Effects Of Habitat Characteristics Research Articles

Review of range-wide vital rates quantifies eastern wild Turkey population trajectory.

Recent declines in eastern wild turkeys (Meleagris gallopavo silvestris) have prompted increased interest in management and research of this important game species. However, the mechanisms underlying these declines are unclear, leaving uncertainty in how best to manage this species. Foundational to effective management of wildlife species is understanding the biotic and abiotic factors that influence demographic parameters and the contribution of vital rates to population growth. Our objectives for this study were to (1) conduct a literature review to collect all published vital rates for eastern wild turkey over the last 50 years, (2) perform a scoping review of the biotic and abiotic factors that have been studied relative to wild turkey vital rates and highlight areas that require additional research, and (3) use the published vital rates to populate a life-stage simulation analysis (LSA) and identify the vital rates that make the greatest contribution to population growth. Based on published vital rates for eastern wild turkey, we estimated a mean asymptotic population growth rate (λ) of 0.91 (95% CI=0.71, 1.12). Vital rates associated with after-second-year (ASY) females were most influential in determining population growth. Survival of ASY females had the greatest elasticity (0.53), while reproduction of ASY females had lower elasticity (0.21), but high process variance, causing it to explain a greater proportion of variance in λ. Our scoping review found that most research has focused on the effects of habitat characteristics at nest sites and the direct effects of harvest on adult survival, while research on topics such as disease, weather, predators, or anthropogenic activity on vital rates has received less attention. We recommend that future research take a more mechanistic approach to understanding variation in wild turkey vital rates as this will assist managers in determining the most appropriate management approach.

ODONATA DIVERSITY AT THE MOUNT PERMISAN NATURAL TOURISM PARK SOUTH BANGKA REGENCY, BANGKA BELITUNG

Mount Permisan Natural Tourism Park, South Bangka regency is a conservation area that contains flora and fauna. The diversity of fauna in conservation areas is important to note because fauna can maintain the balance of natural ecosystems. This study aims to analyze the diversity of species and the effect of habitat characteristics on the Odonata population. Odonata sampling was carried out using an insect net randomly at a predetermined point in the left and right directions of the 100 m transect line. Identification was carried out at the Entomology Laboratory, Agricultural Quarantine Center Pangkalpinang, and compared with a comparison sample at the Zoology Laboratory, Biology Department, Universitas Bangka Belitung. Based on the research that has been done, found 14 species of Odonata from the sub-order Anisoptera and 11 species of damselfishes from the sub-order Zygoptera. The species diversity at that location was classified as moderate because H' was 1.56 to 2.05. The evenness value is high with a value of 0.62 to 0.90. The species of wealth (Margalef) is in the range of values from 2.55 to 2.75 which indicates the species richness of dragonflies in the Mount Permisan Natural Tourism Park index is classified as moderate.

Keanekaragaman Semut (Hymenoptera: Formicidae) di Beberapa Tegakan di Taman Hutan Raya Sultan Thaha Syaifuddin Jambi

Biodiversity can act as an indicator of the ecological system and as a medium for knowing species changes. Insects are living things in a world that has a high species diversity. One insect that has a functional role in the ecosystem is ants. The purpose of this study was to calculate and analyze diversity of the types of ants in four types of ecosystems and analyze the effect of habitat characteristics on the abundance of ants. Ant sampling using the hand sorting method was taken from the soil and litter parts in four ecosystems, namely secondary forest, ulin stands, oil palm plantations, and rubber stands in Sultan Thaha Syaifuddin Forest Park Batanghari District, Jambi Province. The results showed a total of 940 ants were obtained, from 296 individuals in Secondary Forest, 198 individuals in oil palm plantations, 307 individuals in ulin stand, 139 individuals in rubber stand. Ants are more commonly found in parts of the soil than litter. The highest ant diversity in the soil and litter is found in secondary forest. Environmental factors that influence the presence of ants in each ecosystem are soil temperature and thickness of litter.
 Keywords: ants, biodiversity, ecosystems, hand sorting, tahura.

Nest site selection and breeding ecology of the Ferruginous Duck (Aythya nyroca) in Algeria

Ecologically, the Nature Reserve of Tonga Lake (northeastern Algeria) is very important for waterbirds. This study investigates breeding biology of an emblematic species of this region: The Ferruginous Duck (Aythya nyroca), a duck ranked globally 'Near Threatened' on the IUCN Red List. This study aimed to determine wetland environmental variables influencing nest site selection and breeding success of the species. Over two successive breeding seasons (2016 and 2017), the effects of habitat characteristics and nest traits on breeding parameters of 50 nests constructed on alder carr of the lake and offshore floating vegetation islets in the center of the waterbody were analyzed using generalized linear models (GLM). Clutch size averaged 9.8 ± 0.7 eggs (range: 2–26 eggs) with 66% hatching success. Desertion of the nest (i.e. nest abandonment by the parents during the period of egg-laying and/or incubation) was the main cause for breeding failure (18% of total nests). Clutch size was positively related to nest surface and nest depth, but it decreased with the increase in the distance of nest on the vegetation platform to water. GLM revealed that breeding success was positively associated with late clutches; with a negative effect of conspecific nest density on clutch size and breeding success. Nest-site choice is resulted from interspecific competition and/or is affected by the reduced number of favorable nesting sites. Nine nests (18%) were parasitized by the same species of which 67% were central nests. Only 2% of the nests studied were parasitized by Oxyura leucocephala nesting at the site. Possible explanations of nest site selection of Aythya nyroca in the study area are discussed. Variations in selection pressures may explain the relationships between the choice and characteristics of nest site in the Ferruginous duck at Lake Tonga.

Habitat‐specific survival of golden‐winged warblers Vermivora chrysoptera during the non‐breeding season in an agricultural landscape

Nearctic‐Neotropical migratory birds are considered priority species for conservation because they are subject to threats at distinct breeding, migratory and stopover locations throughout their annual cycle, and many species have undergone severe population declines. Research during the non‐breeding season has focused on identifying the locations and habitats that migrants use, but wintering migrants are known to occupy habitats of both high and low quality, especially when the best sites are saturated by conspecifics. Thus, the presence or abundance of a species may not be a reliable indicator of winter habitat quality. The habitat associations of the golden‐winged warbler Vermivora chrysoptera, a Nearctic‐Neotropical migrant bird species of elevated conservation concern, are relatively well studied, yet conservation efforts are hindered by lack of information about basic demographic rates. In particular, no published estimates exist for non‐breeding season survival, which can be a key vital rate affecting population viability, nor how survival rates vary among habitats, which is important to designing conservation programs to support populations during the winter period. We studied a color‐banded population of golden‐winged warblers in Costa Rica over a three‐year period and estimated overall survival rates, and the effects of habitat characteristics on survival. We found that monthly survival of juveniles (0.881) was lower than adult birds (0.978). Monthly survival during the non‐breeding season (0.967) was higher than monthly survival during the rest of the annual cycle (0.930). Survival was negatively related to canopy height, and we observed a significant quadratic effect where survival peaked at intermediate levels of vine tangles and dead hanging leaves, which corresponds to habitat features associated with abundance in prior studies at this same site. Our findings contribute to our existing knowledge about the potential impacts of winter‐season events on Nearctic‐Neotropical migratory bird populations, and also informs potential conservation strategies for wintering golden‐winged warblers.

Do the ecological drivers of lake littoral communities match and lead to congruence between organism groups?

Lake littoral environments are heterogeneous, and different organisms typically show specific responses to this environmental variation. We examined local environmental and spatial factors affecting lake littoral biodiversity and the structuring of assemblages of phytoplankton, zooplankton and macroinvertebrates within and among three basins of a large lake system. We explored congruence of species composition and species richness among the studied organism groups to evaluate their general indicator potential to represent spatial variation in other groups. We expected that effects of water chemistry on plankton assemblages were stronger than effects of habitat characteristics. In contrast, we anticipated stronger effects of habitat on macroinvertebrates due to their mainly benthic mode of life. We also expected that within-basin spatial effects would be strongest on macroinvertebrates and weakest on phytoplankton. We predicted weak congruence in assemblage composition and species richness among the organism groups. Phytoplankton assemblages were mainly structured by the shared effects of water chemistry and large-scale spatial factors. In contrast to our expectations, habitat effects were stronger than water chemistry effects on zooplankton assemblages. However, as expected, macroinvertebrate species composition and richness were mainly affected by habitat conditions. Among-group congruence was weak for assemblage composition and insignificant for richness. Albeit weak, congruence was strongest between phytoplankton and zooplankton assemblages, as we expected. In summary, our analyses do not support the idea of using a single organism group as a wholesale biodiversity indicator.

Effect of reef morphology and depth on fish community and trophic structure in the northcentral Gulf of Mexico

Reef fish resources provide numerous ecosystem services in the northern Gulf of Mexico (nGOM) large marine ecosystem. Artificial reefs (ARs) have been distributed across the nGOM in attempts to enhance reef fish habitat and increase fishery productivity, but few data exist to distinguish ecological from fishery functions of ARs compared to natural reefs (NRs), particularly at the regional scale. Therefore, we conducted remotely operated vehicle surveys of reef fish communities at 47 reef sites within a ~20,000 km2 area of the nGOM shelf and tested the effect of reef type (NR versus AR), depth (≤35 or >35 m), relief (≤2 m or >2 m), and complexity (low or high) on fish diversity and community structure as well as trophic guild- and species-specific densities. Twenty-one species were present at >20%, nine at >50%, and three at >75% of study reefs. Fishery species (i.e., Lutjanus campechanus, Seriola dumerili, and Rhomboplites aurorubens) and invasive Pterois volitans were frequently observed (>50% of sites) or numerically dominant, especially at ARs. Main effects did not significantly affect the presence of specific species or trophic guilds, but interactions among factors significantly affected species- and trophic guild-specific densities. Our results indicate that effects of habitat characteristics on fish communities are more nuanced than previously described. Fish communities are moderately similar at the majority of sites but specific habitat characteristics can interact to dramatically affect densities of some species, particularly those that depend on complex structures for refuge. Simple ARs tend to concentrate high densities of a few important fishery species with low densities of other small demersal reef fishes. Complex NRs with high relief also support high densities of planktivorous fishery species but greatly increase densities of small, demersal, non-fishery species that directly utilize complex reef structure for refuge.

Effects of habitat features and season on vertebrate communities in Southern Georgia, U.S.A.

ABSTRACTAlthough the southeastern U.S.A. contains a high diversity of species and habitats, this region is also experiencing rapid human development. Humans are modifying ecosystems in complex ways, and these changes often result in shifts in biodiversity. Therefore, examining habitat use in human-altered ecosystems gives insight into how animals will continue to respond to their rapidly changing environments. Biodiversity and abundance can be influenced by several factors, including habitat structure and seasonal variation. Understanding how these factors influence biodiversity is particularly important in areas that are experiencing high levels of human activity. Thus, we surveyed artificial cover objects to examine the effects of forest structure and season on several indices of diversity in vertebrates (mammals, reptiles, and amphibians) in forested sites in the southeastern U.S.A., a region characterised by rapid human population growth. Vertebrate abundance varied by season where abundance in the fall and winter were lower than in the spring and summer. The proximity to roads affected vertebrate abundance where abundance was higher under cover objects farther from roads. Our results provide evidence that anthropogenic, biotic, and temporal factors can influence vertebrate abundance and biodiversity. We also provide insight into the role of forest structure in vertebrate biodiversity, and we encourage future efforts focusing on the role of structural variation across different ecosystems.

Spatial distribution of male display sites in a North African population of Houbara Bustard Chlamydotis undulata undulata

Understanding the effect of habitat characteristics on the distribution of threatened species are fundamental in conservation planning and management. Here, we explore the spatial distribution pattern of display site by the North African Houbara Bustard Chlamydotis undulata undulata males. For this purpose, we examined 81 sites in an area of 255 km2 located in the Jbil National Park. We hypothesised that in such an area, displaying males prefer sites that may ensure maximum survival, to find a mate and reproduce. We showed that the maximum display-sites density did not exceed 0.04 adult males km−2 with significant patterns of non-random distribution. The fact that display sites exhibit significant positive spatial autocorrelation, as indicated by Moran’s I, is consistent with a lek mating system. We also found a significant relationship between the selection of display sites and the following environmental variables: perennial species covers, annual species covers, percentage of gravel, percentage of other soil surface, plant height, and elevation. Moreover, simultaneous autoregressive models suggest that the inclusion of spatial autocorrelation globally gives better estimates of the regression coefficients.

Different in the dark: The effect of habitat characteristics on community composition and beta diversity in bromeliad microfauna.

The mechanisms which structure communities have been the focus of a large body of research. Here, we address the question if habitat characteristics describing habitat quality may drive changes in community composition and beta diversity of bromeliad-inhabiting microfauna. In our system, changes in canopy cover along an environmental gradient may affect resource availability, disturbance in form of daily water temperature fluctuations and predation, and thus may lead to changes in community structure of bromeliad microfauna through differences in habitat quality along this gradient. Indeed, we observed distinct changes in microfauna community composition along the environmental gradient explained by changes in the extent of daily water temperature fluctuations. We found beta diversity to be higher under low habitat quality (low canopy cover) than under high habitat quality (high canopy cover), which could potentially be explained by a higher relative importance of stochastic processes under low habitat quality. We also partitioned beta diversity into turnover and nestedness components and we found a nested pattern of beta diversity along the environmental gradient, with communities from the lower-quality habitat being nested subsets of communities from the higher-quality habitat. However, this pattern resulted from an increase in microfauna alpha diversity with an increase in habitat quality. By providing insights into microfauna-environment relationships our results contribute to the mechanistic understanding of community dynamics in small freshwater bodies. Here, we highlight the importance of habitat characteristics representing habitat quality in structuring communities, and suggest that this information may help to improve conservation practices of small freshwater ecosystems.

Nocturnal bird diversity in forest fragments in north-west Ecuador

Abstract:Habitat preferences and response to habitat conversion remain under-studied for many groups in the tropics, limiting our understanding of how environmental and anthropogenic factors may interact to shape patterns of diversity. To help fill this knowledge gap, we surveyed nocturnal birds such as owls, nightjars and potoos through auditory transect surveys in 22 forest fragments (2.7 to 33.6 ha) in north-west Ecuador. We assessed the relative effect of habitat characteristics (e.g. canopy height and openness, and density of large trees) and fragment attributes (e.g. area, altitude and proportion of surrounding forest cover) on species richness and community composition. Based on our previous work, we predicted that nocturnal bird richness would be highest in relatively larger fragments with more surrounding forest cover. We recorded 11 total species with an average ± SD of 3.4 ± 1.4 (range = 2–7) species per fragment, with higher richness in fragments that were larger, at lower altitudes, and characterized by more open canopies. Nocturnal bird community similarity was not significantly correlated with any measured environmental variable. These results indicate that both landscape (e.g. altitude) and fragment-specific (e.g. size, forest structure) attributes are likely to interact to shape patterns of diversity among this poorly known but ecologically important guild in fragmented tropical landscapes.

Divergences in learning and memory among wild zebrafish: Do sex and body size play a role?

Given its diverse ecological distribution, zebrafish has great potential for investigations on the effect of habitat characteristics on cognition. Studies were conducted on four wild-caught zebrafish populations to understand the role of native habitat, sex, and body size in determining learning through a novel task associated with a food reward. The habitat variables, namely, the relative abundances of zebrafish and predatory fish and the substrate and vegetation diversity, were quantified during fish sampling. Fish were subjected to a novel task to find a food reward in a maze over successive training trials followed by a test for memory. Performances of subjects were based on time taken to find the food reward and number of mistakes made during trials, and tests for memory. The experiments revealed significant differences in learning rates and memory across populations. Males made significantly fewer mistakes than females only within two populations. No relationship between performance and body size was observed. The differences in learning and memory among wild zebrafish could be due to differences in predation, complexity, and stability of the native habitats. These findings suggest the possible role of multiple interacting factors in determining learning and memory among populations and point to a need for incorporating effects of several factors in future studies.

Seasonal abundance and habitat use of bird species in and around Wondo Genet Forest, south-central Ethiopia.

The habitat use and seasonal migratory pattern of birds in Ethiopia is less explored as compared to diversity studies. To this end, this study aimed at investigating the patterns of distribution related to seasonality and the effect of habitat characteristics (elevation, slope, and average vegetation height) on habitat use of birds of Wondo Genet Forest Patch. A stratified random sampling design was used to assess the avian fauna across the four dominant habitat types found in the study area: natural forest, wooded grassland, grassland, and agroforestry land. A point transect count was employed to investigate avian species richness and abundance per habitat type per season. Ancillary data, such as elevation above sea level, latitude and longitude, average vegetation height, and percent slope inclination, were recorded with a GPS and clinometers per plot. A total of 33 migratory bird species were recorded from the area, of which 20 species were northern (Palearctic) migrants while 13 were inter‐African migrants. There was a significant difference in the mean abundance of migratory bird species between dry and wet seasons (t = 2.13, p = .038, df = 44). The variation in mean abundance per plot between the dry and wet seasons in the grassland habitat was significant (t = 2.35, p = .051, df = 7). In most habitat types during both dry and wet seasons, omnivore birds were the most abundant. While slope was a good predictor for bird species abundance in the dry season, altitude and average vegetation height accounted more in the wet season. The patch of forest and its surrounding is an important bird area for migratory, endemic, and global threatened species. Hence, it is conservation priority area, and the study suggests that conservation coupled with ecotourism development is needed for its sustainability.

Effects of habitat features on size-biased predation on salmon by bears.

Predators can drive trait divergence among populations of prey by imposing differential selection on prey traits. Habitat characteristics can mediate predator selectivity by providing refuge for prey. We quantified the effects of stream characteristics on biases in the sizes of spawning salmon caught by bears (Ursus arctos and U. americanus) on the central coast of British Columbia, Canada by measuring size-biased predation on spawning chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon in 12 streams with varying habitat characteristics. We tested the hypotheses that bears would catch larger than average salmon (size-biased predation) and that this bias toward larger fish would be higher in streams that provide less protection to spawning salmon from predation (e.g., less pools, wood, undercut banks). We then we tested for how such size biases in turn translate into differences among populations in the sizes of the fish. Bears caught larger-than-average salmon as the spawning season progressed and as predicted, this was most pronounced in streams with fewer refugia for the fish (i.e., wood and undercut banks). Salmon were marginally smaller in streams with more pronounced size-biased predation but this predictor was less reliable than physical characteristics of streams, with larger fish in wider, deeper streams. These results support the hypothesis that selective forces imposed by predators can be mediated by habitat characteristics, with potential consequences for physical traits of prey.

Effects of habitat differences on the genetic diversity of Persicaria thunbergii

To understand the effects of habitat characteristics on the genetic diversity of Persicaria thunbergii, three sites of different environmental conditions in a water system were surveyed. Site A was the closest to the source of the water system, and there was a dam between sites A and B. Site C is located on the lowest downstream in the water system. Vegetation survey of four quadrats at each site was performed, and soil samples were collected for physicochemical analysis. Random amplification of polymorphic DNA (RAPD) analysis of ten P. thunbergii individuals at each site was conducted to calculate population genetic diversity and genetic distance among populations. Soil was sterile sand at site A, whereas loamy soil at sites B and C. A pure stand of P. thunbergii appeared at site A, while other species occurred together (such as Humulus japonicus and Phragmites australis) at sites B (Shannon-Wiener index; H B = 0.309) and C (H C = 0.299). Similar to the species diversity, genetic diversity (Nei’s gene diversity; h) within population of site A (h A = 0.2381) was relatively lower than sites B (h B = 0.2761) and C (h C = 0.2618). However, site C was separated from sites A and B in genetic distance rather than the geographical distance (Nei’s genetic distance; A~B, 0.0338; B~C, 0.0685; A~C, 0.0833).

Predator identity influences the effect of habitat management on nest predation.

Predation is the leading cause of nest failure for many passerines and considerable effort is devoted to identifying the habitat characteristics and management practices that influence nest loss. The habitat components associated with nest loss are strongly influenced by the ecology of nest predators and differ among predator species as a result. Nevertheless, there is a tendency to generalize about the effects of habitat features and management on nest failure without considering how resulting patterns are influenced by nest predators. We examined how predator-specific patterns of nest loss differed among predators and in response to grassland management with fire and grazing by cattle (Bos taurus). We used video cameras to monitor and identify predators at nests of the Grasshopper Sparrow (Ammodramus savannarum), a species of conservation concern throughout its range. We observed predation by 15 different species that differed in their response to management and the habitat characteristics associated with nests they preyed on. Losses to mammals and snakes were more likely at nests with greater amounts of litter cover and tall fescue (Schedonorus phoenix). Mammals were less likely to prey on nests surrounded by greater forb cover. Nest predation by snakes was lower in burned areas, whereas predation by mammals and Brown-headed Cowbirds (Molothrus ater) was unaffected by the use of fire. Neither vegetation density at the nest, nor landscape context was related to nest loss by any predator taxon. Although there were many similarities, we identified important differences in the species composing the nest predator community between our. study and other published research. These differences are likely to be responsible for geographic variation in the influence of habitat features and management actions on nest success. Our results demonstrate the need for natural resource managers to incorporate knowledge of local nest predators and their ecology when developing management prescriptions aimed at enhancing the reproductive success of songbirds.

Effect of habitat characteristics on mesocarnivore occurrence in urban environment in the Central Europe

Although urbanization is generally considered a major threat to local and global biodiversity, some recent studies have shown that urban environments provide suitable habitat for some wildlife species, including carnivores, yet little is known about the factors that determinate their occurrence and habitat preferences. The main aim of this study was to examine the relative importance of habitat characteristics in relation to carnivore occurrence along an urban–rural gradient in the Central Europe. Carnivore occurrence was monitored using scent stations (summer period) and snow tracking (winter period) in the regional city which was divided into the network of 154 quadrates (25 ha/quadrate) for the purposes of this study. From a total of six recorded native carnivore species, the stone marten Martes foina and the least weasel Mustela nivalis were the most dominant and widespread species in both study periods. PCA analysis revealed the existence of two informative axes corresponding to (A) urban vs. non-urban habitat and (B) residential vs. industrial areas. Surprisingly, the only species exhibiting marked habitat selectivity and avoidance of highly urbanized areas was the red fox (i.e. negative correlation with the first PCA axis). The stone marten tends to avoid industrial areas and prefers residential areas; however its presence/absence was not associated with the first PCA axis. On the other hand, the ermine stoat and the least weasel were relatively unselective according to our results. In conclusion, our results demonstrate high adaptability of various species of carnivore mesopredators to urban environment; however their response to the level of urbanization and habitat characteristics exhibits interspecific variation.

Effect of habitat characteristics on the distribution and abundance of damselfish within a Red Sea reef

For coral reef fish with an obligate relationship to their habitat, like Pomacentrid damselfish, choosing a suitable home amongst the reef structure is key to survival. A surprisingly small number of studies have examined patterns in adult damselfish distributions compared to other ontogenetic phases. The aim of this study was to determine which reef and coral colony characteristics explained adult damselfish distribution patterns in a Red Sea reef. The characteristics investigated were reef type (continuous or patchy), coral species (seven species of Acropora), and coral morphology (coral size and branching density). The focal damselfish species were Dascyllus aruanus, D. marginatus, Chromis viridis, and C. flavaxilla. Occupancy (presence or absence of resident damselfish), group size and fish species richness were not significantly different between the seven Acropora species. However, within each coral species, damselfish were more likely to occupy larger coral colonies than smaller coral colonies. Occupancy rates were also higher in patchy reef habitats than in continuous sections of the reef, probably because average coral colony size was greater in patchy reef type. Fish group size increased significantly with coral colony volume and with larger branch spacing. Multi-species groups of fish commonly occurred and were increasingly likely with reduced branching density and increased coral size.

Distribution, Abundance and Habitat Selection by Breeding Yellow-billed Terns (Sternula superciliaris), Large-Billed Terns (Phaetusa simplex) and Black Skimmers (Rynchops niger) in the Brazilian Amazon

The distribution and abundance of Yellow-billed Terns (Sternula superciliaris), Large-billed Terns (Phaetusa simplex) and Black Skimmers (Rynchops niger) were estimated, and the effects of habitat features on site occupancy by colonies of these three species nesting in the Anavilhanas Archipelago, Amazonas, Brazil, were examined. Individuals were recorded on beaches during the 2008 and 2009 breeding seasons, with 26 (2008) and 30 (2009) potential nesting beaches (sites) surveyed. In both years, one site included 28% of all the Yellow-billed Terns, while two sites included 65% of all the Large-billed Terns. Site occupancy, the probability that a site is occupied (range ψ;), was moderate to low for all three species, but higher for Yellow-billed Terns (0.58–0.63) than for Large-billed Terns (0.40–0.50) and Black Skimmers (0.23–0.54). Yellow-billed and Large-billed terns and Black Skimmers generally nested on larger beaches on islands that had little vegetative cover and that were exposed to open water, remote from river margins, distant from other islands and closer to large colonies of the same species. Abundance estimates (individuals per breeding season in the archipelago ± SE) in 2009 varied considerably among species (Yellow-billed Terns: 192 individuals ± 1; Large-billed Terns: 80 ± 1; Black Skimmer: 31 ± 1). These results suggest that habitat features that influence breeding site use by Yellow-billed and Large-billed terns and Black Skimmers include physical and vegetation characteristics as well as social attraction. While the probability of site occupancy increased with measures related to beach size and geographical isolation, closeness to large colonies indicates the relevance of social interactions for these species and, as such, the importance of large areas for the occurrence of their colonies.

A quantitative estimate of the function of soft-bottom sheltered coastal areas as essential flatfish nursery habitat

Essential fish habitat suitability (EFHS) models and geographic information system (GIS) were combined to describe nursery habitats for three flatfish species (Solea solea, Pleuronectes platessa, Dicologlossa cuneata) in the Bay of Biscay (Western Europe), using physical parameters known or suspected to influence juvenile flatfish spatial distribution and density (i.e. bathymetry, sediment, estuarine influence and wave exposure). The effects of habitat features on juvenile distribution were first calculated from EFHS models, used to identify the habitats in which juvenile are concentrated. The EFHS model for S. solea confirmed previous findings regarding its preference for shallow soft bottom areas and provided new insights relating to the significant effect of wave exposure on nursery habitat suitability. The two other models extended these conclusions with some discrepancies among species related to their respective niches. Using a GIS, quantitative density maps were produced from EFHS models predictions. The respective areas of the different habitats were determined and their relative contributions (density × area) to the total amount of juveniles were calculated at the scale of stock management, in the Bay of Biscay. Shallow and muddy areas contributed to 70% of total juvenile relative abundance whereas only representing 16% of the coastal area, suggesting that they should be considered as essential habitats for these three flatfish species. For S. solea and P. platessa, wave exposure explained the propensity for sheltered areas, where concentration of juveniles was higher. Distribution maps of P. platessa and D. cuneata juveniles also revealed opposite spatial and temporal trends which were explained by the respective biogeographical distributions of these two species, close to their southern and northern limit respectively, and by their responses to hydroclimatic trends.