DOI: 10.5061/dryad.wwpzgmsrs
title: Effects of leaf litter traits on terrestrial isopod and millipede consumption, assimilation and growth

description: Nutrient cycling through leaf litter consumption is an essential
 ecological function performed by macrodetritivorous invertebrates such as
 isopods and millipedes. Leaf litter consumption rates can vary greatly
 depending on the environment, consumer identity, and litter traits, but
 generalizations about the effects of plant traits on macrodetritivore leaf
 litter consumption, assimilation and growth are not well established and
 mostly indirectly inferred. We conducted a systematic search of the global
 literature and obtained 456 standardized measures from laboratory
 experiments of relative consumption (RCR), assimilation (RAR) and growth
 (RGR) rates of terrestrial isopods and millipedes, extracted from 56
 different articles. We investigated if commonly measured leaf traits,
 plant functional groups, prior microbial conditioning of leaves, and
 climatic conditions affected these rates. We obtained data on commonly
 measured leaf traits from the TRY global plant trait database, inferred
 plant functional groups from taxonomic groupings, and obtained climatic
 data from information reported within articles. RCR, RAR and RGR varied
 greatly among macrodetritivore and plant species, but overall, there were
 no differences between isopods and millipedes. Microbial conditioning of
 litter greatly increased RCR. Plant functional group was an important
 predictor of RCR, with eudicot trees and forbs being consumed in greater
 quantities than magnoliid trees and grasses. Fresh leaf N:P ratio had a
 positive effect on RAR, and leaf N and C:N ratio had positive and negative
 effects on RGR respectively, while climatic variables had weak effects on
 the three rates. Our work shows that plant traits (both those associated
 with plant functional groups and commonly measured leaf traits) exert
 strong effects on resource processing rates by terrestrial
 macrodetritivores. Further, prior microbial conditioning of leaf litter
 has a large and globally consistent positive effect on macrodetritivore
 litter consumption, suggesting that they may consume little, if any,
 freshly senesced leaf material when microbially conditioned litter is
 available. Our results suggest that, where extremes of temperature or
 precipitation do not occur, variables reflective of food quality (leaf
 traits and microbe conditioning) are more important drivers of
 macrodetritivore leaf litter consumption than are extrinsic climatic
 variables.
description: We searched in Scopus for all peer-reviewed scientific articles
 published in English up to October 2023 whose titles, keywords or abstract
 met the search criteria defined by the Boolean expression: “(isopod* OR
 millipede OR diplopod* OR ((pill OR sow) AND bug) OR (wood AND (louse OR
 lice))) AND (feed* OR fed OR consum* OR ingest* OR assimil* OR grow*) AND
 (rate* OR efficiency)”. This search resulted in 785 articles (see Fig. S1
 for the Preferred Reporting Items for Systematic Reviews and Meta-Analyses
 [PRISMA] diagram). However, some ecological papers that measured the
 relevant rates but used highly generalizable terminology in titles,
 abstracts and keywords could not be discovered by this search methodology.
 We thus added to this collection 17 additional articles identified through
 our knowledge of the literature, references made by other studies, or
 identified by data contributors and reviewers. We then manually screened
 each article and looked for data on RCR, RAR and RGR that were either
 reported directly by the authors or could be derived from the data
 provided. Definitions of RCR, RAR, and RGR are described in the online
 supporting information (supplementary methods). If rates were calculated
 but the data were not reported in texts or tables, we contacted authors to
 obtain the raw data, or read the rates off of figures (mostly bar plots)
 using Fiji ImageJ (Schindelin et al., 2012) if authors could not be
 contacted or no longer had the raw data. Authors were not contacted if the
 paper was published more than 30 years ago. Data were
 only recorded from studies or treatment levels that approximated
 physiologically benign (e.g., spring temperatures) and natural current-day
 field conditions. For example, in studies investigating the effects of
 elevated CO<sub>2</sub> levels (Hattenschwiler et al., 1999;
 Hattenschwiler & Bretscher, 2001) heavy metal pollution (Calhôa et
 al., 2006; da Silva Junior et al., 2013; Tourinho et al., 2015; Valant et
 al., 2012), pesticides (Ribeiro et al., 2001), antibiotics (Zimmer et al.,
 2001), biodegradable plastics (Wood & Zimmer, 2014), desiccation
 (Iatrou & Stamou, 1989; Leclercq-Dransart et al., 2019) and
 salinity (Škarková et al., 2016) on RCR/RAR/RGR, only data from the
 control groups were utilized. RCRs from the consumption of mixed-species
 litters or artificial resources were also excluded since plant trait data
 could not be obtained for these. Only data from terrestrial isopod,
 millipede and plant species were collected.
description: # Effects of leaf litter traits on terrestrial isopod and millipede
 consumption, assimilation and growth
 Dataset of relative
 consumption (RCR), assimilation (RAR) and growth (RGR) rates of
 terrestrial isopods and millipedes feeding on leaf litter, compiled from
 56 published articles. ## Description of the data and file structure Data
 file contains the following columns: * Article: Citation in author(s) year
 format * Location: City and country from which isopods/millipedes and leaf
 litter were collected * Lat/Lon: coordinates (units: degrees) of location
 from which isopods/millipedes and leaf litter were collected. Most are
 best guess locations based on verbal descriptions reported in studies. *
 Temperature: experiment temperature (units: degrees Celsius) at which
 experiment was conducted. Mean of day/night temperatures, if these were
 different in an experiment. * Consumer_sp. Consumer_group,
 Consumer_family: Species, higher order classification (Isopoda or
 Diplopoda), and family of the consumer * Resource_sp: Species of the leaf
 litter resource being consumed * Resource_predigested: wheter or not leaf
 litter was microbially conditioned on the forest floor of natural habitats
 (1 = yes, microbially conditioned for 2 or more weeks; 0 = no, freshly
 senesced) * RCR, RCR_SE: RCR and the standard error of it (units: mg g-1
 day-1; dry weight of litter consumed in mg per live weight of
 isopod/millipede in g per day) * RAR, RAR_SE: RAR and the standard error
 of it (units: mg g-1 day-1; dry weight of litter consumed but not
 defecated in mg per live weight of isopod/millipede in g per day) * RGR,
 RGR_SE: RGR and the standard error of it (units: mg mg-1 day-1; change in
 live weight of isopod/millipede in mg per live weight of isopod/millipede
 in g per day) * AE, AE_SE: Assimilation efficiency (AE) and the standard
 error of it (units: %) * Sample_size: number of experiments conducted to
 estimate the RCR/RAR/RGR reported here * N_indiv_per_sample: the number of
 individual animals used in each of the experiments mentioned above *
 Experiment_type: whether experiment was a choice ("Cafeteria")
 or no-choice ("Isolation") experiment * No_food_choices: number
 of food choices available to isopod/millipede test subjects. In isolation
 type experiments, this is always 1. * Cafeteria_ID: ID for the cafeteria
 experiment. Rows sharing the same value in this column belong to different
 food resources in the same experiment In all cases, NA represents data
 that was not collected or could not be determined from the original
 published articles