Differences In Habitat Preferences Research Articles

Culicoides Midge Abundance across Years: Modeling Inter-Annual Variation for an Avian Feeder and a Candidate Vector of Hemorrhagic Diseases in Farmed Wildlife

(1) Background: Epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) are orbiviruses that cause hemorrhagic disease (HD) with significant economic and population health impacts on domestic livestock and wildlife. In the United States, white-tailed deer (Odocoileus virginianus) are particularly susceptible to these viruses and are a frequent blood meal host for various species of Culicoides biting midges (Diptera: Ceratopogonidae) that transmit orbiviruses. The species of Culicoides that transmit EHDV and BTV vary between regions, and larval habitats can differ widely between vector species. Understanding how midges are distributed across landscapes can inform HD virus transmission risk on a local scale, allowing for improved animal management plans to avoid suspected high-risk areas or target these areas for insecticide control. (2) Methods: We used occupancy modeling to estimate the abundance of gravid (egg-laden) and parous (most likely to transmit the virus) females of two putative vector species, C. stellifer and C. venustus, and one species, C. haematopotus, that was not considered a putative vector. We developed a universal model to determine habitat preferences, then mapped a predicted weekly midge abundance during the HD transmission seasons in 2015 (July–October) and 2016 (May–October) in Florida. (3) Results: We found differences in habitat preferences and spatial distribution between the parous and gravid states for C. haematopotus and C. stellifer. Gravid midges preferred areas close to water on the border of well and poorly drained soil. They also preferred mixed bottomland hardwood habitats, whereas parous midges appeared less selective of habitat. (4) Conclusions: If C. stellifer is confirmed as an EHDV vector in this region, the distinct spatial and abundance patterns between species and physiological states suggest that the HD risk is non-random across the study area.

Assessing Contamination Profiles in Livers from Road-Killed Owls.

Raptors are recognized as valuable sentinel species for monitoring environmental contaminants owing to their foraging behavior across terrestrial and aquatic food webs and their high trophic position. The present study monitored environmental contaminants in livers from road-killed owls to evaluate differences in the exposure patterns due to factors such as species, age, and sex of individuals. Carcasses of road-killed individuals of eagle owl (Bubo bubo), long-eared owl (Asio otus), little owl (Athene noctua), tawny owl (Strix aluco), and barn owl (Tyto alba) were collected in Alentejo (Portugal). Eighty-one organic contaminants were analyzed, including organochlorine pesticides (OCPs), per- and polyfluoroalkyl substances (PFAS), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals, in-use pesticides, and organophosphate esters (OPEs). Overall, 21 contaminants were detected. In all species ∑OCPs were prevalent at concentrations from 3.24 to 4480 ng/g wet weight, followed by perfluorooctane sulfonic acid (PFOS), the only PFASs detected (from 2.88 to 848 ng/g wet wt) and ∑PCBs (1.98-2010 ng/g wet wt); ∑PAHs were ubiquitous but detected at the lowest concentrations (7.35-123 ng/g wet wt). Differences among species were observed according to principal component analysis. Eagle owl and long-eared owl presented the highest levels of ∑OCPs, ∑PCBs, and PFOS, consistent with its higher trophic position, while ∑PAHs prevailed in tawny owl, barn owl, and little owl, related to their frequent use of urban areas for nesting and roadsides for hunting. Adults presented higher concentrations of ∑OCPs and ∑PCBs than juveniles, while no differences were observed for PFOS and ∑PAHs. Pharmaceuticals, in-use pesticides, and OPEs were not detected. Overall, the present study shows specific contamination patterns in five species with similar diet but with differences in habitat preferences. Environ Toxicol Chem 2024;43:821-832. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Understanding the Dynamics of Sex-Specific Responses Driven by Grassland Management: Using Syrphids as a Model Insect Group

Grassland ecosystems, managed by various grassland managements strategies, are the world’s most important land use. However, insect’s sex-specific responses within the context of grassland management have never been considered before. Therefore, our aim was to expand the understanding to the dynamics of grassland managements that drive sex-specific responses by using syrphids as a model insect group. We hypothesize that (1) male and female syrphids exhibit differential habitat preferences in grassland managements, (2) abundance and activity of male and female syrphid levels are influenced by vegetation structure in grassland habitats. Extensive and intensive grassland exhibited significantly different male and female syrphid abundance compared to abandoned grassland. Surprisingly, grassland management had a significant impact on male syrphids richness only, not on female. Flower cover significantly increased male and female syrphid abundance and richness. However, plant height significantly increased female syrphid abundance and richness only. Interestingly, abandoned grassland supports a higher amount of unique female syrphids than male syrphids. The dynamics of grassland management are not unidirectional, but they are multifaceted and multidirectional. Considering the importance of sex-specific responses by insects can provide a more comprehensive understanding of dynamics of grassland managements.

Flexible genomic island conservation across freshwater and marine Methylophilaceae.

The evolutionary trajectory of Methylophilaceae includes habitat transitions from freshwater sediments to freshwater and marine pelagial that resulted in genome reduction (genome-streamlining) of the pelagic taxa. However, the extent of genetic similarities in the genomic structure and microdiversity of the two genome-streamlined pelagic lineages (freshwater "Ca. Methylopumilus" and the marine OM43 lineage) has so far never been compared. Here, we analyzed complete genomes of 91 "Ca. Methylopumilus" strains isolated from 14 lakes in Central Europe and 12 coastal marine OM43 strains. The two lineages showed a remarkable niche differentiation with clear species-specific differences in habitat preference and seasonal distribution. On the other hand, we observed a synteny preservation in their genomes by having similar locations and types of flexible genomic islands (fGIs). Three main fGIs were identified: a replacement fGI acting as phage defense, an additive fGI harboring metabolic and resistance-related functions, and a tycheposon containing nitrogen-, thiamine-, and heme-related functions. The fGIs differed in relative abundances in metagenomic datasets suggesting different levels of variability ranging from strain-specific to population-level adaptations. Moreover, variations in one gene seemed to be responsible for different growth at low substrate concentrations and a potential biogeographic separation within one species. Our study provides a first insight into genomic microdiversity of closely related taxa within the family Methylophilaceae and revealed remarkably similar dynamics involving mobile genetic elements and recombination between freshwater and marine family members.

Relative importance of vegetation features and intra- and inter-specific interactions on habitat preferences of a raptor guild in eucalypt plantations

Forest plantations are increasingly recognized for their role in providing ecosystem services in agroforestry systems. Understanding the habitat preferences of potentially beneficial birds supports effective forest management. Our study focused on identifying breeding habitat preferences of a raptor guild and assessing exotic eucalypt plantations as potential breeding sites. We explored preferences at various spatial scales considering vegetation features, intraspecific territorial behaviour, and interspecific interactions within the guild to determine their importance. We hypothesized that feeding habits and body mass explain differences in habitat preferences among three diurnal raptors (Northern goshawk, Common buzzard, Eurasian sparrowhawk). We employed random forest models to differentiate breeding sites from control plots, assessing factors' relative importance and unravelling the hierarchical process of habitat selection in southwestern Europe's eucalypt plantations. The studied eucalypt plantations emerged as suitable breeding habitats, harbouring dense breeding populations with uniform spatial distribution. Intraspecific territoriality and vegetation significantly influenced breeding habitat selection, while interspecific interactions held lesser influence. Species-specific variations were attributed to feeding habits and body masses. Tall eucalypt trees and mature-like patches were crucial elements driving breeding habitat selection. Raptors' preference for specific woody elements primarily influences areas within a relatively small radius around their nests (including the nest tree, nest site −10 m radius, and nest stand −50 m), with sparrowhawks showing preferences extending to 125 m. Raptors' inclination for mature woody elements and mature forest patches should steer forest management to bolster these apex predators and their contributions in eucalypt plantations within agroforestry systems.

Dynamic human, oceanographic, and ecological factors mediate transboundary fishery overlap across the Pacific high seas

AbstractThe management and conservation of tuna and other transboundary marine species have to date been limited by an incomplete understanding of the oceanographic, ecological and socioeconomic factors mediating fishery overlap and interactions, and how these factors vary across expansive, open ocean habitats. Despite advances in fisheries monitoring and biologging technology, few attempts have been made to conduct integrated ecological analyses at basin scales relevant to pelagic fisheries and the highly migratory species they target. Here, we use vessel tracking data, archival tags, observer records, and machine learning to examine inter‐ and intra‐annual variability in fisheries overlap (2013–2020) of five pelagic longline fishing fleets with North Pacific albacore tuna (Thunnus alalunga, Scombridae). Although progressive declines in catch and biomass have been observed over the past several decades, the North Pacific albacore is one of the only Pacific tuna stocks primarily targeted by pelagic longlines not currently listed as overfished or experiencing overfishing. We find that fishery overlap varies significantly across time and space as mediated by (1) differences in habitat preferences between juvenile and adult albacore; (2) variation of oceanographic features known to aggregate pelagic biomass; and (3) the different spatial niches targeted by shallow‐set and deep‐set longline fishing gear. These findings may have significant implications for stock assessment in this and other transboundary fishery systems, particularly the reliance on fishery‐dependent data to index abundance. Indeed, we argue that additional consideration of how overlap, catchability, and size selectivity parameters vary over time and space may be required to ensure the development of robust, equitable, and climate‐resilient harvest control rules.

Phylogeographic and demographic patterns reveal congruent histories in seven Amazonian White‐Sand ecosystems birds

AbstractAimThe drivers of genetic diversity in Amazonia, the most species‐rich set of ecosystems on Earth, are still incompletely understood. Species from distinct Amazonian ecosystems have unique biogeographic histories that will reflect regional landscape and climatic drivers of genetic diversity. We studied bird species from patchy Amazonian white‐sand ecosystems (WSE) to evaluate the occurrence of shared biogeographic patterns to better understand the complex environmental and landscape history of Amazonia and its biodiversity.LocationNorthern South America; Amazonia.TaxonPasseriformes.MethodsWe sequenced Ultra‐conserved Elements (UCEs) from 177 samples of seven bird species associated with WSE that have overlapping ranges. We used the SNP matrices and sequence data to estimate genetic structure and migration surfaces using ‘conStruct’ and eems, performed model‐selection to obtain the most probable demographic histories on ‘PipeMaster’ and implemented analyses of shared demography with ecoevolity.ResultsShallow genetic structure patterns varied among species. The Amazon river was the only barrier shared among them. Population structure dates to no more than 450,000 years ago. Nine geographically structured populations showed signals of population size changes and eight of these occur in Northern Amazonia. Population expansion was inferred at two distinct times: ~100,000 and ~ 50,000 years ago. The timing of co‐expanding populations is consistent with differences in habitat preference, as species that prefer dense scrubby to forested vegetation expanded more recently compared to species that prefer open vegetation.Main conclusionsWSE species responded in concert to environmental and landscape changes that occurred in the relatively recent past. Population expansions were likely driven by the genesis of new WSE patches and a return to wetter conditions after glacial periods. Pleistocene climatic cycles affected the distribution and dynamics of open vegetation habitats in Amazonia, especially in the Northern region, driving genetic diversity and demographic patterns of its associated biota.

Abundance and characterization of microplastics in amphipods from the Japanese coastal environment.

Microplastics can be ingested by tiny detritivores such as amphipods, with potential consequences on the food chain. The present study characterizes the abundance, chemical composition, and size of microplastics in amphipods found in the Japan Sea coastal environment, which is a hotspot for microplastic accumulation. High amounts of microplastic ingestion and a large discrepancy by amphipod species, Talorchestia nipponensis, Ampithoe valida, and Trinorchestia trinitatis, were observed (between 0.2 and 76.3 particles/individual) which may be due to differences in habitat preference and background contamination. This result indicates that coastal amphipods in particular may ingest large amounts of microplastics. The average microplastic particle size in amphipods was 59 ± 8.6µm, with 83% of particles smaller than 90µm, and polyethylene was dominant. This study provides insights into microplastic abundance in coastal amphipods and the context for further studies on coastal amphipod microplastic ingestion.

Habitat preference influences response to changing agricultural landscapes in two long-horned bees

Agricultural intensification and urban development have drastically influenced pollinators living in semi-natural grasslands. Pollinators are likely to have different responses to more intensive land uses; some decline rapidly, whereas others maintain or increase their populations. We predicted that differences in interspecific responses to different land uses are partly attributed to differences in habitat preference. We examined the distribution and flower use patterns of two closely related Eucera species with different habitat preferences. Study sites were narrow belt-like meadows within traditional, intensified, and urbanised agricultural lands in the Osaka-Kobe metropolitan area, Japan. Forest-associated Eucera nipponensis were significantly fewer in consolidated and urbanised meadows than in traditional meadows, whereas open land-associated E. spurcatipes exhibited the opposite pattern. A significant negative relationship between their abundance was also found. Both species foraged on legume flowers most frequently (83.5%), but their floral use patterns differed significantly in traditional and consolidated meadows. The bee species that preferred stable habitats were vulnerable to land consolidation and urbanisation, while the species associated with disturbed habitats maintained or increased its population size in meadows with these intensive land uses. Thus, recent land-use changes may have different impacts on species with different habitat preferences.

Use of the generalist predator Anystis baccarum in greenhouse IPM: Interactions with other biological control agents, a laboratory study

A generalist predatory mite, Anystis baccarum (L.), was developed as a new biocontrol agent in Canada, and became commercially available in 2022. Because successful biological control programs in greenhouse crops rely on the release of several natural enemies simultaneously to deal with multiple pest species, this study assessed the interaction of A. baccarum with other commonly used biocontrol agents in laboratory trials. Note that only adult stages were used, because the agents tested are predominantly sold and released as adults. Anystis baccarum killed and consumed the generalist phytoseiid mites, Neoseiulus cucumeris (Oudemans) and Amblyseius swirskii Athias-Henriot; however, the mortality of the phytoseiid mites was reduced when an alternative food, Ephestia kuehniella Zeller eggs, was available. There was no intra-guild interaction between A. baccarum and the soil-dwelling predatory mite, Stratiolaelaps scimitus (Womersley). No statistically significant mortality was observed when Orius insidiosus (Say), a generalist hemipteran, or Delphastus catalinae (Horn), a coccinelid beetle used to control whiteflies, were confined with A. baccarum without alternative food for 24 h. The susceptibility of A. baccarum to the entomopathogenic fungus Beauveria bassiana (Balsamo) GHA strain was evaluated by exposing the mites to conidia in a filter paper bioassay. Differences in mite mortality were not significant across all treatments, and only one case of successful sporulation fungal growth was observed from cadavers recovered in the experiments; similarly, differences in the number of eggs produced were not significant across all treatments. Although the laboratory trials sometimes showed severe predation pressure from A. baccarum on other biocontrol agents, they are likely to be functionally compatible in the greenhouse owing to differences in habitat preferences and availability of other prey (pests) or another food source. Results of the current study provide insights that will enable the development of rational biocontrol programs that include A. baccarum.

Sexual segregation occurs in bats within fragmented remnant woodlands in an agricultural landscape.

Species‐specific responses to landscape configuration and landscape composition have been studied extensively. However, little work has been done to compare intraspecific differences in habitat preferences. Bats have potential as good bioindicator taxa in woodland habitats. Therefore, studying sex differences in responses to woodland and the wider landscape can allow us to gain insight into the relative importance of these habitats for both bats and other taxa. In this study, we aimed to test the predictions that (i) habitat type and connectivity will influence the probability of recording female bats in woodlands and (ii) sex differences in response to habitat type and connectivity will be species‐specific. Bat capture data was collected in 206 woodlands over 3 years in England. The probability of detecting females relative to males was modeled in response to a range of woodland characteristics and landscape metrics for six bat species. We recorded sex differences in responses to landscape features in three species. We found a higher probability of capturing female Myotis nattereri in woodlands that were surrounded by a higher proportion of improved grasslands, whereas female Myotis mystacinus were less likely to be recorded in woodlands surrounded by semi‐natural vegetation. Female Plecotus auritus were more likely to be recorded in isolated woodlands with less connectivity to other woodlands and where agriculture dominated the surrounding landscape. Our findings indicate that sexual segregation occurs across several UK bat species in response to landscape connectivity and composition. Sexual segregation in response to landscape characteristics in bats should therefore be an important consideration in the management of fragmented agricultural landscapes.

Spatial dynamic N‐mixture models with interspecific interactions

Abstract Interspecific interactions and movement are key factors that drive the coexistence of metapopulations in heterogenous landscapes. Yet, it is challenging to understand these factors because separating movement from local population processes relied on capture‐based data that are difficult to collect. Recent development of spatial dynamic N‐mixture models (SDNMs) made it possible to draw inferences on local population growth and movement using count data of unmarked populations. However, no SDNMs have been developed to account for interspecific interactions and double‐counting observation errors. In this study we further developed SDNMs to account for interspecific interactions and both false‐negative and double‐counting observation errors. We conducted simulation studies to evaluate the inferential performance of these models under different ecological systems (competition, predator–prey), observation processes (binomial, Poisson) and sampling situations including the number of surveyed sites, detection and the adoption of robust sampling design. We then illustrated the applications of these models with two case studies, one representing a competition system (mallard Anas platyrhynchos, northern pintail Anas acuta) with binomial observations and the other representing a predator–prey system (bobcat Lynx rufus, wild turkey Meleagris gallopavo) with Poisson observations. The results of the simulation studies showed that the models provide unbiased parameter estimates regardless of the ecological system, observation process and sampling situation. Case studies further demonstrated the capabilities of these models in revealing important ecological processes. More specifically, the first case study revealed a negative effect of the superior competitor, Mallard, on the population growth of the inferior competitor, pintail as well as different movement patterns between these species, whereas the second case study reveal a top‐down effect of bobcat abundance on wild turkey population growth and their differential habitat preferences. The models developed in this study could be used by themselves on count data or serve as population sub‐models in integrated modelling frameworks to provide insights about metapopulation dynamics of interacting species in heterogeneous landscapes. The flexible structures of these models made them highly adaptive and relevant in population and community ecology.

Fish diversity and habitat ecology of Tel River, a tributary of Mahanadi River

Ichthyofaunal survey was conducted in Tel River, an important tributary of Mahanadi River to document the diversity and distribution of freshwaterfishes along with evaluation of the habitat characteristics. A total of 71 fish species belonging to 48 genera, 22 families and 8 orders were recorded fromthe study area. Cypriniformes was found to be the most dominant order 53.5%), followed by Siluriformes (19.7%) and Perciformes (14.1%). It is of high concernthat some of the food fishes exploited by the local communities fall in "Near Threatened" or "Endangered" category of IUCN. Higher species richness anddiversity were observed at Belgaon and Kisinga in the midstream. Shannon-Weiner diversity index ranged between 2.33 and 3.705 indicating well-being of the river. Habitat and water quality parameters were documented and correlation analysis between the parameters was carried out. Canonical Correspondence Analysis (CCA) was employed to understand the differential habitat preferences of biota and environmental variables and cyprinids were found to have a positive relationship with wetted area and channel width. Fish diversity can be periodically monitored to form basis for future conservation plans. The study would assist in formulating strategies for management of this riverine ecosystem and livelihood support of fisher communities.

Seasonal modifications of longitudinal distribution patterns within a stream: Interspecific interactions in the niche overlap zones of two Ephemera mayflies.

Niche differentiation between closely related species leads to differentiation of their habitats. Segregation based on slight differences in environmental factors, that is niche differentiation on the microhabitat scale, allows more species to inhabit a certain geographic space. Therefore, such fine scale niche differentiation is an important factor in the support of species diversity. In addition, niche differentiation on the microhabitat scale and/or the differentiation of breeding seasons can be considered typical mechanisms that facilitate multispecies’ co‐existence. In this study, sister species (Commonly, Ephemera japonica inhabit at upstream region and Ephemera strigata inhabit at middle stream region), which often coexist in the upper to middle reaches of river systems of the Japanese Islands, were targeted and the following aspects were investigated. First, differences in habitat preference and interspecific differences in flow distribution patterns on a geographically fine scale were tracked in detail. Subsequently, the temporal transitions of their distribution patterns were investigated in detail and seasonal changes were investigated. Finally, we thoroughly investigated the disappearance of nymphs of each species from the river due to emergence affected the distribution of each species (by conducting daily emergence surveys). Combining results of these multiple studies also suggested that there may be spatiotemporal interspecial interaction between these two species within/around their overlapping regions. Traditionally, the longitudinal distribution pattern of these two Ephemera mayflies has been thought to be established based on a difference in habitat preferences, but this study revealed that the interspecific interaction between the two species also plays an important role. This study provides new insights into species diversity and distribution pattern formation in river‐dwelling species.

Micro-endemic species of snails and amphipods show population genetic structure across very small geographic ranges.

Understanding variation in population genetic structure, even across small distances and for species with extremely limited ranges, is critical for conservation planning and the development of effective management strategies for imperiled species. Organisms that occupy the same geographic extent can maintain different population structures, ranging from highly diverged to panmictic. Such differences can result from differences in biological characteristics such as dispersal ability or demographic history. We used microsatellite loci to evaluate population genetic structure and variation of four desert spring invertebrates having high to low dispersal ability: the lung snail Physa acuta, two species of gilled snails (Juturnia kosteri and Pyrgulopsis roswellensis; family Hydrobiidae) and the amphipod Gammarus desperatus. The study location represents entire species ranges for the micro-endemic hydrobiids and G. desperatus, while P. acuta is ubiquitous throughout much of North America. We found little evidence of significant population genetic structure for P. acuta and J. kosteri, but much more for P. roswellensis and G. desperatus. Our results demonstrate differences in habitat preference and/or dispersal ability between the species. This information provides insight into how gene flow shapes varying population genetic structure between species across small spatial scales (<100 km2). Most importantly, our results suggest that conservation agencies should not consider these micro-endemic species to be composed of single populations, but rather, that management plans for such species should account for population genetic variation across the species' ranges.

Niche segregation on the landscape scale of two co-existing related congeners in the sympatric zone – modelling approach

Co-occurence of related congeners is one of the most complicated ecological phenomena. Although such species are characterised by niche conservatism, which should exclude their stable co-existence, a communities often consist of sister species. Thus, there must be some ecological mechanism that separates them spatially or temporally. This study advocates that the answer is niche divergence that results from interspecific competition. Despite numerous studies documenting this biotic interaction as an important ecological process that segregates species spatially, only few deal with niche divergence between allotopy and syntopy in a mosaic of a large sympatric zone. That is why I decided to analyse the co-existence of two sister species, the Whinchat Saxicola rubetra and the Stonechat Saxicola rubicola in a sympatric zone, where both species occur alongside in syntopic sites, and separately in allotopic sites. Besides, I analyse the Whinchat's potential niche divergence between sympatric and allopatric zones which can be designated on the territory of Poland. It is assumed that niche divergence resulting from interspecific competition can be observed on the basis of differences in habitat preferences of one or both species between syntopy and allotopy, and also for the Whinchat between the sympatric and the allopatric zone. The assumptions were tested in generalised mixed-effect modelling and contrast analyses based on a large dataset of bird density in Poland. Both species demonstrated shifted environmental preferences between syntopy and allotopy, while in allopatry both species had similar niche preferences. The Whinchat also indicated no differences between allopatry and allotopy. Thus, the adopted analytical system clearly proves that the co-existence of congeneric species is possible due to niche divergence, which most likely results from interspecific competition.

Relationship between the distribution of vegetation and the environment in the coastal embryo dunes of Jalisco, México.

BackgroundThe poorly developed soils of the embryo dunes imply little capacity for plant support, however, the adaptation mechanisms of plants respond sensitively to environmental variations, even when these variations are small, which results in a set of specialized habitats and flora that are rarely shared with other terrestrial ecosystems. The coastal dunes of the Mexican Pacific remain vaguely studied, this is why this research explored the relationship between environmental properties and the presence of plant species in the embryo dunes of the coast of Jalisco, Mexico.MethodsTwenty-nine sites were sampled, one or two sites per embryo dune, with a random stratified design. Geomorphological and vegetation data were collected at site. Laboratory determinations included soil color, particle size, organic matter, pH, electrical conductivity, magnetite content, and moisture retention. Statistical analysis included correlation analysis to identify relationships between environmental variables; principal component analysis (PCA) and cluster analysis to group dune sites by environmental properties; canonical correspondence analysis (CCA) to determine a possible significant relationship between the presence of plant species and environmental variables; cluster analysis to group dune sites by presence/absence of plant species and correlate both clusters to validate the relationship between them, the salient aspects of this relationship were described and the spatial distribution of the groups was mapped.ResultsEleven plant species were identified, six of them exclusive to the embryo dunes and the rest ubiquitous. The incipient development of these soils is reflected in a low content of organic matter, silt, clay, and moisture retention, with scattered data on granulometry, electrical conductivity, organic matter, and magnetite. Some significant correlations were found between some environmental properties, and the CCA showed a significant relationship between the presence of plant species and environmental variables (p-value of the Monte Carlo test = 0.026). The cluster analysis of dune sites according to environmental variables and the cluster analysis by presence/absence of plant species produces the formation of five groups of sites with significant environmental differences and five groups of sites with significant floristic differences. A significant connection (r = 0.471, p = 0.01) between the two clustering schemes also evidences the meaningful relationship between the presence of plant species and the environmental characteristics of the embryo dunes of Jalisco, Mexico. Differences in habitat preferences were observed among plant species exclusive to the embryo dunes; thus, Abronia maritima, Uniola pittieri, and Pectis arenaria showed a preference for embryo dunes with poor edaphic conditions, in contrast to Okenia hypogaea, Canavalia rosea, and Scaevola plumieri, which were mostly found in embryo dunes with higher fertility.

Simple and complex burrow morphology in two Macrophthalmus species on the intertidal mudflats of Barr Al Hikman, Sultanate of Oman

ABSTRACT Burrowing Ocypodoidea crabs are an abundant component of many tropical and temperate coastal areas and central to the ecosystem functioning, for instance because they recycle nutrients, are important food for many shorebirds and alter the sediment through their burrowing behaviour. The burrow morphology of these crabs may differ between and within species, often correlated with differences in habitat preferences, crab morphology and life-history traits. Here we studied the burrow morphology and complexity of Macrophthalmus sulcatus and Macrophthalmus depressus, by means of casts (n = 7 and 10, respectively) and burrow excavations (n = 17 and 16, respectively) at the pristine intertidal mudflats of Barr Al Hikman in the Sultanate of Oman. We found that M. sulcatus construct simple burrows that were in all but one case inhabited by a single crab. By contrast, all burrows of M. depressus were complex, with multiple entrances and many (deep-reaching) branches. There was a strong relationship between M. sulcatus carapace width and burrow entrance size, indicating that the simple burrows are adapted to and made by the occupant. There was no relation between M. depressus carapace width and burrow entrance size, and in six burrows more than one crab was encountered, suggesting that the complex burrows are not made by and adapted to a single occupant. The complex burrows were found close to the shore whereas the simple burrows were found at the intermediate tidal zone. We speculate that the striking differences in burrow morphology may be explained by difference in habitat selection of the studied crabs, which most importantly relates to differences in sediment structure and tidal height. Crab morphology and life-history traits of the studied crabs could also account for the observed difference in burrow morphology.

First insights into population parameters and spatial distribution of the two morphotypes of Mactra stultorum (brownish and whitish) (Linnaeus, 1758) (Mollusca: Bivalvia) along the southwestern Spanish coast

ABSTRACT The aim of this study was to address an analysis of spatial distribution, reproduction, population parameters and secondary production of the natural beds of the well-defined morphotypes of the clam Mactra stultorum (brownish and whitish variants) along the SW Spanish coast. The main findings showed that the presence and the frequencies of both morphotypes increased near the estuaries of rivers, particularly the Guadalquivir River. However, subtle differences in habitat preferences have been revealed and the brownish variant showed a wider and deeper distribution. High similarity in the gonadal development was recorded for both variants. It started in January, continued into late winter and early spring and ended with a spawning period from April to August. An energy storage-utilization cycle, coupled to the reproductive and resting periods and driven by seawater temperature variations and food availability, was also observed. The abovementioned period of gamete emissions resulted in a recruitment pattern with a one-time settlement period per year. Von Bertalanffy growth functions provided an asymptotic length of 46.7 mm (whitish) and 50 mm (brownish) and growth constants of 0.55 (whitish) and 0.50 year−1 (brownish). The mean annual biomass () ranged between 0.062 (whitish) and 0.076 g AFDW m−2 year−1 (brownish) (AFDW: ash-free dry mass). Individual somatic production showed the highest value at 32 and 34 mm shell length, and annual production (P) ranged between 0.075 and 0.113 g AFDW m−2 year−1, resulting in renewal rate (P/) values between 1.21 and 1.37 for the whitish and brownish variants, respectively. These results provide basic knowledge about the reproduction and population dynamics of this species along the Atlantic coast, particularly in the sandflats near the estuary of the Guadalquivir River. They could also shed additional light upon taxonomic differentiation and clarify the ecological role of both variants when compared with two bivalve sympatric species of the intertidal and subtidal areas.

DNA Metabarcoding Revealed Interspecific Dietary Difference and Prey Selectivity in Juvenile Horseshoe Crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus From Hong Kong

Horseshoe crabs provide important ecological services including bioturbation and linking of food web in the shallow waters, but their populations are declining globally, leading to major concerns on conservation of these iconic animals. Baseline information of horseshoe crab ecology, such as their trophic role and food source, is pre-requisite for habitat protection plan and captive restocking program. Trophic ecology of Asian horseshoe crabs is relatively poorly understood and previous studies on their juveniles have suggested that they are selective feeders rather than opportunistic generalists. This study demonstrates a non-invasive approach, using DNA metabarcoding analyses of the nuclear 18S rRNA gene on fecal samples to assess the dietary compositions of Carcinoscorpius rotundicauda and Tachypleus tridentatus juveniles to (1) determine their dietary compositions and trophic roles in their ecosystem, (2) determine any prey selectivity, and (3) distinguish the interspecific dietary differences with potential implications on the habitat requirement and ecological partitioning between these two horseshoe crab species. The results based on relative read abundance (RRA) suggested that oligochaetes were the major prey items for both C. rotundicauda (41.6%) and T. tridentatus (32.4%). Bivalves and crustaceans were second major prey groups for C. rotundicauda (8.6 and 8.4%, respectively). Surprisingly, anthozoans contributed a considerable portion of T. tridentatus’s diet (22.8%), which has never been reported. Furthermore, the major prey groups identified in the fecal samples were not the dominant benthic organisms in the studied area as revealed by environmental DNA (eDNA) analyses on the sediment samples, implying that both species are selective feeders rather than dietary generalists. Significant differences observed in the dietary compositions of the two species might be partially due to the difference in habitat preference between the two species. This study provides new insights into the trophic ecology of the two Asian horseshoe crab species in the estuarine habitat and establishes a new framework for future detailed molecular dietary analyses on all developmental stages of horseshoe crabs around the world, which will allow us to evaluate the food sources needed for the survival of horseshoe crabs and facilitate future conservation strategies without killing the animals.