Insect herbivory within modern forests is greater than fossil localities

Abstract

Fossilized leaves provide the longest running record of hyperdiverse plant–insect herbivore associations. Reconstructions of these relationships over deep time indicate strong links between environmental conditions, herbivore diversity, and feeding damage on leaves. However, herbivory has not been compared between the past and the modern era, which is characterized by intense anthropogenic environmental change. Here, we present estimates for damage frequencies and diversities on fossil leaves from the Late Cretaceous (66.8 Ma) through the Pleistocene (2.06 Ma) and compare these estimates with Recent (post-1955) leaves collected via paleobotanical methods from modern ecosystems: Harvard Forest, United States; the Smithsonian Environmental Research Center, United States; and La Selva, Costa Rica. Total damage frequency, measured as the percentage of leaves with any herbivore damage, within modern ecosystems is greater than any fossil locality within this record. This pattern is driven by increased frequencies across nearly all functional feeding groups within the Recent. Diversities of total, specialized, and mining damage types are elevated within the Recent compared with fossil floras. Our results demonstrate that plants in the modern era are experiencing unprecedented levels of insect damage, despite widespread insect declines. Human influence, such as the rate of global climate warming, influencing insect feeding and timing of life cycle processes along with urbanization and the introduction of invasive plant and insect species may drive elevated herbivory. This research suggests that the strength of human influence on plant–insect interactions is not controlled by climate change alone but rather, the way in which humans interact with terrestrial landscape.

Convergent evolution of fern nectaries facilitated independent recruitment of ant-bodyguards from flowering plants

“…A more detailed analysis of herbivore groups and the complex multi-species interactions may resolve these fine-scale relationships. Interestingly, however, our observations of increased nectary presence in ferns corresponds with a more general pattern of increased Cenozoic herbivory identified in the fossil record 75,76 . Undoubtedly more information is needed to confidently determine what drove the Cenozoic increase of nectary-bearing ferns; however, our observations hint at a possibility that increased herbivory may have contributed.…”

Leaf traits linked to structure and palatability drive plant–insect interactions within three forested ecosystems

“…Insect herbivory measured within Harvard Forest (HF), the Smithsonian Environmental Research Center (SERC), and La Selva (LS) was compared with leaf traits to investigate their influence on insect herbivore damage recorded on leaf tissue. As plant–insect interactions are being disrupted by human influence (Zvereva and Kozlov, 2006; Dyer et al, 2018; Azevedo‐Schmidt et al, 2022) and forest health is influenced by insect herbivory (e.g., Nabity et al, 2009), it is increasingly important to understand these relationships across a wider breadth of evolutionary time via the geologic record. To facilitate collaboration between modern and deep‐time ecology, paleobotanical methods were replicated in modern ecosystems.…”

Fossil leaves reveal drivers of herbivore functional diversity during the Cenozoic

“…Various approaches for sampling standardization of fossil floras have been proposed in the literature, with a dichotomy between subsampling all leaves versus subsampling only those leaves with traces of herbivory (i.e., subsampling all leaves or damaged leaves, respectively) ( 54 – 57 ). Previous studies of damage type diversity typically subsampled fossil floras to 300–400 leaves, irrespective of traces of herbivory ( 12 , 58 , 59 ). However, this approach can be problematic when the aim is to quantify and compare the host specificity of herbivores across fossil floras with varying rates of herbivory.…”