Epizoochorous seed dispersal by an Afroalpine savanna primate

Abstract

Primates are prolific dispersers of seeds via endozoochory (i.e., defecation and spitting). In contrast, epizoochorous seed dispersal (i.e., via adhesion to fur) has rarely been observed in primates. On the Guassa Plateau in north-central Ethiopia, grasseating geladas (Theropithecus gelada) regularly carry on their fur the barbed seeds of a commonly eaten plant, a low-lying herbaceous forb called Agrocharis melanantha [Apiaceae]. Here, we describe the basic ecology of this plant-primate relationship.For 24 months (November 2017-December 2019), we monitored the number and location of A. melanantha seeds on the fur of geladas (n = 225 individuals) from four age-sex classes: adult males, adult females, juveniles, and infants. Seed accumulation (n = 12649 seeds in total) was seasonal and closely tracked patterns of landscape vegetation phenology, peaking in September near the end of the rainy season. During seasonal periods of heavy seed accumulation, larger animals carried more seeds, which accumulated most often on the hindlimbs and on the long-haired "cape" (a secondary sexual characteristic) of adult males. Geladas almost never removed seeds during self-or social grooming. Rather, data on seed gain and loss from focal follows indicate that geladas gain and lose seeds every few minutes as they walk and sit in an upright feeding position amidst terrestrial vegetation. We estimate that, on average, geladas disperse seeds roughly 80 m from their parent plants. Geladas appear to exert negative and positive fitness impacts on A. melanantha by regularly consuming its herbaceous and underground tissues and dispersing its seeds.