Response to Kozlovet al.: Inaccurate estimation of biases in herbarium specimen data

Abstract

SummaryKozlov and colleagues1 call into question the application of herbarium specimens to quantify historical patterns of herbivory2–5. It is already widely appreciated that collectors of herbarium specimens may tend to avoid insect damage, thus making herbivory estimates from herbarium specimens potentially down-biased2. However, Kozlov et al. additionally suggest that variation in sampling selectivity among collectors may misrepresent patterns of herbivory in nature. The authors sought to quantify these biases by collecting and contrasting insect herbivory data across 17 plant species from herbarium versus standard field ecological sampling procedures. They concluded that herbivory estimates from herbarium specimens are highly variable, rendering them an inaccurate representation of herbivory in nature. Our re-analysis of Kozlov et al.’s data, in contrast, reveals that herbarium specimens indeed provide a useful record of these symbioses. We demonstrate that Kozlov et al. were misled by analyzing comparisons derived from very few samples, which provide highly noisy estimates.

Testing enemy release of non‐native plants across time and space using herbarium specimens in Norway

“…These differences varied between species, which suggests that assuming lower levels of herbivory across all herbarium specimens is not valid when using herbarium data (Kozlov et al, 2020). However, a recent re-analysis of the data collected by Kozlov et al (2020) showed that with sufficient samples (more than 10 data points), herbivory levels of field-observed samples and herbarium specimens are highly correlated, and that there is little difference in sampling bias across species (Meineke et al, 2020). For our study, we therefore assume that if a collection bias exists, it would be consistent for native and non-native species and would therefore not affect the interpretation of our results.…”

Reversing extinction trends: new uses of (old) herbarium specimens to accelerate conservation action on threatened species

“…1). Despite the tendency of botanists to collect attractive specimens (and those potentially free of pests; Kozlov et al ., 2020), recent evidence indicates that these collecting biases are not strong enough to offset the generation of meaningful conclusions (Meineke et al ., 2020b).…”

Bias assessments to expand research harnessing biological collections

“…In another example, Kozlov et al [36] compared herbivory estimates from herbarium specimens and randomized samples and found that collectors may manifest biases in herbivory captured on herbarium specimens by collecting leaves that are minimally damaged. However, this study also represents a cautionary example of why robust sample sizes are needed to develop baseline datasets [37] and underscores the need for statistical tools that assess the sample sizes needed to achieve accurate estimates, such as power analyses and rarefaction curves.…”