Avian seed dispersal out of the forests: A view through the lens of Pleistocene landscapes

Abstract

Recent evidence supports that, prior to the impact of modern humans, the temperate zone of Europe was not dominated by a closed continuous forest, but consisted of heterogeneous landscapes with grasslands, light woodlands and forests. Until the late Pleistocene, this region held a diverse community of megaherbivores that maintained the open and semi-open vegetation through grazing and browsing. This new baseline is congruent with the fact that many European woody species are light-demanding and fail to regenerate in the shaded interiors of temperate forests. Notably, most of these species are dispersed by frugivorous and seed-caching animals, mostly birds. Nowadays, avian seed dispersers play a key role for the connectivity and expansion of woodland patches in fragmented anthropogenic landscapes. Indeed, avian seed dispersal within and across the deforested matrix is the norm rather than the exception. Here, I reflect on the current patterns of avian seed dispersal in the fragmented anthropogenic landscapes of Europe from a Pleistocene perspective. The aim of this exercise is to discuss linkages between past and present landscapes, seeking an historical understanding of the high spatial complementarity of avian seed dispersal in and out of the forests. Synthesis: I conclude that the spatial patterns of avian seed dispersal in anthropogenic landscapes are congruent with an ecological and evolutionary history with open and semi-open habitats created and maintained by megaherbivores (ecological memory). By shaping the environmental conditions for millions of years, megaherbivores would have created selective pressures on animals and plants for life in landscape mosaics with forests and open habitats (niche construction). Finally, I discuss differences in landscape patterns today and in the Pleistocene, as well as the generality of these ideas to other biogeographical regions.