PLANT-INSECT INTERACTIONS THROUGHOUT GEOLOGIC HISTORY: HOW DO CHANGES IN ABIOTIC VARIABLES INFLUENCE PLANT-INSECT COMMUNITY DYNAMICS? ARE INSECTS HUNGRIER IN THE MODERN? (Invited Presentation)

The fossil record preserves snapshots of ecosystems past, and these snapshots can be used to investigate the influence of abiotic variables and biotic interactions on ecosystem structure and function. Biotic interactions among plants and insects are integral to terrestrial ecosystems, as the two groups account for up to 75% of non-microbial terrestrial biodiversity. Ancient plant-insect herbivore associations can be studied directly through observation of feeding damage on well-preserved leaf compression fossils, and quantitative analyses of insect herbivory have taken off since the establishment of the insect damage census protocol by Wilf and Labandeira in 1999.

We compiled published insect damage census data for over 60 angiosperm-dominated ecosystems that included at least 300 fossil dicot leaves. Datasets range from Late Cretaceous to Pleistocene in age and were collected in Europe, North America, Africa, South America, Antarctica, and New Zealand. Analyzed at the regional scale, these datasets have documented the impact of the Cretaceous-Paleogene mass extinction and Cenozoic climate change on plant-insect ecology and evolution. They also illustrate the importance of leaf traits, particularly leaf mass per area, leaf lifespan, and leaf nitrogen content, and regional species pools on patterns of herbivory. Insect herbivore damage frequency observed in ancient assemblages is typically far lower than the range observed using similar methods in modern ecosystems. Leaf litter censuses conducted in 17 modern tropical and temperate forests ranged from 60-95% of leaves with insect damage, whereas mean damage frequency for the fossil assemblages is ~32% and just 10% of sites exceed 60% damage. This result is surprising because the number of insect mouthpart classes has remained static since the Cretaceous (Labandeira and Sepkoski 1993) and temperature and atmospheric carbon dioxide levels in the fossil dataset far exceed modern values. It remains unclear whether damage frequency is actually higher today than it has ever been in the past or whether this discrepancy is due to taphonomic biases.

C.C. Labandeira and J.J. Sepkoski, 1993. Insect diversity in the fossil record. Science261, 310-315.