In the elephant's seed shadow: the prospects of domestic bovids as replacement dispersers of three tropical Asian trees

Abstract

As populations of the world's largest animal species decline, it is unclear how ecosystems will react to their local extirpation. Due to the unique ecological characteristics of megaherbivores such as elephants, seed dispersal is one ecosystem process that may be affected as populations of large animals are decimated. In typically disturbed South Asian ecosystems, domestic bovids (cattle, Bosprimigenius, and buffalo, Bubalus bubalis) may often be the species most available to replace Asian elephants (Elephas maximus) as endozoochorous dispersers of large-fruited mammal-dispersed species. We use feeding trials, germination trials, and movement data from the tropical moist forests of Buxa Tiger Reserve (India) to examine whether domestic bovids are viable replacements for elephants in the dispersal of three large- fruited species: Dillenia indica, Artocarpus chaplasha, and Careya arborea. We find that (1) once consumed, seeds are between 2.5 (C. arborea) and 26.5 (D. indica) times more likely to pass undigested into elephant dung than domestic bovid dung; and (2) seeds from elephant dung germinated as well as or better than seeds taken from bovid dung for all plant species, with D. indica seeds from elephant dung 1.5 times more likely to germinate. Furthermore, since wild elephants have less constrained movements than even free-roaming domestic bovids, we calculate that maximum dispersal by elephants is between 9.5 and 11.2 times farther than that of domestic bovids, with about 20% of elephant-dispersed seeds being moved farther than the maximum distance seeds are moved by bovids. Our findings suggest that, while bovids are able to disperse substantial numbers of seeds over moderate distances for two of the three study species, domestic bovids will be unable to routinely emulate the reliable, long-distance dispersal of seeds executed by elephants in this tropical moist forest. Thus while domestic bovids can attenuate the effects of losing elephants as dispersers, they may not be able to prevent the decline of various mammal-dispersed fruiting species in the face of overhunting, habitat fragmentation, and climate change.

Pleistocene megafaunal extinctions and the functional loss of long‐distance seed‐dispersal services

“…Seed-dispersal services may be partially compensated by other potential seed dispersers, including birds and smaller mammals (Jansen et al 2012), or by haphazard, sporadic dispersal by gravity or runoff (Pérez-Méndez et al 2016). However, this does not seem to be the case for many largeseeded plants, as several studies suggest that the surrogate seed disperser may not be as effective as the largest ones (Poulsen et al 2002, Donatti et al 2009, Campos-Arceiz et al 2012, Bueno et al 2013, Kistler et al 2015, Sekar et al 2015. Modeling approaches like the one presented here and in other studies on seed dispersal (Doughty et al 2016) can be a useful tool to examine how biodiversity loss impacts ecosystem processes and, more specifically, to what extent surrogate species or other seed-dispersal mechanisms compensate the loss of seed-dispersal services.…”

“…The most vulnerable animals are often the largest Dirzo 2013, Dirzo et al 2014) and the effects of losing large frugivores can already be seen in some places where plants dispersed by smaller dispersal agents or abiotic means are becoming overrepresented (Wang et al 2007, Wright et al 2007, Harrison et al 2013. However, this does not seem to be the case for many largeseeded plants, as several studies suggest that the surrogate seed disperser may not be as effective as the largest ones (Poulsen et al 2002, Donatti et al 2009, Campos-Arceiz et al 2012, Bueno et al 2013, Kistler et al 2015, Sekar et al 2015. However, this does not seem to be the case for many largeseeded plants, as several studies suggest that the surrogate seed disperser may not be as effective as the largest ones (Poulsen et al 2002, Donatti et al 2009, Campos-Arceiz et al 2012, Bueno et al 2013, Kistler et al 2015, Sekar et al 2015.…”

Seed dispersal effectiveness by a large‐bodied invasive species in defaunated landscapes

“…On the other hand, alien ecological surrogates are not always able to compensate for the services provided by native species (Lynes & Campbell, ). For example, the use of cattle and buffalo as replacements for threatened elephants for dispersal of large‐seeded plants in continental India showed that bovids do not compensate for either the quantity nor the quality of the services provided by elephants (Sekar, Lee, & Sukumar, ). Yet, in the case of wild pigs, there are simply no large‐bodied frugivores left in most of the Atlantic forest, and the seed dispersal services we uncover here would be limited if they were absent.…”

Ecological consequences of forest elephant declines for Afrotropical forests

“…Elephants travel much greater distances than most other dispersers (Sekar et al. ), yielding a higher proportion of seeds that escape heavy seed predation near parent plants (Yumoto et al. ).…”

“…Elephants are keystone dispersers for numerous tree species: 30 plant species in Taï National Park, Ivory Coast (Alexandre 1978), and 13 species in the Nouabalé-Ndoki National Park, Republic of Congo (Blake et al 2009), are dispersed solely or predominantly by elephants. Elephants travel much greater distances than most other dispersers (Sekar et al 2015), yielding a higher proportion of seeds that escape heavy seed predation near parent plants (Yumoto et al 1995). In a study of 4 GPS-collared elephants in Congo, 88% of dispersed seeds were transported over 1 km and some were dispersed up to 57 km from the parent tree (Blake et al 2009).…”