Inter‐group variability in seed dispersal by white‐handed gibbons in mosaic forest

Abstract

Seed dispersers, like white-handed gibbons (Hylobates lar), can display wide inter-group variability in response to distribution and abundance of resources in their habitat. In different home ranges, they can modify their movement patterns along with the shape and scale of seed shadow produced. However, the effect of inter-group variability on the destination of dispersed seeds is still poorly explained. In this study, we evaluate how seed dispersal patterns of this arboreal territorial frugivore varies between two neighboring groups, one inhabiting high quality evergreen forest and one inhabiting low quality mosaic forest. We predicted a difference in seed dispersal distance between the two groups (longer in the poor quality forest). We hypothesized that this difference would be explained by differences in home range size, daily path length, and ranging tortuosity. After 6 months of data collection, the evergreen group had a smaller home range (12.4 ha) than the mosaic group (20.9 ha), significantly longer daily path lengths (1507 m vs. 1114 m respectively) and greater tortuosity (39.1 vs. 16.1 respectively). Using gut passage times and displacement rates, we estimated the median seed dispersal distance as 163 m for the evergreen group (high quality forest) and of 116 m for the mosaic group (low quality forest). This contradiction with our initial prediction can be explained in term of social context, resource distribution, and habitat quality. Our results indicate that gibbons are dispersers of seeds between habitats and that dispersal distances provided by gibbons are influenced by a range of factors, including habitat and social context.

Identifying priority areas for the conservation of the Critically Endangered northern white-cheeked gibbonNomascus leucogenysin northern Lao

“…These authors observed that deciduous trees in this forest type often carry flowers or fruit sufficient to support low density gibbon populations. Future studies should examine whether northern white-cheeked gibbons maintain larger home ranges in less productive habitats as observed elsewhere for lar gibbons (Savini et al, 2008; Phiphatsuwannachai et al, 2017). A study of Nomascus gabriellae in Seima Biodiversity Conservation Area, Cambodia, found no significant differences in group densities across evergreen, semi-evergreen and deciduous forest, supporting the view that gibbons are more flexible than previously thought with regard to habitat usage (Rawson et al, 2009).…”

“…Although apparently suboptimal, the large continuous areas of deciduous forest could be adequate for gibbon persistence, as indicated by Phiphatsuwannachai et al (2017) for lar gibbons. These authors observed that deciduous trees in this forest type often carry flowers or fruit sufficient to support low density gibbon populations.…”

“…with local residents). Recent work elsewhere in the region has found viable, breeding lar gibbon Hylobates lar groups in a mosaic of mixed deciduous and dry dipterocarp forest (Phiphatsuwannachai et al, 2017), demonstrating that gibbons can adapt to dry habitats with low fruit availability.…”

Seed Shadows of Northern Pigtailed Macaques within a Degraded Forest Fragment, Thailand

“…Because we could not control the effect of foraging prior to our observations, gut retention times were not estimated for seeds defecated in the first two days of the data collection periods [46]. We discarded from the gut retention estimation all defecated seeds of which we were unable to determine the defecation time (e.g., found at the sleeping site) [30]. We used the same technique to estimate the cheek pouch retention times by recording the time of storing seeds and location of feeding tree.…”

“…Determining seed shadow generated by frugivores is difficult and requires considerable information. In fact, a realistic description of plant seed shadows needs to take into account seasonal resource availability, plant traits, as well as the disperser morphology, physiology, movement and behavior [12,[29][30][31]. The main objective of this study is to illustrate a modeling approach of simulated seed shadows which incorporates field-collected data and account for primates' movement patterns, feeding behavior and seasonal variations of resources.…”