In an era of rapid environmental change, it is important to understand how organisms that play key functioning roles will respond. While there is some work showing the impact of pollinator communities on floral traits, it is less known how frugivores influence fruit traits. The Mariana Islands are an ideal study system to understand how fruit traits are changing in forest communities with and without loss of frugivore dispersers. Previous work has shown smaller and more numerous seeds in three species on Guam, an island without avian dispersal, relative to the other islands. This result could be plastic, or could be due to other factors, such as a founder effect or environmental differences. While we cannot rule out environmental differences, our study increased number of focal species and collected more samples to establish if this pattern exists on a broader scale. We collected fruit from individual trees, at multiple sites and on four islands to gauge variation of seed number, seed mass, seed size, fruit mass and fruit size within and across levels. We hypothesize that if plants can respond to changes in their biotic dispersers, we will see differences in fruit traits between Guam and surrounding islands.
Results/Conclusions
We collected trait data for 2500 fruits from over 200 trees belonging to 16 species across the Mariana Islands. Across all islands, intraspecific variation of fruit size across the majority of plant species was high but fruit size was not significantly different between islands. Site to site variation within islands was higher than variation between islands. Supporting previous findings, we found that several species has more seeds per fruit on Guam, an island without avian dispersers, compared to nearby islands. This confirms previous findings, and suggests the possibility of a plastic response to frugivore presence. Further studies are needed to investigate the cause behind differences in seed number. A thorough and extensive understanding of phenotypic response by plants to environmental stressors such as changes in their biotic interactions, will help us better predict responses to future environmental change.