Eligibility: This project is only available to students on the online MSc Statistics and Data Science programme. If you are interested, please contact Dr. Rishabh Vishwakarma at rishabh.vishwakarma@tcd.ie.
Biodiversity and ecosystem function (BEF) studies investigate how diversity, including the number of species and their relative proportions affect the outputs (functions) of an ecosystem. Commonly, BEF experiments establish communities with different species and varying sown proportions at a timepoint t and measure a response of interest such as dry matter yield or forage quality at time point t+1. The aim of the experiment is to quantify the effect of manipulation in species diversity on the response of interest. Diversity-Interactions models (DI; Kirwan et al., 2007) are one approach for modelling the BEF relationship and use the sown proportions of species as predictors to quantify the effects of species identities (i.e., inherent contribution) and their interactions on the response.
It is often of ecological interest to determine if community A performs better than community B for a specific response and this can be accomplished using conventional hypothesis tests, such as t-tests or model based contrasts. However, sometimes, the ecological question is if two or more communities have equivalent performance for a given response. This can be assessed using equivalence tests, which evaluate whether the difference in response between communities of interest falls within a pre-specified “equivalence margin”. However, equivalence tests are generally more data hungry and require a larger sample size than conventional t-tests, particularly for smaller equivalence margins.
This project will use simulation studies to investigate the optimal number of community replicates and overall sample size needed for reliably conducting equivalence tests between communities in BEF experiments while also providing recommendations on choosing reasonable equivalence margins. The results will inform best practices for designing future BEF experiments that wish to investigate if two or species perform similar roles within an ecosystem. If you are interested, please contact Dr. Rishabh Vishwakarma at rishabh.vishwakarma@tcd.ie.
Recommended reading (in order):
Kirwan, L., Connolly, J., Finn, J. A., Brophy, C., Luscher, A., Nyfeler, D., & Sebastià, M. T. (2009). Diversity-interaction modeling: Estimating contributions of species identities and interactions to ecosystem function. Ecology, 90, 2032–2038.
Connolly, J., Bell, T., Bolger, T., Brophy, C., Carnus, T., Finn, J. A., Kirwan, L., Isbell, F., Levine, J., Lüscher, A., Picasso, V., Roscher, C., Sebastia, M. T., Suter, M., & Weigelt, A. (2013). An improved model to predict the effects of changing biodiversity levels on ecosystem function. Journal of Ecology, 101, 344–355.
Moral, R.A., Vishwakarma, R., Connolly, J., Byrne, L., Hurley, C., Finn, J.A. and Brophy, C., 2023. Going beyond richness: Modelling the BEF relationship using species identity, evenness, richness and species interactions via the DImodels R package. Methods in Ecology and Evolution, 14(9), pp.2250-2258.