An ecophysiologically informed model of seed dispersal by orangutans: linking animal movement with gut passage across time and space

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.

Overlooked and undervalued: the neglected role of fauna and a global bias in ecological restoration assessments

“…Moreover, only so much may be learnt from assessing faunal biodiversity. Key ecosystem functions can result or fail as a result of altered animal behaviour and movement patterns (Fahrig 2007;Tarszisz et al 2018), ecological energetics (Tomlinson et al 2014), or nutritional physiology (Birnie-Gauvin et al 2017). This can result in cryptic disruptions to key services such as insect pollination (e.g.…”

The Time Local Convex Hull method as a tool for assessing responses of fauna to habitat restoration: a case study using the perentie (Varanus giganteus : Reptilia : Varanidae)

“…Methods for analysing home-range data are constantly evolving, and recent years have seen the implementation of increasingly complex statistical algorithms for assessing home range and habitat selection by animals (Lele et al, 2013), including methods such as the Brownian Bridge Movement Model (BBMM), and the Time Local Convex Hull (T-LoCoH) method of home range construction, both of which have been used successfully to elucidate movements of animals within their home range (Byrne et al, 2014;Lyons et al, 2013;Tarszisz et al, 2018). T-LoCoH and the BBMM method not only include points of presence of an animal, but also include spatial and temporal information, allowing for a complex understanding of habitat use and behavioural ecology (Byrne et al, 2014).…”

“…Here, we report on the range of applications of the T-LoCoH method of home range construction for understanding the responses of fauna to habitat change and restoration using a young adult female V. giganteus as a case study. T-LoCoH has been used successfully in previous studies of animal movement, however these have been limited to either simulated data or mammalian studies, and have not sought to determine differential habitat use in altered or restored landscapes, but primarily spatial utilisation of home ranges (e.g., Lyons et al, 2013;Stark et al, 2017), with one ecophysiological study of movement and seed dispersal (Tarszisz et al, 2018). Here we discuss how T-LoCoH can be applied to ectothermic animals and studies of conservation, habitat alteration, and ecophysiology.…”

Crossing boundaries in conservation physiology

“…Insofar as physiology influences ecology, so too does ecology influence physiology. While this may seem as intransigent as the question about the chicken and the egg, there is an emerging recognition that physiological constraints and influences can be and should be incorporated into a number of ecological modelling processes to better understand how physiological traits influence ecological patterns and conservation challenges ( Bourbonnais et al , 2014 ; Jachowski and Singh, 2015 ; Tarszisz et al , 2018 ). Understanding home ranges and habitat use are critical to developing flexible and adaptable management programs at effective spatial scales for threatened species.…”

“…Understanding home ranges and habitat use are critical to developing flexible and adaptable management programs at effective spatial scales for threatened species. Yet, the physiological components underpinning movement ecology and space use, ranging from the anthropogenic antagonism of stress ( Bourbonnais et al , 2014 ) to the ecological service of seed dispersal based upon digestive physiology ( Tarszisz et al , 2018 ), are only just now being explored. Interestingly, these concepts were raised decades ago by Huey (1991) in a paper titled ‘the physiological consequences of habitat selection’ but only today are we conducting the ecophysiology-grounded empirical research to understand relationships between physiology and ecological processes.…”