Bird dispersal of fruits of species introduced into eastern North America

Abstract

We compared bird use of fruits of introduced and native plant species to explore the roles of coevolution, ecological fitting, and chance in shaping seed dispersal interactions. Of 45 bird-dispersed species recorded at three sites in central New Jersey, 15 (33%) were nonnative. In fall samples from seed traps and fecal droppings, introduced species accounted for 0.4–14% of fruit biomass overall and 3 – 30% of the biomass of low-quality fruits. Although absolute fruit use declined from fall to winter, relative use of introduced species increased seasonally to as high as half of winter fruit biomass. Heavy use of non-native fruits appears recent; introductions accounted for only 2% of plant species occurrences in fall and winter records of stomach contents for nine passerine species in New England and mid-Atlantic states between 1881 and 1950. Introduced fruits with fall maturation, low-quality pulp, and high durability now rival native species in fruit diets of birds in late fall and winter. The success of introductions demonstrates coadaptation through ecological fitting of preadapted partners; nevertheless, the predominant use of introduced fruits after peak bird migration suggests that introduced fruits may be less well matched to local dispersal opportunities than native ones. Key words: birds, coevolution, fruits, introductions.