Abstract
There is increasing evidence that large-bodied primates play important roles as seed dispersers and in the maintenance of tree diversity in forest ecosystems. In this study we compared forest regeneration at two sites with differing primate abundances in the Ecuadorian Chocoan rainforest. We predicted: (1) significant differences in primate abundance between the two sites; (2) higher understory tree species richness and density at the site with greater primate abundance; (3) the site with lower primate abundance characterized by tree species dispersed by non-primate biotic agents and/or abiotic factors. We compared two sites, Tesoro Escondido (TE) a campesino cooperative, and the El Pambilar (EP) wildlife refuge that both maintain populations of mantled howler monkey (Alouatta palliata), the brown-headed spider monkey (Ateles fusciceps fusciceps) and the capuchin monkey (Cebus capucinus). We characterized canopy structure by point-quadrant sampling, determined primate abundance and sampled seedlings/saplings in 1 m2 plots, classifying tree species based on three dispersal syndromes: adapted for primate dispersal, dispersed by other biological agents, and abiotic dispersal. We compared sites in terms of primate abundance (groups and individuals observed per day) and regeneration characteristics (overall density, species richness, and dispersal syndrome). We carried out within site comparisons and constructed understory tree species accumulation curves. Overall the forests were structurally similar - with significantly higher densities of A. f. fusciceps at TE. Encounter rates for the other two primate species were similar at both sites. Understory tree density and species richness was significantly higher in TE with no stabilization of tree species accumulation curves. The species accumulation curve for understory trees at EP stabilized. Higher densities and species richness of primate dispersed tree species were observed at TE, with non-primate biotically dispersed tree species the dominant dispersal syndrome at both sites. Our observations are consistent with those from other studies investigating the role of large-bodied frugivorous primates in forest regeneration, and point to a general pattern: future lowland tropical forest tree diversity depends on maintaining robust populations of large primate species in these systems. It is highly probable that the maintenance of high levels of tree diversity in Chocoan rainforests is dependent on the conservation of its largest resident primate, the critically endangered brown-headed spider monkey (A. f. fusciceps).
Highlights
Myers, Thomsen, da Fonseca, & Olivieri, 1998; Olson & Dinerstein, 1998, 2002; Myers et al, 2000)
Alouatta palliata and Cebus capucinus are found on Barro Colorado Island in Panama (Leighton & Leighton, 1982; Wehncke et al, 2003) where tree density is 371-383 trees / ha (DeWalt & Chave, 2004); Alouatta palliata is found at La Selva Biological Station in Costa Rica (Stoner, 1996) where tree density ranges between 426515 trees / ha (DeWalt & Chave, 2004); Ateles geoffroyi and Alouatta palliata occupy forest fragments in Los Tuxtlas, Mexico (Estrada & Coates-Estrada, 1996), where tree density is 737-834 trees / ha (Arroyo-Rodríguez, Mandujano, & Cuende-Fanton, 2005); and Ateles belzebuth, Alouatta seniculus and Cebus albifrons are found in Yasuní in the Ecuadorian Amazon (Pozo & Youlatos, 2005), where tree density is approximately 701 trees / ha (Valencia et al, 2004)
All are similar to the values reported here for both study sites, suggesting that the tree density does not account for the primate differences between El Pambilar (EP) and Tesoro Escondido (TE)
Summary
Thomsen, da Fonseca, & Olivieri, 1998; Olson & Dinerstein, 1998, 2002; Myers et al, 2000). Atelids, especially Ateles and Lagothrix, are characterized by their wide ranging behavior, by their dietary preference for large quantities of the fruit from a wide range of tree species, and their tendency to swallow and defecate intact large seeds far from where they were found (Defler & Defler, 1996; Link & Di Fiore, 2006; Stevenson, 2000) Because of this it had been suggested that decreasing primate populations could result in important ecosystem changes due to diminished recruitment of their large seeded food plant species and proportionally greater representation of smaller seeded species dispersed by abiotic or other biotic agents (Effiom, Nuñez-Iturri, Smith, Ottosson, & Olsson, 2013; Nuñez-Iturri & Howe, 2007; Nuñez-Iturri et al, 2008; Terborgh et al, 2008). Political, economic, and cultural processes ‒ including high levels of poverty amongst rural peasants and indigenous people, unsustainable hunting, commercial logging, the establishment of huge oil palm plantations, and the lack of governmental policies recognizing the ecological value of zones outside protected areas‒ are accelerating forest loss and decimating animal populations in the region (Justicia, 2007; Sierra & Stallings, 1998; Southgate & Whitaker, 1992)
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