Diversification patterns of Solanum L. (Solanaceae), plant macroecology and responses to land-use change

Abstract

Current patterns of biodiversity reflect, to a certain degree, the legacy effects of species adaptations to past environmental and geological settings. A more in-depth understanding of this history and the traits that shape it, therefore, will help us to improve our predictions of how species will respond to current environmental change. In this thesis, I apply different analytical approaches to a range of case studies at a variety of taxonomic and geographic scales to test the importance of this fundamental hypothesis. To examine the consequences of evolutionary and biogeographic history on the evolution of global biodiversity, in Chapter 2, I focus on the hyperdiverse plant genus Solanum (ca. 1300 species). This genus is an ideal case study since it combines a complete high-level phylogeny with global species distribution data, and covers an ecological spectrum from endemics to weeds. Chapter 2 shows that the vast diversity of Solanum is the result of at least two radiations. The majority of the lineages distributed in the Old World represent the most significant recent radiation, diversifying nearly twice as rapidly as any other group of solanums. This chapter also provides a brief comparison of the current approaches for modelling multi-rate diversification. In Chapter 3, I explore how the evolutionary legacy of colonisation, dispersal and climatic history have affected patterns of diversity in the genus. In this chapter, I show how successful colonisation of new areas and environmental changes can — but does not always — drive explosive diversification. In Chapter 3, I show how arid-adapted lineages within Solanum have benefited from widespread habitat drying over the last few million years. This successful expansion reveals the potential evolutionary capacity of this group to expand and colonise currently disturbed and open areas, which is supported by the spread of some species considered as weeds such as S. elaeagnifolium, S. torvum, S. nigrum. In Chapter 4, therefore, I undertake a global analysis to assess whether the climatic preferences that have shaped the macroevolution of Solanum are now also shaping plant macroecology worldwide. For this analysis, I broaden my taxonomic scope to consider all plants, analysing an extensive global database that I helped to compile on how terrestrial assemblages respond to land use change, using a simple and very coarse classification of land use. In this chapter, I demonstrate that species adapted to mesic conditions are highly sensitive to habitat conversion, compared with widespread arid and warmer-adapted species. These results show how land-use and climate change may favour similar species, thus potentially increasing the rate of homogenisation caused in the Anthropocene. As shown in Chapter 4 species’ responses to current environmental changes vary widely, depending on their ecological traits and climatic adaptations. This heterogeneity of responses could drive significant rearrangements in the composition of ecosystems, especially in the tropics where most of the species with narrow geographic and climatic ranges are found. In chapter 5, therefore, I quantify the impacts of land-use change on the composition of tropical assemblages using Colombia as a case study. In this chapter, I statistically analyse plant and animal data from 285 sites in Colombia to model how terrestrial assemblages are responding to land use change, using a much more finely resolved land-use classification than that used in Chapter 4. I combine these models with four projections of land use to investigate how diversity is expected to change under future scenarios associated with different climate change policies. Here I demonstrate that land-use change has driven an increasing change in the composition of the ecological assemblages in Colombia and that depending on the policies implemented in the future, this negative effect could continue, risking the quality of ecosystems unless the impacts are mitigated.