DOI: 10.5061/dryad.qrfj6q5b0
title: Multiple metrics of latitudinal patterns in insect pollination and herbivory for a tropical-temperate congener pair

description: The biotic interactions hypothesis posits that biotic interactions are
 more important drivers of adaptation closer to the equator, evidenced by
 “stronger” contemporary interactions (e.g. greater interaction rates)
 and/or patterns of trait evolution consistent with a history of stronger
 interactions. Support for the hypothesis is mixed, but few studies span
 tropical and temperate regions while experimentally controlling for
 evolutionary history. Here, we integrate field observations and common
 garden experiments to quantify the relative importance of pollination and
 herbivory in a pair of tropical-temperate congeneric perennial herbs.
 Phytolacca rivinoides and P. americana are pioneer species native to the
 Neotropics and the eastern USA, respectively. We compared plant-pollinator
 and plant-herbivore interactions between three tropical populations of P.
 rivinoides from Costa Rica and three temperate populations of P. americana
 from its northern range edge in Michigan and Ohio. For some metrics of
 interaction importance, we also included three subtropical populations of
 P. americana from its southern range edge in Florida. This approach
 confounds species and region but allows us, uniquely, to measure
 complementary proxies of interaction importance across a
 tropical-temperate range in one system. To test the prediction that
 lower-latitude plants are more reliant on insect pollinators, we
 quantified floral display and reward, insect visitation rates, and
 self-pollination ability (autogamy). To test the prediction that
 lower-latitude plants experience more herbivore pressure, we quantified
 herbivory rates, herbivore abundance, and leaf palatability. We found
 evidence supporting the biotic interactions hypothesis for most
 comparisons between P. rivinoides and north-temperate P. americana (floral
 display, insect visitation, autogamy, herbivory, herbivore abundance, and
 young-leaf palatability). Results for subtropical P. americana
 populations, however, were typically not intermediate between P.
 rivinoides and north-temperate P. americana, as would be predicted by a
 linear latitudinal gradient in interaction importance. Subtropical
 young-leaf palatability was intermediate, but subtropical mature leaves
 were the least palatable, and pollination-related traits did not differ
 between temperate and subtropical regions. These nonlinear patterns of
 interaction importance suggest future work to relate interaction
 importance to climatic or biotic thresholds. In sum, we found that the
 biotic interactions hypothesis was more consistently supported at the
 larger spatial scale of our study.
description: See methods in Carina A. Baskett, Lucy Schroeder, Marjorie G.
 Weber, and Douglas W. Schemske. Multiple metrics of latitudinal patterns
 in insect pollination and herbivory for a tropical-temperate congener
 pair. <i>Ecological Monographs</i>. 2019.
 Table 2 of the manuscript provides a summary of results and a
 figure reference for each measurement, and each corresponds to a dataset
 uploaded here. The uploaded data is that which was used for analysis,
 after any "data wrangling" was performed. For example, multiple
 measurements of nectar volume were made per individual, but we analyzed
 individual means, so the deposited dataset is the individual
 means.
description: Each dataset has an associated ReadMe to explain its
 columns.