The variety of life forms within a given species, ecosystem, biome or planet is
known as biodiversity. Biodiversity can also be referred as species diversity and species richness. Understanding the drivers of biodiversity requires an
understanding of intertwined biotic and abiotic factors, including climate
patterns over the earth, primary productivity processes, e.g. photosynthetic
pathways which change with climate and latitude; latitude, geology, soil
science, ecology and behavioural science.
Diversity of living organisms is not evenly distributed; instead it differs
significantly across the globe as well as within regions. The aim of my study is to try to understand the diversity patterns of aquatic plants, using both information derived from previous studies and by collecting new data across the globe, allowing me to examine the underlying mechanisms driving biodiversity at regional and local scales. Both geographical location and local environmental factors were found to contribute to variation in macrophyte assemblage and alpha diversity (i.e. number of species in a locality), with important roles being played by local biotic interactions and abiotic environmental factors.
Overall aquatic plants, or macrophytes, play a significant role in the ecology of large numbers of freshwater ecosystems worldwide. For the purpose of my study only calcareous steams, located in both temperate and tropical/subtropical regions were included. Such streams are common in catchments throughout the world because approximately one fifth of the earth’s surface is underlain by carbonate-containing rock.
Overall my findings in Chapter 3 provide evidence that there is a high variation in macrophyte assemblages of calcareous rivers across the different countries included in my study, broadly agreeing with information from the literature. I found two large groups based on species assemblages across the different countries included, i.e. a subtropical/tropical and a temperate group. As demonstrated in different parts of Chapter 4, it is possible to identify different 4 diversity responses of macrophyte functional groups to environmental conditions, at local scale, in hardwater rivers. Width and flow were found to be significantly affecting the distribution patterns of diversity of free-floating and floating-leaved rooted species, whereas diversity of marginal species was significantly related to alkalinity and width, and floating-leaved rooted diversity was significantly related to alkalinity. Last but not least submerged species were related to shading. Chapter 5 shows that variation in richness and community structure for hardwater river macrophytes can be partly explained by environmental variation relative to spatial processes in the British Isles (temperate scenario) and in Zambia (tropical scenario). Among the environmental variables, climatic ones explained a great part of species richness and composition distribution for the British Isles. Conversely in Zambia spatial processes made the greatest contribution to variation in hardwater river macrophyte species richness and community structure. Moreover Chapter 6 illustrates how macrophyte species richness, measured as alpha-diversity in calcareous rivers, was at best only very weakly attributed to latitudinal gradient. This is most likely due to the effect of other physical, chemical and biotic variables overriding broader-scale influences on species richness, at more local scales
