Small mammals reduce distance dependence and increase seed predation risk in tropical rainforest fragments

Abstract

Seed predation and reduced predation risk with distance from conspecific trees are important influences on tree regeneration in tropical forests. Shifts in animal communities, such as an increase in rodents and other small mammals due to forest fragmentation, could alter patterns of seed predation and affect tree regeneration and community dynamics in forest fragments. We performed a field experiment on four native rainforest tree species in the Western Ghats, India, to test whether fragmentation increases seed predation by mammals and alters the distance dependence of seed predation. We monitored seed predation within open and mammal exclosure plots, near and far from the canopies of conspecific trees, in contiguous and fragmented forests. Seed predation of Cullenia exarillata, Ormosia travancorica, and Syzygium rubicundum was markedly higher in forest fragments, and more so within open plots than exclosures, while the predominantly insect‐predated Acronychia pedunculata experienced similar predation in contiguous forests and fragments. Seed predation of C. exarillata and S. rubicundum was unrelated to distance from conspecific trees in open plots in both contiguous forests and fragments, in contrast to exclosures that showed marked near versus far differences in seed predation. Our findings suggest that by increasing overall seed predation risk and imposing similar seed predation risk near and far from adults variably across the tree species, small mammals could alter processes that shape tree diversity and species composition in fragmented tropical rainforests.

Frugivory and seed predation of fishtail palm (Caryota mitis Lour.) on the remote oceanic island of Narcondam, India

“…However, we did not alter the number of fallen seeds outside the plot. The number of seeds in away-high-density plots was decided based on earlier studies (Sidhu and Datta 2015, Krishnan et al 2022) and due to logistical constraints. For low-density plots, we have used the number of seeds that are scatter-dispersed by hornbills in tropical forests as estimated at other sites in north-east India (Naniwadekar et al 2021b).…”

Biodiversity of India: Evolution, biogeography, and conservation

“…Lone et al (2021) demonstrate that invasion of Lantana camara significantly decreases the density, basal area, species richness, and evenness of saplings and juvenile trees and herbaceous plants, increases soil organic carbon, nitrogen, and moisture and decreases pH in forests in Central India, thereby underscoring the environmental impact of the invasive species on Indian forest ecosystems. Krishnan et al (2022) shows higher seed predation by mammals in fragmented forests but no difference in seed predation by insects between contiguous forests and fragmented forests. Ramalingam and Dharma Rajan (2021) showcases the higher diversity of insect taxonomic groups and functional feeding guilds in smaller fragments and the presence of invasive ants in fragments with low quality vegetation, suggesting a possibility of using insect community data as a tool to assess effectiveness of forest restoration.…”

Distance and density dependence in two native Bornean dipterocarp species

“…Studies on Janzen-Connell effects come from the Neotropics, particularly in Central and South America (Augspurger & Kitajima, 1992;Dalling et al, 1998;Forget, 1992;Peres & Baider, 1997;Roberts & Heithaus, 1986;Sanchez-cordero & Martinez-gallardo, 2010;Stevenson et al, 2005;Swamy & Terborgh, 2010). By comparison, there is a relative dearth in Africa (Chapman & Chapman, 1996;Hart, 1995;Matthesius et al, 2011), and Asia (Bagchi, Press, & Scholes, 2010;Bagchi, Swinfield, et al, 2010;Krishnan et al, 2022;Massey et al, 2006;Takeuchi & Nakashizuka, 2007;Viswanathan et al, 2020). This geographic gap is important to address because, globally, forests differ from each other in important ways.…”