow depth range and short distance from shore and highlighted the importance of a solid substratum. Implications It is likely that the ecological interactions between corals and macroalgae vary considerably over narrow spatial gradients.

Review and Synthesis of Estimated Vital Rates for Terrestrial Salamanders in the Family Plethodontidae

Population models depend on reliable estimates of vital rates, yet for many taxa, such estimates and how they vary in response to spatial or temporal environmental gradients are lacking. The goal of this review was to determine whether existing estimates of vital rates for temperate, direct-developing plethodontid salamanders (subfamily Plethodontinae) could be used to reasonably project values for populations or species where such estimates are lacking, or whether current estimates are biased in a manner that limits their utility. We synthesized current knowledge of stage-specific survival rates, age- and size-at-maturity at first clutch, and clutch frequency. We tested for expected correlations among published vital rates (e.g., age at maturity and survival) and between vital rates and factors such as body size or latitude. We used matrix projection models to judge whether published estimates were reasonably possible for stable salamander populations. The largest number of published vital rates were for clutch size, clutch frequency (proportion of females with clutches), size at maturity or first clutch, and age at maturity or first clutch, though the latter vital rate is primarily inferred from size distribution and growth rate data. Among these vital rates, we found expected correlations with body size and latitude suggesting these rates were reasonable and somewhat predictable among species or populations. In contrast, there were few estimates of egg hatch rate or juvenile or adult survival. Hatch and survival rate estimates were widely variable; estimates seldom included measures of uncertainty, but when uncertainty measurements were included, they were generally high. Based on projection models, few survival estimates were likely unbiased or realistic for stable populations given other salamander vital rates. Additionally, few studies quantified how vital rates vary with spatial or temporal environmental gradients. We outline the key knowledge gaps that limit basic demographic modeling of these remarkably common, influential, and otherwise well-studied salamanders, and make recommendations for future research efforts.

Phenotypic stability in scalar calcium of freshwater fish across a wide range of aqueous calcium availability in nature.

Spatial environmental gradients can promote adaptive differences among conspecific populations as a result of local adaptation or phenotypic plasticity. Such divergence can be opposed by various constraints, including gene flow, limited genetic variation, temporal fluctuations, or developmental constraints. We focus on the constraint that can be imposed when some populations are found in locations characterized by low levels of an essential nutrient. We use scales of wild fish to investigate phenotypic effects of spatial variation in a potentially limiting nutrient—calcium. If scale calcium (we use “scalar” calcium for consistency with the physiology literature) simply reflects environmental calcium availability, we expect higher levels of scalar calcium in fish from calcium‐rich water, compared to fish from calcium‐poor water. To consider this “passive response” scenario, we analyzed scalar calcium concentrations from three native fish species (Lepomis gibbosus, Percina caprodes, and Perca flavescens) collected at multiple sites across a dissolved calcium gradient in the Upper St. Lawrence River. Contradicting the “passive response" scenario, we did not detect strong or consistent relationships between scalar calcium and water calcium. Instead, for a given proportional increase in water calcium across the wide environmental gradient, the corresponding proportional change in scalar calcium was much smaller. We thus favor the alternative “active homeostasis” scenario, wherein fish from calcium‐poor water are better able to uptake, mobilize, and deposit calcium than are fish from calcium‐rich water. We further highlight the importance of studying functional traits, such as scales, in their natural setting as opposed to only laboratory studies.

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

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

Local timing of rainfall predicts the timing of moult within a single locality and the progress of moult among localities that vary in the onset of the wet season in a year-round breeding tropical songbird

Rainfall seasonality is likely an important cue for timing key annual cycle events like moult in birds living in seasonally arid environments, but its precise effect is difficult to establish because seasonal rainfall may affect other covarying annual events such as breeding in the same way. In central Nigeria, however, Common Bulbuls Pycnonotus barbatus moult in the wet season but only show weak breeding seasonality. This suggests that moult is more sensitive to rainfall than breeding, but a similar outcome is possible if moult is simply periodic. We tested the relationship between rainfall and moult in Common Bulbuls at a single location over 18 years: on average moult started 5th May (± 41 days: 25th March–15th June), being on average later than the onset of the rains which is usually mid-April. The likelihood of finding a moulting Common bulbul was best predicted by rainfall 9–15 weeks before moult was scored. We then tested the generality of this across populations: the progress of moult should, therefore, correlate with the average timing of the wet season along a spatial environmental gradient where the rains start at different times each year south-to-north of Nigeria. To test this, we modelled moult progress just before the rains across 15 localities 6°–13° N as a function of the onset of the wet season among localities. As predicted, moult progressed further in localities with earlier wet seasons, confirming that the onset of moult is timed to the onset of the wet season in each locality despite weak breeding seasonality in the Common Bulbul. This strategy may evolve to maintain optimal annual cycle routine in seasonal environments where breeding is prone to unpredictable local perturbations like nest predation. It may, however, be less obvious in temperate systems where all annual cycle stages are seasonally constrained, but it may help with explaining the high frequency of breeding–moult overlaps in tropical birds.

Phylogenetic diversity and environment form assembly rules for Arctic diatom genera—A study on recent and ancient sedimentary DNA

AbstractAimThis study investigates taxonomic and phylogenetic diversity in diatom genera to evaluate assembly rules for eukaryotic microbes across the Siberian tree line. We first analysed how phylogenetic distance relates to taxonomic richness and turnover. Second, we used relatedness indices to evaluate if environmental filtering or competition influences the assemblies in space and through time. Third, we used distance‐based ordination to test which environmental variables shape diatom turnover.LocationYakutia and Taymyria, Russia: we sampled 78 surface sediments and a sediment core, extending to 7,000 years before present, to capture the forest–tundra transition in space and time respectively.TaxonArctic freshwater diatoms.MethodsWe applied metabarcoding to retrieve diatom diversity from surface and core sedimentary DNA. The taxonomic assignment binned sequence types (lineages) into genera and created taxonomic (abundance of lineages within different genera) and phylogenetic datasets (phylogenetic distances of lineages within different genera).ResultsContrary to our expectations, we find a unimodal relationship between phylogenetic distance and richness in diatom genera. We discern a positive relationship between phylogenetic distance and taxonomic turnover in spatially and temporally distributed diatom genera. Furthermore, we reveal positive relatedness indices in diatom genera across the spatial environmental gradient and predominantly in time slices at a single location, with very few exceptions assuming effects of competition. Distance‐based ordination of taxonomic and phylogenetic turnover indicates that lake environment variables, like HCO3− and water depth, largely explain diatom turnover.Main conclusionPhylogenetic and abiotic assembly rules are important in understanding the regional assembly of diatom genera across lakes in the Siberian tree line ecotone. Using a space—time approach we are able to exclude the influence of geography and elucidate that lake environmental variables primarily shape the assemblies. We conclude that some diatom genera have greater capabilities to adapt to environmental changes, whereas others will be putatively replaced or lost due to the displacement of the Arctic tundra biome under recent global warming.

Plant functional trait response to environmental drivers across European temperate forest understorey communities.

Functional traits respond to environmental drivers, hence evaluating trait-environment relationships across spatial environmental gradients can help to understand how multiple drivers influence plant communities. Global-change drivers such as changes in atmospheric nitrogen deposition occur worldwide, but affect community trait distributions at the local scale, where resources (e.g. light availability) and conditions (e.g. soil pH) also influence plant communities. We investigate how multiple environmental drivers affect community trait responses related to resource acquisition (plant height, specific leaf area (SLA), woodiness, and mycorrhizal status) and regeneration (seed mass, lateral spread) of European temperate deciduous forest understoreys. We sampled understorey communities and derived trait responses across spatial gradients of global-change drivers (temperature, precipitation, nitrogen deposition, and past land use), while integrating in-situ plot measurements on resources and conditions (soil type, Olsen phosphorus (P), Ellenberg soil moisture, light, litter mass, and litter quality). Among the global-change drivers, mean annual temperature strongly influenced traits related to resource acquisition. Higher temperatures were associated with taller understoreys producing leaves with lower SLA, and a higher proportional cover of woody and obligate mycorrhizal (OM) species. Communities in plots with higher Ellenberg soil moisture content had smaller seeds and lower proportional cover of woody and OM species. Finally, plots with thicker litter layers hosted taller understoreys with larger seeds and a higher proportional cover of OM species. Our findings suggest potential community shifts in temperate forest understoreys with global warming, and highlight the importance of local resources and conditions as well as global-change drivers for community trait variation.

Female solo song and duetting are associated with different territoriality in songbirds

Abstract Recently, there has been an increased effort to unravel selective factors behind female song evolution in songbirds. Female birds which produce songs may sing either solo or in duets; although the 2 vocal performances likely evolved through different selection forces and mechanisms, the majority of large-scale studies to date have focused only on duetting or female song in general (pooling female solo song and duetting into a single category). Hence, here we estimate the effect of behavioral life-history traits (territoriality, social bonds, and cooperative breeding) and environmental productivity on the occurrence of female solo song and duetting separately in songbirds of South Africa and Lesotho. The focal region is characterized by subtropical/tropical climate, clear spatial environmental productivity gradient, and detailed knowledge on avian species distribution and behavioral life-history traits. Phylogenetically informed comparative analyses revealed that species where females produce only solo songs exhibited higher levels of territoriality than species with nonsinging females (in an univariable model) but, simultaneously, lower levels than duetting species. Although both species with female solo song and duetting establish mainly long-term social bonds, the former defend their territories seasonally while the latter exhibit mainly year-round territoriality. Cooperative breeding and environmental productivity were not associated with the distribution of female solo song and duetting in any model. Our results indicate that when exploring female song ecology and evolution, female solo song and duetting are likely to be distinct song categories associated with different levels of territoriality.