How complementary are large frugivores for tree seedling recruitment? A case study in the Congo Basin

Abstract

Large frugivores provide critical seed dispersal services for many plant species and their extirpation from forested ecosystems can cause compositional shifts in regenerating plant cohorts. Yet, we still poorly understand whether large seed-dispersers have complementary or redundant roles for forest regeneration. Here, to assess the functional complementarity of large-bodied frugivores in forest regeneration, we quantified the effects of varying abundance of hornbills, primates and the forest elephant on the density, species richness and the mean weighted seed length of animal-dispersed tree species among seedlings in five sites in a forest–savanna mosaic in D. R. Congo, while accounting for percentage forest cover and the local presence of fruiting trees. We found that the abundance of primates was positively associated with species richness of seedlings, while percentage forest cover was negatively associated (R2 = 0.19). The abundance of hornbills, the presence of elephants and percentage forest cover were positively associated with mean seed length of the regenerating cohort (R2 = 0.13). Spatially explicit analysis indicated that some additional processes have an important influence on these response indices. Primates would seem to have a preponderant role for maintaining relatively high species richness, while hornbills and elephant would seem to be predominantly responsible for the recruitment of large-seeded trees. Our results could indicate that these taxa of frugivores play complementary functional roles for forest regeneration. This suggests that the extirpation of one or more of these dispersers would likely not be functionally compensated for by the remaining taxa, hence possibly cascading into compositional shifts.

Spatial distribution patterns of Afzelia africana (Fabaceae – Detarioideae) in a tropical savanna of Benin: implications for management

“…The aggregative patterns observed for seedlings and saplings in the hunting zone can be attributed to high fruit/ seed rain combined with reduced activities of predators (Jansen & Zuidema 2001). Hunting and anthropogenic activities in this zone might have also reduced the density of dispersers, and hence seed dispersal of A. africana (Trolliet et al 2019). Limited seed dispersal and limited seed predation are therefore plausible explanations of the aggregative patterns of seedlings and saplings.…”

Efeito Da Defaunação Na Diversidade E Regeneração Florística Das Florestas

“…A respeito das consequências das alterações antrópicas no recrutamento de plântulas, estudos têm procurado demonstrar se a diminuição ou a ausência dos dispersores influencia o estabelecimento das mesmas (WRIGHT et al, 2007;VANTHOMME et al, 2010;ANZURES-DADDA et al, 2011;NEUSCHULZ et al, 2011;MENKE et al, 2012;HARRISON et al, 2013;TROLLIET et al, 2019 A respeito dos efeitos negativos da defaunação sobre o estabelecimento de plântulas, sugere-se que os dispersores contribuam para a manutenção da diversidade da assembleia de plantas, uma vez que em áreas defaunadas a fragmentação ou a caça excessivas, ou ambas: 1) diminuem o recrutamento de plântulas; 2) reduzem a dispersão de sementes, com maior proporção de espécies dispersadas por espécies não cinegéticas e por fatores abióticos; 3) reduzem à abundância de espécies vegetais, sugerindo uma mudança na comunidade (NUNEZ-ITURRI; HOWE, 2007); 4) reduzem as espécies dispersadas por grandes dispersores (aves e mamíferos); 5) há uma tendência das plântulas estarem agrupadas próximas aos adultos coespecíficos (TERBORGH et al, 2008). Stevenson (2011) e Trolliet et al (2019), por exemplo, verificaram uma correlação positiva entre a abundância de primatas (Atelinae) com a diversidade e riqueza de plântulas, destacando que o processo de dispersão de sementes por este grupo é importante para o sucesso reprodutivo das plantas.…”

Trait matching and sampling effort shape the structure of the frugivory network in Afrotropical forests

“…We know from other parts of the world that frugivory interactions are mostly governed by trait matching, with the size of fruits and seeds ingested constrained by the size of the fruit eaters (Kitamura et al ., 2002 ; Forget et al ., 2007 ; Donatti et al ., 2011 ; Dehling et al ., 2016 ). We also know that frugivore body mass is related to specialization, with the biggest species tending to be more generalist than the smaller ones, as they are able to ingest both small and large fruits and seeds (Trolliet et al ., 2019 ; Godínez‐Alvarez et al ., 2020 ). These large‐bodied species increase network cohesion and thereby network stability (Vidal et al ., 2014 ).…”