Professor Cornell University Ithaca, New York, United States
Abstract: Plant-pollinator interactions provide essential services to plants in both natural and agricultural systems, but these interactions are particularly vulnerable to anthropogenic disturbances. Even without species extinctions, changes in pollinator behavior in response to disturbance can fundamentally alter the quality of these interactions. As such, understanding how these interactions have changed over time is critical for their conservation, but documenting changes in pollinator behavior is limited by the difficulty of inferring species interactions in the past.
Here, we examine the pollens carried by preserved hawkmoths in collections as a record of historical foraging patterns in order to test how floral specialization and plant-pollinator network structure have changed in the Caribbean over the past 100 years. Hawkmoths (Lepidoptera: Sphingidae) are prolific pollinators that accumulate less biased pollen loads than other pollinator groups and are well represented in collections. After non-destructively removing the pollen from pinned hawkmoth specimens, the pollen grains carried by each specimen were identified visually and genetically. We hypothesized that disturbances such as deforestation and habitat fragmentation would reduce the abundance of preferred floral species over time, causing moths to opportunistically visit a higher diversity of plants, rather than remain specialized on flowers they match morphologically. This shift in specialization would cause more recent networks to be more redundant, but would also reduce the quality of pollination for isolated populations.
We found that across all sites and time periods, moth-flower networks were much less nested, less redundant, and more specialized than expected by chance, with many pollen morphotypes represented despite each moth individual carrying relatively few pollen species. Contrary to predictions, however, the richness of pollen morphotypes carried by moths has declined over time: both the average number of morphotypes carried and the probability of carrying at least some pollen declined between the 1910s and 2020s. This suggests that the moths are sensitive to changes in floral availability, and that those plants still receiving visits are unlikely to lose the pollination services they rely on. Furthermore, individual moths within species were also more variable in the identity of flowers they interacted with in Jamaica compared to Cuba or Haiti, suggesting that despite showing relatively specialized foraging patterns, hawkmoths within the historical networks opportunistically took advantage of diverse flowers when they were available. Our results highlight the complex ways in which plant-pollinator interactions can shift over time, as well as the value of historical records of species interactions.
