Data and code from: Enemy release in salt marshes: How herbivorous crabs help an invasive grass to outcompete the native reed
Data files
Sep 15, 2026 version files 40.77 KB
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code_data_crab.zip
29.22 KB
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README.md
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Abstract
Biological resistance plays a key role in minimizing plant invasions, even when abiotic conditions are favorable for invasion. Through competition with native plants and herbivory by native herbivores, invasive plants can impact ecosystem functions profoundly. While the effect of invasive plants on native plants’ performance via competition has been well documented across ecosystems, less is known about the role of facilitation versus inhibition by herbivores in plant invasions, especially in stressful environments. Our main aims were to investigate the role of herbivores (crabs) in plant invasions in coastal wetlands and understand the underlying mechanisms of competition and herbivory on invader performance (i.e., growth and reproduction). We investigated the crabs’ effects on the growth (plant mean height, relative growth rate (RGR), and aboveground biomass) and reproduction (sprout density) of the invasive species Spartina alterniflora and the native grass Phragmites australis in East China. Thereto, we conducted a two-year crab exclusion experiment across three different habitats (low S. alterniflora zone, middle S. alterniflora and P. australis zone, and high P. australis zone) in a salt marsh wetland and a feeding preference trial of crabs in terms of plant traits in the lab. Our results showed that crabs had a strong negative effect on the plant mean height, aboveground biomass, RGR, and sprout regeneration of P. australis in both the middle S. alterniflora and P. australis zone and high P. australis zone, and the absence of crabs significantly decreased the density of new sprouts of S. alterniflora in both the low S. alterniflora zone and middle S. alterniflora and P. australis zone. Our lab feeding experiments showed that crabs had a feeding preference for P. australis, as related to its lower total organic carbon content and smaller C/N ratio, and higher N content and N/P ratio compared to S. alterniflora. These findings are consistent with the enemy release hypothesis as opposed to the biological resistance hypothesis. That is to say, S. alterniflora appeared to benefit from not having co-evolved with native herbivorous crabs; hence, the preferential feeding by native crabs on P. australis facilitated the success of S. alterniflora introduced to a novel wetland area. Thus, our study provides a new perspective for understanding how native herbivores contribute to the competitive advantage of an invasive plant species to outcompete the native reed through enemy release.
https://doi.org/10.5061/dryad.0rxwdbsbq
Description of the data and file structure
This dataset contains data from a two-year field crab-exclusion experiment, a seasonal crab survey in a coastal salt marsh in eastern China, and laboratory feeding trials related to plant traits. These data were collected to investigate how herbivorous crabs influence the regeneration and growth of the invasive Spartina alterniflora and the native Phragmites australis, and to examine the role of herbivores in plant invasion processes in coastal wetlands.
Files and variables
File: code_data_crab.zip
Description:
This zip file contains the raw data and R code to reproduce the analyses.
Soil properties data
Data_envi_CNP.csv：Contains soil carbon, nitrogen, and phosphorus measurements from the experimental tidal zones, as presented in Table S1.
Data_envi_conductivity.csv：Contains soil conductivity, water content and salinity measurements from the experimental tidal zones, as presented in Table S1.
variables:
- tidal_zone: The position of the sampling site along the tidal marsh elevation gradient, including 3 levels: low, middle, high.
- conductivity: Soil electrical conductivity (S/m).
- WC: Soil moisture content (%).
- Salinity: Soil salinity (‰).
- TOC: Total organic carbon content (g kg⁻¹).
- TP: Total phosphorus content (g kg⁻¹).
- TN: Total nitrogen content (g kg⁻¹).
Growth and regeneration data
Abbreviations：
LS: S. alterniflora in the low tidal zone
MS: S. alterniflora in the middle tidal zone
MP: P. australis in the middle tidal zone
HP: P. australis in the high tidal zone
RGRH: height-based relative growth rate
Data_Sprout_density.csv: Contains sprout density measurements of S. alterniflora and P. australis under different crab-access treatments, tidal zones, sampling months, and years, as presented in Figure 2.
variables:
- year: Experimental year (2018 or 2019).
- month: Sampling month: apr = April, jul = July, sep = September, and nov = November.
- tidal_zone: Tidal zone combined with two plant species (S. alterniflora and P. australis): LS, MS, MP, HP. See abbreviations above
- treatment: Different crab-access treatments: uncaged, plots allowing free crab access, caged, crab-exclusion plots, cage_control, cage-control plots allowing crab access while controlling for possible cage effects.
- block: Block number
- sprout_density: Density of newly emerged plant sprouts within the sampling plot
Data_mean_height.csv: Contains plant mean height measurements of S. alterniflora and P. australis under different crab-access treatments, tidal zones, sampling months, and years, as presented in Figure S2.
variables:
- year: Experimental year (2018 or 2019).
- month: Sampling month: apr = April, jul = July, sep = September, and nov = November.
- tidal_zone: Tidal zone combined with two plant species (S. alterniflora and P. australis): LS, MS, MP, HP. See abbreviations above
- treatment: Different crab-access treatments: uncaged, plots allowing free crab access, caged, crab-exclusion plots, cage_control, cage-control plots allowing crab access while controlling for possible cage effects.
- block: Block number
- mean_height: Mean height of plants measured within the experimental plot.
Data_RGRH.csv: Contains height-based relative growth rate (RGRH) measurements of S. alterniflora and P. australis under different crab-access treatments, tidal zones, and years, as presented in Figure 3.
variables:
- year: Experimental year (2018 or 2019).
- tidal_zone: Tidal zone combined with two plant species (S. alterniflora and P. australis): LS, MS, MP, HP. See abbreviations above
- treatment: Different crab-access treatments: uncaged, plots allowing free crab access, caged, crab-exclusion plots, cage_control, cage-control plots allowing crab access while controlling for possible cage effects.
- block: Block number
- RGRH: Height-based relative growth rate of plants.
Data_Biomass.csv: Contains aboveground biomass measurements of S. alterniflora and P. australis under different crab-access treatments, tidal zones, and years, as presented in Figure 3.
variables:
- year: Experimental year (2018 or 2019).
- tidal_zone: Tidal zone combined with two plant species (S. alterniflora and P. australis): LS, MS, MP, HP. See abbreviations above
- treatment: Different crab-access treatments: uncaged plots, plots allowing free crab access, caged plots, crab-exclusion plots, cage_control, and cage-control plots allowing crab access while controlling for possible cage effects.
- block: Block number
- biomass: Aboveground plant biomass (g/m2) measured within the experimental plot.
Data_Biomass_Figure_4.csv: Contains the biomass data arranged for calculating the log response ratio (lnRR) and the net crab effect on the competitive outcome between S. alterniflora and P. australis, as presented in Figure 4 and Figure S3.
variables:
- year: Experimental year (2018 or 2019).
- tidal_zone: The position of the sampling site along the tidal marsh elevation gradient, including 3 levels: Low, Middle, High.
- species: Two plant species, including Phragmites (P. australis) and Spartina (S. alterniflora).
- treatment: Different crab-access treatments: uncaged, plots allowing free crab access, caged, crab-exclusion plots, cage_control, cage-control plots allowing crab access while controlling for possible cage effects.
- block: Block number in each tidal zone.
- pair_block: Block number used to pair samples between the low and high tidal zones. Blocks with the same number were compared between the two zones (e.g., block 1 in the low tidal zone was paired with block 1 in the high tidal zone).
- Biomass: Aboveground plant biomass measured within the experimental plot.
Crab survey data
Data_crab_survey.csv: Contains seasonal crab abundance data collected across three tidal habitats in 2019, including the dominant crab species Sesarma plicata and Helice tientsinensis, as presented in Table S8.
variables:
- month: Sampling month: apr = April, jul = July, sep = September, and nov = November.
- habitat: The position of the sampling site along the tidal marsh elevation gradient, including 3 levels: low, middle, high.
- replicate: Replicate number of crab trapping buckets in each habitat.
- Sesarma: The total number of Sesarma (S. plicata) individuals captured in each replicate of crab trapping buckets.
- Helice: The total number of Helice (H. tientsinensis) individuals captured in each replicate of crab trapping buckets.
Crab feeding preference data
Data_Consume.csv: Contains crab consumption measurements from laboratory feeding trials on different plant tissues of S. alterniflora and P. australis, as presented in Figure 5.
Abbreviations：
AL: Adult leaf
AS: Adult stem
FR: Fine root
SS: Sprout stem
SL: Sprout leaf
variables:
- crab: Crab species, Sesarma (S. plicata) and helice (H. tientsinensis).
- replicate: Replicate number of crab feeding experiment.
- plant: Two plant species, including Phragmites (P. australis) and Spartina (S. alterniflora).
- organ: Plant tissue type used in the feeding experiment, including AL, AS, FR, SL, and SS (see abbreviations above).
- dry_mass_consumption: Dry mass of plant tissue consumed by each crab during the feeding experiment (g).
Data_trait_crab.csv: Contains the combined crab consumption and plant trait data used to examine relationships between crab feeding and plant traits, as presented in Table S15.
variables:
- crab: Crab species, S (S. plicata) and H (H. tientsinensis).
- ID: Identifier combining plant species, plant developmental stage, crab species, and tissue type. The first letter represents plant species (P = Phragmites australis, S = Spartina alterniflora), the second letter represents plant stage (A = adult, S = sprout), the third letter represents crab species (S = S. plicata, H = H. tientsinensis), and the final part indicates tissue type (leaf or stem).
- Consume: Dry mass of plant tissue consumed by crabs during the feeding experiment (g).
- Toughness: Plant toughness.
- DMC: Plant dry matter content (%).
- TOC: Total organic carbon content (g kg⁻¹).
- TP: Total phosphorus content (g kg⁻¹).
- TN: Total nitrogen content (g kg⁻¹).
- C/N: Carbon-to-nitrogen ratio of plant tissue.
- N/P: Nitrogen-to-phosphorus ratio of plant tissue.
- WC: Plant water content (%).
Data_trait_nu.csv: Contains chemical traits of plant tissues, including total organic carbon, total nitrogen, total phosphorus, C: N ratio, and N:P ratio, as presented in Table S14.
variables:
- plant_species: Two plant species, including Phragmites (P. australis) and Spartina (S. alterniflora).
- stage: Development stage of plant, A (adult) and S (sprout).
- tissues: Plant tissues, leaf, stem and root.
- ID: Identifier combining plant species, plant developmental stage, and tissue type. The first letter represents plant species (P = P. australis, S = S. alterniflora), the second letter represents plant stage (A = adult, S = sprout), and the last letter represents tissue type (L = leaf, S = stem, R = root).
- TOC: Total organic carbon content (g kg⁻¹)
- TP: Total phosphorus content (g kg⁻¹)
- TN: Total nitrogen content (g kg⁻¹)
- C/N: Carbon-to-nitrogen ratio of plant tissue.
- N/P: Nitrogen-to-phosphorus ratio of plant tissue.
Data_trait_phy.csv: Contains physical traits of plant tissues, including toughness, water content, and dry matter content, as presented in Table S14.
variables:
- plant_species: Two plant species, including Phragmites (P. australis) and Spartina (S. alterniflora).
- stage: Development stage of plant, A (adult) and S (sprout).
- tissues: Plant tissues: leaf, stem, and root.
- ID: Identifier combining plant species, plant developmental stage, and tissue type. The first letter represents plant species (P = P. australis, S = S. alterniflora), the second letter represents plant stage (A = adult, S = sprout), and the last letter represents tissue type (L = leaf, S = stem, R = root).
- Toughness: Plant toughness.
- WC: Plant water content (%).
- DMC: Plant dry matter content (%).
Code_Crab_Ecology.R：R script used for data processing, statistical analyses, and preparation of figures presented in the main text and supplementary materials.
The script includes data processing, analyses of soil properties, seasonal patterns of crab density, effects of crab exclusion on plant regeneration and growth, laboratory feeding trials, plant trait analyses, and preparation of all figures.
Software and packages:
All analyses and figures were conducted using R version 4.4.2.
Required R packages:
- tidyverse
- patchwork
- lme4
- lmerTest
- emmeans
- MuMIn
- cowplot
- multcomp
- dunn.test
- GGally
- grid
Other publicly accessible locations of the data:
- NA
Data were derived from the following sources:
- NA