Seed shadows of northern pigtailed macaques within a degraded forest fragment, Thailand

Determining seed shadow (i.e. seed deposition pattern of a plant population) produced by frugivores is difficult to evaluate by direct observations, although of
paramount importance to understand their effectiveness as seed dispersal agents in degraded habitat. We developed a modeling approach of seed shadows incorporating field-collected data on a troop of 141 ± 10 individuals of northern pigtailed macaques (Macaca leonina) inhabiting a degraded forest fragment in Thailand, by implementing a mechanistic model of seed deposition with random components. We parameterized the model with macaque feeding behavior (i.e. consumed fruit species, seed treatments), gut and cheek pouch retention time, location of feeding sites and sleeping sites, monthly photoperiod, and movement patterns based on monthly native fruit availability using Hidden Markov models (HMM). We found that northern pigtailed macaques dispersed a majority of medium- to large-seeded species across large distances (mean > 500 m, maximum distance of 2300 m), promoting genetic mixing and colonization of plantation forests. Additionally, the macaques produced complementary seed shadows, with a sparse distribution of seeds spat out locally (mean > 50 m, maximum distance of 870 m) that probably ensures seedling recruitment of the immediate plant populations. Macaques’ large dispersal distance reliability is often underestimated and overlooked; however, their behavioral flexibility places them among the last remaining dispersers of large seeds in disturbed habitats. Our study shows that this taxon is likely to maintain significant seed dispersal services and promote forest regeneration in degraded forest fragments.