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 and that the rarefaction of interactions represent a valid, reliable, and interpretable method for comparing compound communities. Both beta diversity and rarefaction of interactions avoid the potential pitfalls of multiple comparisons. Finally, we found that the host specificity of individual damage types is challenging to assess. Whereas bipartite network metrics 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.

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.…”

“…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. The Currano et al (2021) publication, which is the only contribution before that of SEA to have calculated bipartite network metrics for the assemblages evaluated here, presented generalized linear models involving a number of “selected network properties.” A bipartite network metric called “vulnerability” was included in those models but was not evaluated by SEA; bipartite network metrics called “togetherness,” “resilience slope,” and “robustness” were evaluated by SEA but were not included in the previous generalized linear models (Currano et al, 2021, Table S4). 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. Damage types are functional data: a single damage type observed on multiple specimens can be induced by a variety of distantly-related insect taxa—most if not all of whom may be specialists.…”

“…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. Damage types are functional data: a single damage type observed on multiple specimens can be induced by a variety of distantly-related insect taxa—most if not all of whom may be specialists.…”

Evolution of terrestrial herbivory: nutrient stoichiometry, body size, and dietary diversity

“…Even when a damage type is deemed diagnostic for a particular insect lineage, that can still mean thousands of species given the prodigiousness of insects (Wilf et al, 2000) and dozens of insect species may be capable of making similar damage even at individual localities (Carvalho et al, 2014). Furthermore, modern ecological analyses have been worked out assuming the sampling to completion of the entire fauna and flora as available to modern ecology, but complete sampling is never available from the fossil record (Schachat et al, 2023). Acknowledging these limitations, metrics have been advocated for comparing damage richness across fossil localities without requiring full species-level resolution and complete sampling (Schachat et al, 2022).…”

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

“…This article published with an error in the legend of Figure 6 (Schachat et al 2023). In the bottom of the three panels, the labels “1,000” and “750” are swapped from their proper positions.…”