Lost mutualisms: Seed dispersal by Sumatran rhinos, the world’s most threatened megafauna

Abstract

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fruit traits from a 2-month field study (Sumatra), local ecological knowledge (Peninsular Malaysia), and published and unpublished accounts.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-colored," fruits and seeds, and were mainly drupes and berries; 61% of these were megafaunal-syndrome fruits (>4 cm wide).Understorey plants (herbs, shrubs, and 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 behavior of Sumatran rhinos and elephants, we suggest that 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.

Induced pluripotent stem cells and cerebral organoids from the critically endangered Sumatran rhinoceros

“…Loss of keystone species, especially megavertebrates, can initiate so called "vortex effects" (Lacy, 1993), i. e. accelerated loss of species or entire species societies whose life histories are directly or indirectly connected to the keystone species. The Sumatran Rhino (SR) is known to play a key role in shaping forests and spreading seeds of at least 79 different plant species (McConkey et al, 2022). Many of those evolved alongside megafauna and are designed to be eaten and dispersed by large animals such as elephants and rhinos.…”

“…Many of those evolved alongside megafauna and are designed to be eaten and dispersed by large animals such as elephants and rhinos. Given the differences in ranging and foraging behavior of SRs and elephants, and the fact that 35% of the identified megafaunal-fruits are only distributed by SRs (McConkey et al, 2022), the composition and ecological balance of the Asian rainforest seems highly depending on the SR and loss of the species could have catastrophic consequences.…”

Megafruit and megafauna diversity are positively associated, while megafruit traits are related to abiotic factors, in tropical Asia

“…A 44-kg cut-off includes smaller mammals that cannot manipulate large fruits efficiently; these are classified as large mammals in our study. A 1,000-kg cut-off excludes the smaller forest-dwelling Sumatran rhinoceros (775 kg), which can disperse very large seeds (McConkey et al, 2022;Strien, 1974). Our criterion includes the largest bovids (700-800 kg), which are considered poor seed dispersers but regularly consume fruit and have rarely been studied (Sridhara et al, 2016).…”

“…They were, and still are, essential seed dispersers in many systems, because of their capability for moving many seeds across long distances (Campos-Arceiz & Blake, 2011;McConkey et al, 2022;Pires et al, 2018;Tan et al, 2021). Megafauna can disperse seeds of fruits that are too large for other animals to handle efficiently (Cochrane, 2003;Sekar & Sukumar, 2013), possibly allowing plants to circumvent trade-offs between fruit size, seed number, and dispersal distance (Guimarães et al, 2008).…”

“…Herbivorous and frugivorous megafauna have been abundant across the globe for most of the past 40 million years, playing vital roles in moving nutrients, creating habitats for other species, and linking diverse ecosystems (Galetti et al., 2018; Malhi et al., 2016). They were, and still are, essential seed dispersers in many systems, because of their capability for moving many seeds across long distances (Campos‐Arceiz & Blake, 2011; McConkey et al, 2022; Pires et al., 2018; Tan et al., 2021). Megafauna can disperse seeds of fruits that are too large for other animals to handle efficiently (Cochrane, 2003; Sekar & Sukumar, 2013), possibly allowing plants to circumvent trade‐offs between fruit size, seed number, and dispersal distance (Guimarães et al., 2008).…”