The editor’s choice for our April issue is “Pre-dispersal seed predation could help explain premature fruit drop in a tropical forest” by Jackson et al. Here, Associate Editor Ayub Oduor explains the importance of this research.
Premature fruit drop is an important phenomenon that determines fitness of individual plants and plant population and community dynamics. Several causes of premature fruit drop have been identified, and they include fruit and seed predation, pollen limitation, resource limitation, sexual selection, unfavourable abiotic conditions (e.g., leaf shading, drought, and frost), developmental and genetic abnormalities, and pollen quality. However, premature fruit drop and its causes and implications remains little studied in tropical forest ecosystems. Whereas the role of natural enemy attacks in shaping up plant species diversity has been studied extensively in tropical forests, most of the studies have focused on natural enemy attacks on seeds or seedlings after their dispersal from the mother plant. Jackson et al. in their paper “Pre-dispersal seed predation could help explain premature fruit drop in a tropical forest” used a 31-year dataset on seed and fruit rain in the extensively studied woody plant community of Barro Colorado Island, Panama to infer pre-dispersal seed predation as a potential cause of premature fruit drop for 201 plant species.
The study produced two striking findings. First, there was a high rate of premature fruit drop in the plant community, which resulted in 39% of seeds failing to attain maturity. The rates of seed abscission varied considerably among species but was not influenced by phylogenetic relatedness among the species. Second, the study signalled that plants potentially dropped their fruit prematurely due to insect herbivory. Plant species that exhibited higher fruit drop rates had traits which have generally been linked to increased susceptibility to herbivory, including: (1) production of larger seeds, (2) greater plant height, (3) predictable fruiting patterns, and (4) greater abundance of susceptible host plants. Overall, these results have interesting implications for the maintenance of diversity in tropical forests, as they suggest that herbivory-mediated premature fruit drop is an important ecological process that ensures maintenance of plant biodiversity in tropical forests. The results also open the door for future studies on the causes and ecological and evolutionary consequences of premature fruit drop. For example, does herbivory interact with other known causes of premature fruit drop to affect plant fitness? Will future variations in major global change factors, such as elevated CO2, drought, UV light and temperature, affect herbivory-mediated premature fruit drop indirectly through plant chemistry? Manipulative long-term experiments which measure the reproductive output of trees in the presence versus absence of seed predators under gradients of biotic and abiotic factors would be helpful for addressing these questions.