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.
Seedling growth and survival
This file describes the growth and survival of individual Miliusa horsfieldii (Annonaceae) seedlings censused annually in 3 m x 3 m plots from 2009-2011. Column 1 (PLOT_ID) is the unique identifier of each 3 m x 3 m plot, Column 2 (TAG) is the unique identifier of each seedling, Column 3 (HEIGHT_1) is the height (in cm) of each seedling during the first census, Column 4 (HEIGHT_2) is the height (in cm) of each seedling during the second census, Column 5 (SURVIVAL) is the survival of seedlings from the first to the second census (1=alive, 0=dead), and CONSPECIFIC_seedlings is the count of conspecific seedlings in 1 m x 1 m quadrats containing the focal seedling. The 11 columns titled "DBH_1" to "DBH_11" are the DBH (in cm) of neighboring conspecific trees in a 20 m radius. The 11 columns titled "DIS_1" to "DIS_11" are the distance (in m) of neighboring conspecific trees in a 20 m radius. "NA" values in the neighborhood matrices indicate 0 trees were present.
SEEDLINGS.csv
Seed germination from seed addition experiment
Data on seed germination of Miliusa horsfieldii collected using a seed addition experiment in 95 plots. In these plots, a total of 6,500 marked seeds were added in 3 piles of 5, 15 or 45 seeds during June-July 2009 and monitored for survival for three months, at which time all seeds had either germinated or died. Column 1 (PLOT) is the unique identifier of each seed addition plot, Column 2 (GERMINANTS) is the total number of seeds that successfully germinated, column 3 (TOTAL_ADDED) is the total number of seeds added to each pile, and CONSPECIFIC_SEEDLINGS is the count of conspecific seedlings in 1 m x 1 m quadrats containing the focal seed pile. The four columns titled "DBH_1" to "DBH_4" are the DBH (in cm) of neighboring conspecific trees in a 10 m radius. The four columns titled "DIS_1" to "DIS_4" are the distance (in m) of neighboring conspecific trees in a 10 m radius. "NA" values in the neighborhood matrices indicate 0 trees were present.
SEEDS.csv
Fruit production as a function of tree size
Data on fruit production of Miliusa horsfieldii trees measured in June-July 2011. Fruits were counted in three 3 m x 3 m quadrats beneath 14 reproductive trees. Column 1 (FRUIT_COUNT) indicates the total number of fruits counted, Column 2 is the DBH of the focal tree (in cm) and Column 3 (TREE_ID) is a unique identifier for each individual tree.
TREES.csv
Counts of naturally-dispersed newly-established seedlings
Data on counts of newly established Miliusa horsfieldii (Annonaceae) seedlings censused in 3 m x 3 m plots. Column 1 (PLOT_ID) is the unique identifier of each 3 m x 3 m plot, Column 2 (RECRUIT_COUNTS) is the count of newly recruited seedlings in each plot, Column 3 (CONSPECIFIC_seedlings) is the count of previously established conspecific seedlings in 1 m x 1 m quadrats containing the recruits. The 11 columns titled "DBH_1" to "DBH_11" are the DBH (in cm) of neighboring conspecific trees in a 20 m radius. The 11 columns titled "DIS_1" to "DIS_11" are the distance (in m) of neighboring conspecific trees in a 20 m radius. "NA" values in the neighborhood matrices indicate 0 trees were present.
RECS.csv