Sampling fossil floras for the study of insect herbivory: how many leaves is enough?

Abstract

Abstract. Despite the great importance of plant–insect interactions to the functioning of terrestrial ecosystems, many temporal gaps exist in our knowledge of insect herbivory in deep time. Subsampling of fossil leaves, and subsequent extrapolation of results to the entire flora from which they came, is practiced inconsistently and according to inconsistent, often arbitrary criteria. Here we compare herbivory data from three exhaustively sampled fossil floras to establish guidelines for subsampling in future studies. The impact of various subsampling routines is evaluated for three of the most common metrics of insect herbivory: damage type diversity, nonmetric multidimensional scaling, and the herbivory index. The findings presented here suggest that a minimum fragment size threshold of 1 cm2 always yields accurate results and that a higher threshold of 2 cm2 should yield accurate results for plant hosts that are not polyphyletic form taxa. Due to the structural variability of the plant hosts examined here, no other a priori subsampling strategy yields consistently accurate results. The best approach may be a sequential sampling routine in which sampling continues until the 100 most recently sampled leaves have caused no change to the mean value or confidence interval for damage type diversity and have caused minimal or no change to the herbivory index. For nonmetric multidimensional scaling, at least 1000 cm2 of leaf surface area should be examined and prediction intervals should be generated to verify the relative positions of all points. Future studies should evaluate the impact of subsampling routines on floras that are collected based on different criteria, such as angiosperm floras for which the only specimens collected are those that are at least 50 % complete.

Insect herbivory on Catula gettyi gen. et sp. nov. (Lauraceae) from the Kaiparowits Formation (Late Cretaceous, Utah, USA)

“…The rarefaction analysis by total sampled surface area was used instead of number of specimens because this standardizes differences in leaf size and leaf completeness between species. A rarefaction analysis and resulting curves were created using code developed by S. Schachat [89,90] for R statistical software [83]. Rarefaction curves were bootstrapped 5,000 times to generate 84% confidence intervals.…”

Understanding the ecology of host plant–insect herbivore interactions in the fossil record through bipartite networks

“…(Sample sizes were WD with 2127, CCP with 883, SAP with 570, and MCF with 142 specimens.) Consequently, issues such as sampling effort may have contributed to disparities in network complexity (Schachat et al 2020).…”

“…There are inherent problems regarding the use of fossil data for constructing networks, such as preservation, collection bias, number of specimens for each taxon, non-spatiotemporal overlap, and time averaging (Kidwell and Bosence 1991;Dunne et al 2008Dunne et al , 2014Roopnarine 2010;Muscente et al 2018;Shaw et al 2021). Many of these issues, particularly sampling strategies and standardization of plant-insect interactions, have been explicitly addressed for the fossil record (Schachat et al 2018(Schachat et al , 2020. Through our dataset, these problems are addressed by (1) having a large collection of specimens to prevent statistical errors due to small sample size; (2) collecting a fossil flora from a locality that has narrow temporal variance; and (3) constructing networks with and without rare host-plant species in order to explore the importance of community structure (also see Schachat et al 2018Schachat et al , 2020.…”

Ecology and Evolution of Gall-Inducing Arthropods: The Pattern From the Terrestrial Fossil Record

“…In the five habitats among the 10 localities where the DT70 gall is present-Sphenobaiera Closed Woodland, Mature Dicroidium Riparian Forest, Immature Dicroidium Riparian Forest, Heidiphyllum Thicket, and Dicroidium Open Woodland-DT70 lacks a community-level preference, indicating that the distribution of this gall is not determined by ecological setting, but rather by specificity for a particular host-plant species. DT70 has not been recorded on any plant host, D. crassinervis or otherwise, in coeval strata of other Gondwanan continents such as Australia, South America, and Antarctica, a consequence attributable to low sampling levels (Schachat et al, 2020).…”