Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages.
Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now.
Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA Conservation Ecology Program, King Mongkut's University of Technology Thonburi, 49 Soi Tientalay 25, Bangkhuntien-Chaitalay Road, Thakham, Bangkhuntien, Bangkok 10150, Thailand trevorcaughlin@ufl.edu.
T Trevor
TT
Caughlin
Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA.
Jake M
JM
Ferguson
Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA.
Jeremy W
JW
Lichstein
Forest Ecology and Forest Management Group, Wageningen University and Research Centre, PO Box 47, 6700 AA Wageningen, The Netherlands.
Pieter A
PA
Zuidema
Royal Thai Forest Department, Chatuchak, Bangkok 10900, Thailand.
Sarayudh
S
Bunyavejchewin
Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA Division of Environmental Biology, National Science Foundation, Arlington, VA 22230, USA.
Douglas J
DJ
Levey
D000818:Animals; D029061:Annonaceae / Q000502:physiology*; D044822:Biodiversity; D003247:Conservation of Natural Resources; D053476:Extinction, Biological; D005247:Feeding Behavior; D065928:Forests; D008322:Mammals / Q000502:physiology*; D008954:Models, Biological; D011156:Population Density; D058614:Seed Dispersal; D013785:Thailand; D014329:Tropical Climate
extinction; overhunting; seed dispersal; spatial model; tree population; tropical forest dynamics