Elephants versus butterflies: the ecological role of large herbivores in the evolutionary history of two tropical worlds

Abstract

Aim Large herbivores have important effects upon Paleotropical ecosystems, but attain much lower biomass densities in the Neotropics. We assess how this difference in herbivore activity has generated different ecological and evolutionary trajectories in the New and Old World tropics. We also propose an explanation for how the greater biomass density in the Old World came about. Location Data were compiled primarily from moist tropical forests, although more of the relevant information to address most of our hypotheses was available from the mainland areas of Africa, Asia, and South America than elsewhere. Methods We gleaned data from published information and personal communication. We compared body masses and a variety of other types of information for the New‐ and Old‐World tropics. We proposed that interhemispheric differences exist in a variety of processes, including herbivory, frugivory, and flower visitation. We erected hypotheses and evaluated them qualitatively, and, when information was available, tested them using simple ratios of species in various taxonomic and trophic categories. To make the comparisons more meaningful, we specified appropriate data selection criteria. Results A general pattern of differences emerges from this review. Compared with Neotropical forests, the much greater biomass densities of large herbivores in Paleotropical forests are associated with a lesser diversity of small herbivores, different hunting methods used by indigenous humans, larger arboreal vertebrates, larger fruits, different patterns of fruit and flower dispersion in space and time, a lesser abundance of most types of reproductive plant parts, and other features. The existence of a species‐rich fauna of large herbivores in the pre‐Holocene Neotropical rain forest was not supported. Main conclusions The potential for large herbivores to cause functional differences between the New and Old World tropical forests has been virtually unexplored, despite the well‐known importance of large herbivores in the Old World tropics. The evaluations of our hypotheses suggest that the abundance of large herbivores in the Old World tropics has launched it onto a different evolutionary trajectory than that of the NewWorld tropics. The relevant evidence, although scanty, suggests that the interhemispheric ecological differences are not an artefact of recent megafaunal extinctions in the New World. Recent human activities have, however, reduced population sizes of large wild herbivores in the Old World, and increased population sizes of livestock. This has likely created a rather homogeneous, anthropogenic selection pressure that tends to erase the evolutionary differences between the two tropical worlds.

Seed dispersal of woody plants in tropical forests: concepts, examples and future directions

“…We know animal assemblages (as well as plant communities) vary among tropical forests, especially between neotropical and palaeotropical forests (Cristoffer & Peres 2003). We do not know how these differences affect seed dispersal and thereby plant regeneration.…”

The Paleogene fossil record of birds in Europe

“…Future research will thus also have to focus on ecological characteristics that distinguish New World biotas, especially in South and Central America, from those in the Old World. Large herbivores, for example, occur in much lower biomass densities in the Neotropics (Cristoffer & Peres, 2003), and in order to explain absence of hummingbirds in the Old World, Cristoffer & Peres (2003, p. 1369 hypothesized that the nectar-rich and highly nutritient understorey flowers that are pollinated by hummingbirds in the Neotropics would be eaten by mammalian herbivores in the Palaeotropics. At present this assumption cannot be tested, as we do not know when exactly hummingbirds disappeared from the Old World and whether this date coincides with the appearance of large herbivores.…”

Large-Herbivore Distribution and Abundance: Intra- And Interspecific Niche Variation in the Tropics

“…When attempting to model the ecological complexity and variability of species-habitat relationships over large spatial scales, the ITA allows simultaneous comparison of the likelihood of competing models, given the data and model set. Among vertebrates, large herbivores provide an excellent group for macroecological study because they occur in a diverse array of habitats, exhibit considerable morphological variation, have extensive distributions, and shape ecosystem function through the effects of grazing (Cristoffer andPeres 2003, Gordon et al 2004). Furthermore, large herbivores represent a significant part of the food resources and economies of human communities, and have strong cultural significance in many parts of the world (Yibarbuk et al 2001, Gordon et al 2004).…”