Linking host plants to damage types in the fossil record of insect herbivory

Abstract

Studies of insect herbivory on fossilized leaves tend to focus on a few, relatively simple metrics that are agnostic to the distribution of insect damage types among host plants. More complex metrics that link particular damage types to particular host plants have the potential to address additional ecological questions, but such metrics can be biased by sampling incompleteness due to the difficulty of distinguishing the true absence of a particular interaction from the failure to detect it—a challenge that has been raised in the ecological literature. We evaluate a range of methods for characterizing the relationships between damage types and host plants by performing resampling and subsampling exercises on a variety of datasets. We found that the components of beta diversity provide a more valid, reliable, and interpretable method for comparing component communities than do bipartite network metrics. We found the rarefaction of interactions to be a valid, reliable, and interpretable method for comparing compound communities. Both beta diversity and rarefaction of interactions avoid the potential pitfalls of multiple comparisons. Lastly, we found that the host specificity of individual damage types is challenging to assess. Whereas some previously used methods are sufficiently biased by sampling incompleteness to be inappropriate for fossil herbivory data, alternatives exist that are perfectly suitable for fossil datasets with sufficient sample coverage.

Arthropod and Pathogen Damage on Fossil and Modern Plants: Exploring the Origins and Evolution of Herbivory on Land

“…Six metrics have been used to assess FFG and DT richness and intensity, provided that there is appropriate sample coverage (112). The three richness metrics are DT richness, based on presence-absence data; the structure of an herbivore community, based on the spectrum of DTs present on a host-plant species; and DT host-plant specialization, as determined by the degree to which a particular DT occurs on one or more host-plant species in a plant assemblage (103,112). The DT host-plant specialization metric assumes a functional approach that is defined by a DT having a broader (generalized) or narrower (specialized) occurrence on plant species within a plant assemblage (128,129).…”

“…This study initiated the functional feeding group (FFG)-damage type (DT) system of herbivory analysis by demonstrating in detail how insect damage on fossil plants could be used quantitatively to understand ecological, evolutionary, and environmental events in the fossil record (22). Since that time, approximately 165 journal articles have been published that variously use the FFG-DT system (Figure 1), often employing newer quantitative techniques, briefly discussed below, to document, analyze, and test hypotheses related to the history of arthropods and pathogens on plants (23,103) (Figure 2).…”

Sampling bias and the robustness of ecological metrics for plant–damage-type association networks: Comment

“…The first contribution that addressed the appropriateness of bipartite network analysis for fossil herbivory data, Schachat et al (2023), raised additional issues that were not fully addressed by SEA. The first of these issues is "metric hacking" sensu Webber et al (2020): the opportunistic selection of a subset of the dozens of available bipartite network metrics.…”

“…Furthermore, as Fründ et al (2016) pointed out, "Many network descriptors relate directly or indirectly to specialization." But, as detailed by Schachat et al (2023), the concepts of generalization and specialization become muddied when techniques that were intended for use with taxonomic data (such as bipartite networks, which can link host plant taxa to herbivorous insect taxa) are repurposed for use with functional data.…”