Response of galling invertebrates on Salix lanata to reindeer herbivory

• Published in: Oikos
• Main Authors: Olofsson, Johan, Strengbom, Joachim
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2000
• Subjects: Ecology, Evolution, Behavior and Systematics; Salix lanata
• Online Access: http://dx.doi.org/10.1034/j.1600-0706.2000.910310.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1034%2Fj.1600-0706.2000.910310.x; https://onlinelibrary.wiley.com/doi/pdf/10.1034/j.1600-0706.2000.910310.x

Browsing and defoliation often increase the densities of insect herbivores on woody plants. Densities of herbivorous invertebrates were estimated in a long‐term grazing manipulation experiment. More then 30‐yr‐old fences allow us to compare densities of invertebrate herbivores on Salix lanata in areas heavily grazed and areas lightly grazed by reindeer. The number of gall‐forming insects ( Pontania glabrifons) and gall‐forming mites were higher on the heavily grazed shrubs than on lightly grazed shrubs. In contrast to most short‐term studies, the heavily grazed S. lanata had shorter current annual shoots. No difference in leaf size, leaf nitrogen content, or C:N ratio between grazing intensities were detected. However, the enhanced natural δ15N value indicates that heavily grazed shrubs get a higher proportion of their N directly from reindeer faeces. Leaf weight per unit area and relative fluctuating asymmetry of leaf shape increased in heavily grazed S. lanata . Enhanced relative fluctuating asymmetry might indicate higher susceptibility to herbivores. Long‐term grazing seems to increase the density of invertebrate herbivory in the same way as short‐term grazing, even if the plant responses differ substantially.