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

Abstract

Aim: For tens of millions of years, herbivorous megafauna were abundant across the globe, fulfilling important ecological roles including seed dispersal. Megafruits are very large fruits that are dispersed most effectively by megafauna. However, megafruits also occur in ecosystems where megafauna are extinct or were never present, emphasizing our incomplete understanding of megafauna-megafruit relationships.Here we use the complex biogeography of tropical Asia to investigate how megafruit diversity and traits are associated with the diversity of megafauna, smaller animals, and abiotic factors. Location: Tropical Asia, from the Indian subcontinent in the west to tropical China in the north to the Maluku archipelago (Indonesia) in the east. Time period: Late Pleistocene to the present day.Major taxa studied: Megafauna (body weight > 500 kg) that consume fruits, including stegodons, elephants, rhinoceroses, giant tapirs, and large bovids. Fleshy-fruited plant species across the region with a fruit width > 40 mm (i.e., megafruits). Methods:We compiled a list of all megafruits along with selected plant, fruit, and seed traits in 16 subregions across tropical Asia. We explored biogeographical patterns in megafruit diversity and traits in relation to the diversities of past and present megafauna, large-and medium-sized animals and abiotic factors (mean temperature, mean precipitation, precipitation seasonality, insularity). Results:We identified 496 megafruits in tropical Asia. Megafruit diversity was highest in subregions with high megafaunal diversity, particularly extant species. Megafruit traits were influenced most strongly by abiotic factors (mainly temperature and land area), and weakly by megafauna and smaller dispersers. Main conclusions:Our results are consistent with megafauna maintaining or responding to megafruit diversity, but variation in megafruit traits is primarily associated with abiotic factors. Given the massive megafaunal losses in tropical Asia since the Late Pleistocene, it is important to identify fruit traits that can increase megafaunadependence and thus vulnerability to these losses.

Environment‐dependent influence of fruit size upon the distribution of the Malesian archipelagic flora

“…That association is probably explained by fewer energetic constraints in the productive lowland wet tropics, where species have the requisite resources to produce large fruit (Bonte et al, 2012; McFadden et al, 2022; Moles et al, 2007). In addition, large fruit dispersal rates may also be higher in the wet lowlands because of the greater diversity of megafauna (McConkey, Campos‐Arceiz, et al, 2022). Local population extinctions would be reduced due to greater movement of propagules via megafauna, resulting in a positive effect upon large fruit species persistence in these environments (Bush et al, 2020; McConkey, Aldy, et al, 2022).…”

Environmental stress influences Malesian Lamiaceae distributions

“…Our study focuses upon the Lamiaceae; other plant family distributions may or may not follow the pattern we have observed. Firstly, Lamiaceae species have relatively small drupaceous or schizocarpic fruits, families that have larger and different fruit types such as drupes and berries could be more closely linked to frugivore distributions across islands (Crayn et al, 2015 ; McConkey et al, 2022 ; McFadden et al, 2022 ; Yap et al, 2018 ). Wind‐dispersed seeds may also facilitate patterns different to our observations; noticeably, wind‐dispersed Asteraceae have been shown to be less speciose than expected on islands except when insular diversification has occurred (König et al, 2021 ).…”

“…Smaller leaves are less at risk of extreme water loss via transpiration (Wright et al, 2017 ) and shorter species have smaller conduit size that reduces chance of embolism‐linked death (Olson et al, 2018 ). Fruit size likely follows a similar pattern whereby low‐productivity high‐stress environments limit the production of large, high‐energy cost fruit (McConkey et al, 2022 ; Moles et al, 2007 ). Smaller fruit, however, could also promote dispersal because they can be consumed by both small and large frugivores meaning dispersal is possible via a greater number of agents (Chen and Moles, 2015 ; Green et al, 2022 ).…”

Threatened species are disproportionately important interactors in a seed dispersal network in Southeast Asia

“…Indeed, megafaunal fruits are not common in Khao Yai's seasonally wet evergreen forests (eight species recorded in studies conducted over about 10 years; Kitamura et al, 2002), while many megafaunal‐sized fruit species are described for Peninsular Malaysia (37 species identified in a 2‐year study; Ong et al, 2022). This discrepancy is surprising considering Indochina, generally, has a diverse range of megafaunal fruits (McConkey et al, 2022), further reinforcing the need for frugivory and seed dispersal studies from a range of locations. The lack of a strong community role in frugivory for elephants in Khao Yai does not down play their high importance in seed dispersal for the plant species they do consume in Khao Yai, due to their capacity to consume many fruits (which was not measured in this study) and the high survival rates in elephant dungs (McConkey et al, 2015, 2018), nor the other pivotal ecological roles they might perform (Terborgh et al, 2017).…”

“…Sambar and macaques are common visitors to tourist‐occupied areas within the park where they scavenge food, which drastically reduces their ranges and consequently their dispersal capacity (Domínguez et al, 2015). A major missing interactor in the network is the Sumatran rhino, which was likely to have occurred in Khao Yai's forests in historical times and was an important seed disperser (McConkey et al, 2022). In the mid‐1970s, Sumatran rhinos were recorded close to Khao Yai's forests (McNeely & Laurie, 1977), but this rhino now has a highly restricted and critically low population on Sumatra, and possibly Borneo (IUCN, 2021).…”