How Do Birds and Ants Contribute to the Recruitment of a Tropical Tree?

In most tropical ecosystems, birds play a crucial role as primary dispersers (Phase 1) by removing seeds from the plant crown. Following primary dispersal, ground-dwelling animals, notably ants, often disperse seeds secondarily (Phase 2). However, the relative contributions of each phase to seed dispersal effectiveness until plant establishment remains unclear. We combined observational and manipulative experiments to quantify the contributions of birds and ants to seed dispersal effectiveness of the ornithochoric tree Xylopia sericea in the Brazilian Atlantic Rainforest. Birds dispersed 17.2% of diaspores, with a dispersal distance (6.6 m +/- 6.7 m) twenty times greater than that of ants (0.3 m +/- 0.5 m). Notably, birds often dispersed seeds beyond the parental canopy, where seedling survival is higher. Ants were quantitatively more important to seed dispersal, with relative diaspore removal 221.3% higher than birds. Despite the limited dispersal-distance by ants, proximity to ant nests increased seedling survival. Phase 1 led to the establishment of 16.26 seedlings per 100 diaspores produced, and Phase 2 increased the number of seedlings established by 28.6% (N = 20.91). Ants enhanced seed recruitment and improved seedling survival both away and near the parental plant, likely due to ant nests providing favorable microsites for establishment. Conversely, plants distant from ant nests performed better when away from the parental plant, underscoring the importance of birds in seed dispersal. Birds promote long-distance dispersal and ants redistribute diaspores to microsites that increases establishment, so the dispersal of X. sericea is highly dependent on both dispersers.Abstract in Portuguese is available with online material. Na maioria dos ecossistemas tropicais, as aves desempenham um papel crucial como dispersoras prim & aacute;rias de sementes, removendo-as da copa das plantas (fase 1 de dispers & atilde;o). Ap & oacute;s a dispers & atilde;o prim & aacute;ria, frequentemente formigas dispersam as sementes secundariamente (fase 2 de dispers & atilde;o). Por & eacute;m, as contribui & ccedil;& otilde;es relativas de cada fase para a efetividade da dispers & atilde;o de sementes at & eacute; o estabelecimento de plantas permanecem incertas. N & oacute;s combinamos experimentos observacionais e manipulativos para quantificar as contribui & ccedil;& otilde;es de aves e formigas para a efetividade da dispers & atilde;o de sementes de Xylopia sericea, uma & aacute;rvore ornitoc & oacute;rica, na Mata Atl & acirc;ntica brasileira. As aves dispersaram 17,2% dos di & aacute;sporos a uma dist & acirc;ncia m & eacute;dia de dispers & atilde;o (6,6 m +/- 6,7 m), vinte vezes maior que as formigas (0,3 m +/- 0,5 m), comumente para al & eacute;m da copa parental, onde a sobreviv & ecirc;ncia das pl & acirc;ntulas & eacute; maior. As formigas foram quantitativamente mais importantes para a dispers & atilde;o de sementes, com remo & ccedil;& atilde;o de di & aacute;sporos relativa 221.3% maior do que a de aves. Apesar de a dist & acirc;ncia de dispers & atilde;o realizada por formigas ter sido limitada, a proximidade aos ninhos de formigas aumentou a sobreviv & ecirc;ncia das pl & acirc;ntulas. A fase 1 levou ao estabelecimento de 16,26 pl & acirc;ntulas a cada 100 di & aacute;sporos produzidos, enquanto a fase 2 aumentou o n & uacute;mero de pl & acirc;ntulas estabelecidas em 28,6% (N = 20,91). As formigas aumentaram o recrutamento e a sobreviv & ecirc;ncia de pl & acirc;ntulas tanto longe quanto perto da planta parental, provavelmente porque seus ninhos podem fornecer micro-habitats favor & aacute;veis para o seu estabelecimento. Por outro lado, plantas distantes de ninhos de formigas se sa & iacute;ram melhor quando distantes da planta parental, destacando a import & acirc;ncia das aves na dispers & atilde;o de sementes. Portanto, o sistema de dispers & atilde;o de X. sericea & eacute; complementar, com as aves promovendo a dispers & atilde;o a longa dist & acirc;ncia e as formigas redistribuindo di & aacute;sporos para micro-habitats que favorecem o estabelecimento. We combined observational and manipulative approaches to quantify the contribution of birds and ants, two of the main Neotropical seed dispersers, to the seed dispersal effectiveness of a tree species. We observed that seed dispersal occurring in two dispersal phases (diplocory) increases seed dispersal effectiveness by approximately 28%. Birds and ants have complementary roles in seed dispersal, with birds promoting long-distance dispersal and ants reshaping the seed shadow and secondarily dispersing seeds to favorable locations and increasing seedling establishment.image