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Macroevolution & Biogeography of flowering plants

Why are some regions species poor and others species rich — despite similar climate?

Zizka et al., Ecography 41(2), Wiley

The unequal distribution of biodiversity has puzzled humans for centuries. Despite similar climate, geographic regions may differ considerably in the number of occurring plant species and their functional diversity. For instance, the South American tropics harbor more than three times as many plant species as the African tropics! The large-scale drivers of these geographic hot- and cold-spots remain unclear, partly because the geographic distribution of many tropical plant species is incompletely documented.  We combine innovative analyses of existing “big data” with targeted data collection in the field to describe large-scale patterns of taxonomic and functional plant diversity, in particular in South America. For instance we have documented distribution patterns of rare species in Amazonia (Zizka et al. 2018) compiled a comprehensive dataset on the distribution of pineapple relatives (Bromeliaceae; Zizka et al. 2020), and identified plant species with a conspicuous disjunct distribution in the open biomes of South America (Colli-Silva et al. 2021).

Why are some evolutionary lineages species poor and others species rich - despite similar age?

Alexander Zizka

Some evolutionary lineages comprise thousands of species, others remain species poor. For instance, the palm family comprises more than 2000 species are a dominating element of tropical rainforests worldwide, whereas their putative evolutionary sister group, the Dasypogonaceae, comprise only few dozen species endemic to Australia. We strive to understand the evolutionary mechanisms underlying these difference in diversification, particularly how the evolution of specific morphologic or physiologic characters relate to their evolutionary success. In particular we are interested in the role of growth form, and the origin of the biota of open biomes (savannas, grasslands, and woodlands). Recently results from our lab suggest, that the connectivity of different biomes (Antonelli, Zizka et al. 2018) and especially transitions of evolutionary lineages between wet and dry biomes (Zizka et al. 2020) may be central to the hyperdiversity of South America. In this context, we investigate the role of plant growth form, in particular the repeated re-evolution of wood formation in herbaceous lineages—phylogenetically derived woodiness—afunctional trait potentially affecting diversification and facilitating such biome transitions. In collaboration with researchers at the Naturalis biodiversity center Leiden, we try to synthesize the adaptive role of phylogenetically derived woodiness, especially on oceanic islands (Zizka et al. 2022).