Frédéric Ysnel

Spiders (Araneae) useful for pest limitation and bioindication

Abstract In northern Europe at least, extensive knowledge of the systematics and ecology of spiders leads the authors to consider them as a very suitable group for pest limitation and for biodiagnostic purposes. An examination of both the qualitative and quantitative aspects of perdition by spider populations and communities is discussed as well as the evolution of some human factors occurring in agroecosystems that are likely to induce changes in spider predation such as chemical spraying and cultural practices. Studies addressing the recolonisation of agroecosystems by spiders, taking into account their dispersing abilities and habitat selection are summarised, followed by a discussion of the global efficiency of spiders as predators in such environments, the risks associated with their use and how to maximise their efficiency. The bioindicative value of spiders is presented by referring successively to population level and community level. The growth rate or the reproductive rate observed in natural populations can be correlated with the amount of prey ingested in the field. Thus, these parameters give an indirect estimation of the habitat quality. Two specific field experiments are presented to illustrate this ecological concept. Moreover, the role of spiders as indicators of heavy metal pollution (atmospheric or soil pollution) integrated by organisms living close to sources of pollution is discussed by reference to a set of laboratory and field experiments. Due to the close correspondence between the vegetation architecture and the composition of the associated spider community, it is argued (with a list of examples) that fluctuations in the spider community structure allows the bioevaluation of human disturbances. Based on the composition of the spider communities, methods of ecological classifications of natural habitats in several European countries are presented.

Spider biodiversity in connection with the vegetation structure and the foliage orientation of hedges.

Abstract The relationship between the structure of spider communities and an index of hedge ecological quality (based on an analysis of vegetation architecture using vegetation diversity and foliage cover) was investigated. The comparison deals with six hedges each of low, medium and high ecological value. The species richness and species composition of dominant spiders was the same for hedges of different quality. Thus it is concluded that these two simple parameters cannot reflect the diversity of the hedge foliage. Indicating species of the differences between ecological quality of two hedges could be required among the groups of species absent from one type of hedge. However, the foliage orientation of the hedges may induce substitution of spider species; thus special attention must be paid to the foliage orientation when comparing the spider communities inhabiting the hedges.

Habitat use and mating system of the houbara bustard (Chlamydotis undulata undulata) in a semi-desertic area of North Africa: implications for conservation

Studies of the movements and home-ranges of houbara bustards (Chlamydotis undulata undulata) showed sexual and seasonal differences in the use of space, with a polygynous mating system similar to an ‘exploded-lek’ or a ‘resource-defence-polygyny’, that remains undefined. We used the arthropod biomass as an index of the trophic quality of six defined habitats and we radio-tracked 7 females and 13 males to test whether sexual and seasonal variations in habitat use were related to resource availability, and to verify if critical resources for breeding females were monopolised by males. We analysed habitat selection in both sexes separately. We used the habitat type composition of buffer zones around radio-locations to study annual and seasonal habitat selection and to identify preferred habitats, using the chi-square goodness-of-fit test. Habitat use between sexes and between seasons were compared using MANOVA based on log-ratios of habitat proportions. During the year, and in each season, both sexes appeared to be significantly selective for habitats in comparison to their availability. But males avoided esparto grass, while females used all habitats. Habitat use differed between sexes in the breeding season, but not in the non-breeding season. In spring, when food resources were abundant and uniformly distributed in space, males preferred ‘temporarily flooded areas’ and females preferred ‘reg with tall perennials’ that offered both food and cover for brooding. Critical resources were not monopolised by males and the mating system fulfilled the definition of the ‘exploded-lek’. Leks are key sites for reproduction and should be considered as priority areas in further conservation plans.

Improving occurrence-based rarity metrics in conservation studies by including multiple rarity cut-off points

Abstract.  1. This study aims to develop a new method for assigning rarity weights to species in evaluations of the relative rarity of arthropod assemblages in conservation/monitoring studies.

ARE SALT MARSH INVASIONS BY THE GRASS ELYMUS ATHERICUS A THREAT FOR TWO DOMINANT HALOPHILIC WOLF SPIDERS

Abstract As a result of the Elymus athericus (Poaceae) invasion in the last ten years, a major change in vegetation cover has occurred in salt marshes of the Mont Saint-Michel bay (France). In this study, we investigated if the high conservation value of invaded salt marshes is preserved. Abundances, densities and flood resistance abilities of the dominant halophilic species Arctosa fulvolineata (nocturnal lycosid) and Pardosa purbeckensis (diurnal lycosid) were compared in both natural and invaded habitats. Elymus invasion involved both positive and negative aspects with respect to the conservation value of the salt marshes invaded: the P. purbeckensis population was clearly reduced in invaded habitats, whereas A. fulvolineata seemed to derive high benefits from the invasion. We supposed that abiotic parameters of the new habitat (mainly vegetation and litter characteristics) affected the two species differently with respect to their aut-ecology and their flood resistance abilities. Furthermore, food resources (estimated by different macrofauna density measurements) were likely to be reduced for P. purbeckensis in invaded habitats and unchanged for A. fulvolineata. Lastly, we hypothesize that individuals of P. purbeckensis are subject to increased interspecific competition (measured as intra-guild densities), whereas spiders from the same guild as A. fulvolineata have not increased in invaded habitats, resulting in an unchanged competition level.

Assessing habitat and resource availability for an endangered desert bird species in eastern Morocco: the Houbara Bustard

In Morocco we tested the consistency between an a priori habitat classification based on topography, hydrology, vegetation structure and composition, and an a posteriori classification based on arthropod assemblages, in a plain supporting wild endangered Houbara Bustards. According to vegetation structure, we defined seven a priori habitats that differed significantly in perennial cover and height. A multivariate multiple regression analysis showed a significant relationship between arthropod assemblages and vegetation structure. Canonical Analyses of Principal Coordinates, conducted simultaneously on direct searches of arthropods and trapping data, showed significant differences between assemblages in both cases, and produced two similar constrained ordinations of six a posteriori habitats: esparto grass (Stipa tenacissima), temporarily flooded areas, fields, “reg” with short perennials, “reg” with tall perennials and wadis. The two sampling methods reflected a dominance of ants and beetles. Arthropod biomasses increased significantly in spring and then decreased significantly in summer for beetles, and in autumn for ants. No strong differences appeared between habitats within seasons, especially in spring, indicating a uniform distribution of food resources during the Houbara breeding season. The “reg” with short perennials had the highest ant biomass in summer. This “reg” and fields also supported the highest arthropod biomass in autumn. Variation in arthropod biomass was a pertinent factor that should be integrated into Houbara habitat selection studies. The definition of habitat availability based on easily identifiable landscape units, combined with empirical tests on arthropod communities provided an accurate classification for habitat selection studies and conservation planning.

How Do Alterations in Habitat Structure by an Invasive Grass Affect Salt-Marsh Resident Spiders?

In European salt marshes, recent invasions by the grass Elymus cithericus raise questions regarding subsequent habitat modification and its effects on the resident biota. In this study, we studied the effects of modified salt-marsh structure on occurring spider assemblages, especially on salt exposure and flood resistance. We showed that locations having tall and deep-rooted invasive vegetation contained more species able to resist tidal floods as compared with locations with natural vegetation. Dominant species displayed different temporal trends between habitat types after flooding, with some species being less affected by floods either in invaded or in natural habitats. Some cursorial species were able to (re)colonize salt marshes after a spring flood as salinity levels decreased. Finally, stand characteristics of E. athericus did not affect the distribution of halotolerant spiders. As a habitat structure relates to flood resistance and/or risk-avoiding strategies, our results indicate that the status of salt-marsh resident species should be considered according to their habitat affinity.

Assessing the conservation value of the spider fauna across the West Palearctic area

Abstract Making use of the recent publication of a catalogue of spider species from Europe and the Mediterranean Basin, we built a computer database which indexes all specific and subspecific taxa reported from countries or islands in Platnicks world catalogue as well as in regional or national catalogues. We used this database to analyze the distribution of conservation values at the West Palearctic scale. Three indices of conservation value were calculated and compared between mainland and island territories: species richness, number of endemic species, and Ic, a “Conservation Value Index.” Species richness increases with the size of the area being considered, either in islands or in mainland countries, and is highest in Southern Europe. The number of endemics also increases with area, but only for mainland countries, suggesting that different factors determine endemism on islands and in mainland areas. The conservation index shows that several island territories are of a high conservation interest: the Mediterranean and Atlantic islands clearly exhibit the highest conservation value and some islands (mainly Canary and Balearic islands) can be considered hotspots of biodiversity for the West Palearctic area; other hotspots are some small Mediterranean islands.

Optimization of an “in situ” subtidal rocky-shore sampling strategy for monitoring purposes

This study compared 2 standardized protocols to monitor subtidal rocky shores. We tested 2 sampling methods (temporal unit and quadrat) to assess the efficiency of extracting biota parameters (diversity, abundance, and biomass) of macroalgae, Mollusca, and Porifera with respect to time-cost and the number of sampling units. Species richness and occurrence of rocky subtidal habitats were better described by visual censuses than by quadrats. The same estimated richness was provided by the 2 methods. The association of a visual census and a quadrat was the most efficient way for responding to the requirements. A minimum of 5 sampling units per discrete area is recommended for accurately describing habitats. Then, we tested the sensitivity of the proposed protocol on the Bizeux Islet to study the variations of community structures according to depth and station. Based on the results, recommendations for monitoring purposes have been proposed according to European directives.

Validation of Eustiromastix guianae (Caporiacco, 1954) (Araneae, Salticidae) with a first description of the female, and additions to the salticid fauna of French Guiana.

Abstract In this paper, we validate the doubtful species status of E. guianae, with redescriptions of (supposedly lost) type and holotype males, and a first description of the female. Both sexes are measured and illustrated by pictures of habitus and copulatory organs. Seventeen new salticid species for French Guiana are also reported and a detailed catalogue of all salticid species from the Trinité National Nature Reserve is provided.