Assessing the impact of fire on spider abundance through a global comparative analysis

Fire is an important ecological disturbance; however, in many regions fire regimes are changing due to anthropogenic factors. Understanding the responses of species and ecosystem to fire can help to develop predictive models and inform fire management decisions. Despite their massive diversity and abundance, relatively little is known about the impacts of fire on invertebrates. Spiders are a diverse and ubiquitous group, with variation in ecological, behavioural and life history traits, and can offer important insights into the impacts of fire on invertebrates and whether these depend on environmental factors, phylogenetic history, or species traits. We conducted phylogenetic comparative analyses of published data from studies investigating the impacts of fire on spiders. We investigated whether fire affects family level abundance and whether this effect depends on ecologically relevant traits or site-specific factors (vegetation, latitude, fire type, time since fire). We found that time since fire had a significant effect on the abundance of some spider families (Lycosidae, Linyphiidae, Agelenidae), and within forest vegetation types. There was no relationship between family level traits and response to fire, suggesting that a trait-based approach does not increase predictive power in this group at this taxonomic level. Overall, it is difficult to make broad generalisations about the impacts of fire on spider abundance due to variation in site- and fire-specific factors. We did, however, find evidence that short fire intervals may be a threat to some spider families, and in forest ecosystems, where abundance initially decreased after fire, which may have important implications for fire management strategies. Finally, we show that analyses of published data can be used to detect broad scale ecological patterns and provide an alternative to traditional meta-analytical approaches.

Cascading Effects of Birds and Bats in a Shaded Coffee Agroforestry System

Volant vertebrate insectivores, including birds and bats, can be important regulators of herbivores in forests and agro-ecosystems. Their effects can be realized directly through predation and indirectly via intraguild predation. This paper examines data from bird and bat exclosures in coffee farms in Chiapas, Mexico in order to determine their effect on herbivores. Arthropods were sampled in 32 exclosures (with 10 coffee plants in each) and their paired controls three times during 6 months. After 3 months, herbivore and spider abundance increased, underscoring the importance of both intertrophic predation between volant vertebrate insectivores and herbivores and intraguild predation between volant vertebrate insectivores and spiders. After 6 months, herbivore abundance increased in the exclosures, which is indicative of a direct negative effect of birds and bats on herbivores. We suggest that intraguild predation is important in this food web and that seasonality may change the relative importance of intraguild vs. intertrophic predation. Results suggest a dissipating trophic cascade and echo the growing body of evidence that finds birds and bats are regulators of herbivores in agro-ecosystems.

Differing impacts of two major plant invaders on urban plant-dwelling spiders (Araneae) during flowering season

Plant invasions can have major impacts on ecosystems and influence global species diversity. In Central Europe, Himalayan balsam (Impatiens glandulifera) and American goldenrods (Solidago canadensis and S. gigantea) are important invaders often establishing dense and homogeneous stands, especially in urban and other disturbed habitats. We investigated their impacts on plant-dwelling spiders (abundance, family structure, guild structure) and potential spider prey items during flowering season within an urbanized landscape using a paired design comparing invaded and native reference vegetation plots. In general, flowering American goldenrods and Himalayan balsam had no significant impacts on the spider family composition. Invasion of American goldenrods further had no effect on total spider abundance and potential prey item abundance. In contrast, goldenrods showed a significantly increased crab spider (Thomisidae) abundance while being less inhabited by web builders. Himalayan balsam negatively influenced free hunters and running crab spider (Philodromidae) abundance, while we found no effects on other groups and total spider abundance. For Himalayan balsam, potential prey item abundance was higher than in native vegetation stands. Notwithstanding that our results only represent a snapshot of the system, they suggest that large-scale removal of urban goldenrod stands during flowering season might negatively influence local spider abundance, especially of crab spiders. Management efforts should therefore be accompanied by compensation measures to avoid disruptive effects on local plant-dwelling spider communities.

Spiders (Arachnida: Araneae) in organic apple (Rosaceae) orchards in southeastern France

The role of spiders (Arachnida: Araneae) in biological control programmes has received less attention than that of insect natural enemies. The aim of this two-year study was to obtain descriptive data on spider spring field population structure and dynamics. The study was carried out in one insecticide-free and four organic apple orchards in southeastern France. Rolls and bands of corrugated cardboard near the ground and shoots infested with Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae) in the tree canopy were used to sample spiders. Thirty-three spider species belonging to 14 families were identified from both sampling methods. Cheiracanthium mildei Koch (Araneae: Cheiracanthiidae) was clearly the predominant arboreal spider species in aphid-infested shoots (>57%). More than half of the spiders recorded in cardboard bands belonged to three species Drassodes pubescens (Thorell) (Araneae: Gnaphosidae), Pseudeuophrys erratica (Walckenaer) (Araneae: Salticidae), and Icius hamatus (Koch) (Araneae: Salticidae). Salticidae (39.9%) and Gnaphosidae (23.4%) families dominated significantly the spider assemblages observed in the cardboard rolls and were present on almost all sampling dates. However, in the two shelter types, the spider abundance curve clearly had a poly-modal shape. This may be due to the sequential arrival of some spider species or their dominance in a certain period of our study.

Ground spiders (Arachnida, Araneae) associated with urban forest fragments in southern Amazon

Forest fragments in urban areas comprise important habitats for a wide variety of species, however, conservationist policies for their maintenance and conservation are still incipient. This study examined the richness and abundance of the ground-spider assemblage in five forest fragments, with areas ranging between 18.5 and 103.98 ha, in the urban perimeter of Sinop, northern Mato Grosso State, southern Amazon region of Brazil. Sampling was carried out using the mini-Winkler extractor and pitfall traps in the dry (July) and rainy (November) seasons of 2017. All fragments were characterized in relation to the area and the Index of Biotic Integrity (IBI), to assess the effect of these variables on richness and abundance of soil spider assemblage. A total of 653 spiders were sampled, corresponding to 25 families and 52 species. Salticidae, Theridiidae, Lycosidae, Linyphiidae, Oonopidae and Symphytognathidae were the most abundant families (63.3% of the total sample). The assemblage was characterized by the dominance of hunting spiders (393 ind.; 60.2%) over web-building spiders (260 ind.; 39.8%). Greater spider abundance and richness was obtained during the rainy season (517 ind.; 79.2%; 41 spp.) as compared with the dry season (136 ind.; 20.8%; 24 spp.). Only 13 species occurred in dry and rainy season. Two species were recorded for the first time in the Amazon region, namely, Anapistula aquytabueraRheims & Brescovit, 2003 (Symphytognathidae) and Opopaea concolor (Blackwall, 1859) (Oonopidae). Species richness was not affected by IBI and area of fragment. Although the statistical model is not significant, species richness increases slightly with IBI and area of fragment. Similarly, abundance of spiders was not affected by IBI and area of fragment. Regardless of the area size, all evaluated forest fragments showed a low and regular IBI, demonstrating that these habitats have suffered with the pressures inherent from the urban perimeter, including the constant expansion of human occupation as well as misuse by the population. Nonetheless, these same fragments revealed considerable richness of species of ground spiders and can thus be categorized as important habitats for the maintenance of regional biodiversity. Therefore, action strategies must be set out to ensure their conservation.

Abundance and species diversity of predatory arthropods inhabiting rice of refuge habitats and synthetic insecticide application in freshwater swamps in South Sumatra, Indonesia

Karenina T, Herlinda S, Irsan C, Pujiastuti Y. 2019. Abundance and species diversity of predatory arthropods inhabiting rice of refuge habitats and synthetic insecticide application in freshwater swamps in South Sumatra, Indonesia. Biodiversitas 20: 2375-2387. Rice cultivation in freshwater swamps in Indonesia is specific, among other things, there is no synthetic pesticide spraying and vegetable growing on rice field embankments. This specific cultivation technique can affect the abundance and diversity of rice-dwelling arthropods species. The study aimed to compare the abundance and species diversity of predatory arthropods inhabiting rice surrounded both by refugia and vegetables and by those being applied with synthetic insecticide in the rice field of freshwater swamps. This study used rice plots surrounded by refugia flower (Zinnia sp., Tagetes erecta, Cosmo caudatus, and Sesamum indicum); vegetables (Cucumis sativus, Vigna sinensis, Luffa acutangula, and Momordica charantia); untreated; and synthetic insecticide. Twenty-five herbivore species of 12 families, 34 spider species of 8 families, and 24 species of predatory insects of 12 families were found on rice during a planting season. The lowest herbivore population and spider abundance were found on synthetic insecticide sprayed rice and they were significantly different from those of refugia-rice plots. The most abundant spiders and predatory insects were found on rice surrounded by refugia and were not significantly different from those of rice surrounded by vegetables. The highest species diversity for spiders and predatory insects was found on rice surrounded by refugia, whereas the lowest species diversity was found on synthetic pesticide sprayed rice. Therefore, rice surrounded by refugia flowers and vegetables was the most appropriate for habitat and niche of predatory arthropods.

Biotic predictors complement models of bat and bird responses to climate and tree diversity in European forests

Bats and birds are key providers of ecosystem services in forests. How climate and habitat jointly shape their communities is well studied, but whether biotic predictors from other trophic levels may improve bird and bat diversity models is less known, especially across large bioclimatic gradients. Here, we achieved multi-taxa surveys in 209 mature forests replicated in six European countries from Spain to Finland, to investigate the importance of biotic predictors (i.e. the abundance or activity of defoliating insects, spiders, earthworms and wild ungulates) for bat and bird taxonomic and functional diversity. We found that nine out of 12 bird and bat diversity metrics were best explained when biotic factors were added to models including climate and habitat variables, with a mean gain in explained variance of 38% for birds and 15% for bats. Tree functional diversity was the most important habitat predictor for birds, while bats responded more to understorey structure. The best biotic predictors for birds were spider abundance and defoliating insect activity, while only bat functional evenness responded positively to insect herbivory. Accounting for potential biotic interactions between bats, birds and other taxa of lower trophic levels will help to understand how environmental changes along large biogeographical gradients affect higher-level predator diversity in forest ecosystems.