It is a particularly important step in ecosystems modelling as it identifies the basic structures that become the inputs of the model, thus making the outputs more interpretable ( Fulton, Smith & Johnson, 2003). There are two primary uses of functional groups: to simplify the numerous species contained in an ecosystem for modelling and to assess the diversity of an ecosystem. This provides a basis from which food web analysis and relationships with other components of the ecosystem can be derived ( Gravel, Albouy & Thuiller, 2016). Defining functional groups “allows a context-specific simplification of the real world.” (pg. In other words, a functional group comprises species with similar life history that respond to environmental fluctuations in a similar way within a given habitat. The groups are defined by the niche requirements of the species, rather than by their taxonomy ( Root, 1967), or their economic importance. One such simplification is the construction of functional species groups, which involves creating distinct sets of species according to a selection of their functional traits ( Tilman, 2001). Marine ecosystems are large and complex, requiring simplification of their components in order to be studied and understood. ![]() We visualise the clustering in two dimensions and the stability of clusters is assessed through bootstrapping. This revealed the choice of number of clusters, distance matrix and linkage method greatly affected the overall within- and between- cluster variability. The resulting clusters are evaluated using internal metrics developed specifically for nominal clustering. Within this clustering paradigm there are a number of distance matrices and linkage methods available, several combinations of which we test. ![]() Hierarchical clustering is utilised to search for underlying data structure in the data that may represent functional groups. Some data were missing, so the benefit of imputing data was assessed using four approaches on data with known missing values. Data collected from photographs and published literature were predominantly nominal, and a small number of continuous traits were discretized. ![]() To do so, we produced a species by trait matrix of 22 traits from 116 fish species from Tasman Bay and Golden Bay, New Zealand.
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