From Plants to Birds: Higher Avian Predation Rates in Trees Responding to Insect Herbivory

Abstract

BackgroundAn understanding of the evolution of potential signals from plants to the predators of their herbivores may provide exciting examples of co-evolution among multiple trophic levels. Understanding the mechanism behind the attraction of predators to plants is crucial to conclusions about co-evolution. For example, insectivorous birds are attracted to herbivore-damaged trees without seeing the herbivores or the defoliated parts, but it is not known whether birds use cues from herbivore-damaged plants with a specific adaptation of plants for this purpose.MethodologyWe examined whether signals from damaged trees attract avian predators in the wild and whether birds could use volatile organic compound (VOC) emissions or net photosynthesis of leaves as cues to detect herbivore-rich trees. We conducted a field experiment with mountain birches (Betula pubescens ssp. czerepanovii), their main herbivore (Epirrita autumnata) and insectivorous birds. Half of the trees had herbivore larvae defoliating trees hidden inside branch bags and half had empty bags as controls. We measured predation rate of birds towards artificial larvae on tree branches, and VOC emissions and net photosynthesis of leaves.Principal Findings and SignificanceThe predation rate was higher in the herbivore trees than in the control trees. This confirms that birds use cues from trees to locate insect-rich trees in the wild. The herbivore trees had decreased photosynthesis and elevated emissions of many VOCs, which suggests that birds could use either one, or both, as cues. There was, however, large variation in how the VOC emission correlated with predation rate. Emissions of (E)-DMNT [(E)-4,8-dimethyl-1,3,7-nonatriene], β-ocimene and linalool were positively correlated with predation rate, while those of highly inducible green leaf volatiles were not. These three VOCs are also involved in the attraction of insect parasitoids and predatory mites to herbivore-damaged plants, which suggests that plants may not have specific adaptations to signal only to birds.

Effects of forest heterogeneity on the efficiency of caterpillar control service provided by birds in temperate oak forests

“…As the predation rate primarily depends on bird abundance, this is a result consistent with former ideas, according which birds exhibit numerical response to prey density (e.g. Holmes, 1990;Mantyla et al, 2008). In other words, the bird abundance and thereby the predation pressure is higher in areas, where the caterpillar density is high.…”

New particle formation from the oxidation of direct emissions of pine seedlings

“…According to the measurements made in two locations in Finland, the major emitted compounds from Scots pine are α-pinene, β-pinene and 3 -carene, with approximate contributions of 60-85% to the total observed monoterpene emission rates, although late in autumn β-phellandrene can make 20% of total monoterpene emission (Räisänen et al, 2008). Lindfors and Laurila (2000) estimated that total biogenic VOC emissions from Finnish forest are dominated by monoterpenes, which contribute approximately 45%, while in deciduous trees the percentage can be as low as 10-15% (Mäntylä et al, 2008), and isoprene emissions are only 7% of the annual total. In the USA the main biogenic monoterpene emissions are α-pinene, β-pinene, and limonene (Sakulyanontvittaya et al, 2008).…”

Alarm Pheromones—Chemical Signaling in Response to Danger

“…Herbivore-induced volatiles also serve as key foraging cues for natural enemies of the feeding herbivores, including insect predators and parasitoids (e.g. Turlings et al, 1998) and even for insectivorous birds (Mäntylä et al, 2008). Moreover, these signals can convey complex and highly specific information about the status of emitting plants.…”