Insect herbivory may cause changes in the visual properties of leaves and affect the camouflage of herbivores to avian predators

Abstract ‘Cry for help’ hypothesis predicts that attraction of predators with chemical or visual cues can decrease insect damage of plants. Visual cues involve changes in photosynthetic activity and the reflectance of leaves, and there is some evidence that birds may use these changes as foraging cu...
Ausführliche Beschreibung

Abstract ‘Cry for help’ hypothesis predicts that attraction of predators with chemical or visual cues can decrease insect damage of plants. Visual cues involve changes in photosynthetic activity and the reflectance of leaves, and there is some evidence that birds may use these changes as foraging cues. However, changes in the visual properties of leaves have not been quantified and it is not known how birds see these changes. We also presented and tested a new ‘reduction in camouflage’ hypothesis (not mutually exclusive with cry for help) stating that herbivore-mediated changes in leaf colour can increase the conspicuousness of herbivore against leaves. To define changes in the visual properties of leaves, their detectability to birds, and whether these changes affect the conspicuousness of herbivore, we manipulated the level of herbivory in silver birch trees (Betula pendula) with autumnal moth (Epirrita autumnata) larvae, and used blue tit (Cyanistes caeruleus) vision models to images of leaves and larvae. Hue, luminance (lightness), contrast, light transmission, chlorophyll content, photosynthetic activity and water content of the leaves were compared between herbivore-damaged and control trees. The leaves of herbivore-damaged trees had a decreased chlorophyll a concentration, increased contrast and they reflected more longer wavelengths. However, these changes are likely not obvious to birds. In contrast to our expectation, there were only minor differences in conspicuousness of larvae against the leaves of damaged trees, which may be very subtle to predator vision. Nevertheless, according to visual models, larvae should be easily detectable to birds from both herbivore-damaged and control trees. Significance statement Herbivory affects photosynthetic machinery and light reflectance of leaves, and may thus provide visual foraging cues to birds, although it is not known how these changes appear to birds. We also hypothesized that the changes in leaves may reduce the camouflage of the herbivore. After applying herbivore treatment and using the avian vision models, we found that the leaves of herbivore damage may cause the leaves to appear to birds with higher contrast and greener or a more yellowish colour than control leaves. In addition, although the herbivore was visible to birds, it was slightly less conspicuous when on damaged trees, indicating that the herbivore can be adapted to changes in the food plant. Our results indicate that herbivory causes changes visual properties of leaves, but these changes are likely not obvious to birds. Ausführliche Beschreibung

Autor*in:	Koski, Tuuli-Marjaana [verfasserIn] Lindstedt, Carita Klemola, Tero Troscianko, Jolyon Mäntylä, Elina Tyystjärvi, Esa Stevens, Martin Helander, Marjo Laaksonen, Toni

Format:	E-Artikel
Sprache:	Englisch

Erschienen:	2017

Schlagwörter:	Trophic interactions Avian vision model Background matching Herbivory Camouflage

Anmerkung:	© Springer-Verlag Berlin Heidelberg 2017

Übergeordnetes Werk:	Enthalten in: Behavioral ecology and sociobiology - Berlin : Springer, 1976, 71(2017), 6 vom: 30. Mai
Übergeordnetes Werk:	volume:71 ; year:2017 ; number:6 ; day:30 ; month:05

Links:	Volltext

DOI / URN:	10.1007/s00265-017-2326-0

Katalog-ID:	SPR003321851