How ecological context shapes mutualistic relationships remains poorly understood. We combined long-term tree census data with ant censuses in a permanent 25-ha Amazonian forest dynamics plot to evaluate the effect of the mutualistic ant Myrmelachista schumanni (Formicinae) on the growth and survival of the common Amazonian tree Duroia hirsuta (Rubiaceae), considering its interactions with tree growth, population structure, and habitat. We found that the mutualist ant more than doubled tree relative growth rates and increased odds of survival. However, host tree size and density of conspecific neighbors modified the effect of the ant. Smaller trees hosting the mutualist ant consistently grew faster when surrounded by higher densities of conspecifics, suggesting that the benefit to the tree outweighs any negative effects of high conspecific densities. Moreover, our findings suggest that the benefit afforded by the ant diminishes with plant age and also depends on the density of conspecific neighbors. We provide the first long-term large-scale evidence of how mutualism affects the population biology of an Amazonian tree species.
Dhirsuta1995.2013
All measures are for Duroia hirsuta trees in a 50 ha permanent plot at the Yasuni National Park. Diameter at breast height (DBH) (1.30 m) of each tree measuring at least 1 cm DBH. DBH1995= tree DBH in 1995, DBH2013= tree DBH in 2013, Neighbors= number of D. hirsuta trees within 5 m of a focal tree.Habitat= type of habitat where each tree was located, three categories: ridge, slope, valley. Ant.type= ant indicates that the mutualist ant (Myrmelachista schumanni) was recorded in the D. hirsuta tree in 2010, the tree had signs of hosting the tree (ant understory clearings) in 2010, and the ant was recorded in the tree in 2013; no ant= the ant was recorded either in 2010, 2013, or in none of these years.
Dhirsuta2007.2013
All measures are for Duroia hirsuta trees in a 50 ha permanent plot at the Yasuni National Park. Diameter at breast height (DBH) (1.30 m) of each tree measuring at least 1 cm DBH. DBH1995= tree DBH in 1995, DBH2013= tree DBH in 2013, Neighbors= number of D. hirsuta trees within 5 m of a focal tree.Habitat= type of habitat where each tree was located, three categories: ridge, slope, valley. Surv= whether the tree was alive (A) of died (D) in 2013, considering only trees that were alive in 2010. All measures are for Duroia hirsuta trees in a 50 ha permanent plot at the Yasuni National Park. Diameter at breast height (DBH) (1.30 m) of each tree measuring at least 1 cm DBH. DBH1995= tree DBH in 1995, DBH2013= tree DBH in 2013, Neighbors= number of D. hirsuta trees within 5 m of a focal tree.Habitat= type of habitat where each tree was located, three categories: ridge, slope, valley. Ant.type= ant indicates that the mutualist ant (Myrmelachista schumanni) was recorded in the D. hirsuta tree in 2010, the tree had signs of hosting the tree (ant understory clearings) in 2010, and the ant was recorded in the tree in 2013; no ant= the ant was recorded either in 2010, 2013, or in none of these years. Ant.type1= whether M. schumanni was present (1) or absent (0); ant present was in trees that had a record of M. schummani and ant-understory clearing in 2010 and the M. schumanni was present in 2013, or absent was when none of the three conditions were met.
