DOI: 10.5061/dryad.tqjq2bvvk
title: Data from: Seed size predicts global effects of small mammal seed predation on plant recruitment

description: We conducted a global literature review and meta-analysis to evaluate
 whether seed size could predict post-dispersal seed predator effects on
 seed removal and plant recruitment,
 respectively.  Datasets were built using data extracted
 from published studies focusing on seed predation by small mammals (see
 Methods for criteria and data extraction protocol).  We found
 that seed size predicted small mammal seed removal rates and their impacts
 on plant recruitment consistent with optimal foraging theory, with
 intermediate seed sizes most strongly impacted globally - for both native
 and exotic plants.  However, differences in seed size
 distributions among ecosystems conditioned seed predation patterns, with
 relatively larger-seeded species most strongly affected in grasslands
 (smallest seeds), and relatively smaller-seeded species most strongly
 affected in tropical forests (largest seeds).  Such
 size-dependent seed predation has profound implications for coexistence
 among plants because it may enhance or weaken opposing life-history
 tradeoffs in an ecosystem-specific manner.  Our results suggest
 that seed size may serve as a key life-history trait that can integrate
 consumer effects to improve understandings of plant coexistence. 
description: We conducted a global literature review to obtain data related to
 small mammal effects on plant species, as measured in each of two types of
 studies - each producing a separate dataset included in this archive. 
 First, we examined studies wherein researchers offered seeds in the field
 to quantify seed removal rates by post-dispersal seed predators.  Second,
 we evaluated experiments wherein researchers sowed seeds in paired cages
 that allowed or precluded seed predator access in order to quantify
 post-dispersal seed predator effects on plant recruitment. To obtain studies
 that quantified small mammal seed removal rates and/or experimentally
 evaluated the effects of seed removal on plant recruitment, we first
 considered data from the global literature review conducted by Moles et
 al. (2003; <i>Ecology</i>, 84,
 3148-3161).  We then supplemented these studies with more
 recent work (published from January 2002 through November 2019) by
 searching the Web of Science Core Collection for peer-reviewed studies
 using the search term combination: ("seed remov*" OR "seed
 predat*" OR "seed offer*") AND ("small mammal*"
 OR "rodent*" OR "granivor*").  We also screened
 studies found through this search for relevant
 citations. From this literature pool, we
 filtered studies based on the following criteria.  All studies considered
 for our evaluation were conducted in natural systems, i.e. not urban or
 agricultural settings.  In this definition, we included European
 grasslands, which are often sustained by mowing, and North American
 old-field systems, which are seral stages of post-agricultural systems
 returning to their natural state.  We focused on studies examining
 primarily seeds, not fruits, though studies incorporating seeds removed
 from fruits were included.  Likewise, seeds attached to well-developed
 samara or samara-like dispersal structures (e.g., <i>Acer</i>,
 <i>Fraxinus</i>) were excluded, as these adaptations can
 affect total diaspore mass and shape in ways that alter seed handling and
 removal.  Seed offerings above the ground surface were excluded.  Because
 consumer origins could influence outcomes (Parker et al. 2006), we also
 excluded studies where small mammal seed predators could be identified as
 introduced (e.g., from some island systems), as these were too few to
 address consumer origins in analyses.  In all cases, only studies that
 reported results by individual plant species could be included. 
 Additionally, for seed removal studies, given that study-level variables
 such as study design, seed predator community, and environmental context
 (e.g., background resource levels, competition, etc.) could have large
 effects on measured responses, we only included studies that provided data
 for &gt;1 plant species to control for such variation.  We did not
 impose this restriction on plant recruitment studies given that such
 studies were limited in number, but exclusion of single-species studies
 did not alter meta-analysis results (Appendix S1). Data
 from qualifying studies were extracted directly from the text or tables of
 publications, or from figures using Web Plot Digitizer Version 4.0
 (https://automeris.io/WebPlotDigitizer/).  For seed removal studies, we
 obtained data on the proportion of seeds removed per plant species during
 seed removal trials.  In studies reporting multiple seed removal rates per
 species, we used the following rules to select one value (to overcome the
 complication of trying to account for non-independence among species x
 study replicates in models).  When seed removal studies presented data for
 multiple trials or time points per species, we used data from the last or
 longest reported time interval with one exception: if the removal rate
 approached 100% for multiple plant species (potentially truncating
 responses), we used the middle trial or median time point.  In studies
 presenting data for multiple sites or ecological contexts (e.g., variation
 by habitat, distance from habitat edge, or forest age), we randomly chose
 a single scenario.  For studies of seed predator effects on plant
 recruitment, we extracted data on the mean number of seedlings or
 proportion of seedlings recruiting per species, associated measures of
 variation (SD or SE), and sample size for both small mammal exclusion
 (treatment) and small mammal access plots (control).  In studies reporting
 small mammal effects multiple times per species, we selected one estimate
 (for reasons noted above) using the following criteria.  For studies
 reporting effects over multiple years and/or ecological contexts, we
 selected the scenario with the highest overall recruitment in the control
 plots to maximize potential to detect seed predator effects.  The
 exception to this rule was that in studies including both disturbed and
 undisturbed treatments, we used data only from disturbed treatments to
 exclude effects of plant competition, which can vary by seed
 size.  Geographic and habitat information was recorded
 for all studies.  The latter was used to define the following ecosystem
 types: grasslands (including European grasslands and old-field systems as
 defined above), temperate forest, tropical forest, and other (e.g.,
 desert, shrublands, coastal dunes).  Plant species provenance (i.e.,
 native or exotic) was taken directly from the study when possible (most
 cases), and otherwise from the Plants of the World online database (Royal
 Botanic Gardens Kew 2020).  Seed mass data for studies from Moles et al.’s
 (2003) global review were obtained from Appendix I in that publication. 
 For remaining studies, we gathered seed mass data directly from the source
 publication or a related publication when possible (85% of cases).  If
 authors did not include seed mass, we obtained this information from the
 following published databases, prioritized in the order listed: Seed
 Information Database (Royal Botanic Gardens Kew 2019), LEDA for Northwest
 European flora (Kleyer et al. 2008), and Botanical Information and Ecology
 Network Database (Maitner et al. 2018).  In cases where multiple seed
 masses were given per species in a database, we chose the record from the
 most proximate geographic region, when given, otherwise we chose the first
 record listed.  Seed mass (+1) was natural log-transformed for
 analysis. 
description: Small mammal seed predation x seed size datasets.
 All variables included in the two datasets are detailed on the
 README tab associated with each file. Please note that
 the seed removal dataset was updated to rebut a technical comment by Chen
 et al. (2021).  The updated seed removal dataset is associated with a
 separate Dryad archive
 (https://doi.org/10.5061/dryad.hqbzkh1fp).