Trophic consequences of mast seeding for avian and mammalian seed and non-seed consumers in European temperate forests

Abstract

Resource pulses are wide-ranging, influential ecosystem processes with effects permeating throughout the food web, sometimes over several years. In temperate forests, resource pulses may be triggered by mast seeding of one or several tree species, providing a key food source to a multitude of species. However, direct and indirect consequences of mast seeding for various seed and non-seed consumers, and interactions among them, are often poorly understood. Based on a 16-year data set from Germany, we evaluated several hypotheses concerning the relationships between (1) mast seeding and seed consumers, (2) seed and non-seed consumers, and (3) seed or non-seed consumers and extrinsic factors other than mast seeding. Abundances of Eurasian Jays Garrulus glandarius correlated negatively, but abundances of voles positively, with mast seeding of oak in the previous fall, while the abundances of Great Tits Parus major did not appear to be linked to mast seeding. The abundance of non-seed consumers, such as Wood Warblers Phylloscopus sibilatrix, but not Chiffchaffs Phylloscopus collybita, appeared to be linked indirectly to mast seeding of oak via voles. Specifically, Wood Warbler abundance negatively correlated with abundances of voles. Extrinsic factors other than mast seeding appeared to be unimportant. This study shows how the set of factors affecting a species at a large spatial scale may vary from the set of factors acting at smaller spatial scales, as obtained from the literature. Lastly, we illustrate how several taxa at various trophic levels of a temperate forest ecosystem in Central Europe are linked via resource pulses. Assessing ecological processes revolving around seed-based resource pulses is pivotal to understanding how changing mast seeding dynamics may alter an ecosystem.