Exclusion of birds from bilberry stands: impact on insect larval density and damage to the bilberry

Abstract

The bilberry (Vaccinium myrtillus L.), is the dominant plant in the field layer of many boreal forests in northern Sweden. It is utilized by several herbivorous insect larvae as food (i.e. Lepidoptera: Geometridae, Tortricidae and Hymenoptera: Symphyta). Total density of insect larvae was 63% lower where birds had access to larvae compared to exclosures. Larvae with a feeding behaviour which exposes them to birds (geometrids and sawflies) showed a pronounced reduction in density when exposed to bird predators. Density of larvae with a concealed feeding behaviour (tortricids) was unaffected by birds. The frequency of larval damage to bilberry annual shoots was significantly higher in areas where larval density was high due to exclusion of birds. I concluded that birds have the potential to heavily modify the interaction between bilberry and insect larvae.

Gleaning bats as underestimated predators of herbivorous insects: diet of Micronycteris microtis (Phyllostomidae) in Panama

“…For instance on BCI, herbivorous insects destroy about 20% of the entire annual leaf production (Leigh & Windsor 1982). Exclosure experiments in the tropics increasingly reveal the importance of birds and other taxa including ants and lizards as predators on herbivorous insects (Atlegrim 1989, Gradwohl & Greenberg 1982, Greenberg et al 2000, Marquis & Whelan 1994, Murakami & Nakano 2000, Philpott et al 2004, Strong et al 2000, Van Bael et al 2003. The impact of bat predation on herbivorous insects still remains unknown, because exclosure studies in the tropics did not distinguish between diurnal and nocturnal predation, and thus attributed reductions in herbivorous insects primarily to birds.…”

“…The regulation of plant populations, maintenance of diversity, and evolution of plant chemical defence all depend in part on the strong selection pressure from herbivorous insects (Coley & Barone 1996, Connell 1971, Janzen 1970, Leigh & Smythe 1978. The impact of herbivorous insects on tropical forests has led to a corresponding appreciation of predators such as birds and insects, that control herbivore populations and thus reduce levels of herbivory (Atlegrim 1989, Greenberg et al 2000, Marquis & Whelan 1994, Strong et al 2000, Van Bael et al 2003. However, to date, no study has explicitly addressed the potential impact of insectivorous bats (Microchiroptera) as predators of herbivorous insects in tropical forests, probably because so few data are available on diet, feeding rates and prey biomass.…”

The direct and indirect effects of insectivory by birds in two contrasting Neotropical forests

“…Foliage-gleaning birds can limit herbivorous arthropod densities and their damage to plants in temperate forests (Atlegrim 1989;Marquis and Whelan 1994;Murakami and Nakano 2000;Sanz 2001;Sipura 1999;Strong et al 2000), tropical forests (Van Bael et al 2003) and in agricultural systems (Greenberg et al 2000;Mols and Visser 2002). Although nearly all studies document decreases in arthropod abundance due to bird predation, indirect effects on the plant community are not observed in all systems or for all plant species (Wiens et al 1991;Sipura 1999;Forkner and Hunter 2000;Lichtenberg and Lichtenberg 2002).…”

Birds defend trees from herbivores in a Neotropical forest canopy

“…Proponents of the latter theory suggest that higher diversity in terrestrial systems leads to diffuse food webs, rendering trophic levels nonexistent (7). Field experiments demonstrate that insectivorous birds can limit arthropod abundances and decrease damage to plants, but these tests have been conducted in settings with relatively low tree species diversity such as temperate forests (8)(9)(10)(11) or agricultural systems (12,13). Along with high tree species diversity, tropical forests support a high diversity and biomass of leaf-chewing arthropods (14) as well as a high biomass of birds that consume them (15).…”