Contagious Deposition of Seeds in Spider Monkeys' Sleeping Trees Limits Effective Seed Dispersal in Fragmented Landscapes

Abstract

The repeated use of sleeping sites by frugivorous vertebrates promotes the deposition and aggregation of copious amounts of seeds in these sites. This spatially contagious pattern of seed deposition has key implications for seed dispersal, particularly because such patterns can persist through recruitment. Assessing the seed rain patterns in sleeping sites thus represents a fundamental step in understanding the spatial structure and regeneration of plant assemblages. We evaluated the seed rain produced by spider monkeys (Ateles geoffroyi) in latrines located beneath 60 sleeping trees in two continuous forest sites (CFS) and three forest fragments (FF) in the Lacandona rainforest, Mexico. We tested for differences among latrines, among sites, and between forest conditions in the abundance, diversity (α-, β- and, γ-components) and evenness of seed assemblages. We recorded 45,919 seeds ≥5 mm (in length) from 68 species. The abundance of seeds was 1.7 times higher in FF than in CFS, particularly because of the dominance of a few plant species. As a consequence, community evenness tended to be lower within FF. β-diversity of common and dominant species was two times greater among FF than between CFS. Although mean α-diversity per latrine did not differ among sites, the greater β-diversity among latrines in CFS increased γ-diversity in these sites, particularly when considering common and dominant species. Our results support the hypothesis that fruit scarcity in FF can ‘force’ spider monkeys to deplete the available fruit patches more intensively than in CFS. This feeding strategy can limit the effectiveness of spider monkeys as seed dispersers in FF, because (i) it can limit the number of seed dispersers visiting such fruit patches; (ii) it increases seed dispersal limitation; and (iii) it can contribute to the floristic homogenization (i.e., reduced β-diversity among latrines) in fragmented landscapes.

Which is the appropriate scale to assess the impact of landscape spatial configuration on the diet and behavior of spider monkeys?

“…This coincided with the dry season, and beginning of the rainy season and one of the annual peaks in fruit production in the region (May) [González-Zamora et al, 2014;Ochoa-Gaona & Domínguez-Vázquez, 2000]. We documented the diet and daily activity pattern of our study communities from 0700 to 1530 hours during 3 consecutive days, approximately once every 3 weeks.…”

Toucans (Ramphastos ambiguus) facilitate resilience against seed dispersal limitation to a large‐seeded tree (Virola surinamensis) in a human‐modified landscape

“…In disturbed forests, spider monkeys seem to adjust their feeding patterns to cope with fruit scarcity by intensively depleting the richest patches of food trees available ( i.e ., large crop size) of the most preferred fruit species (González‐Zamora et al . ). This feeding behavior would explain why we observed four times more feeding visits by spider monkeys at HDF fruiting trees than at LDF fruiting trees, as the genus Virola is one of the top‐ranked fruit item in the Ateles diet (González‐Zamora et al .…”

Taxonomic and functional divergence of tree assemblages in a fragmented tropical forest

“…, González‐Zamora et al. ), which in turn can result in more homogeneous (and even monospecific) seedling carpets with clumped distribution throughout the forest (Dirzo and Miranda ). Although such seedling carpets are expected to experience a very high density‐dependent mortality, local conditions can be suitable for recruitment, contributing to generate areas within the forest dominated by a few different species (e.g., Mesquita et al.…”