TROPICAL CANOPY INSECTS LINK LEAF DAMAGE IN FOSSIL AND LIVING FORESTS

Insect-mediated damage on leaves has been widely used in paleoecological studies as a direct measure of ancient herbivory. The quantification of distinct insect-mediated damage types (DT) on fossil leaf assemblages has revealed consistent, long-term patterns of DT richness (DTR) responding to biotic and abiotic disturbance. External feeding is the most abundant and diverse type of leaf damage in living and fossil forests; however, due to mouthpart convergence across various insect lineages, the relation between external-DTR and insect richness (IR) has remained unknown, restricting the use of external-DTR in describing past and extant herbivory. We explore the relation between leaf chewing insect species and external-feeding DTR in two lowland tropical forests in the Republic of Panama. Herbivorous insects feeding on the canopy of dominant plant species at each site were collected, and their induced DTs recorded. A robust, positive correlation between IR and external-DTR was found across host plants at both sites, linking the number of insect species on a host species to the number of recorded external-DTs. External-DT turnover across plant hosts was found to follow insect species turnover, suggesting that herbivore assemblages are to some extent reflected in external-feeding DT composition in living forests. DTs recorded by multiple insect species in Panama are also the most abundant in two South American Paleogene floras, indicating that abundant DTs in fossil floras may underestimate the number of culprit insects. External DT composition is quantifiable in living and fossil forests, and is promising for insect herbivore turnover across host plant species. These findings validate underlying assumptions in fossil-based interpretations of DTR and suggest that external DTR, when used in combination with endophagous and specialized feeding traces (known to represent single insect species on single host species), can be a robust proxy for tracking relative (not absolute) changes in insect richness in the fossil record.