Niche-habitat mechanisms and biotic interactions explain the coexistence and abundance of congeneric sandgrouse species

Ascertaining which niche processes allow coexistence between closely related species is of special interest in ecology. We quantified variations in the environmental niches and densities of two congeneric species, the pin-tailed and the black-bellied sandgrouse (Pterocles alchata and Pterocles orientalis) in allopatry and sympatry under similar abiotic, habitat and dispersal contexts to understand their coexistence. Using principal component analysis, we defined environmental gradients (niche dimensions) including abiotic, habitat and anthropogenic variables, and calculated niche breadth, position and overlap of both species in sympatry and allopatry. Additionally, sandgrouse density was modelled as a function of the niche dimensions and the density of the other species. We found evidence that each species occupies distinct environmental niches in sympatry and in allopatry. The black-bellied sandgrouse exploits a broader range of environmental conditions (wider niche breadth) while the pin-tailed sandgrouse reaches high densities where conditions seem to match its optimum. In sympatry, both species shift their niches to intermediate positions, indicating the importance of abiotic factors in setting coexistence areas. Environmental conditions determine regional densities of pin-tailed sandgrouse whereas biotic interactions explain the density of the black-bellied sandgrouse in areas with abiotic conditions similarly conducive for both species. Highly suitable areas for the pin-tailed sandgrouse fall beyond the upper thermal limit of the black-bellied sandgrouse, leading to niche segregation and low densities for the latter. Finally, local niche shift and expansion plus possible heterospecific aggregation allow the pin-tailed sandgrouse to thrive in a priori less favourable environments. This work provides insight into how different mechanisms allow species coexistence and how species densities vary in sympatry compared to allopatry as a result of environmental filtering and biotic interactions.     

A multi-scale approach for identifying conservation needs of two threatened sympatric steppe birds

Habitat selection is an inherently scale-sensitive process in which detected selection patterns frequently depend on the scale of analysis employed. We used a multi-scale modelling approach to identify how the distributions of two sympatric birds are shaped by differential selection at the landscape, land use and microhabitat scales and by human infrastructures as possible sources of disturbance. We studied two threatened steppe birds, the pin-tailed sandgrouse (PTS) and black-bellied sandgrouse (BBS) in central Spain. Land use gradients explained most of the variation in PTS and BBS occurrence, but there was cross-scale interdependence between the lower (microhabitat) and upper (landscape) spatial scales for the PTS. Synergies between the three scales highlighted the importance of integrating habitat scales in a single modelling framework. The process of habitat selection was also modulated by human disturbance. Both species selected ploughs of large size distant from houses, tracks and other infrastructures, although BBS exhibited broader habitat tolerance than the PTS, and was more sensitive to human disturbance. At microhabitat scale, PTS selected ploughs with greater green vegetation cover and insect abundance and fallows with lower dry vegetation cover and height but greater stone cover. This might reflect a trade-off between camouflage (vegetation and stone cover for concealment) and visibility for predator detection and escape. Ploughs and fallows should be maintained by means of traditional 2-year rotations and low management during the breeding season. Ongoing urbanization trends and infrastructure development inside protected areas should be limited. Multi-scale models were key to identify scale-specific factors that determine sandgrouse habitat preferences and conservation requirements at appropriate levels, and are recommended to better guide regional and local conservation efforts of threatened species.     

An improved night-lighting technique for the selective capture of sandgrouse and other steppe birds

The night-lighting technique is routinely used to catch birds. We improved this technique using a thermal infrared camera to catch steppe birds such as the sandgrouse. Target birds were located by an observer using the thermal camera, and approached and dazzled by another observer carrying a spotlight attached to a helmet and a hand-held net together with a playback noise to camouflage the footsteps of the observer. Using this improved technique, we caught on average 1.14 individuals per 3-h capture session (N = 81) and a total of 92 sandgrouse in 2007–2010 (86 pin-tailed sandgrouse Pterocles alchata and six black-bellied sandgrouse Pterocles orientalis). Capture rate and success were negatively influenced by moonlight (lowest during full moon nights). Our night-lighting technique is a highly selective and harmless method to capture sandgrouse and can be used for other small/medium-sized open-land birds or mammals.     

四川卧龙国家级自然保护区多空间尺度下绿尾虹雉的生境选择

动物的生境选择具有空间尺度依赖性, 在不同空间尺度上影响生境选择的环境因素有所不同。研究不同空间尺度下动物生境选择的关键影响因子及其季节性变化, 对于全面了解物种的生境资源需求和开展生境保护具有重要意义。绿尾虹雉(Lophophorus lhuysii)是中国特有的高山雉类, 国家一级重点保护野生动物, 具有极高的保护价值。然而, 目前尚未对其不同尺度和时期的生境选择进行过探究。本研究于2019年10月至2020年10月, 在四川卧龙国家级自然保护区的羊角湾、魏家沟和文扎都3个区域共布设15条样线、303个样方, 并结合红外相机监测(176个红外相机位点), 对保护区内绿尾虹雉种群的生境利用状况进行了调查, 使用主成分分析和逻辑斯蒂回归模型分别从景观和微生境两个尺度对繁殖期(3‒8月)和非繁殖期(9月至翌年2月)的生境选择模式进行了分析。结果显示, 在景观尺度上, 在繁殖期和非繁殖期都显著偏好海拔较高(3,700‒ 4,300 m)、坡度较小(27°‒33°)、靠近阳坡、草甸和流石滩比例较高而森林和灌丛比例较低的生境。在微生境尺度上, 绿尾虹雉在繁殖期显著偏好岩石盖度较高的生境; 而非繁殖期则显著偏好草本盖度较高、灌木盖度和落叶盖度较低的生境。研究表明, 绿尾虹雉在景观和微生境尺度上均对生境有明显的选择性, 并且其微生境选择还存在季节性变化, 反映了该物种在生活史不同阶段具有不同的资源需求。本研究丰富了绿尾虹雉的基础生态学信息, 为卧龙及其他自然保护区绿尾虹雉的生境管理和种群保护工作提供了参考。     

Determinants of Plant Community Assembly in a Mosaic of Landscape Units in Central Amazonia: Ecological and Phylogenetic Perspectives

The Amazon harbours one of the richest ecosystems on Earth. Such diversity is likely to be promoted by plant specialization, associated with the occurrence of a mosaic of landscape units. Here, we integrate ecological and phylogenetic data at different spatial scales to assess the importance of habitat specialization in driving compositional and phylogenetic variation across the Amazonian forest. To do so, we evaluated patterns of floristic dissimilarity and phylogenetic turnover, habitat association and phylogenetic structure in three different landscape units occurring in terra firme (Hilly and Terrace) and flooded forests (Igapó). We established two 1-ha tree plots in each of these landscape units at the Caparú Biological Station, SW Colombia, and measured edaphic, topographic and light variables. At large spatial scales, terra firme forests exhibited higher levels of species diversity and phylodiversity than flooded forests. These two types of forests showed conspicuous differences in species and phylogenetic composition, suggesting that environmental sorting due to flood is important, and can go beyond the species level. At a local level, landscape units showed floristic divergence, driven both by geographical distance and by edaphic specialization. In terms of phylogenetic structure, Igapó forests showed phylogenetic clustering, whereas Hilly and Terrace forests showed phylogenetic evenness. Within plots, however, local communities did not show any particular trend. Overall, our findings suggest that flooded forests, characterized by stressful environments, impose limits to species occurrence, whereas terra firme forests, more environmentally heterogeneous, are likely to provide a wider range of ecological conditions and therefore to bear higher diversity. Thus, Amazonia should be considered as a mosaic of landscape units, where the strength of habitat association depends upon their environmental properties.     

Resource use by the dryad butterfly is scale-dependent

The factors shaping the ways in which animals use resources are a key element of conservation biology, but ecological studies on resource use typically neglect to consider how the study’s spatial scale may have affected the outcomes. We used the dryad butterfly, inhabiting xerothermic grassland and wet meadow, to test for differences in its resource use at two scales–habitat patch and landscape. Based on records of plant species composition from random points within four habitat patches and from points in 53 patches along surveyed transects, we compared the microhabitat preferences of the butterfly on the patch scale, and species occurrence and abundance patterns on the landscape scale. We distinguished four main groups of factors related to vegetation structure which affected the butterfly’s resource use—factors having similar effects on both spatial scales, factors operating primarily on one of the scales considered, factors relevant only on a single spatial scale, and factors operating on both scales but with effects differing between the two habitat types. We suggest that invertebrates may respond on two spatial levels or on only one, and conclude that larger-scale studies can meet the challenges of a sophisticated metapopulation approach and can give insight into the habitat characteristics affecting the persistence of species in landscapes. We stress the value of large-scale studies on species’ habitat preferences when planning conservation strategies, while pointing out that small-scale studies provide useful information about species ecology and behavior, especially if conducted in multiple habitats.     

Recruitment limitations in Primula vulgaris in a fragmented landscape

Plant recruitment is limited by dispersal, if seeds cannot arrive at potential recruitment sites, and by establishment, due to a low availability of safe sites for recruitment. Seed-sowing experiments, scarcely applied along gradients of landscape alteration, are very useful to assess these limitations. Habitat loss and fragmentation may foster recruitment limitations by affecting all the processes from seed dispersal to seedling establishment. In this study, we perform a seed-sowing experiment to disentangle the importance of dispersal and establishment limitations in different stages of recruitment of the perennial herb Primula vulgaris in fragmented forests of the Cantabrian Range (Northwestern Spain). We evaluated the influence of ecological gradients resulting from habitat loss and fragmentation (modifications of habitat amount at the landscape and microhabitat scales, changes in the species’ population size, changes in seed predation and seedling herbivory) on seedling emergence, survival and early growth. We found strong evidence of dispersal limitation, as seedling emergence was very low in experimental replicates where no seeds were added. This limitation was independent of landscape alterations, as we found no relation with any of the ecological gradients studied. Establishment limitations at the germination phase were also unrelated to ecological gradients, probably because these limitations are more related to fine-scale environmental gradients. However, further monitoring revealed that seedling survival after summer and winter periods and seedling growth were conditioned by landscape alteration, as we found effects of habitat amount at the landscape and microhabitat scales, of presence of populations of P. vulgaris and of seedling herbivory. These effects were complex and sometimes opposite to what can be expected for adult plants, revealing the presence of different requirements between life stages.     

Can pinewoods provide habitat for a deciduous forest specialist? A two-scale approach to the habitat selection of Bechstein's bat

Populations of Myotis bechsteinii in Sierra de Cazorla, Segura y Las Villas Natural Park (southwestern Spain) survive in a large, old-growth coniferous woodland, which is in contrast with known ecological preferences of the species. We tracked ten lactating females and studied patterns of habitat selection by Bechstein's bat (Myotis bechsteinii) at two spatial scales: macrohabitat and microhabitat, regarding forest essence (coniferous vs. deciduous). The tracked individuals always foraged within forested areas and did not use areas devoid of trees. At the macrohabitat level, no positive selection of deciduous stands was apparent, suggesting selection studies of coarse resolution may not be able to capture subtle selection patterns. At the microhabitat level Myotis bechsteinii selected deciduous patches within the coniferous matrix, therefore, our results corroborate the perception of this species as dependent of services provided by deciduous woodlands. Larger foraging home ranges and commuting distances as compared with other Mediterranean localities suggest that our studied population inhabits a marginal or suboptimal environment in terms of habitat quality. We argue that this population of Bechstein's bat has survived as a relict one probably as a consequence of fragmentation and transformation of deciduous forest ecosystems in the Mediterranean range.     

Urbanisation at Multiple Scales Is Associated with Larger Size and Higher Fecundity of an Orb-Weaving Spider

Urbanisation modifies landscapes at multiple scales, impacting the local climate and changing the extent and quality of natural habitats. These habitat modifications significantly alter species distributions and can result in increased abundance of select species which are able to exploit novel ecosystems. We examined the effect of urbanisation at local and landscape scales on the body size, lipid reserves and ovary weight of Nephila plumipes, an orb weaving spider commonly found in both urban and natural landscapes. Habitat variables at landscape, local and microhabitat scales were integrated to create a series of indexes that quantified the degree of urbanisation at each site. Spider size was negatively associated with vegetation cover at a landscape scale, and positively associated with hard surfaces and anthropogenic disturbance on a local and microhabitat scale. Ovary weight increased in higher socioeconomic areas and was positively associated with hard surfaces and leaf litter at a local scale. The larger size and increased reproductive capacity of N.plumipes in urban areas show that some species benefit from the habitat changes associated with urbanisation. Our results also highlight the importance of incorporating environmental variables from multiple scales when quantifying species responses to landscape modification.     

Relationships between stream macroinvertebrates and environmental variables at multiple spatial scales

1. Aquatic communities are structured by multiple forces, and identifying the driving factors over multispatial scales is an important research issue. The East Asian monsoon region is globally one of the richest environments in terms of biodiversity, and is undergoing rapid human development, yet the river ecosystems in this region have not been well studied. We applied a hierarchical framework to incorporate regional and local environmental effects on stream macroinvertebrate communities in this region. The knowledge gained is expected to improve the understanding of the importance of spatial scale on regional and local diversity in the East Asian monsoon region. 2. A national data set of benthic macroinvertebrates and environmental variables (geographical, land‐use, hydrological, substratum and physicochemical elements) in Korean rivers was used to determine the habitat preferences of macroinvertebrates. 3. Latitude, proportion of forest coverage, riffle habitat, silt substratum and temperature were the most important determinants for the ordinations of macroinvertebrate communities in each category evaluated by canonical correspondence analysis (CCA). The optimal habitats for stream macroinvertebrates are not the same for all species, and overall community metrics and abundance of sensitive species tended to be lower in open agricultural and urban streams than in forested streams. The sensitivity of mayflies and stoneflies to anthropogenic disturbances implicated them as good indicators to assess the effects of urban and agricultural activities. 4. A partial CCA was used to evaluate the relative importance of macrohabitat and microhabitat variables on community composition at three spatial scales (whole country, the large Han River basin and two small sub‐basins in the lowlands and highlands). The majority of community variation (17–22% for each environmental element) was explained by macrohabitat variables at the regional spatial scale. In contrast, large proportions (15–18%) were explained by microhabitat variables at the local spatial scale. 5. Our findings indicate that the relative importance of habitat scales should be determined by geographical size and that comprehensive understanding of multispatial scale patterns can be important for implementing sound biodiversity conservation programmes.     

丹顶鹤多尺度生境选择机制——以黄河三角洲自然保护区为例

生境在鸟类生活史中发挥着重要的作用,关系到鸟类的生存和繁衍。由于鸟类对环境变化的响应发生在等级序列空间尺度上,基于多尺度的研究更能深入刻画鸟类-环境之间关系。以丹顶鹤(Grus japonensis)为研究对象,以其迁徙和越冬的重要地区-黄河三角洲自然保护区为研究区域,应用等级方差分解法和等级划分法,分析丹顶鹤与微生境、斑块、景观尺度因子之间的关系,探求丹顶鹤生境选择的主要影响因素和尺度。等级方差分解结果表明,在第1等级水平,景观尺度因子与微生境、斑块尺度因子之间的联合效应大于独立效应,景观尺度因子的独立效应大于微生境和斑块尺度因子;在第2等级水平,景观尺度上的景观组成因子重要性大于景观结构因子,微生境尺度上的植被和水分因子为重要影响因素。等级划分结果表明,景观尺度上,翅碱蓬滩涂、水体面积大小是主要影响因素;微生境尺度上,植被盖度和水深为主要限制因子;在斑块尺度上,斑块类型对丹顶鹤生境选择最为重要。研究认为,在黄河三角洲自然保护区,景观尺度是影响丹顶鹤生境选择的主要尺度,景观尺度因子通过与微生境和斑块尺度因子的独立和联合作用制约着丹顶鹤在保护区的生境选择和空间分布格局。建议加强对翅碱蓬滩涂、芦苇沼泽、水体等湿地生境的保护和管理,规范和控制保护区内人类活动强度。     

Effect of landscape configuration and habitat quality on the community structure of waterbirds using a man-made habitat

Species occurrence and community structure are strongly influenced by multiple factors like habitat selection, species movement capabilities, competition, or conspecific and heterospecific attractions. More specifically, in waterbird communities, previous studies have identified the importance of environmental and structural characteristics of wetlands for their occupation and use. However, the effect of the surrounding landscape configuration remains unknown. In this article, we use a large network of artificial irrigation ponds to evaluate the importance of pond features in comparison to the effect of landscape and spatial configuration on the community at three different spatial scales. Our results show that landscape configuration has relatively little influence on structure of the waterbird community. Pond features were by far the most important variables to describe waterbird abundance and richness. At the species level, we detected differences in habitat preferences relating to species-specific ecological requirements. Our results highlight the importance of using a multiscale approach to understand and predict richness and abundance in waterbird communities. Our findings emphasize the need to maintain high-quality ponds to enhance their suitability for use as breeding and foraging sites.     

Thermoregulation and microhabitat use in mountain butterflies of the genus Erebia: Importance of fine-scale habitat heterogeneity

Mountain butterflies have evolved efficient thermoregulation strategies enabling their survival in marginal conditions with short flight season and unstable weather. Understanding the importance of their behavioural thermoregulation by habitat use can provide novel information for predicting the fate of alpine Lepidoptera and other insects under ongoing climate change. We studied the link between microhabitat use and thermoregulation in adults of seven species of a butterfly genus Erebia co-occurring in the Austrian Alps. We captured individuals in the field and measured their body temperature in relation to microhabitat and air temperature. We asked whether closely related species regulate their body temperature differently, and if so, what is the effect of behaviour, species traits and individual traits on body to air and body to microhabitat temperature differences. Co-occurring species differed in mean body temperature. These differences were driven by active microhabitat selection by individuals and also by species–specific habitat preferences. Species inhabiting grasslands and rocks utilised warmer microclimates to maintain higher body temperature than woodland species. Under low air temperatures, species of rocky habitats heated up more effectively than species of grasslands and woodlands which allowed them to stay active in colder weather. Species morphology and individual traits play rather minor roles in the thermoregulatory differences; although large species and young individuals maintained higher body temperature. We conclude that diverse microhabitat conditions at small spatial scales probably contribute to sympatric occurrence of closely related species with different thermal demands and that preserving heterogeneous conditions in alpine landscapes might mitigate detrimental consequences of predicted climate change.     

A multi-scale analysis of breeding site characteristics of the endangered fire salamander (Salamandra infraimmaculata) at its extreme southern range limit

Understanding species’ distributions often requires taking into consideration the characterization of the environment at different spatial scales. The habitat characteristics of the endangered fire salamander, S. infraimmaculata, have received little attention. In this study, at this species’ most peripheral and xeric limit (Mt. Carmel, Israel), we examined predictors of the larval distribution of S. infraimmaculata at aquatic-breeding sites at both local and landscape scales. We investigated the predictive power of environmental variables using two methods: generalized linear models and conditional inference trees (CTREE). Both multi-model approaches yielded similar results. At the local site scale, hydroperiod predicted breeding site use. At the landscape scale, Salamandra presence was best predicted by proximity to other breeding sites. In addition, our study indicates that sites selected for breeding are far from roads and agricultural fields. Overall, this study demonstrates that ultimately, both local and landscape scale predictors are necessary to understand properly a species’ habitat requirements and thus can help in planning future management around the breeding sites.     

Determinants of avian species richness at different spatial scales

ABSTRACT. Studies of factors influencing avian biodiversity yield very different results depending on the spatial scale at which species richness is calculated. Ecological studies at small spatial scales (plot size 0.0025–0.4 km²) emphasize the importance of habitat diversity, whereas biogeographical studies at large spatial scales (quadrat size 400–50,000 km²) emphasize variables related to available energy such as temperature. In order to bridge the gap between those two approaches the bird atlas data set of Lake Constance was used to study factors determining avian species diversity at the intermediate spatial scales of landscapes (quadrat size 4–36 km²). At these spatial scales bird species richness was influenced by habitat diversity and not by variables related to available energy probably because, at the landscape scale, variation in available energy is small. Changing quadrat size between 4 and 36 km², but keeping the geographical extension of the study constant resulted in profound changes in the degree to which the amount of different habitat types was correlated with species richness. This suggests that high species diversity is achieved by different management regimes depending on the spatial scale at which species richness is calculated. However, generally, avian species diversity seems to be determined by spatial heterogeneity at the corresponding spatial scale. Thus, protecting the diversity of landscapes and ecosystems appears to ensure also high levels of species diversity.     

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site’s location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species’ preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the US Geological Survey, Virginia Polytechnic Institute and State University, Virginia Department of Game and Inland Fisheries, and Wildlife Management Institute.     

Forest and Landscape Structure as Predictors of Capercaillie Occurrence

ABSTRACT Capercaillie (Tetrao urogallus) is a large, endangered forest grouse species with narrow habitat preferences and large spatial requirements that make it susceptible to habitat changes at different spatial scales. Our aim was to evaluate the relative power of variables relating to forest versus landscape structure in predicting capercaillie occurrence at different spatial scales. We investigated capercaillie-habitat relationships at the scales of forest stand and forest-stand mosaic in 2 Swiss regions. We assessed forest structure from aerial photographs in 52 study plots each 5 km². We classified plots into one of 3 categories denoting the observed local population trend (stable, declining, extinct), and we compared forest structure between categories. At the stand scale, we used presence-absence data for grid cells within the plots to build predictive habitat models based on logistic regression. At this scale, habitat models that included only variables relating to forest structure explained the occurrence of capercaillie only in part, whereas variables selected by the models differed between regions. Including variables relating to landscape features improved the models significantly. At the scale of stand mosaic, variables describing forest structure (e.g., mean canopy cover, proportion of open forest, and proportion of multistoried forest) differed between plot categories. We conclude that small-scale forest structure has limited power to predict capercaillie occurrence at the stand scale, but that it explains well at the scale of the stand mosaic. Including variables for landscape structure improves predictions at the forest-stand scale. Habitat models built with data from one region cannot be expected to predict the species occurrence in other regions well. Thus, multiscale approaches are necessary to better understand species-habitat relationships. Our results can help regional authorities and forest-management planners to identify areas where suitable habitat for capercaillie is not available in the required proportion and, thus, where management actions are needed to improve habitat suitability.     

Relationships between life-history strategies of European freshwater fish species and their habitat preferences

1. Focusing on the current environmental characteristics, the ‘habitat template’ theory proposes that life‐history strategies summarise how evolution has shaped species to cope with the temporal and spatial variability of their present environment. The hierarchical ‘landscape filters’ concept predicts that the distribution of species reflects their specific traits that allow them to pass through multiple habitat filters. Together, these theories showed the importance of identifying the functional relationships of species to selective habitat forces in order to predict the organisation and response of communities to the environment. 2. We test the relationships between life‐history traits of European freshwater fish species’ and their habitat preferences, to detect the strategies adopted by fish to cope with their current habitat. For this purpose, we use published data on species traits and habitat preferences (microhabitat hydraulics, temperature and oxygen level). We use multivariate analyses to classify fish species’ strategies and test the relationships between strategies and habitat preferences. 3. We identified a continuum of life‐history patterns between two extremes, with opportunistic and periodic species. Our study supports the idea that microhabitat hydraulics plays a more important role as a template for these species ecological strategies than temperature and oxygen level. Indeed, riffle habitats may select opportunistic species whereas weak relationships are found between species strategies and both their temperature and oxygen level preferences. In addition, the ratio between mortality and growth rate (dimensionless trait), reflecting a trade‐off between growth and survival, varied among species according to the use of their hydraulic habitat, with species using deep habitats exhibiting the highest values. 4. These general relationships between hydraulics and traits may be of importance in community ecology to develop predictive models to understand how fish communities change with the hydraulic environment.     

Coupling inter-patch movement models and landscape graph to assess functional connectivity

Landscape connectivity is a key process for the functioning and persistence of spatially-structured populations in fragmented landscapes. Butterflies are particularly sensitive to landscape change and are excellent model organisms to study landscape connectivity. Here, we infer functional connectivity from the assessment of the selection of different landscape elements in a highly fragmented landscape in the Île-de-France region (France). Firstly we measured the butterfly preferences of the Large White butterfly (Pieris brassicae) in different landscape elements using individual release experiments. Secondly, we used an inter-patch movement model based on butterfly choices to build the selection map of the landscape elements to moving butterflies. From this map, functional connectivity network of P. brassicae was modelled using landscape graph-based approach. In our study area, we identified nine components/groups of connected habitat patches, eight of them located in urbanized areas, whereas the last one covered the more rural areas. Eventually, we provided elements to validate the predictions of our model with independent experiments of mass release-recapture of butterflies. Our study shows (1) the efficiency of our inter-patch movement model based on species preferences in predicting complex ecological processes such as dispersal and (2) how inter-patch movement model results coupled to landscape graph can assess landscape functional connectivity at large spatial scales.     

An ‘ecological trap’ for yellow warbler nest microhabitat selection

Contrary to assumptions of habitat selection theory, field studies frequently detect ‘ecological traps’, where animals prefer habitats conferring lower fitness than available alternatives. Evidence for traps includes cases where birds prefer breeding habitats associated with relatively high nest predation rates despite the importance of nest survival to avian fitness. Because birds select breeding habitat at multiple spatial scales, the processes underlying traps for birds are likely scale‐dependent. We studied a potential ecological trap for a population of yellow warblers Dendroica petechia while paying specific attention to spatial scale. We quantified nest microhabitat preference by comparing nest‐ versus random‐site microhabitat structure and related preferred microhabitat features with nest survival. Over a nine‐year study period and three study sites, we found a consistently negative relationship between preferred microhabitat patches and nest survival rates. Data from experimental nests described a similar relationship, corroborating the apparent positive relationship between preferred microhabitat and nest predation. As do other songbirds, yellow warblers select breeding habitat in at least two steps at two spatial scales; (1) they select territories at a coarser spatial scale and (2) nest microhabitats at a finer scale from within individual territories. By comparing nest versus random sites within territories, we showed that maladaptive nest microhabitat preferences arose during within‐territory nest site selection (step 2). Furthermore, nest predation rates varied at a fine enough scale to provide individual yellow warblers with lower‐predation alternatives to preferred microhabitats. Given these results, tradeoffs between nest survival and other fitness components are unlikely since fitness components other than nest survival are probably more relevant to territory‐scale habitat selection. Instead, exchanges of individuals among populations facing different predation regimes, the recent proliferation of the parasitic brown‐headed cowbird Molothrus ater, and/or anthropogenic changes to riparian vegetation structure are more likely explanations.