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A decrease in the surface area per unit volume is a well known constraint setting limits to the size of organisms at both the cellular and whole-organismal levels. Similar constraints may apply to social groups as they grow in size. The communal three-dimensional webs that social spiders build function ecologically as single units that intercept prey through their surface and should thus be subject to this constraint. Accordingly, we show that web prey capture area per spider, and thus number of insects captured per capita, decreases with colony size in a neotropical social spider. Prey biomass intake per capita, however, peaks at intermediate colony sizes because the spiders forage cooperatively and larger colonies capture increasingly large insects. A peaked prey biomass intake function would explain not only why these spiders live in groups and cooperate but also why they disperse only at large colony sizes, thus addressing both sociality and colony size range in this social spider. These findings may also explain the conspicuous absence of social spiders from higher latitudes and higher elevations, areas that we have previously shown to harbor considerably fewer insects of the largest size classes than the lowland tropical rainforests where social spiders thrive. Our findings thus illustrate the relevance of scaling laws to the size and functioning of levels of organization above the individual. Anelosimus | cooperation | group foraging | sociality | allometry

Landscape-driven processes impact the magnitude and direction of cross-ecosystem resource subsidies, but they may also control consumers' numerical and functional responses by altering habitat availability. We investigated effects of the interaction between habitat availability and subsidy level on populations of a riparian fishing spider, Dolomedes aquaticus, using a flood disturbance gradient in the Waimakariri River catchment, New Zealand. D. aquaticus predominantly eat aquatic prey as they hunt from the water surface. However, D. aquaticus biomass peaked at rivers with intermediate flood disturbance, rather than at less flood-prone rivers where the biomass of aquatic insect prey was markedly higher. Flooding positively influenced spider habitat quality, and an experimental manipulation at stable rivers indicated that unembedded cobbles, preferred D. aquaticus habitat, were a limiting factor, preventing response to the increased prey resource at stable sites. Potential terrestrial prey abundance was low, did not vary across the disturbance gradient, and is likely to have been a much smaller component of the fishing spiders' diet than aquatic insect prey. Thus landscape-driven factors not only controlled the magnitude of resource subsidies, but also influenced the ability of consumers to respond to them by altering the physical nature of the ecosystem boundary. Key words: disturbance; Dolomedes aquaticus; fishing spider; flood disturbance gradient; predator-prey interactions; river; Waimakariri River catchment, New Zealand.

Mass-action models of predator-prey interactions assume that predators encounter prey according to their relative densities as scaled by functional responses, although models seldom specify critical natural history and behavioral mechanisms that ensure that encounters actually occur. As a case study of this assumption, we assess the hypothesis that daily and seasonal activity and microhabitat use by wandering wolf spiders (Lycosidae: Schizocosa) searching for four common grasshopper species (Orthoptera: Acrididae) are coincident under natural conditions. There was great overlap in seasonal phenology and use of microhabitats between spiders and grasshoppers. Grasshoppers that were suitably sized (10-20 mm in length) as prey for spiders were relatively abundant from late spring through summer in this grassland. Three of the four common grasshopper species used microhabitat in a similar way, but differed from a fourth common species, Phoetaliotes nebrascensis. However, when they were active, spiders were about equally distributed between open microhabitats on the ground and up in the vegetation so that all grasshopper species were at risk. In response to temperature, spiders were active for only a portion of the day during which grasshoppers were also active so that the actual daily 'window-of-opportunity' for capture each day was much smaller than expected. Spiders were more likely to be active during the early morning and evening, while grasshoppers were active during all daylight hours, most likely because of differences in thermal preferences. Schizocosa and their grasshopper prey are largely coincident in time and space except for overlap in daily activity which, presumably, reflects differences in thermal preferences. Consequently, overlap in daily time budgets that ensure actual encounter was reduced about 50%. The significance of this difference to the inclusion of simple mass-action dynamics in predator-prey models requires further consideration, but may be important.

Argyrodes ululans, a kleptoparasitic spider that specializes in stealing prey from the social spider, Anelosimus eximius, faces a variety of foraging situations depending upon the number of host spiders involved in prey capture and defence, and prey availability. The ability of A. ululans to modify its mode of attack may therefore be essential to ensure its success in obtaining food. Kleptoparasite hunger level, host colony size and prey size were manipulated and detailed observations of behaviour were made to determine whether A. ululans modifies its stealing strategy in response to these changing conditions. Argyrodes ululans initiated an attack based on its hunger state and the size of the prey tackled, and altered the relative frequencies of its component stealing behaviour patterns according to the number of host spiders that responded to capture the prey. These adjustments in stealing tactics allow A. ululans to maximize its success in acquiring prey and to conserve energy used for foraging.

A study examines staged mixed phenotype feeding bouts in the socially polymorphic spider Anelosimus studiosus to explore the impact of phenotype frequency on the foraging success of the social (cooperative) and asocial (cheater) phenotypes. Findings indicate that asocial (cheater) individuals exhibit negative frequency-dependent foraging success in the bouts, losing their advantage when their number increases, which serves to limit their spread within the colonies.

A study investigates whether tracing stable isotopes would allow distinction between different types of predation and confirmation of intraguild predation (IGP). Results reveal that stable isotope analysis serves as a proven powerful tool to investigate animal behavior without direct observation, and allows disentangling predator feeding behavior when more than one type of prey is present.

A series of field experiments were conducted to test the population response of two ecologically-divergent wolf spider species (Hogna helluo and Pardosa milvina) to correlates of land fragmentation. It was found that these two synoptic wolf species have distinctly different responses to landscape fragmentation.

A discussion that research on sexual selection in spiders has been biased towards modalities that are easily accessible to the human observer is presented. Although the research has progressed since Darwin, whose spider examples are reanalyzed in the context of contemporary knowledge, the same biases and methodological constraints have persisted almost unchanged through the current boom of research.

A study of the functions of societies and the evolution of group living using spider societies as a test case is presented. It is found that the group characteristics of eusocial insects are governed by the reproductive function of their groups, while those of social spiders are largely governed by the foraging function of the group.

The way in which the visual signals of prey carcass decorations were perceived by predators is examined. The conclusion stated that prey carcass decorations do not attract insects but might redirect the attack of Vespa affinis and thus enhance the survival of spiders.

Data on the diet of the web-invading spider Mimetus notius were collected to determine the diet of this araneophagic spider. Mimetus notius primarily invades Theridiidae and Aaraneidae webs and is capable of preying upon at least seven families of spiders, principally in the genus Theridion (Araneae: Theridiidae). Mimetus notius invades the webs of several species on which no successful predation was observed. These data provide the first field data showing significant insectivory by a web invading mimetid, constituting 29% of the prey in this study. The presence of insects in the diet provides a potential explanation for the invasion of webs where successful predation on the resident is unlikely.