Diverse guilds provide complementary dispersal services in a woodland expansion process after land abandonment

摘要

Land abandonment due to increasing depopulation of rural areas is an ongoing trend in developed countries worldwide. Abandoned lands represent an opportunity for ecosystem recovery, an urgent need for biodiversity conservation. Seed dispersal services provided by animals are a key feature for this process. Different dispersers may differentially contribute to plant recruitment under different ecological conditions, leading to complementary dispersal services. We studied the dispersal services, quantified as the contribution to plant recruitment, provided by the main dispersal guilds of Spanish juniper Juniperus thurifera L.: small-to-medium-sized strongly frugivorous birds (thrushes) and medium-to-large-sized carnivorous mammals (red fox and stone marten). To do this, we studied seed fate from seed dispersal to seedling survival during 2years and estimated seed dispersal effectiveness (seedlings recruited per m(2)) in two ecological contexts derived from ecosystem recovery after a historical period of degradation: remnant woodlands and old fields. Results showed a clear shift in the contribution to plant recruitment between these guilds, resulting in complementary and non-redundant dispersal services. Thrushes were the main contributors to plant recruitment in woodlands (73%), leading to population growth but with a reduced impact on the colonization of old fields where carnivores contributed to 80% of recruitment (42% red fox, 38% stone marten). The dispersal complementarity observed for thrushes and carnivores is a consequence of their functional diversity, mainly driven by their differences in feeding and movement behaviour.Synthesis and applications. The combination of short-distance, strongly frugivorous dispersers (e.g. passerine birds) together with big generalist frugivores with long-distance movements (e.g. carnivorous mammals) maintained (i) effective seed dispersal services in remnant woodlands and (ii) the connectivity between patches promoting old fields colonization and woodland expansion. Thus, it is in heterogeneous landscape mosaics ecosystems (e.g. agro-environments) where functionally diverse disperser communities play a key role in ecosystem recovery. By performing effective dispersal services across an array of habitat types, functionally diverse disperser communities assist natural restoration of human-impacted ecosystems all over the world. Thus, dispersal communities provide an important ecosystem service that may replace costly human-mediated restoration projects.