Negative effects of ant foraging on spiders in Douglas-fir canopies

Abstract

Spiders and ants are potential competitors and mutual predators. Indirect evidence from previous research has suggested that ant foraging may significantly lower the abundance of arboreal spiders in young Douglas-fir plantations in western Oregon. This study tested the effect of foraging by ants, dominated by Camponotus spp., on spider assemblages in Douglas-fir canopies in a 5-month ant-exclusion experiment. The biomass of potential prey organisms on foliage, dominated by Psocoptera, increased significantly by 1.9- to 2.4-fold following ant exclusion. The removal of ants did not affect the abundance of flying arthropods in the vicinity of tree canopies as indicated by sticky trap catches. The abundance of hunting spiders, the majority being Salticidae, increased significantly by 1.5- to 1.8-fold in trees without ants in the late summer; neither the abundance of web-building spiders nor the average body size of hunting and web-building spiders were significantly affected by ant removal. Spider diversity and community structure did not differ significantly between control and ant-removal trees. The majority of prey captured by ants were Aphidoidea (48.1%) and Psocoptera (12.5%); spiders represented only 1.4% of the ants' diet. About 40% of observed ants were tending Cinara spp. aphids. Our observations suggest that the lower abundance of hunting spiders in control canopies with ants may be due to interference competition with ants resulting from ant foraging and aphid-tending activities. Direct predation of spiders by ants appeared to be of minor importance in this study system. This study did not provide sufficient evidence for exploitative competition for prey between ants and spiders.

A novel property of spider silk: chemical defence against ants

“…Many orb-web spiders store the remains of prey in their webs [9], and these items, together with other prey entangled in the web, the protein-rich composition of silk [8] and the resident spider itself, provide nutritional resources for predators and scavengers, particularly small kleptoparasitic Argyrodes spiders [10,11]. Ants can be major predators of spiders [12][13][14], and workers of some species invade spider webs, establishing foraging trails on the non-sticky silk strands to access large caches of food [15,16]. Nevertheless, ants are rarely reported foraging on the webs of orb-web spiders, despite their diversity, abundance and vulnerability during moulting [17][18][19][20], and the superabundance and formidable predatory capabilities of ants [21].…”

Do Female Spiders Select Heavier Males for the Genes for Behavioral Aggressiveness They Offer Their Offspring?

“…However, ants may also interact with spiders. In an experimental study in Oregon, Halaj et al (1997) showed that competition can occur between canopy-living ants and spiders in Douglas-fir (Pseudotsuga menziesii). Although the abundance of hunting spiders (mostly Salticidae) increased significantly in trees without ants, web-building spiders (e.g., Theridiidae, Araneidae, Linyphiidae) did not respond numerically to ant removal.…”

Increasing Trophic Complexity Influences Aphid Attendance by Ants (Hymenoptera: Formicidae) and Predation

“…Ant presence can affect hunting behavior of other organisms (Halaj et al 1997) and cause higher occupation of prey refugia (Crutsinger and Sanders 2005). In these cases, however, herbivory is increased by aphid presence and therefore the association is likely to impact the host plant in a negative way.…”