The Influence of Hunting Manner on Prey Size, Particularly in Spiders with Long Attack Distances (Araneidae, Linyphiidae, and Salticidae)

Abstract

Several classifications of foraging manner are related along two axes: the time (from within feeding bouts to among generations) during which locomotion occurs, and the actual level of locomotion. Habitat specialization as "searchers" seems to occur in large species of araneid (orb-web) spider and in small species of salticid (jumping) spider, while small araneid and large salticid species seem to show more specialization for size of prey as "pursuers." The use of larger prey by web than by nonweb spiders is related to the peaked lognormal curve of abundance of insects. Specialization for prey size as a pursuer, then, seems more common in spiders using prey of intermediate sizes, which are most abundant. Specialists for habitat are more usual at the two tails of the insect (prey) abundance curve. The use of nets and poison apparently increases the size of prey used, relative to the predator's size, since web spiders take larger prey than nonweb spiders and the latter take larger prey than chewing insectivores. Nets, poison, surprise, and pack hunting may occur as tools to increase the relative size of prey in both arthropods and vertebrates. Pack hunters seem to be more olfactory, terrestrial, and diurnal in their habits, while hunters which use the other tools are more tactile, arboreal, and nocturnal. A complementary relative species abundance between the Linyphiidae (sheet-web spiders) and Salticidae is discussed in relation to their probable use of similarsized prey. The linyphiids dominate the spider fauna at high latitudes and, in one case at least, replace the salticids among habitats within a latitude, in those habitats with the ground surface disturbed. There may be a relative rarity of small insects in the tropics, or competition with ants may be involved. Analysis of the size, abundance, and motility of insectivores, including insectivorous insects, should predict the relative abundance in particular habitats of species of the various guilds of web and nonweb spider modes, as well as the species, degree of specialization for prey size or for habitat.