The herpetofauna of the Eastern Afromontane: evolutionary history, biogeography and conservation

Menegon, Michele (2015) The herpetofauna of the Eastern Afromontane: evolutionary history, biogeography and conservation. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

There is consensus that we are in the midst of the sixth great mass extinction (Barnosky et al., 2011), with a current rate of extinction around 1,000 times the background rate. Current extinction risk has, however, been formally evaluated for less than 5% of the world's described species, but information on the proportion of total species assessed and threatened offers a clear indication of the current trend of biodiversity loss (Baillie et al., 2004). The situation is particularly critical for the class Amphibia, with nearly one-third (32%) of the world’s amphibian species listed as threatened (IUCN, 2014). The Eastern Afromontane region is one of the most diverse areas on the Earth. A large proportion of its biodiversity and underlying evolutionary history is concentrated in small forest fragments on mountains, where both ancient lineages and more recently speciated taxa co-occur and a large proportion of the currently known taxa is formally undescribed. Compared to other tropical areas of the planet, East Africa has been characterized by pronounced climatic and geological turbulence, which, has led to a general faunal impoverishment. Despite this, the combination of the age of the forest fragments, their geographic and ecological isolation and the habitat persistence, makes the vast complex of forest fragments an ancient and stable archipelago of individually evolving sites, especially for the less vagile organisms. Research that assesses the actual patterns of diversity of the region and the definition of the most appropriate conservation strategies that can be effective in a world changing at unprecedented rate is crucial and timely. The aims of this PhD were to investigate historical and current biogeography of the herpetofauna of the Eastern Afromontane, to describe patterns of species richness and endemism across the region and to identify some of the main environmental drivers that have played a significant role in shaping the current scenario. Focused analyses on forest vipers (Atheris) and on dwarf forest bufonids (Nectophrynoides) were carried out in order to understand elements of evolutionary history of the herpetofauna across the region and to prioritize sites for conservation. Chapter 2 focuses on the past and present of herpetological discoveries in the Eastern Afromontane region and identified priority areas where future research could lead to significant herpetofaunal discoveries. I discuss how survey effort, different taxonomic approaches and the use of biodiversity indexes, have important implications for our understanding of the importance of individual sites since both species delimitation methods and the use of indices capture different aspects of biological diversity. The chapter includes 5 appendixes of which three are published papers – two on the description of species new to science and one is a herpetological inventory of a previously overlooked submontane forest in Tanzania. In the fourth appendix I identify priority sites for further inventories (e.g Gura Ferda in Ethiopia, Imatong Mts. in South Sudan, Itombwe and Misotshi-Kabogo ranges in DRC and Mt. Chiperone in Mozambique). The fifth appendix introduces a work-in-progress to publish an e-book on the region’s amphibians and reptiles, which will aid inventory and ecological work across the region. Chapter 3 investigates patterns of species richness and endemism of mountainrestricted amphibians across the Eastern Afromontane region by mapping the distributions of 3,488 geo-referenced records of 274 taxa. Results show a strong geographical congruence between species richness and endemism and how the Albertine Rift and the Eastern Arc mountains appear to have accumulated high amphibian diversity in different ways, with the latter having exceptional diversity despite their small sizes. Finally, results failed to support the idea that the Eastern Afromontane is a discrete zoogeographic region. Chapter 4 focuses on the phylogenetic relationships and historical biogeography of the East African vipers in the genus Atheris and explores temporal and spatial relationships between the different species across Africa. Results showed congruent temporal patterns that link diversification to major tectonic and aridification events within East Africa over the last 15 million years. This points to a diversification pattern of the East African species consistent with a scenario of a delayed direct West-East colonization of the Eastern Arc Mountains, influenced by the formation of the western rift. Possible cryptic taxa in the Atheris genus are also identified. Chapter 5 examined radiations and evolution of forest-associated toad in the genus Nectophyrnoides, through phylogenetic reconstruction, finding that the Eastern Arc Mountains are characterized by the presence of both very ancient paleoendemic species, along with more recent radiations. I then identify key conservation sites using different importance metrics. Congruence between richness of Nectophrynoides and amphibians as a whole was strongly positive, suggesting that this now better-known and conspicuous group could act as a proxy for assessing relative importance of sites for amphibians generally. The high spatial and elevational turnover of Nectophrynoides species indicates the importance of conserving forest at all altitudes and across the entire fragments in order to address the differences that exist between sites at different altitudes, within the same fragment, and at similar altitudes in different fragments on the same mountain block. The results of this thesis highlight the biological importance of the Eastern Afromontane as a key area for the study of the evolution of life and biodiversity conservation, both at African and global levels. It provides original, updated knowledge on species occurrence and biogeographic pattern at regional level. Results also provide and interpretation of the signature left by geographic and climatic events in the pattern of species diversification, clarifying the importance of specific historical events in shaping what we see across the Eastern Afromontane today. The recent surge in biodiversity studies, including the remarkable increase in species description, represents a significant advance in geographic sampling and this, coupled with the effectiveness of new methods for delimiting species, is helping in the assessment of the actual biological value of areas. Furthermore the increasing availability of genetic information on taxa should promote the use of phylogenetic indexes in order to move from a conservation approach solely based on species richness to a more inclusive one, that can inform conservation on the underlying functional diversity and evolutionary potential both at species and site level. The Eastern Afromontane represents the most important area of mainland Africa for conservation of amphibians and reptiles and it offers an extraordinary conservation challenge. Because of the extreme species turnover across mountain ranges and individual forest fragments, a small number of protected areas, however well managed and resourced, will never fully capture the biodiversity of the region. Thus, a specific strategy aimed at identification and implementation of conservation initiatives at forest fragment scale must be considered. Moreover, as a reaction to a lucid assessment of global trends in population growth and associated habitat and species loss and increasing resource demands, there is an urgent need to try new conservation approaches. In the context of a more holistic and radical approach to biodiversity conservation, an active management of the surrounding matrix of the protected areas should be taken into consideration, with the aim of maintaining connectivity between areas of less disturbed habitat and to minimize damage to biodiversity, for unprotected lands, where resource extraction, agriculture, and other productive activities occur.