Abstract
Fauna-mediated ecosystem service provision (e.g. seed dispersal) can be difficult to quantify and predict because it is underpinned by the shifting niches of multiple interacting organisms. Such interactions are especially complex in tropical ecosystems, including endangered peat forests of Central Borneo, a biodiversity hot spot and home to the critically endangered orangutan (Pongo pygmaeus wurmbii). We combined studies of the digestive physiology of captive orangutans in Australia with detailed field studies of wild orangutans in the Natural Laboratory of Peat-Swamp Forest of Sabangau, Central Kalimantan, Indonesia. By measuring the gut transit time (TT) of indigestible seed mimics (beads) in captivity and applying this as a temporal constraint to movement data of wild orangutans, we developed a mechanistic, time-explicit spatial model to project the seed dispersal patterns by these large-bodied, arboreal frugivores. We followed seven orangutans and established home range kernels using Time Local Convex Hull (T-LoCoH) modelling. This allowed us to model individual orangutan movements and to adjust these models according to gut transit times to estimate seed dispersal kernels. Female movements were conservative (core ranges of 55 and 52 ha in the wet and dry seasons, respectively) and revisitation rates to the same location of n = 4 in each 24-h block. Male movements were more unpredictable, yielding fragmented core ranges and revisitation rates to the same location of only 1.2 times each 24 h; males also demonstrated large disjunctions where they moved rapidly over long distances and were frequently lost from view. Seed dispersal kernels were nested predictably within the core ranges of females, but not males. We used the T-LoCoH approach to analyse movement ecology, which offered a powerful tool to predict the primary deposition of seeds by orangutans, thereby providing a reliable method for making a priori predictions of seed dispersal dynamics by other frugivores in novel ecosystems.
Highlights
The ecosystem services provided by animal–plant interactions are complicated and are governed by numerous co-evolved ecological processes (Tylianakis et al, 2010)
By measuring the gut transit time (TT) of indigestible seed mimics in captivity and applying this as a temporal constraint to movement data of wild orangutans, we developed a mechanistic, time-explicit spatial model to project the seed dispersal patterns by these large-bodied, arboreal frugivores
There were no significant differences in the TTs between any seed mimic (Supplementary Material, F = 0.36, d.f. = 2; P = 0.54), and the common TTmax, averaged 133 h, while the average TT for all seed mimics was 76 h
Summary
The ecosystem services provided by animal–plant interactions are complicated and are governed by numerous co-evolved ecological processes (Tylianakis et al, 2010) Many of these services and their persistence may be sensitive to disruption (McCauley et al, 2012). Fauna-mediated ecosystem service provision can be highly context-specific, in especially biodiverse systems where there are numerous biotic and abiotic interactions. One such region includes the tropical peat forests of south eastern Asia, which are notably biodiverse and represent major carbon sinks (Posa et al, 2011). With ongoing pressures of logging and fragmentation, details concerning orangutans and their seed dispersal capacity are much needed
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