دانلود رایگان مقاله تسهیل زیستگاه فصلی کوتاه مدت توسط حشرات گیاهخوار

Abstract

In nature some organisms may facilitate others by creating shelter or other niches that they use for variable periods. We describe a natural multitrophic-species complex in the Netherlands involving a plant, the common hogweed (Heracleum sphondylium) a specialist chewing herbivore, the parsnip webworm (Depressaria pastinacella) and various arthropods associated with them. Larvae of D. pastinacella feed on H. sphondylium seeds and, after they have finished feeding, chew holes in the hollow stems where they pupate. In some areas of the country almost 50% of plants are attacked by webworms. The holes are used by other arthropods to gain access to the stems including herbivores, omnivores, predators and decomposers. The duration of plant occupancy varies between 3 and 4 months, until the plants die. Plants without moth-produced holes were always free of other arthropods, whereas plants with holes, in addition to pupae (and/or mummified-parasitized webworm larvae), often contained many woodlice, earwigs and/or spiders. Earwigs and woodlice perform important ecological functions as predators (in orchards) and decomposers respectively. Our results show that the simple biological activity of one herbivore species can have at least short-term effects on the local arthropod community.

Discussion

Our results unambiguously show that D. pastinacella caterpillars are important small-scale habitat facilitators through the holes the larvae chew in the stems of H. sphondylium plants. These holes facilitate access to the hollow stems by a range of other arthropods. The most frequently observed were the woodlouse P. scaber, an important detritivore that eats decaying plant tissue inside of the stems (Fig. 1), an omnivore, the common earwig F. auricularia (Dermaptera: Forficulidae, Fig. 1), and a predator, the sac spider C. phragmitis (Arachnida: Clubionidae, Fig. 1). The earwig is considered to be an important biological control agent of several aphid species in orchards (Moerkens, Leirs, Peusens, & Gobin 2009; Romeu-Dalmau, Pinol, ˜ & Agustí 2012; Monteiro et al. 2013) whereas woodlice are important macro-detritivores that enhance decomposition or organic matter (Souty-Grosset, Badenhausser, Reynolds, & Morel 2005; Vos, van Ruijven, Berg, Peeters, & Berendse 2011; Crowther et al. 2013). Of the many hundreds of plantsthat were sampled that had not been attacked by D. pastinacella, not a single stem contained an entrance hole and thus the hollow compartments of these plants were always unoccupied. H. sphondylium has very potent chemical defences – furanocoumarins – that inhibit the colonization and attack of many herbivores (Sheppard 1991; McGovern, Zangerl, Ode, & Berenbaum 2006). D. pastinacella is probably the most important insect herbivore of H. sphondylium and is the only one that perforates holes in the stem in order to seek a pupation site. Plants with holes in the stems very often contained one to several species of other arthropods across a broad trophic spectrum. The most abundant were the woodlouse, P.scaber, the earwig F. auricularia and the spider C. phragmitis. However, stems were also occasionally found to harbour other spiders, centipedes, millipedes, ground beetles, collemboles and bugs, revealing that the ability to ascend plant stems to access the holes was not an impediment to their use by generally ground-dwelling arthropods.