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Impacts of rodent eradication on seed predation and plant community biomass on a tropical atoll

Citation

Miller-ter Kuile, Ana et al. (2020), Impacts of rodent eradication on seed predation and plant community biomass on a tropical atoll, Dryad, Dataset, https://doi.org/10.5061/dryad.xsj3tx9cp

Abstract

Invasive rodent eradications are frequently undertaken to curb island biodiversity loss. However, the breadth of rodents’ ecological impact, even after eradication, is not always fully recognized. For example, the most widespread invasive rodent, the black rat (Rattus rattus), while omnivorous, eats predominantly seeds and fruit. Yet, the effects of seed predation release after eradication on plant communities and ecological functions are not well understood, posing a gap for island restoration. We examined the role of seed predation release following black rat eradication in changes to tree composition and above-ground biomass across an islet network (Palmyra Atoll) in the Central Pacific. We conducted repeated surveys of seed, juvenile, and adult tree biomass and survival in permanent vegetation plots before and after the eradication of rats. We observed a 95% reduction in seed predation for an introduced, previously cultivated tree population (Cocos nucifera). Juvenile tree biomass of all species increased 14-fold, with C. nucifera increasing the most, suggesting that eradication increased this tree’s competitive advantage. Indeed, based on stage-structured demographic models, rat eradication led to a 10% increase in C. nucifera population growth rate. The effect of invasive rodent seed predation varies considerably among the plant species in a community and can shift competitive dynamics, sometimes in favor of invasive plants. These bottom-up effects should be considered in evaluating the costs and benefits of eradication.  Documenting the variation in invasive rodent diet items, along with long-term surveys, can help prioritize island eradications where restoration is most likely to be successful.  

Methods

Datasets and scripts included in the final archive are stored in the following subfolders. We include brief descriptions below and more detailed descriptions are available in a .docx file contained in each subfolder.

1) "biomass_seedlings_and_future": This folder contains data and a .R script to convert sizes and ages to biomass for all tree species and age classes in our dataset and uses the resulting biomass data with a stage-structured demographic model to predict how rat eradication influenced plant community biomass.

2) "dem_model_transition_stats": This folder contains data and a .R script to examine whether seed survival and germination, seedling survival and transition to adulthood (all vital rates in our stage-structured demographic model) were influenced by the loss of rat seed and seedling predation and herbivory. 

3) "forest_cover_percents": This folder contains data and a .R script to look at the forest cover of Palmyra Atoll, including GIS shape file layers of both canopy types and the locations of permanent vegetation plots used in this study.

4) "seedling_nut_lmes": This folder contains data and a .R script used to build generalized linear mixed effects models on seed numbers on the ground with and without rat seed predation and also includes several supplemental datasets and models we used to compare seedling counts across years, precipitation effects that may confound rat effects, and the number of seeds counted in the canopy across sampling years. 
 

Usage Notes

These data and scripts were used to build the analyses for the main text and supporting information for this manuscript. See the README.txt document for descriptions and each folder's content descriptions (.docx) for more detailed information on data and scripts. We encourage the user to contact the corresponding author (Ana Miller-ter Kuile, ana.miller-ter.kuile@lifesci.ucsb.edu) with any additional questions regarding data usage. 

Funding

National Science Foundation, Award: #1457371

National Science Foundation, Award: #0639185

National Science Foundation, Award: #1714426

National Science Foundation, Award: #1820379

National Science Foundation, Award: #1620366

National Geographic Society, Award: #9698-15