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DOMINANCE HIERARCHY ON PALM RESOURCE PARTITIONING AMONGST NEOTROPICAL FRUGIVOROUS MAMMALS
In tropical forests, the diets of many frugivorous mammals overlap, particularly during periods of low fruit availability. Yet, how hyper-diverse assemblies of consumers exploit resources and coexist despite high diet overlap remains poorly understood. Palm fruits, for example, are a key resource shared by many terrestrial forest-dwelling mammals, so that diet overlap might promote competition amongst such frugivores. Furthermore, habitat destruction and fragmentation can also increase resource overlap and exacerbate competition. We evaluated competitive interactions among three species of terrestrial frugivorous mammals, the ungulate Tayassu pecari (white-lipped peccary), their close relative Pecari tajacu (collared peccary), and a large rodent (Dasyprocta azarae, agouti), in their exploitation strategies of palm resources of different quality in a large isolated fragment at the tropical Atlantic Forest of Brazil, where they show high spatial and temporal overlap. We evaluated if body mass and foraging group size define a hierarchy in exploitation of preferentially richer palm resources. The study was conduct at the Ecological Station of Caetetus (22º30’ S, 49º45’W), an 2178 ha semideciduous Atlantic Forest remnant located in the interior of São Paulo State, with altitudes varying from 500 to 690 meters, temperatures from 10ºC to 30ºC, and rainfall around 1480 mm, with dry winter and rainy summer. We used 29 cameras-traps that remained in field from March to September 2017 (3216 traps/days), and two-species occupancy models to examine patterns of co-occurrence and variable interaction strengths between these consumers and three species of palms in the presence and absence of potential competitors. We constructed paired dominant-subordinate models reflecting alternative competitive/coexistence hypotheses. Our analyses supported the hypothesis of partial resource overlap but no competition amongst frugivores, and a hierarchical exploitation of resources. The larger frugivore (white-lipped peccary) dominated patches of the lipid-rich palm Euterpe edulis, where the smallest frugivore (agoutis) were absent. In turn, the smallest frugivore concentrated their foraging on areas with poorest palm resource, Syagrus oleracea. Collared peccaries preferred areas of high abundance of S. romanzoffiana when the other two species were rarely detected or absent, strongly avoided patches of E. edulis, and showed their higher average detection rates when agoutis were present.Our study highlights the important role of behavioural plasticity in promoting coexistence, and indicates that through context-dependent interaction strengths and hyrerachical partitioning of resources, consumers can avoid strong competition, even under conditions of high habitat overlap, high spatial and temporal overlap and high levels of habitat fragmentation and isolation.
Atlantic forest of Brazil; Arecaceae; camera-trap; coexistence; competition; mammalian frugivores; niche partitioning; occupancy modelling
Capes, Biota Fapesp (Processo 2014/01986-0) e Idea Wild
Paula Akkawi, Nacho Villar, Calebe Mendes, Mauro Galetti