White‐tailed deer as the last megafauna dispersing seeds in Neotropical dry forests: the role of fruit and seed traits

Abstract

Endozoochory is a prominent form of seed dispersal in tropical dry forests. Most extant megafauna that perform such seed dispersal are ungulates, which can also be seed predators. White-tailed deer (Odocoileus virginianus) is one of the last extant megafauna of Neotropical dry forests, but whether it serves as a legitimate seed disperser is poorly understood. We studied seed dispersal patterns and germination after white-tailed deer gut passage in a tropical dry forest in southwest Ecuador. Over 23 mo, we recorded ca 2000 seeds of 11 species in 385 fecal samples. Most seeds belonged to four species of Fabaceae: Chloroleucon mangense, Senna mollissima, Piptadenia flava, and Caesalpinia glabrata. Seeds from eight of the 11 species dispersed by white-tailed deer germinated under controlled conditions. Ingestion did not affect germination of C. mangense and S. mollissima, whereas C. glabrata showed reduced germination. Nevertheless, the removal of fruit pulp resulting from ingestion by white-tailed deer could have a deinhibition effect on germination due to seed release. Thus, white-tailed deer play an important role as legitimate seed dispersers of woody species formerly considered autochorous. Our results suggest that more research is needed to fully understand the ecological and evolutionary effects of the remaining extant megafauna on plant regeneration dynamics in the dry Neotropics.Abstract in Spanish is available with online material.

Anthropogenic Seed Dispersal: Rethinking the Origins of Plant Domestication

“…Evolutionary studies illustrate that mutualism often evolves from a predatory relationship [11,12]. In some cases, plants evolved sugar-rich fruits in order to recruit dispersers, and in other cases, dispersers were enticed by the green foliage that surrounded small, dry-fruited seeds.…”

“…In plants, both intra-and interspecies gene flow push evolution forward [18,19]. As part of the gene flow system, seed dispersal allows plants to (i) avoid kin (sibling and parent) competition [20][21][22], (ii) avoid interspecific competition, (iii) reduce inbreeding [11,12], and (iv) colonize new areas [23][24][25]. Biotic dispersal can also lead to directed dispersal, targeting prime colonization areas and allowing greater offspring success rates than if dispersal were random [26].…”

“…Often these dense, clonally reproducing wild stands continue to produce extensive generations with energetically costly fruits, which then decompose under the trees, leading to density-dependent seed death through fungal attack, fermentation, seed predation from small animals, or parent/sibling competition. Large fruits coevolved with megafaunal mammals around the world [12,25], and humans are the most ubiquitous megafaunal mammal to survive the Pleistocene/Holocene boundary. The evolution of even larger fruits and larger seeds under human dispersal is substantially no different from the evolution of large fruits in response to proboscideans (notably gomphotheres), Xenarthra (e.g., Glyptodon spp., megalonychids, megatheriids), Perissodactyl (e.g., rhinoceroses, equids), or earlier large primates.…”

“…The restricted cecum of most ruminants, combined with double digestion, heavy mastication, and fermentation, constrains the size and the physiomorphological makeup of seeds that can pass through the digestive system and remain viable [51,64]. Ruminant-dispersed plants are mostly herbaceous, contain hard seed coats, and have small seeds, which are often round with smooth surfaces [12,39,51,64]. Most of these plants evolved to display seeds on top of their terminal leaves, often lack mechanical dehiscence, and produce abundant generations [52,53].…”

“…Paleogene megafaunal Perissodactyla (including equids, rhinoceroses, and tapirs) were far more likely than true ruminants to disperse large seeds and consume sugary fruits. Artiodactyla (including bison, deer, and their relatives) are responsible for the prominence of small-seeded herbaceous plants that dominate grasslands today [12,54]. In some cases, the evolution of annuals in response to ruminant grazing led to herbivory defenses, such as an increased production of phytoliths or secondary compounds.…”