Vladimír Hula

Inverse link between density and dispersal distance in butterflies: field evidence from six co-occurring species

A pertinent question in animal population ecology is the relationship between population abundance, density, and mobility. Two extreme ways to reach sufficient abundance for long-term persistence are to inhabit restricted locations at high densities, or large areas in low densities. The former case predicts low individual mobility, whereas the later predicts high one. This assumption is rarely tested using across-species comparisons, due to scarcity of data on both mobility and population sizes for multiple species. We used data on dispersal and local population densities of six butterfly species gained by mark-recapture, and data on their (relative) regional abundance obtained by walking transects in a landscape surrounding the mark-recapture sites. We correlated both local density and regional abundance against slopes of the inverse power function, appropriate for describing the shape of dispersal kernel. Local densities correlated negatively with the dispersal kernel slopes both when sexes were treated as independent data points and if treated together. For regional abundance, the correlation was also negative but only marginally significant. Our results corroborate the notion that a trade-off exists between living in dense populations and having poor dispersal, and vice versa. We link this observation to resource use by individual species, and distribution of such resources as host plants in the study landscape.

Impact of Canopy Openness on Spider Communities: Implications for Conservation Management of Formerly Coppiced Oak Forests

Traditional woodland management created a mosaic of differently aged patches providing favorable conditions for a variety of arthropods. After abandonment of historical ownership patterns and traditional management and the deliberate transformation to high forest after World War II, large forest areas became darker and more homogeneous. This had significant negative consequences for biodiversity. An important question is whether even small-scale habitat structures maintained by different levels of canopy openness in abandoned coppiced forest may constitute conditions suitable for forest as well as open habitat specialists. We investigated the effect of canopy openness in former traditionally coppiced woodlands on the species richness, functional diversity, activity density, conservation value, and degree of rareness of epigeic spiders. In each of the eight studied locations, 60-m-long transect was established consisting of five pitfall traps placed at regular 15 m intervals along the gradient. Spiders were collected from May to July 2012. We recorded 90 spider species, including high proportions of xeric specialists (40%) and red-listed threatened species (26%). The peaks of conservation indicators, as well as spider community abundance, were shifted toward more open canopies. On the other hand, functional diversity peaked at more closed canopies followed by a rapid decrease with increasing canopy openness. Species richness was highest in the middle of the canopy openness gradient, suggesting an ecotone effect. Ordinations revealed that species of conservation concern tended to be associated with sparse and partly opened canopy. The results show that the various components of biodiversity peaked at different levels of canopy openness. Therefore, the restoration and suitable forest management of such conditions will retain important diversification of habitats in formerly coppiced oak forest stands. We indicate that permanent presence of small-scale improvements could be suitable conservation tools to prevent the general decline of woodland biodiversity in the intensified landscape of Central Europe.

Sublethal effect of agronomical surfactants on the spider Pardosa agrestis

In addition to their active ingredients, pesticides contain also additives - surfactants. Use of surfactants has been increasing over the past decade, but their effects on non-target organisms, especially natural enemies of pests, have been studied only very rarely. The effect of three common agrochemical surfactants on the foraging behavior of the wolf spider Pardosa agrestis was studied in the laboratory. Differences in short-term, long-term, and overall cumulative predatory activities were investigated. We found that surfactant treatment significantly affected short-term predatory activity but had no effect on long-term predatory activity. The surfactants also significantly influenced the cumulative number of killed prey. We also found the sex-specific increase in cumulative kills after surfactants treatment. This is the first study showing that pesticide additives have a sublethal effect that can weaken the predatory activity of a potential biological control agent. More studies on the effects of surfactants are needed to understand how they affect beneficial organisms in agroecosystems.

Niche differentiation of two sibling wolf spider species, Pardosa lugubris and Pardosa alacris, along a canopy openness gradient

Abstract Phylogenetic niche conservatism can cause strong interspecific competition among closely related species leading to competitive exclusion from local communities or meta-communities. However, the coexistence of close relatives is often reported. One of the most frequent mechanisms mediating such coexistence is resource partitioning. Here, we investigated the niche differentiation of two sibling spider species, Pardosa alacris C.L. Koch, 1833 and P. lugubris Walckenaer, 1802, along a canopy openness gradient. We further investigated differences in body size as an additional axis for niche partitioning. We explored niche partitioning along the canopy openness gradient at eight locations. In each afforested location, 60-m-long transects were established consisting of five pitfall traps placed at regular 15-m intervals along the gradient. We measured the body size of individuals of both species collected at the gradients extremes. We found that the two Pardosa species occurred syntopically but had clearly differentiated spatial niches along the canopy openness gradient. Pardosa lugubris displayed a preference for closed canopies in dense forest habitats and its abundance gradually decreased as the canopy opened while the opposite was the case for P. alacris. The two species also differed in body size. Each species was larger at its preferred gradient extreme than was the other species. The coexistence of the two Pardosa species was mediated mainly by spatial niche partitioning. Body size differences may represent another axis for niche partitioning.

New records of the huntsman spider genus Olios (Araneae: Sparassidae) from Iran, Iraq and Afghanistan

Two species of the spider genus Olios are recorded for the first time from the Middle East, namely O. sericeus (Kroneberg, 1875) from Afghanistan and Iran, and O. iranii (Pocock, 1901) from Iraq. Previously recorded species of Olios are shown to be mis-identifications. A comparative diagnosis is provided for these two newly recorded-species.

Patterns of functional diversity of two trophic groups after canopy thinning in an abandoned coppice

Coppice abandonment had negative consequences for the biodiversity of forest vegetation and several groups of invertebrates. Most coppicing restoration studies have focused only on a single trophic level despite the fact that ecosystems are characterized by interactions between trophic levels represented by various groups of organisms. To address the patterns of functional diversity in the perspective of coppicing restoration, we studied the short-term effects of conservation-motivated tree canopy thinning in an abandoned coppice with standards in Central Europe, a region where such attempts have been rare so far. The functional diversity of vascular plants and spiders, chosen as two model trophic groups within the forest ecosystem, was compared between thinned and control forest patches. To characterize functional patterns, we examined several functional traits. These traits were assigned to two contrasting categories: response traits reflecting a change of environment (for both vascular plants and spiders) and effect traits influencing the ecosystem properties (only for vascular plants). Functional diversity was analysed by CCA using two measures: community-weighted means (CWM) and Rao’s quadratic diversity (RaoQ). CCA models revealed that the canopy thinning had a positive effect on the diversity of the response traits of both trophic groups and negatively influenced the diversity of effect traits. In addition, we found distinct seasonal dynamics in functional diversity of the spider communities, which was probably linked to leaf phenology of deciduous trees. We conclude that canopy thinning affected functional diversity across trophic groups during the initial phase of coppicing restoration. With necessary precautions, careful canopy thinning can be effectively applied in the restoration of functional diversity in abandoned coppices.

Effects of glufosinate-ammonium herbicide and pod sealant on spider Pardosa agrestis

Herbicides based upon glufosinate‐ammonium (GLA) are among the worlds most widely used. They also are applied on the most prominent oil crops as desiccants in combination with pod sealants to prevent pod shatter and seed loss close to harvest. Even though these crops occupy a significant part of the worlds agroecosystems, the effects of GLA herbicides on non‐target arthropods, and in particular natural enemies of pests, have been studied very rarely, and such effects of pod sealants have never been studied. We studied in our laboratory mortality as well as prey capture efficiency of the common GLA herbicide and desiccant Basta 15®, pod sealant Arrest®, and a mixture of both on the wolf spider Pardosa agrestis. We found that Basta 15® and the mixture had lethal effect on spiders. We also found significant, short‐term effect on predatory activity of spiders after all treatments. Basta 15® significantly influenced the amount of captured prey also in the long term. This is the first study showing lethal effect on spiders of the herbicide and herbicide plus pod sealant mixture. This is also the first study examining the effects of pod sealant on the mortality and predatory activity of a pest antagonist. More studies regarding the effects of agricultural chemical mixes are needed to uncover their effects on beneficial organisms existing within agroecosystems.

Effect of adjacent steppe-like habitats on spider diversity in vine plants

Spiders are important natural enemies of pests in many agroecosystems. Spiders’ diversity and abundance—and therefore their biological control potential—often increases with the presence of non-crop habitats adjacent to the agroecosystem and/or the abundance of such habitats in the landscape. This research aims to determine whether spider communities dwelling on vine plant trunks are richer and more abundant in terraced vineyards than in plain vineyards. We found that spiders’ abundance and species richness were significantly greater during part of the season in the plain than the terraced types of vineyards. The abundance of spiders on the vine plants in the terraced vineyards decreased gradually from the field margins to the centre while no such pattern was observed in the plain vineyards. Subsequent experiments will be needed in order to elucidate the role of the individual mechanisms and parameters that underpin our findings. For example, the air flow (direction and intensity), the presence of the predators, heterogeneity and the presence of shrubs on the slopes of terraces should be studied further. Particularly, because our findings contradict the general assumption that terraced vineyards should host richer spider communities.