Biology subjects

Lafage, D.

Publications and source records attributed to Lafage, D..

9 recordsLinked to original sources

bioRxiv2024

Spiders bring new insight into the eco-evolutionary drivers of body size variation and sexual size dimorphism in arthropods

Body size has been used thoroughly in arthropod ecology as a reliable trait to assess fitness responses to changes in environmental factors. Among these, spiders represent a large and diverse group, colonizing almost all terrestrial habitats. Here, we propose a review on intraspecific body size variation in arthropods over two main macroecological spatial gradients--latitude and elevation--both of high interest in a global warming context. We found that more species with a direct than with an indirect development present a converse Bergmann cline along both gradients. Focusing on spiders, we propose that life history traits such as voltinism, mobility, and brood care influence intraspecific body size patterns--potentially hiding large-scale patterns. Further, we assessed interspecific sexual size dimorphism (SSD) in spider species. We found that extreme SSD--the most original feature in spider biometry--is influenced by hunting guild rather than phylogeny of spider families, suggesting that ecological factors prevail over evolutionary drivers in shaping SSD.

ecology↗

bioRxiv2021

Biogeographic position and body size jointly set lower thermal limits of wandering spiders

Most species encounter large variations in abiotic conditions along their distribution range. Climate, and in particular temperature, varies along clinal gradients, which determines phenotypic plasticity, local adaptations and associated physiological responses of most terrestrial ectotherms, such as insects and spiders. This study aimed to determine how the biogeographic position of populations and the body size of two wandering spiders set their limits of cold (freezing) resistance. Using an ad-hoc design, we sampled relatively large numbers of individuals from four populations of Dolomedes fimbriatus and one population of the sister species Dolomedes plantarius originating from contrasting climatic areas (temperate and continental climate), and compared their supercooling ability as an indicator of cold resistance. Results indicated that spiders from northern (continental) populations had higher cold resistance than spiders from a southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red-listed and rarest D. plantarius was slightly less cold-tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection.

physiology↗

bioRxiv2021

Drivers of taxonomic, functional and phylogenetic diversities in dominant ground-dwelling arthropods of coastal heathlands

Although functional and phylogenetic diversities are increasingly used in ecology for a large variety of purposes, their relationships remain unclear and likely vary presumably over taxa, yet most recent studies focused on plant communities. Different concepts predict that a community becomes functionally more diverse by adding phylogenetic lineages, subtracting lineages, adding species, reducing or increasing environmental constraints. In this study, we investigated ground-dwelling spider, ground beetle and ant assemblages in coastal heathlands (>11 000 individuals, 216 species), and their estimated functional and phylogenetic diversities as minimum spanning trees using several traits related to the morphology, feeding habits and dispersal of species, and phylogenetic trees, respectively. Correlations were overall positive and high between functional and phylogenetic diversities. Accounting for taxonomic diversities and environments made disappear this relationship in ants, but maintained them in spiders and ground beetles, where taxonomic diversity related to functional diversity only via increasing phylogenetic diversity. Environmental constraints reduced functional diversity in ants, but affected functional diversity only indirectly via phylogenetic diversity (ground beetles) and taxonomic and then phylogenetic diversity (spiders and ground beetles). Results are consistent with phylogenetic conservatism in traits in spiders and ground beetles, while in ants traits appear more neutral with any new species potentially representing a new trait state. Lineage diversities mostly increased with taxonomic diversities, possibly reflecting un-measured environmental conditions.

ecology↗

bioRxiv2020

Characterization of habitat requirements of European fishing spiders

Wetlands are among the most threatened habitats in the world, and so are their species, which suffer habitat loss due to climate and land use changes. Freshwater species and arthropods receive little attention in research and conservation, and the goals to stop and reverse the destruction of wetlands published 25 years ago in a manifesto by the Union of Concerned Scientists have not been reached. In this study, we investigated the occurrence and habitat requirements at two spatial scales of two species of European fishing spiders Dolomedes, which rely heavily on declining wetland habitats in Sweden and southern Norway. We collected occurrence data for Dolomedes plantarius and Dolomedes fimbriatus, using a live-determination-method. We modelled the placement of nursery webs to describe fine scaled habitat requirements related to vegetation and microclimate. Using a machine learning approach, we described the habitat features for each species, and for co-occurrence sites, to provide insight into variables relevant for the detectability of Dolomedes. We found that habitat requirements were narrower for D. plantarius compared to D. fimbriatus; that the detection of nursery webs can be affected by weather conditions and that nursery placement is mostly dependent on the proximity to water, the presence of Carex sp. (Sedges) and of crossing vegetation structures, and on humidity. Furthermore, co-occurring sites were more similar to D. plantarius sites than to D. fimbriatus sites, whereby surrounding forest, water type and velocity, elevation and latitude were of importance for explaining which species of Dolomedes was present. We provide a detailed field protocol for Dolomedes studies, including a novel live-determination method, and recommendations for future field protocols.

ecology↗

bioRxiv2020

Changes in salt-marsh vegetation weakly affect top consumers of aquatic food webs

Salt marshes are under high, and increasing, anthropogenic pressures that have notably been reported to affect the diet of several fish species, probably resulting in nursery function alterations. Most of the previous studies in Europe were yet based on gut content analysis of fish, which can be considered a snapshot of immediate impacts of salt-marsh changes, and hardly of long-term effects of disturbances. In this study, we investigated the impact of vegetation type (resulting from both plant invasion and sheep grazing) by assessing trophic network (and especially fish diet and position) of different salt-marsh conditions. Replicated samples of basic sources (particular organic matter and microphytobenthos), dominant vegetation, potential aquatic and terrestrial prey and fish of 3 main species were taken during summer 2010 in two bays from Western France (Mont -Saint-Michel Bay and Seine Estuary) and analysed using C and N stable isotope compositions. All response variables tested (overall trophic organization, trophic niche and trophic position) provided consistent results, i.e. a dominant site effect and a weaker effect of vegetation type. Site effect was attributed to differences in anthropogenic Nitrogen inputs and tidal regime between the two bays, with more marine signatures associated with a higher frequency of flooding events. A second hypothesis is that E. acuta, which has recently totally replaced typical salt-marsh vegetation in Mont Saint-Michel Bay strongly impacted the nursery function. The trophic status of dominant fish species was unchanged by local salt-marsh vegetation, and considered consistent with their diet, i.e. high for predatory species (the sea bass Dicentrarchus labrax and the common goby Pomatoschistus microps) and lower for biofilm grazing species (the thinlip mullet Chelon ramada). This study finally highlights the relevance of stable isotopes analyses for assessing long-term and integrative effects of changes in vegetation resulting from human disturbances in salt marshes. HighlightsO_LICross-ecosystem subsidies are of high functional importance, notably in salt marshes C_LIO_LIFish are vectors of exchanges, most European studies being based on their gut content C_LIO_LIUsing stable isotopes we analysed the effect of surrounding vegetation on food webs C_LIO_LISurprisingly we found weak vegetation and strong site effects on all metrics C_LIO_LINitrogen inputs, site accessibility and loss of nursery function can explain this fact C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/222406v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@27b54borg.highwire.dtl.DTLVardef@ef583corg.highwire.dtl.DTLVardef@18a0303org.highwire.dtl.DTLVardef@1cbe5d4_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2020

Habitat filtering differentially modulates phylogenetic vs functional diversity relationships between dominant ground-dwelling arthropods in salt marshes

While mechanisms underlying biological diversities at different scales received huge attention over the last decades, whether local abiotic factors driving functional and phylogenetic diversities can differ among ecologically and phylogenetically closely related taxa remains under-investigated. In this study, we compared correlations and drivers of functional (FD) and phylogenetic (PD) diversities between two dominant taxa of ground-dwelling arthropods in salt marshes, spiders and carabids. Pitfall trapping in two sampling sites of N-W France resulted in the collection and identification of more than 7000 individuals belonging to 67 species. Morphological and behavioral traits, as well as molecular sequences of COI gene, were attributed to all species for calculating functional and phylogenetic diversities respectively. Both taxa exhibited high correlation between FD and PD, which was even higher in carabids probably due to their lower species richness. Analyses using Bayesian framework and structural equation modeling revealed that FD and PD were positively influenced by taxonomic diversity in spiders and carabids, but abiotic factors driving FD and PD differed between taxa. Salinity especially drove the taxonomic diversity of carabids, but not that of spiders, suggesting that spiders are more plastic and less selected by this factor. Phylogenetic diversity was conversely influenced by salinity in spiders but not in carabids. This interesting result can be interpreted by different evolutionary history and colonization process of salt marshes between the two model taxa. Our study finally highlights that, even in taxa of the same phylum and occupying the same niche in a highly constrained habitat, functional and phylogenetic diversities can have different drivers, showing different filtering mechanisms and evolutionary history at small spatial and temporal scales.

ecology↗

bioRxiv2020

Explicit integration of dispersal-related metrics improves predictions of SDM in predatory arthropods

Fishing spiders (Dolomedes spp.) make an interesting model to predict the impact of global changes because they are generalist, opportunistic predators, whose distribution is driven mostly by abiotic factors. Yet, the two European species are expected to react differently to forthcoming environmental changes, because of habitat specialization and initial range. We used an original combination of habitat and dispersal data to revisit these predictions under various climatic scenarios. We used the future range of suitable habitat, predicted with habitat variables only, as a base layer to further predict the range or reachable habitat by accounting for both dispersal ability and landscape connectivity. Our results confirm the northward shift in range and indicate that the area of co-occurrences should also increase. However, reachable habitat should expand less than suitable habitat, especially when accounting for landscape connectivity. In addition, the potential range expansion was further limited for the red-listed D. plantarius, which is more habitat-specialist and has a lower ability to disperse. This study highlights the importance of looking beyond habitat variables to produce more accurate predictions for the future of arthropods populations.

ecology↗

bioRxiv2018

Local and landscape drivers of aquatic-to-terrestrial subsidies in riparian ecosystems: a worldwide meta-analysis

Cross-boundary fluxes of organisms and matter, termed \"subsidies\", are now recognized to be reciprocal and of roughly equal importance for both aquatic and terrestrial systems, even if terrestrial input to aquatic ecosystems has received most attention. The magnitude of aquatic to terrestrial subsidies is well documented, but the drivers behind these subsidies and their utilization by terrestrial consumers are characteristically local scale studies, limiting the inferences that can be drawn for broader geographic scales. We therefore built and analyzed a database of stable isotope data extracted from 21 studies worldwide, to identify both landscape and local scale variables that may affect the diet of terrestrial predators in riparian ecosystems. Our meta-analysis revealed a greater magnitude of aquatic-to-terrestrial subsidies (> 50%) than previously reported, albeit with large geographic and inter-annual variations. We demonstrated a large effect of landscape-scale factors on aquatic-to-terrestrial subsidies, particularly anthropogenic land use and tree cover. Local human population was the only relevant factor at the local scale. We also found that studies on landscape-scale and anthropogenic land use effects on aquatic-to-terrestrial subsidies are currently strongly under-represented in the ecological literature. Such studies are needed to improve our understanding of how land use and environmental change might influence future patterns of biodiversity and ecosystem function.

ecology↗

bioRxiv2018

Responses of ground-dwelling spider assemblages to changes in vegetation from wet oligotrophic habitats of Western France

While many arthropod species are known to depend, directly or indirectly, on certain plant species or communities, it remains unclear to what extent vegetation shapes assemblages of other taxa, notably spiders. In this study, we tested whether the activity-density, composition, and diversity of ground-dwelling spiders were driven by changes in vegetation structure. Field sampling was conducted using pitfall traps in bogs, heathlands, and grasslands of Brittany (Western France) in 2013. A total of 8576 spider individuals were identified up to the species level (for a total of 141 species), as well as all plant species in more than 300 phytosociological releves. A generalised linear model showed that spider activity-density was negatively influenced by mean vegetation height and mean Ellenberg value for moisture. Indices of diversity (, {beta}, and functional diversities) increased with increasing vegetation height and shrub cover (GLMs). Variables driving spider composition were mean vegetation height, dwarf shrub cover, and low shrub cover (results from a redundancy analysis). Spiders, some of the most abundant arthropod predators, are thus strongly influenced by vegetation structure, including ground-dwelling species. Although later successional states are usually seen as detrimental to local biodiversity in Europe, our results suggest that allowing controlled development of the shrub layer could have a positive impact on the diversity of ground-dwelling spiders.

ecology↗