Biodiversity in the Anthropocene : quantifying assemblage level change
Abstract
Humans are altering ecosystems at alarming rates, but we do not fully know how
anthropogenic pressures are affecting local biodiversity. This knowledge gap poses problems
for understanding ecological systems and for undertaking effective conservation initiatives.
The aim of this thesis was to increase our understanding of local scale biodiversity change by
focusing on assemblages, which are groups of species from the same taxonomic group that
live in the same place. I focused on assemblage size, structure and species composition, with
the end-goal of making informed suggestions on how to monitor change effectively. First, I
asked whether sampling approach was highly influential when estimating species richness
and composition of Trinidadian freshwater fish assemblages. I compared assemblage
composition of two very different data collections: a systematic survey endeavour and the
historical museum records of The University of West Indies. Both datasets provided
comparable estimates of species richness, and they both contained mostly the same species.
Where they did differ in species lists, they did so among the locally uncommon or specialist
species. Next, I asked how closely changes in assemblage size measured in the currencies of
numerical abundance and biomass relate. My analysis showed that neither assemblage size
quantified in terms of numerical abundance, nor in terms of biomass, is systematically
changing across systems, but that change in one currency usually predicted change in the
other currency. Thirdly, I asked whether there is evidence for other directional changes
across assemblages. There was no evidence of changes in the dominance structure or
dominant species body size. There was, however, evidence from increasing numbers of rare
species entering assemblages and driving up local species richness, as well as a suggestion of
increased turnover among dominant species. Local assemblages therefore are displaying
measurable change, but not all metrics capture these changes.
Type
Thesis, PhD Doctor of Philosophy
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