Importance of habitat structure to the arthropod food‐web in Douglas‐fir canopies

Abstract

2000. Importance of habitat structure to the arthropod food-web in Douglas-fir canopies. -Oikos 90: 139 -152.This study tested the hypothesis that habitat structure dictates the distribution and community composition of arboreal arthropods. A diverse arthropod assemblage of Douglas-fir canopies, which included Araneae, Psocoptera, Collembola and Homoptera, was chosen as a model system. Habitat structural diversity, defined as needle density and branching complexity of Douglas-fir branches, was manipulated in a four-month experiment by needle removal, thinning and tying of branches. Abundance of canopy spiders declined significantly following needle density reduction and branch thinning, branch tying significantly increased spider abundance. Distinct habitat utilization patterns were found among individual spider guilds. Orb weavers (Araneidae) dominated spider assemblages in structurally simple habitats, whereas tied branches were colonized primarily by sheet-web weavers (Linyphiidae) and nocturnal hunting spiders (Anyphaenidae and Clubionidae). Spider species richness and average body size of several spider species increased in structurally more complex habitats. Arboreal spiders appeared to be limited by strong bottom-up effects in the form of habitat quality and, to a lesser degree, prey availability. Habitat manipulations did not affect densities or biomass of flying arthropod colonists in the branch vicinity. Needle removal and branch thinning led to a significant decline in the abundance of Psocoptera and Collembola. Tying of branches resulted in an eight-fold increase in Collembola numbers, organisms most sensitive to habitat alterations. Canopy habitat structure modified vertical dispersal of Collembola from forest litter, which may have significant implications for arboreal consumers. Our results lend strong support to the importance of habitat structural diversity in explaining general patterns of arthropod abundance and diversity on plants.

Effect of canopy openness on the pressure of predatory arthropods and birds on epigeic insects

“…The highest predation rate at the forest interior supports the assumption that abundance of predators also declines with increasing forest fragmentation and isolation [2]. Such findings are in agreement with outcomes of pitfall trap studies, which confirm positive correlations between low canopy openness and predation activity [19][20][21][22]. Differences between forest edge and interior in predation rate recorded in our experiments probably result from temperature variability within and between the two habitats.…”

“…Generally, we can say that litter affects predator abundances through at least four mechanisms: (1) access to alternative prey; (2) reduction of interspecific competition and prevention of intraguild predation [9]; (3) provision of overwintering sites, places for reproduction, and shelters to hide from higher trophic level predators [13][14][15]; and (4) reduction of abiotic stressors [6,9,[16][17][18]. The use of pitfall trapping to study activity of predators has confirmed that vegetation density positively correlates with activity and abundance of predators [19][20][21][22][23].…”

The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

“…species that are specifically adapted for living in forest habitats). Spiders are generalist predators and are more dependent on habitat structure and prey availability than the actual species of tree which they inhabit (Halaj et al 1998(Halaj et al , 2000Purchart et al 2013). By contrast the species richness of canopy-dwelling beetles was consistently higher in oak and ash woodlands than in forest plantations.…”

Comunidade edáfica de Araneae (Arthropoda, Arachnida) em uma floresta sazonalmente inundável na região Norte do Pantanal de Mato Grosso, Brasil

“…Estes organismos caracterizam-se por não apresentarem especificidade hospedeira e por sua distribuição depender, diretamente, da estrutura física do ambiente e da disponibilidade de presas na área (Halaj et al 2000, Sørensen 2003, fornecendo, assim, informações precisas sobre a estrutura de habitats, composição e organização das comunidades de invertebrados terrestres (Silva & Coddington 1996).…”