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Global dynamics of mountain diversification and persistence

Periodic Reporting for period 1 - GAP (Global dynamics of mountain diversification and persistence)

Reporting period: 2019-09-01 to 2021-08-31

The uneven distribution of species diversity across the earth’s surface is a widely appreciated pattern among well-studied animal and plant groups. Yet despite almost two centuries of scientific investigation, limited progress has been made in answering why the number of species found in different global localities varies so much? Among vertebrate groups, including birds, tropical mountain regions represent the global hotspots of species diversity. These areas support a disproportionately large number of species with small geographic ranges that are completely restricted to montane areas. The failure of biologists to explain geographic differences in the distribution of global species diversity can be viewed as a direct consequence of our poor understanding about the evolutionary processes that have generated the high number of species found in tropical mountain ranges. In light of the worldwide decline in biodiversity and natural areas, it is imperative to gain a better understanding of the processes leading to the formation and maintenance of the planets most diverse systems; tropical mountain ranges. Therefore, using the globally distributed songbirds (2/3 of all living birds) as my study system, the main aims of my project were as follows:

(1) Determine the differences in the rates of species formation, and the evolution of their physical characters, comparing montane and lowland areas of the world.

(2) Test the relative importance of mountain systems in generating global species diversity patterns.

(3) Test whether particular mountain regions or elevational zones maintain species that are overly threatened with extinction.
The work to date has mainly involved data generation, collation and preliminary analyses. Specifically, I have downloaded extensive amounts of mitochondrial and nuclear DNA sequence data from the Genbank public repository. These sequences represent several loci, which considered in combination, have been downloaded for the majority of passerine species (~80%). This data has been quality checked and aligned, before preliminary phylogenetic analyses were conducted for several clades that currently lack a well-sampled/supported molecular phylogeny. For clades with high quality publically available phylogenies at the species-level, these have been downloaded and collated. In addition, through consultation with research publications and expert field guides/text books, I have generated a complete passerine species-level data set of montane classification, in terms of whether species are distributed within lowlands, highlands or montane cloud forest. I have further classified species presence in temperate, tropical and insular areas. Both the phylogenetic and montane classifications have been combined with a global dataset of range polygon maps. I have performed a number of preliminary analyses on these combined datasets, and some more specific analyses that have focused on the avifauna of New Guinea. In general the preliminary results seem to support some of the initial hypotheses. Lineages that are currently maintained in mid-elevation cloud forest zones within the topics have on average lower diversification rates compared to species found in other areas. These results are consistent with the idea that areas of cloud forest support species that represent a disproportionately large amount of passerine phylogenetic diversity. In general, diversification rates of tropical species are greater than those currently residing in temperate areas, with particularly high rates noted among taxa that are distributed on islands, or in temperate highlands.

These results remain to be confirmed with more comprehensive complete phylogenetic data. Despite the early termination of the grant, I aim to continue with the research proposed and upon confirming the results publish the findings at a later date, crediting this MSCA-IF for it support to me in achieving this.
The project aims to take large strides towards answering one of the fundamental, but unresolved issues in the biological sciences; why does the distribution of species diversity vary so much across the earth’s surface? Given that this question has remained unanswered since it first came into focus almost 200 years ago, the output of this work could be a significant step forward for the general scientific community. Furthermore, in light of the current crisis with regards to the loss of global biodiversity, the findings could have a broader societal impact towards future conservation efforts and human well-being. Only once the mechanisms that underlie current biodiversity patterns are well understood, can effective conservation actions be taken to maintain this into the future. With respect to going beyond the current state-of-the-art, the results (once confirmed on a complete species-level phylogeny) will show how variation in lineage diversification, phylogenetic diversity and functional diversity change with latitude and elevation. Specifically, these results can illustrate the differential impact that areas of montane cloud forest have on diversification, maintenance, and the accumulation of co-occurring species. This project ultimately aims to demonstrate how these processes contribute to the large scale biodiversity gradients observed in nature, and will be of great use to conservation biologists and planners in terms of where to most optimally focus their efforts into the future.