Experimental sward islets: the effect of dung and fertilisation on Hemiptera and Araneae

Abstract

Abstract. 1. Cattle avoid grazing around their dung. This pattern persists after the decomposition of the initial dung patch leading to the formation of taller grass patches, termed islets. It is known that islets hold a disproportionate amount of the arthropods in grazed grasslands. 2. An experimental manipulation was set up to investigate the relative effects of vegetation structure and nutrient input on arthropod distributions. Herbivorous bugs (Hemiptera) and predatory spiders (Araneae) were sampled in artificially generated islets treated with dung, fertiliser, a cutting regime to mimic grazing and a fallow control. 3. The densities of both Hemiptera and Araneae were affected by the presence of increased nutrient input through dung and fertiliser. The densities of different herbivore taxonomic families were influenced by food plant quality and the predators by the subsequent increase in prey density. 4. Delphacidae (Hemiptera) showed a preference for taller more nutrient rich swards treated with fertiliser, whereas Cicadellidae (Hemiptera) were more abundant in those swards treated with dung. Lycosidae (Araneae) were more common in dung‐treated swards, whereas Linypiidae (Araneae) were more common in the taller fertiliser‐treated swards. 5. Higher Hemiptera species richness was found in the fertiliser‐ and dung‐treated swards. It is believed that this effect was because of nutrient availability. 6. It is likely that the presence of cattle dung islets in grazed grassland plays an important role in the maintenance of biodiversity, through increasing structural heterogeneity.

Experimental evidence for the immediate impact of fertilization and irrigation upon the plant and invertebrate communities of mountain grasslands

“…), but recent studies have pointed out that vegetation structure might be the crux (Woodcock et al. ; Dittrich and Helden ). Our analyses show that all vegetation parameters influence arthropods to a certain degree.…”

“…On the other hand, we predicted that irrigation would have no effect on plant species richness (Riedener et al 2013), but still positive effects on arthropod abundance through an increased phytomass productivity and protection against dessication (Nielsen 1955). Fertilization was also predicted to increase herbivorous arthropod abundances, owing to an increase in plant tissue nitrogen content (Haddad et al 2000;Dittrich and Helden 2011). However, due to a highly diverse plant species pool among all our meadows (given that they have been extensively managed over the past decades), a high ecological stability and resistance against the experimental treatments were expected in the short term (Tilman and Downing 1994), therefore translating into few contrasted effects.…”

“…; Morris ; Woodcock et al. ; Dittrich and Helden ). A more abundant arthropod community will promote higher trophic levels up to vertebrates through a cascading process (Hunter and Price ; Britschgi et al.…”

“…In turn, an increase in plant growth will provide more food, space, and shelters for arthropods, boosting their abundances (e.g., Haddad et al 2000;Perner et al 2005;Dittrich and Helden 2011;Buri et al 2013). Higher plant species richness not only provides more potential host plants for herbivores, but also greater horizontal and vertical vegetation structure complexity, which seems to be crucial to support higher diversity and abundance of arthropods (e.g., Brown et al 1992;Morris 2000;Woodcock et al 2009;Dittrich and Helden 2011). A more abundant arthropod community will promote higher trophic levels up to vertebrates through a cascading process (Hunter and Price 1992;Britschgi et al 2006).…”

Science into practice – how can fundamental science contribute to better management of grasslands for invertebrates?

“…The relationship between sward structure and invertebrate populations may, though, be less straightforward as sward height may be a proxy for a further driver. For example, in this issue, Dittrich and Helden (2011) show how populations of phytophagous and predatory invertebrates can be enhanced in taller sward islets where the driver (for the phytophagous species at least) appears to be a higher nutrient content of the taller vegetation.…”