Myiarchusflycatchers are the primary seed dispersers ofBursera longipesin a Mexican dry forest

Abstract

We evaluated the seed dispersal ofBursera longipesby birds along a successional gradient of tropical dry forest (TDF) in southwestern Mexico.B. longipesis an endemic tree to the TDF in the Balsas basin. The relative abundance of frugivorous birds, their frequency of visits toB. longipesand the number of removed fruits were recorded at three study sites with different stages of forest succession (early, intermediate and mature) characterized by distinct floristic and structural elements. Flycatchers of theMyiarchusandTyrannusgenera removed the majority of fruits at each site. Overall, visits toB. longipeswere less frequent at the early successional site. Birds that function as legitimate dispersers by consuming whole seeds and regurgitating or defecating intact seeds in the process also remove the pseudoaril from seeds, thereby facilitating the germination process. The highest germination percentages were recorded for seeds that passed through the digestive system of two migratory flycatchers:M. cinerascensandM. nutingii. Perch plants, mainly composed of legumes (e.g.,Eysenhardtia polystachya, Acacia cochliacantha, Calliandra eryophylla, Mimosa polyantha), serve also as nurse plants since the number of young individuals recruited fromB. longipeswas higher under these than expected by chance. This study shows thatMyiarchusflycatchers are the most efficient seed dispersers ofB. longipesacross all successional stages. This suggests a close mutualistic relationship derived from adaptive processes and local specializations throughout the distribution of both taxa, as supported by the geographic mosaic theory of coevolution.