DOI: 10.5061/dryad.xsj3tx9gv
title: Lost mutualisms: seed dispersal by Sumatran rhinos, the world’s most threatened megafauna

description: Diverse assemblages of seed-dispersing megafauna once existed in Asian
 rainforests, but are now almost solely represented by elephants. Asia’s
 rhinos persist in remnant, ecologically-extinct populations and the most
 threatened of these is the Sumatran rhino, Dicerorhinus sumatrensis. To
 understand the seed dispersal role of Sumatran rhinos, we consolidated
 information on fruit consumption, seed dispersal and fruit traits from a
 two-month field study (Sumatra), local ecological knowledge (Peninsular
 Malaysia), and published and unpublished accounts. We evaluated
 differences between the taxa and traits of fruits dispersed by rhinos and
 elephants, and identified other dispersers of megafaunal-syndrome fruits
 that were rhino-dispersed. At least 79 plant species were dispersed by
 rhinos: overstorey plants (trees and climbers; 78% of species) had large,
 usually “mammal-coloured”, fruits and seeds, and were mainly drupes and
 berries; 61% of these were megafaunal-syndrome fruits (&gt;4 cm wide).
 Understorey plants (herbs, shrubs, small trees) had small, often capsular,
 fruits and seeds that are potentially dispersed following the
 “foliage-is-the-fruit” hypothesis. Rhinos were the only known disperser
 for 35% of the megafaunal-fruit genera. The highest dispersal overlap
 shown was with elephants: fruits dispersed by rhinos tended to be capsular
 and were smaller than fruits dispersed by both elephants and rhinos. Given
 these findings and the different foraging and ranging behaviour of
 Sumatran rhinos and elephants, we suggest these megafauna had important
 differences in their seed dispersal roles. Asian rainforests have,
 therefore, lost an important seed dispersal mutualist. Conservation
 efforts should aim to protect and restore the ecological function of these
 unique creatures.
description: We review knowledge on seed dispersal by the Sumatran rhino,
 using two newly collected datasets along with published and unpublished
 research collected mainly from the 1960s to the 1980s. The two novel
 datasets on seed dispersal by Sumatran rhinos were from: (a) a brief field
 study on seed dispersal by Sumatran rhinos in Way Kambas National Park,
 Sumatra, Indonesia and (b) interviews with Orang Asli indigenous people,
 about seed dispersal by (the now locally extinct) rhinos in the
 Belum‐Temengor Forest Complex, Peninsular Malaysia.
 <strong>Way Kambas Field Study,
 Sumatra</strong> The field study in Way Kambas
 National Park was conducted across two and a half months spread between
 July and November 2011. We searched for rhino dung along 18.5km of forest
 trails, walking each trail three times. For all dungs found, we recorded
 dung age (&lt;12h, 2–3 d, 3–7 d, 1 wk–1 mo, &gt;1 mo; guesstimated
 by the field team based on previous experience), bolus size, habitat, and
 whether it was a single defecation or occurred in a latrine; rhinos often
 deposit multiple dungs in the same place and these are termed latrines. We
 searched the dungs for seeds, conducting in‐situ searches for large seeds
 (&gt;5 mm wide). For smaller seeds we quantified the number in a
 sample comprising 15% of the dung pile by mass which was later washed over
 a fine‐mesh sieve. Dung mass ranged from 150 g to 3250 g, and averaged 602
 ± 542 g (mean ± SD). Seed length and width were measured. We also
 collected fruits from all sources we found to use as an aid to identify
 seeds in dung. <strong>Interview data from
 Peninsular Malaysia</strong> We documented local
 ecological knowledge as a second source of information to identify plant
 species dispersed by Sumatran rhinos. These interviews were conducted as
 part of a broader study on the seed dispersal network of the
 Belum‐Temengor forest complex (Ong et al., 2021), Peninsular Malaysia,
 where the rhino is presumed to have gone extinct in the early 2000s. We
 interviewed 15 Orang Asli (Peninsular Malaysia's indigenous people)
 from the Jahai and Temiar communities, who are very familiar with the
 local flora and fauna. Since only one respondent claimed to be able to
 identify the fruits consumed by rhinos, these results were not included in
 the final seed dispersal network (Ong et al., 2021) but are presented
 here. The respondents were asked if the animal swallowed, chewed, or
 discarded the seeds of each plant species identified as consumed. We also
 collected measurements and descriptions of the fruits and seeds in the
 region (<em>n</em> = 164 species), so that each rhino–fruit
 interaction we asked about in the interviews was accompanied by fruit and
 seed trait information. We recorded fruit and seed length and width, seed
 number per fruit, color, fruit‐type, and growth form (see Ong et
 al., 2021 for full details). <strong>Publications
 and final data compilation for review</strong>
 Finally, we reviewed previous publications on the ecology of
 Sumatran rhinos, mostly accounts by explorers, hunters, and scientists who
 visited Sumatra and the Malay Peninsula in the 1900s, and collated their
 accounts of the fruit diet and seeds found in dungs. We also included more
 recent unpublished reports written in Bahasa Indonesia. The names of all
 plant species identified were checked on Kew's Plants of the World
 Online database and the list of species we present has the most recent
 names. We also collected information on the vegetative components of the
 rhino's diet to determine which dispersed species might also be
 consumed for other plant parts. We searched for information on the fruit
 and seed traits (see previous section for list), and plant growth form for
 all species identified as having the fruit consumed by Sumatran rhinos,
 using local floras and online sources. We categorized mammal colored
 fruits as colors usually associated with terrestrial mammals (green,
 brown, yellow, and orange) (Bunney et al., 2019; Yokoyama et al., 2005).
 We checked each plant species on the IUCN Red List to determine its
 status. <b>Literature Cited</b>
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 historical distribution of megaherbivores does not determine the
 distribution of megafaunal fruit in southern Africa. Biological Journal of
 the Linnean
 Society, 128, 1039–1051. https://doi.org/10.1093/biolinnean/blz109 Ong, L., Campos‐Arcei, A., Loke, V. P. W., Pura, P. B., Tunil, C. M. T. B., Din, H. S., Angah, R. B., Amirrudin, A. B., Tan, W. H., Lily, O., Solana‐Mena, A., & McConkey, K. R. (2021). Building networks with local ecological knowledge in hyper‐diverse and logistically challenging ecosystems. Methods in Ecology and Evolution, , 2042–2053. Yokoyama, S., Takenaka, N., Agnew, D. W., & Shoshani, J. (2005). Elephants and human color‐blind deuteranopes have identical sets of visual pigments. Genetics, 170, 335–344.