Abstract
Transfer functions are now widely available to infer past environmental conditions from biotic assemblages. Existing transfer functions are based on species assemblages but an alternative is to characterize assemblages based on functional traits, characteristics of the organism which determine its fitness and performance. Here, we test the potential of trait-based transfer functions using testate amoeba functional traits to reconstruct peatland water-table depths.A total of seven functional traits with linkages to peat moisture content were identified and quantified as community weighted-means for each of 43 taxa in a training set from Tierra del Fuego, South America. Transfer functions based on (multiple) linear regression and partial least-squares were produced, validated using cross-validation and an independent test set, and applied to three core records. Trait-based models performed remarkably well. Model performance based on cross-validation and an independent test set was only marginally weaker than for models based on species and reconstructed down-core trends were extremely similar. Trait-based models offer considerable potential for paleoecological reconstruction particularly in no-analogue situations, where no species transfer function is available and for inexperienced analysts. The approach deserves further validation and testing for both testate amoebae and other groups of microfossils.
Highlights
Transfer functions are frequently applied to biostratigraphic indicators from sediments to quantify past changes in environmental variables
S. van Bellen et al / Palaeogeography, Palaeoclimatology, Palaeoecology 468 (2017) 173–183 based transfer functions may have three possible advantages: 1) they may offer superior performance if the functional trait assemblage of a sample is more strongly linked to an environmental variable than the species assemblage; 2) they may be more generalizable, allowing a transfer function to be applied to species not included in the training set based on functional traits which are included, and 3) they may be more robust to problems of taxonomic resolution and error, as traits may often be easier to determine than species
We hypothesized that transfer functions based on traits may result in more accurate reconstructions, because the relationship between traits and environmental variables is likely to be more direct than the relationship between taxa and environmental variables
Summary
Transfer functions are frequently applied to biostratigraphic indicators from sediments to quantify past changes in environmental variables. Used combinations of indicators and predicted variables include pollen-temperature/precipitation (Klemm et al, 2013), chironomids-temperature (Massaferro and Larocque-Tobler, 2013), foraminifera-sea level (Kemp et al, 2013) and testate amoebae-water water-table level (Amesbury et al, 2016; Lamarre et al, 2013). These transfer functions are based on the principle of uniformitarianism and assume that there is a direct relationship between the environmental variable to be reconstructed and the abundance of. We evaluated and compared the performance of transfer functions based on species and trait assemblages, using testate amoebae and peatland water-table reconstructions as a case study
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