Structure and habitat use in a web‐building spider community in northern Italy

Abstract

Animal communities, and particularly terrestrial carnivores, are considered to be strongly influenced by competitive interactions among coexisting species. Spiders are ubiquitous and important components of terrestrial ecosystems, but despite their interest, no studies have been published on the community structure and the resource use in the web-building spiders of southern Europe. We studied species abundance, seasonal occurrence and habitat use by the web-building spiders of a hedgerow biotope over two years. The spider community was composed of 17 species. Web size and position differed among species and life stages. For most species we observed a higher vegetation density towards the background of the web; this may decrease the ability of insects to see and avoid it. We observed differences among all the spider species in many habitat parameters (horizontal distribution, vertical stratification, density of vegetation around webs), and marked differences in seasonal occurrence. The segregation among species was greater in seasonal occurrence (overlap = 0.18-0.19) than in horizontal distribution (overlap = 0.67) and than in vertical stratification within the vegetation (overlap = 0.64). These differences may help species coexistence.

Humidity-mediated changes in an orb spider's glycoprotein adhesive impact prey retention time

“…The performance of A. marmoreus threads is consistent with this species' occupation of forest edge habitats (Bradley, 2013;Fasola and Mogavero, 1995;Jennings and Graham, 2007), where humidity remains elevated during the late morning and early afternoon hours (Fig. 4).…”

“…We studied threads of the orb weaver Araneus marmoreus Clerck 1757, a diurnal species that constructs vertically oriented orb webs in vegetation on forest edges, where humidity remains elevated during the day, and monitors its web using a signal line that extends from the web to the protective confines of the spider's folded leaf retreat (Bradley, 2013;Fasola and Mogavero, 1995;Jennings and Graham, 2007). We inferred the optimal humidity for the adhesive performance of this species' threads from: (1) the conditions of habitats where this species is found, (2) measurements of individual viscous droplet glycoprotein surface area and extensibility, and (3) a model that used these droplet values to estimate the work required to initiate the pull-off of a 4 mm-long capture thread span from a surface.…”

Where have all the spiders gone? Observations of a dramatic population density decline in the once very abundant garden spider,Araneus diadematus(Araneae: Araneidae), in the Swiss midland

“…The question arises whether the method of web counts applied in this study may have resulted in underestimating the true population densities by overlooking a certain percentage of satiated spiders which had not rebuilt their webs at the time when the counts were conducted. On this issue, it may be noted that densities assessed in the past century were for the most part also based on web counts [18,20,21,[26][27][28][29][30][31][32]] so that the same methodological bias was involved in both time periods. Furthermore, since insatiated spiders tend to rebuild their webs more frequently than fully satiated spiders [23,33], and since present-day spiders living in the era of insect loss are more likely to be insatiated compared with half a century ago (Table S2), the frequency of web building nowadays can be expected to be rather higher compared with the situation in the last century.…”

Predator demographics and dispersal in alfalfa trap‐cropped strawberry

“…Sweeping therefore likely led to underestimated predator abundance data for those taxa that are evenly distributed throughout the alfalfa canopy. Furthermore, sweep netting would severely underestimate predator abundance of taxa (i.e., some true bug and spider taxa) that preferentially inhabit the lower portion of the alfalfa canopy (Crocker & Whitcomb, 1980;Nyffeler & Benz, 1988;Fasola & Mogavero, 1995). If predator counts in alfalfa were in fact underestimated, then potential alfalfa sink effects would be masked and, instead, could be falsely interpreted as either having no discernable effect on predator movement or as constituting a source of predators into strawberry.…”