Vertebrate seed dispersers maintain the composition of tropical forest seedbanks

Abstract

Seed dispersal is considered a key mechanism through which the structure and function of forests is maintained. Testing this can be difficult because the large scale over which dispersal operates makes it difficult to examine in a meaningful way. Using the near complete loss of native vertebrate seed dispersers from the island of Guam we examine the importance of seed dispersal for maintaining forest seedbanks. We find that seed dispersers have a strong influence on the species composition of seedbanks. Without seed dispersers seedbanks no longer serve to increase the species pool for tree regeneration following disturbance.

Simplified Communities of Seed-Dispersers Limit the Composition and Flow of Seeds in Edge Habitats

“…Size-biased patterns of seed rain may influence the successional dynamics of plant communities in forest edges over time because these patterns may create opportunities for some species with particular traits to become more prevalent in the edge community (Brodie and Aslan, 2012;Kurten et al, 2015). Seed rain also may influence the composition of the seed bank for future recruitment (Wandrag et al, 2015). The forest edge habitat could become dominated by small-seeded pioneer plants, lose rare tree species, and become homogeneous in terms of floristic composition over time (Oliveira et al, 2004;Melo et al, 2010;Lôbo et al, 2011).…”

Passive restoration following ungulate removal in a highly disturbed tropical wet forest devoid of native seed dispersers

“…The absence of native birds is a probable cause of negligible native plant recruitment in exclusion plots. A large proportion of native plant species found on Guam are dependent on frugivores as primary seed dispersers (Wandrag et al ). Prior studies detected no seed rain from bird‐dispersed trees in Guam's degraded forests, which contrasted to almost two seeds per m 2 on the nearby island of Saipan that has avifauna communities (Caves et al ).…”

“…Natural forest regeneration is necessary for widespread recovery of deforested areas and is desirable to preserve biodiversity, as well as for economic reasons (Chazdon & Guariguata ). Guam's forests, however, are a remarkable and poignant study on the negative ramifications of bird loss for forest succession, structure, and function on island ecosystems (Schreiner ; Caves et al ; Wandrag et al ). Reintroductions and recovery of native animals that provide valuable ecosystem services on Guam are likely critical for long‐term forest restoration.…”

“…Seed disperser loss will impact passive restoration programs, if seeds from intact forests fail to reach degraded areas (Ingle ; Caves et al ). Without seed dispersers, seeds of fruit‐producing, woody perennials rarely move far (Caves et al ; Wandrag et al ). The impact of seed disperser loss on entire communities is, however, rarely studied because such experiments are seldom feasible.…”

Different landscape effects on the genetic structure of two broadly distributed woody legumes, Acacia salicina and A. stenophylla (Fabaceae)

“…Shrubby legumes belonging to the genus Acacia are highly diverse and widespread across the Australian continent. Acacias form major components of many ecosystems across the continent including many arid ecosystems with poor soils (Bui et al., 2014; Maslin et al., 2003) and play an important role in ecosystem functioning including through the provision of resources and habitat to a broad range of insects and animals (Wandrag et al., 2015; Ward & Branstetter, 2017; Young et al., 2008). It also helps rapid colonization supporting ecosystem recovery following disturbance (Spooner, 2005).…”