THE FUNCTIONAL HERBIVORE NICHE IN ANCIENT TERRESTRIAL ECOSYSTEMS

The functional feeding group–damage type (FFG-DT) system that is the basis for the quantitative analysis of arthropod and pathogen herbivory has been used in 170 publications that have examined plant damage from the Middle Devonian to the present day. Historically, the fundamental unit has been the damage type (DT), subsumed under the more inclusive category of the functional feeding group (FFG). Techniques for analyzing herbivory have taken two major approaches. First is the analysis of richness, or ecological diversity, typically using the three metrics of DT richness, DT plant-host specialization level, and occasionally a measure of herbivore community structure. A second approach is the analysis of frequency, or intensity level of herbivory, using the three metrics of DT frequency, herbivorized plant surface area, and most recently, feeding event occurrences (FEOs). FEOs are a measure of the number of times that an arthropod or pathogen engages in a single feeding session at the level of a plant organ such as a leaf. The FEO essentially is the finest grained, discrete, assessment of feeding available for herbivore studies in the fossil record and is essential for establishing the functional structure of the plant herbivore niche based on a behavior. Although studies have assessed multitrophic food-web structure through presence–absence interaction links among trophic groups, best illustrated by the terrestrial community surrounding Eocene Lake Messel, a more focused example has been bipartite networks that link the two node classes of (1) the plant-host taxa node class, with (2) the functional DT node class, connected by (3) FEO links. FEO links provide a quantitative measure of the frequency of pairwise behavioral interactions between a DT and its host-plant species. Such links also provide frequency data to establish interaction strengths necessary for determining the structure and especially the intensity of a herbivore community on a plant-host species.