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Contenuto archiviato il 2024-05-29

Phylogenetic analysis of spatial and temporal patterns of community biodiversity

Final Activity Report Summary - OxPhyloDiv (Phylogenetic analysis of spatial and temporal patterns of community biodiversity)

One of the oldest challenges in ecology is to understand the processes that underpin the composition of communities. It has been recently demonstrated that the diversity in the biological characteristics of species, called traits, and in their common history, namely phylogeny, should be considered to understand how species assemble in space, forming communities, and how these communities change with time. In ecology, these two aspects of the biological diversity, i.e. the biological traits and phylogeny, were often treated separately. For example, traits were used to understand the link between the occurrence of a species and environmental variables (environmental filtering), or other species present (limiting similarity). The phylogeny was used to place the analyses of diversity patterns into biogeographic contexts. Alternatively, research in evolutionary biology focussed on the connections between the trait values of the extant species and their phylogeny.

Feedbacks between ecology and evolutionary biology are now more and more present in biological science. They aim to explain community assemblages both in terms of the biological traits of the species and their phylogeny. Studies of real communities attempted to differentiate the factors associated with past history with recent factors related to ecological processes.

In that context, we developed a series of mathematical methodologies that aimed to describe, analyse and explain combined patterns in trait and phylogenetic diversities in space and time. To measure biological diversity, we used a mathematical function developed jointly in ecology, genetics and statistics, called the quadratic entropy. This index of diversity depended on the abundance of species in communities and on differences between species in terms of biological traits or phylogeny. We obtained new theorems on the mathematical properties of the quadratic entropy that demonstrated this index breaks with traditional ways of measuring biodiversity, such as simply counting the number of species. We also developed a new mathematical function, the mixed-variables coefficient of distance, which allowed for the calculation of distances between species on the basis of a wide range of biological traits, very different from a mathematical point of view. Using the quadratic entropy and the mixed-variables coefficient of distance we partitioned the diversity in biological traits along species’ phylogenies in order to identify random processes, e.g. neutral theories, from ecological processes which were associated with species biological traits, e.g. niche theories. Finally, we developed an apportionment of phylogenetic diversity into local (alpha), turnover (beta) and global (gamma) components either in space or recent time surveys. Each component was divided into time periods, which were evolutionary factors, and abundance distributions, i.e. ecological factors.

When applied to a 20-year survey of rockfish assemblages in Southern California Bight, these methodologies demonstrated that fishing pressures were changing the composition of fish communities both in terms of traits and phylogenies. The intense fishing, along with environmental changes such as warmer ocean water due to anthropogenic drivers, hampered upwelling of cool and nutrient-rich water caused by repeated El Niño events, affected six evolutionary deep lineages. The largest-bodied species were the most affected. The consequences of these findings were that fishing pressures were changing the composition of fish communities both in terms of traits and phylogenies. Changes in trait diversity could lead to deep modifications in the dynamics of populations regarding, for example, predator-prey interactions, mortality rates, probabilities of extinction and speciation, patterns of distribution and abundances.

Such an understanding of the factors that underlined community assembly was a prerequisite to expect predicting the future of biological diversity.