Insect herbivores should follow plants escaping their relatives

Neighboring plants within a local community may be separated by many millions of years of evolutionary history, potentially reducing enemy pressure by insect herbivores. However, it is not known how the evolutionary isolation of a plant affects the fitness of an insect herbivore living on such a plant, especially the herbivore's enemy pressure. Here, we suggest that evolutionary isolation of host plants may operate similarly as spatial isolation and reduce the enemy pressure per insect herbivore. We investigated the effect of the phylogenetic isolation of host trees on the pressure exerted by specialist and generalist enemies (parasitoids and birds) on ectophagous Lepidoptera and galling Hymenoptera. We found that the phylogenetic isolation of host trees decreases pressure by specialist enemies on these insect herbivores. In Lepidoptera, decreasing enemy pressure resulted from the density dependence of enemy attack, a mechanism often observed in herbivores. In contrast, in galling Hymenoptera, enemy pressure declined with the phylogenetic isolation of host trees per se, as well as with the parallel decline in leaf damage by non-galling insects. Our results suggest that plants that leave their phylogenetic ancestral neighborhood can trigger, partly through simple density-dependency, an enemy release and fitness increase of the few insect herbivores that succeed in tracking these plants

Association of vegetation and soil mite assemblages with isolated Scots pine trees on a Scottish wet heath

Isolated trees may significantly enhance biodiversity at the landscape level. However, our understanding of their impacts is still poor, particularly in environments with high soil moisture where research on this topic has been comparatively limited. We examined understorey vegetation and soil oribatid mite assemblages under live and dead Scots pine trees and in open treeless areas, all within the same Scottish upland wet heath system, to determine whether isolated live trees affected the understorey and mite components of the ecosystem, and whether these effects occurred in parallel. We also explored whether these responses might result from tree-driven reductions in soil moisture content. Live trees reduced soil moisture (relative to wet heath and beneath dead trees) and appeared to change vegetation from wet heath to dry heath type communities. These effects were strongly related to tree trunk diameter (tree size). No major effects of dead trees on understorey vegetation or soil moisture were apparent. Higher mite species abundance and richness were found under live trees than in treeless open heath. Although mite abundances were lower under dead trees than live trees, richness remained similar, thus different factors seem to be regulating mite abundance and community composition. These findings indicate that landscape-level biodiversity responses to environmental change such as habitat fragmentation cannot be predicted from vegetation patterns alone, and that even in heavily fragmented landscapes comparatively small patches such as isolated individual trees can enhance biodiversity

Effectiveness of three sampling methods to survey saproxylic beetle assemblages in Mediterranean woodland

The choice of sampling methods to survey saproxylic beetles is a key aspect to assessing conservation strategies for one of the most endangered assemblages in Europe. We evaluated the efficiency of three sampling methods: baited tube traps (TT), window traps in front of a hollow opening (WT), and emergence traps covering tree hollows (ET) to study richness and diversity of saproxylic beetle assemblages at species and family levels in Mediterranean woodlands. We also examined trap efficiency to report ecological diversity, and changes in the relative richness and abundance of species forming trophic guilds: xylophagous, saprophagous/saproxylophagous, xylomycetophagous, predators and commensals. WT and ET were similarly effective in reporting species richness and diversity at species and family levels, and provided an accurate profile of both the flying active and hollow-linked saproxylic beetle assemblages. WT and ET were the most complementary methods, together reporting more than 90 % of richness and diversity at both species and family levels. Diversity, richness and abundance of guilds were better characterized by ET, which indicates higher efficiency in outlining the ecological community of saproxylics that inhabit tree hollows. TT were the least effective method at both taxonomic levels, sampling a biased portion of the beetle assemblage attracted to trapping principles, however they could be used as a specific method for families such as Bostrichiidae, Biphyllidae, Melyridae, Mycetophagidae or Curculionidae Scolytinae species. Finally, ET and WT combination allows a better characterization of saproxylic assemblages in Mediterranean woodland, by recording species with different biology and linked to different microhabitat types.Research Projects CGL2008-04472, CGL2009-09656 and CGL2011-23658 of the Spanish Ministry of Science and Innovation, and LIFE-07/NAT/00762 of the European Commission LIFE-Nature