Broad-scale Variation Research Articles

Partitioning spatial dynamics in abundance of marine fisheries stocks between fine- and broad-scale variation: A Bayesian approach

Fisheries stocks are often characterized by pronounced spatial patterning. This occurs at different scales, which may be driven by separate mechanisms. Regression kriging is often used to generate population estimates which may parse variation among these scales. A previous application of this and other frequentist methods to estimate the abundance of Atlantic sea scallops (Placopecten magellanicus) found that semi-parametric regression kriging performs best among model-based methods. We expanded upon these results by adapting the model structure for a Bayesian framework. This approach demonstrated the trade-off between abundance as a function of depth and broad spatial habitat features, and of fine-scale spatial aggregation. We applied our model to the 2015 belt transect survey of Atlantic sea scallops in Georges Bank and the Mid-Atlantic Bight off the eastern coast of the United States. The overall Bayesian predictions generally agreed with those of the frequentist method. However, the former favored broad spatial trends coupled with very fine-scale aggregation, while the latter favored finer trends and broad aggregation as the dominant driver of scallop abundance. Therefore, one can draw similar conclusions about abundance, yet disparate conclusions about the drivers. Careful consideration of the benefits and limitations of each approach is warranted.

Broad-scale variation in human genetic diversity levels is predicted by purifying selection on coding and non-coding elements.

Analyses of genetic variation in many taxa have established that neutral genetic diversity is shaped by natural selection at linked sites. Whether the mode of selection is primarily the fixation of strongly beneficial alleles (selective sweeps) or purifying selection on deleterious mutations (background selection) remains unknown, however. We address this question in humans by fitting a model of the joint effects of selective sweeps and background selection to autosomal polymorphism data from the 1000 Genomes Project. After controlling for variation in mutation rates along the genome, a model of background selection alone explains ~60% of the variance in diversity levels at the megabase scale. Adding the effects of selective sweeps driven by adaptive substitutions to the model does not improve the fit, and when both modes of selection are considered jointly, selective sweeps are estimated to have had little or no effect on linked neutral diversity. The regions under purifying selection are best predicted by phylogenetic conservation, with ~80% of the deleterious mutations affecting neutral diversity occurring in non-exonic regions. Thus, background selection is the dominant mode of linked selection in humans, with marked effects on diversity levels throughout autosomes.

Factors affecting broadscale variation in nearshore water-column organic carbon concentrations along the Great Barrier Reef

Organic carbon is a key energy source in marine food-webs, but elevated concentrations can have negative ecological impacts. We used 12 years of marine physiochemical, climate, and near-surface sea and meteorological condition data to investigate broadscale correlates and potential drivers of variability in dissolved and particulate organic carbon (DOC and POC, respectively) concentrations in coastal waters of the Great Barrier Reef (GBR), Australia. DOC concentrations were higher when salinity was lower, when the Southern Oscillation Index was more positive, and at times of greater northward wind speeds. POC concentrations were higher in shallower waters and were positively correlated with total suspended solids and chlorophyll a concentrations. Latitude was important for structuring variation in organic carbon concentrations, likely reflecting terrestrial material from rivers and broader marine processes. We conclude that variability in broadscale patterns of DOC concentrations in GBR coastal waters is likely most sensitive to material discharge from rivers as well as oceanographic and climatic processes and forcing. Variability in broadscale patterns of POC concentrations in coastal waters of the GBR is likely most affected by sediment resuspension and phytoplankton biomass accumulation.

Climate drives global functional trait variation in lizards.

A major challenge in ecology and evolution is to disentangle the mechanisms driving broad-scale variation in biological traits such as body size, colour, thermal physiology traits and behaviour. Climate has long been thought to drive trait evolution and abiotic filtering of trait variation in ectotherms because their thermal performance and fitness are closely related to environmental conditions. However, previous studies investigating climatic variables associated with trait variation have lacked a mechanistic description of the underpinning processes. Here, we use a mechanistic model to predict how climate affects thermal performance of ectotherms and thereby the direction and strength of the effect of selection on different functional traits. We show that climate drives macro-evolutionary patterns in body size, cold tolerance and preferred body temperatures among lizards, and that trait variation is more constrained in regions where selection is predicted to be stronger. These findings provide a mechanistic explanation for observations on how climate drives trait variation in ectotherms through its effect on thermal performance. By connecting physical, physiological and macro-evolutionary principles, the model and results provide an integrative, mechanistic framework for predicting organismal responses to present climates and climate change.

Along-strike distribution of seismicity and large slow slip correlated with gravity at the Nankai Trough

Various earthquakes and slow slip phenomena occur in different locations in the down-dip direction at subduction zones, for example, at the Nankai Trough, Japan. Many earthquakes, tectonic tremors, and slow slip events have occurred on the deeper side of the source areas of the past megathrust earthquakes. We show that three regions with high background seismicity correspond to the source areas of the large (> equivalent moment magnitude 6.5) slow slip events. These regions do not correspond to active areas of tectonic tremors. We note that considering broad-scale variations along the strike of the subduction zone, the three regions also correspond to areas with low free-air gravity anomalies. This fact implies that widespread stress perturbations in the along-strike direction, possibly coupled with pore fluid effects, may control the occurrence of seismic and aseismic slip on subduction faults regardless of whether at the plate interface or within the plate.

Local-scale structuration of species-habitat association in the semi-deciduous tropical rainforest in eastern Cameroon

Tropical forests are hyperdiverse, and although broad-scale variation in diversity can be reasonably well explained, local-scale variation in diversity is harder to understand. It has been revealed that species may show species-habitats associations. However, how the assembled species are associated with local habitats and how community-habitat associations vary regarding species abundance and class size remains unclear. Here, we analyzed the community-habitat associations by applying the multivariate regression trees (MRT) technique on data of 22,064 trees distributed across 30 1-ha plots varying in topography and soil conditions in a semi-deciduous tropical rainforest of Cameroon. Further, the indicator species analysis was used to determine the most important species for structuring assemblages.The MRT divides the whole tree community inventoried into four habitats types: Habitat 1 (H1) sandy loamy, acidic soil with a low Na concentration (pH ≤ 6.245 and [Na] < 4.535 cmol kg−1); H2 equal to neutral sandy soil with a small Na concentration (7 ≤ pH > 6.245 and [Na] < 4.535 cmol kg−1); H3 equal to Loamy sandy soil with average Na concentration (4.535 ≤ [Na] < 6.243 cmol kg−1) and; H4 equal to Loamy sandy soil with high nutrients concentration ([Na] ≥ 6.243 cmol kg−1). Coincidentally, the same habitat types were also generated for the understorey and large trees classes taken separately, although a difference was somehow recorded for the small stems class. Among investigated environmental variables, soil Na content and, to a lesser extent, soil pH were identified as the primary responsible for the first split for habitat types for understorey and large trees classes. By contrast, the most determinant for discrimination habitat types for small stems was soil cation exchange capacity, followed by soil moisture content. Overall, 29 species were found as indicators characterizing the four habitat types for the whole tree community, with index values varying between 33% and 99 %. But specifically, the number of indicators species for large trees was 28. Intriguingly, some indicator species within the large trees class changed to either non-indicator or intermediate indicator species in the understorey trees class that was best represented by as less as 16 species. A comparable species richness was recorded across all plots of the studied area; however, significant variability was found regarding species abundance, with habitats H1 and H4 with higher average abundance values. This study highlights that soil variables adding to topographical habitat filtering were important in shaping the composition of local species.

Citizen science reveals broad-scale variation of calling activity of the Mediterranean tree frog (Hyla meridionalis) in its westernmost range

Abstract Population monitoring is essential to determine different aspects of the ecology and conservation of the species. In anurans, recording the acoustic activity of choruses allows surveying populations. Therefore, knowing the timing of male calls is fundamental to achieve this goal. Here we monitored calling activity of the Mediterranean tree frog (Hyla meridionalis) at eight localities in southern Iberian Peninsula and western North Africa in the frame of a citizen science program. Subsequently, after summarizing call activity with Non-metric Multidimensional Scaling, we aimed to identify the geographic and environmental variables that associate with the calling activity of frogs. The results of the 258-hour census showed that male tree frogs called mainly from December to July, although the duration and intensity of choruses varied, depending on the elevation and seasonality of the water bodies. Males sang earlier and had more durable call activities at lower elevation sites, which are sites with higher and more stable ambient temperatures. Also, calling activity was lower in sites where water fluctuates more over the annual cycle. Our results provide a first overview of the calling activity of the Mediterranean tree frog over a relatively large set of populations encompassing a wide variety of environmental conditions in its westernmost range of distribution. However, further studies relying on more intensive sampling, likely using automatic recorders, would be desirable to achieve a full understanding of the calling activity of tree frogs in the region.

The Origin and Evolution of RNase T2 Family and Gametophytic Self-incompatibility System in Plants.

Ribonuclease (RNase) T2 genes are found widely in both eukaryotes and prokaryotes, and genes from this family have been revealed to have various functions in plants. In particular, S-RNase is known to be the female determinant in the S-RNase-based gametophytic self-incompatibility (GSI) system. However, the origin and evolution of the RNase T2 gene family and GSI system are not well understood. In this study, 785 RNase T2 genes were identified in 81 sequenced plant genomes representing broad-scale diversity and divided into three subgroups (Class I, II, and III) based on phylogenetic and synteny network analysis. Class I was found to be of ancient origin and to emerge in green algae, Class II was shown to originate with the appearance of angiosperms, while Class III was discovered to be eudicot-specific. Each of the three major classes could be further classified into several subclasses of which some subclasses were found to be lineage-specific. Furthermore, duplication, deletion, or inactivation of the S/S-like-locus was revealed to be linked to repeated loss and gain of self-incompatibility in different species from distantly related plant families with GSI. Finally, the origin and evolutionary history of S-locus in Rosaceae species was unraveled with independent loss and gain of S-RNase occurred in different subfamilies of Rosaceae. Our findings provide insights into the origin and evolution of the RNase T2 family and the GSI system in plants.

Broad scale assessment of key drivers of streamflow generation in urban and urbanizing rivers

AbstractUrbanization is characterized by increased impervious cover, artificial drainage via sewers, soil compaction, and vegetation removal, which fundamentally alters how water moves across landscapes. Less rainwater and snowmelt infiltrate the subsurface and stream responses to precipitation are faster and larger compared to natural environments. While the impacts of catchment imperviousness on hydrologic processes have been widely investigated, the relationship between stream hydrologic response and infrastructure‐mediated hydrologic connectivity across a wide range of urban watersheds has not. This study examines the relative magnitude of control that catchment characteristics, total impervious area (TIA), and sewer‐corrected TIA have on broad‐scale spatial variability in hydrologic response. Sewer‐corrected TIA accounts for inter‐catchment water transfer via storm and/or combined sewer pipes and is feasible to estimate at the watershed‐scale using urban drainage asset data. Daily stream discharge data were used to calculate the Richards‐Baker Flashiness Index for 96 watersheds located across southern Ontario, Canada. For a subset of watersheds (n = 39) with suitable stream discharge and rainfall data, watershed average event runoff ratio (RR) was calculated, and watersheds with spatial sewer network data (n = 24), were used to assess if sewer‐corrected TIA is a better predictor of hydrologic response than TIA. As expected, stream flashiness and RR increased linearly as a function of TIA and sewer‐corrected TIA, however, sewer‐corrected TIA did not explain any additional variability in the response variables. Likewise, the relative control of catchment characteristics on the spatial variability in streamflow generation were negligible. Despite sewer‐corrected TIA not improving our understanding of broad scale variation in runoff response, it could be a useful metric to consider when assessing inter‐event variability in runoff response of, heavily urbanized sub‐catchments for improved understanding of flooding and water quality.

Local-scale factors matter for tree cover modelling in Mediterranean drylands

Forests contribute directly to ecosystem structure and functioning, maintaining biodiversity, acting as a climate regulator and reducing desertification. To better manage forests, it is essential to have high-resolution forest models and appropriate spatial-explicit variables able to explain tree cover at different scales, including the management scale. Most tree cover models rely only on broad-scale variables (>500 m), such as macroclimate, while only few studies include also local-scale variables (<500 m). This study aimed to identify the importance of local-scale factors relative to broad-scale factors and identify the environmental variables at different scales that explain tree cover in oak woodlands in Mediterranean drylands. Sixty sites previously identified as being covered with Holm oak or Cork oak were stratified by precipitation. Normalized Difference Vegetation Index, used here as a surrogate of tree cover, was modelled using simultaneously broad-scale factors (macroclimate) and local-scale factors (microclimatic and edaphic conditions). The percentage of variance explained by local- and broad-scale factors and the effect size of each environmental variable on tree cover was determined for the study site. It was found that local-scale factors and their interaction with broad-scale factors explained more variance than broad-scale factors alone. The most important local-scale factors explaining tree cover were elevation, potential solar radiation, used as a surrogate of microclimatic conditions, and wetness evaluated terrain used as an indicator of water flow accumulation. The main broad-scale factors were related to temperature and precipitation. The effect of some local-scale variables in tree cover seems to increase in areas where water as a limiting factor is more important. This study demonstrates the critical importance of including local-scale factors in multi-scale modelling of tree cover to obtain better predictions. These models will support well-suited forest management decisions, such as reforestation and afforestation plans to reverse evergreen oaks decline in Mediterranean drylands.

Niche Variation in Endemic Lilium pomponium on a Wide Altitudinal Gradient in the Maritime Alps.

The relationship between altitudinal and ecological gradients has long been a dominant theme in plant ecology; moreover, how species respond to climate change has renewed this interest. Mediterranean mountains are often hotspots of endemism, and some endemic species have local distributions that span different climatic belts; hence, local variations in topography and fine-scaled niche conditions may play crucial roles in their persistence along such gradients. Studies of the fine-scaled niche are, however, very rare; most studies involve broad-scale variations in climatic parameters. The Turban lily, Lilium pomponium L. is endemic to the Maritime and Ligurian Alps, where it occurs across a wide altitudinal gradient. Previous work has shown no link between climatic marginality and geographic range limits on morphological traits and genetic variability; however, possible variations of local topographic and ecological parameters have not yet been examined. The objective of this paper is to characterise local ecological niche conditions of L. pomponium populations in the different bioclimatic zones it occupies along the altitudinal gradient. The species occurs in four main types of microecological niches. One of these niche types, with a high mineral cover, is the most abundant—type 2: it was detected in 39% of sampled quadrats and occurs across the whole bioclimatic gradient. Other niche types are more limited to subsections of the gradient: type 3 (in 19% of sampled quadrats) is restricted to high-altitude sites (>1070 m.a.s.l.) and is characterised by high vegetation and litter cover; type 4 (26%) corresponds to more forested habitats on substrates with low water retention capacities, in more inland zones close to the centre of L. pomponium distribution and across a range of altitudes; and type 1 (16% of quadrat) only occurs in the Mediterranean part of the gradient, close to distribution limits in pockets of soil among large blocks of rocks, mainly found at mid-altitudes. Despite heterogeneity in the spatial locations of niche types, there is no correspondence between ecological gradients and the distribution limits of this species. Knowledge of the fine-scaled ecological conditions that determine niche types is thus essential for conservation management of the habitats of this species and for the exploration of its possible response to ongoing climate change.

Forest Fires Reduce Snow-Water Storage and Advance the Timing of Snowmelt across the Western U.S.

As climate warms, snow-water storage is decreasing while forest fires are increasing in extent, frequency, and duration. The majority of forest fires occur in the seasonal snow zone across the western US. Yet, we do not understand the broad-scale variability of forest fire effects on snow-water storage and water resource availability. Using pre- and post-fire data from 78 burned SNOTEL stations, we evaluated post-fire shifts in snow accumulation (snow-water storage) and snowmelt across the West and Alaska. For a decade following fire, maximum snow-water storage decreased by over 30 mm, and the snow disappearance date advanced by 9 days, and in high severity burned forests snowmelt rate increased by 3 mm/day. Regionally, forest fires reduced snow-water storage in Alaska, Arizona, and the Pacific Northwest and advanced the snow disappearance date across the Rockies, Western Interior, Wasatch, and Uinta mountains. Broad-scale empirical results of forest fire effects on snow-water storage and snowmelt inform natural resource management and modeling of future snow-water resource availability in burned watersheds.

Multi-scale spatial analysis of household car ownership using distance-based Moran's eigenvector maps: Case study in Loire-Atlantique (France)

Analyzing spatial structures of transportation data at various scales can be of prime interest to transportation planning and governance. In recent years, multi-scale spatial analysis methods have been developed and used in fields like ecology and geography, but only a few studies have applied these methods to transportation data. However, such methods can provide an efficient exploratory tool for: identifying those scales at which transportation data vary spatially; modeling the spatial structures at each scale; and determining the processes at work that explain these spatial structures. This paper describes and demonstrates how a multi-scale spatial analysis method, namely distance-based Moran's eigenvector maps (dbMEM), can be applied to study the spatial layout of car ownership. For this analysis, we rely on aggregated census data for small statistical areas within France's Loire-Atlantique administrative region. At first, 176 spatial vectors representing spatial patterns with a positive autocorrelation are constructed. Among the 176 vectors, only 23 significant ones are retained after performing a regression with car ownership as the dependent variable. Next, we divide these spatial vectors into three sub-models representing three spatial scales: broad scale, medium scale, and fine scale. Lastly, we identify a set of sociodemographic factors capable of explaining the spatial variation at each scale, i.e.: the broad-scale variation is mainly explained by population density, couples with children and income variables; the medium scale by couples with children, share of individuals in the 25–54 year age range and income; and the fine scale by couples with children and income variables.

Macrophenology: insights into the broad-scale patterns, drivers, and consequences of phenology.

Plant phenology research has surged in recent decades, in part due to interest in phenological sensitivity to climate change and the vital role phenology plays in ecology. Many local-scale studies have generated important findings regarding the physiology, responses, and risks associated with shifts in plant phenology. By comparison, our understanding of regional- and global-scale phenology has been largely limited to remote sensing of green-up without the ability to differentiate among plant species. However, a new generation of analytical tools and data sources-including enhanced remote sensing products, digitized herbarium specimen data, and public participation in science-now permits investigating patterns and drivers of phenology across extensive taxonomic, temporal, and spatial scales, in an emerging field that we call macrophenology. Recent studies have highlighted how phenology affects dynamics at broad scales, including species interactions and ranges, carbon fluxes, and climate. At the cusp of this developing field of study, we review the theoretical and practical advances in four primary areas of plant macrophenology: (1) global patterns and shifts in plant phenology, (2) within-species changes in phenology as they mediate species' range limits and invasions at the regional scale, (3) broad-scale variation in phenology among species leading to ecological mismatches, and (4) interactions between phenology and global ecosystem processes. To stimulate future research, we describe opportunities for macrophenology to address grand challenges in each of these research areas, as well as recently available data sources that enhance and enable macrophenology research.

Influence of Seascape on Coastal Lagoon Fisheries: the Role of Habitat Mosaic in the Venice Lagoon

Fisheries are a staple human activity supported by coastal lagoons. Together with water quality and trophic status, lagoon morphology is acknowledged as one of the main ecological drivers of fishery yields; however, the role of lagoon seascape structure is still poorly understood. This paper investigates how morphological variables, habitat distribution and seascape diversity and complexity affect yields of artisanal fishery performed with fyke nets in the Venice Lagoon (northern Adriatic Sea, Italy). Two spatial scales were considered in the analysis, with water quality parameters (temperature, salinity, dissolved oxygen, turbidity, water residence times, N, P and chlorophyll-a concentrations) being measured at a fine, fyke-net scale and morphological (average bottom elevation and sediment grain size) and habitat features (habitat proportion, diversity and complexity) being measured at a broader, seascape scale. Generalised linear mixed models were employed to model 8 years of nekton and green crab catches, disentangling the role of broad-scale morphology and seascape from that of fine-scale water quality. Broad-scale variables clearly influenced fishery target species. Among them, lagoon residents were associated with specific morphological and habitat characteristics, while marine migrants showed a stronger link with overall habitat diversity and complexity. This evidence emphasises how artisanal fishery in the Venice Lagoon relies on the conservation of morphological and habitat heterogeneity. Moreover, it highlights how habitat restoration performed at the seascape level should also be taken into account, in addition to controlling hydrology and water quality, when managing fishery resources in coastal lagoons.

The relationship between scale and predictor variables in species distribution models applied to conservation

Species distribution models have been used to assist decision-making in many different aspects of conservation, restoration, and environmental management. However, to apply species distribution models effectively, we need to discriminate between suitable and unsuitable environments and the models need to be developed at fine scales (i.e. covering small areas at a fine resolution). These characteristics allow more precise decision-making for heterogeneous environments in smaller areas, such as biomes. We also need to understand the potential limiting factors in relation to these models better, including the effects of sample bias in species occurrence records and the potential mismatch between the scale at which the models were built and the scale at which the predictor variables interact with species occurrence. Here we evaluate the effects of two methods used to reduce bias (geographic vs. environmental filters) and three predictor variable types (climactic, local and biotic) on model predictions. We explore these issues for the hyacinth macaw (Anodorhynchus hyacinthinus), a globally vulnerable species in the Pantanal biome of central South America. We consider broad-scale variables, local-scale habitat associations, and the interactions of the macaw with two plant species that provide its food and nesting location. Our results show that using broad-scale climate variables for local-scale models (i.e., models with a fine resolution with a small extent) can generate predictive distribution models that underpredict suitability. Using local and biotic variables generates more accurate models with predictions consistent with the known distribution of the bird species. Although not commonly used, local-scale variables strongly affect model performance by increasing accuracy, reducing omission error, and leading to more conservative predictions. On the other hand, these methods lead to variable results in relation to bias reduction, with their efficiency depending on the amount of sampling bias in the occurrence records. In conclusion, local variables and the method of bias reduction play an important role in species distribution models. Fine resolution models constructed at the local scale for small areas show the greatest skill in predicting species distribution.

Reappraisal of the latest Albian (Mortoniceras fallax Zone) cephalopod fauna from the classical Salazac locality (Gard, southeastern France)

The Salazac locality (Gard, southeastern France) is renowned for the richness of its cephalopod fauna (especially ammonites) from the Mortoniceras fallax Zone (uppermost Albian, Lower Cretaceous). However, most ammonite species have paradoxically been scarcely illustrated up to now. Furthermore, the rare assessments of ammonite taxonomic diversity are presumably inaccurate, as they either result from a drastic typological approach or could not benefit from the most recent advances in modern concepts of ammonoid intraspecific and ontogenetic variations. In this work, we document an original cephalopod assemblage from Salazac represented by abundant, well-preserved specimens (564 studied ammonites, including ca. 50% of heteromorphs) constituting a high diversity. The sample size and quality of this new material allowed some extensive morphological and biometric analyses whenever possible (i.e., for subdatasets in which a significant number of measurements is available) and to thoroughly assess intraspecific and ontogenetic variations for a few species. This led to determine the diagnostic value of various shell characters commonly used to characterize both well-documented and poorly-defined species. In particular, we show that a significant part of the variation in the number of ribs per whorl within the heteromorphic genera Mariella and Turrilitoides is directly related to shell size and that the strength of tubercles covaries negatively with the number of ribs in Mariella, therefore challenging the diagnostic value of these characters. We further suggest that rib density covaries with whorl shape in Mariella, following Buckman’s first rule of covariation. In total, one species of nautilid and 38 taxa (25 genera) of ammonites are described, among which five species are documented from Salazac for the first time. In turn, this study provides valuable data for future phylogenetic, biostratigraphical, biogeographical and broad-scale diversity studies.

Life history mediates the effects of habitat variation on salamander abundance: a multiscale assessment

The conservation of aquatic and semi-aquatic species is dependent on our understanding of species responses to fine and broad-scale habitat heterogeneity. This is particularly true for species of semi-aquatic salamanders, which show dramatic differences in life history strategies. To better conserve salamander biodiversity, it is therefore important to identify how species within stream communities respond to environmental conditions at multiple spatial scales. Stream salamanders are a group of amphibians that require permanent stream flow for reproduction and larval development. While research focusing on plethodontid salamander abundance exists, few have identified how abiotic factors at different scales influence stream salamander density. We aim to determine how responses to habitat factors at different scales differ between species of stream salamanders that have variable life history strategies. We conducted area-constrained repeated count surveys in stream reaches across three watersheds in western North Carolina. We surveyed each plot on three occasions and estimated salamander density based on fine and broad-scale habitat covariates. We found species’ responses to stream water-quality and broad-scale landscape variability were dependent on larval period and adult life history. Species with more aquatic life histories had stronger responses to both water-quality and broad-scale variables, while more terrestrial species responded more strongly to broad-scale variables. Responses to fine and broad-scale habitat variation by stream-salamanders is associated with species larval period and adult life history. Proper assessment of communities of semi-aquatic salamanders, therefore, requires an understanding of both upland and stream conditions, especially when diverse life histories are present.

Trophic resource partitioning drives fine-scale coexistence in cryptic bat species.

Understanding the processes that enable species coexistence has important implications for assessing how ecological systems will respond to global change. Morphology and functional similarity increase the potential for competition, and therefore, co‐occurring morphologically similar but genetically unique species are a good model system for testing coexistence mechanisms. We used DNA metabarcoding and high‐throughput sequencing to characterize for the first time the trophic ecology of two recently described cryptic bat species with parapatric ranges, Myotis escalerai and Myotis crypticus. We collected fecal samples from allopatric and sympatric regions and from syntopic and allotopic locations within the sympatric region to describe the diets both taxonomically and functionally and compare prey consumption with prey availability. The two bat species had highly similar diets characterized by high arthropod diversity, particularly Lepidoptera, Diptera and Araneae, and a high proportion of prey that is not volant at night, which points to extensive use of gleaning. Diet overlap at the prey item level was lower in syntopic populations, supporting trophic shift under fine‐scale co‐occurrence. Furthermore, the diet of M. escalerai had a marginally lower proportion of not nocturnally volant prey in syntopic populations, suggesting that the shift in diet may be driven by a change in foraging mode. Our findings suggest that fine‐scale coexistence mechanisms can have implications for maintaining broad‐scale diversity patterns. This study highlights the importance of including both allopatric and sympatric populations and choosing meaningful spatial scales for detecting ecological patterns. We conclude that a combination of high taxonomic resolution with a functional approach helps identify patterns of niche shift.

Spatial ecology and growth in early life stages of bay anchovy Anchoa mitchilli in Chesapeake Bay (USA)

The bay anchovy Anchoa mitchilli is the most abundant fish in Chesapeake Bay (USA) and is a vital link between plankton and piscivores within the trophic structure of this large estuarine ecosystem. Baywide distributions and abundances of bay anchovy eggs and larvae, and larval growth, were analyzed in a 5 yr program to evaluate temporal and spatial variability based on research surveys in the 1995-1999 spawning seasons. Effects of environmental variability and abundance of zooplankton that serve as prey for larval bay anchovy were analyzed. In the years of these surveys, 97.6% of eggs and 98.8% of larvae occurred in the polyhaline lower bay. Median egg and larval abundances differed more than 10-fold for surveys conducted in the 5 yr and were highest in the lower bay. Within years, median larval abundance (ind. m-2) in the lower bay was generally 1-2 orders of magnitude higher than upper-bay abundance. Salinity, temperature, and dissolved oxygen explained 12% of the spatial and temporal variability in egg abundances and accounted for 27% of the variability in larval abundances. The mean, baywide growth rate for larvae over the 5 yr period was 0.75 ± 0.01 mm d-1, and was best explained by zooplankton concentration and feeding incidence. Among years, mean growth rates ranged from 0.68 (in 1999) to 0.81 (in 1998) mm d-1 and were fastest in the upper bay. We identified environmental factors, especially salinity, that contributed to broadscale variability in egg and larval production.