Fossil leaves reveal drivers of herbivore functional diversity during the Cenozoic

Abstract

Herbivorous arthropods are the most diverse group of multicellular organisms on Earth. The most discussed drivers of their inordinate taxonomic and functional diversity are high niche availability associated with the diversity of host plants and dense niche packing due to host partitioning among herbivores. However, the relative contributions of these two factors to dynamics in the diversity of herbivores throughout Earth’s history remain unresolved. Using fossil data on herbivore-induced leaf damage from across the Cenozoic, we infer quantitative bipartite interaction networks between plants and functional feeding types of herbivores. We fit a general model of diversity to these interaction networks and discover that host partitioning among functional groups of herbivores contributed twice as much to herbivore functional diversity as host diversity. These findings indicate that niche packing primarily shaped the dynamics in the functional diversity of herbivores during the past 66 my. Our study highlights how the fossil record can be used to test fundamental theories of biodiversity and represents a benchmark for assessing the drivers of herbivore functional diversity in modern ecosystems.

The interplay between defaunation and phylogenetic diversity affects leaf damage by natural enemies in tropical plants

“…These findings have important implications for understanding the rapid eco‐evolutionary changes in species interactions that might be taking place under contemporary defaunation scenarios. Recent evidence shows that major changes in vegetation structure during the Eocene–Oligocene Transition and Late Miocene cooling climate were associated with declines in functional diversity in the guild of specialised internal herbivores (Albrecht et al., 2023). If dilution effects are responsible for lowering pathogenic infection rates in defaunated areas, as our results suggest, and given that the co‐evolutionary arms race between plants and their natural enemies is one of the main drivers that generate and maintain biodiversity (Connell, 1971; Janzen, 1970; van Valen, 1980), the ‘dilution’ of these interactions via defaunation is likely to affect biodiversity and bring unknown consequences on the evolutionary time scale.…”

“…Insect herbivory is responsible for the consumption of approximately 18% of all biomasses produced annually in tropical forests—the Earth's largest reservoir of abundance and diversity of herbivorous insects (Basset et al., 2012; Janzen & Schoener, 1968). While insects population are experiencing global changes at unprecedented levels, with many losers and a few winning species (Didham et al., 2020; Sánchez‐Bayo & Wyckhuys, 2019), very little is known about the functional consequences of these changes on eco‐evolutionary processes maintained by herbivore insects and whether such changes might jeopardise the potential compensatory effects in the face of concomitant defaunation of large herbivores (Albrecht et al., 2023; Williams et al., 2021). Additionally, bacteria, viruses and fungi that infect leaf cells cause necrosis of the foliar tissues and might sometimes develop serious diseases that compromise plants' fitness (Bell et al., 2006; García‐Guzmán & Dirzo, 2001; Gilbert, 2002; Mordecai, 2011).…”