Abstract
Summary The evolution of secondary (insular) woodiness and the rapid disparification of plant growth forms associated with island radiations show intriguing parallels between oceanic islands and tropical alpine sky islands. However, the evolutionary significance of these phenomena remains poorly understood and the focus of debate.We explore the evolutionary dynamics of species diversification and trait disparification across evolutionary radiations in contrasting island systems compared with their nonisland relatives. We estimate rates of species diversification, growth form evolution and phenotypic space saturation for the classical oceanic island plant radiations – the Hawaiian silverswords and Macaronesian Echium – and the well‐studied sky island radiations of Lupinus and Hypericum in the Andes.We show that secondary woodiness is associated with dispersal to islands and with accelerated rates of species diversification, accelerated disparification of plant growth forms and occupancy of greater phenotypic trait space for island clades than their nonisland relatives, on both oceanic and sky islands.We conclude that secondary woodiness is a prerequisite that could act as a key innovation, manifest as the potential to occupy greater trait space, for plant radiations on island systems in general, further emphasizing the importance of combinations of clade‐specific traits and ecological opportunities in driving adaptive radiations.
Highlights
Evolutionary radiations – episodes of accelerated species diversification and/or trait disparification – are ubiquitous across organismal groups in diverse geographical and ecological settings (Davis et al, 2005; Linder, 2008; Glor, 2010; Hughes et al, 2015; Cardillo et al, 2017; Hutter et al, 2017)
The evolution of secondary woodiness and the rapid disparification of plant growth forms associated with island radiations show intriguing parallels between oceanic islands and tropical alpine sky islands
We explore the evolutionary dynamics of species diversification and trait disparification across evolutionary radiations in contrasting island systems compared with their nonisland relatives
Summary
Evolutionary radiations – episodes of accelerated species diversification and/or trait disparification – are ubiquitous across organismal groups in diverse geographical and ecological settings (Davis et al, 2005; Linder, 2008; Glor, 2010; Hughes et al, 2015; Cardillo et al, 2017; Hutter et al, 2017). All of these settings potentially present ecological opportunities, the new adaptive zones of Simpson (1953), long thought to be the main factor driving radiations (Williams, 1969; Carlquist, 1974; PincheiraDonoso et al, 2015; Stroud & Losos, 2016). In this study we attempt to gain new insights into the importance of ecological opportunity in radiations by revisiting the striking parallels between plant radiations on oceanic islands and tropical alpine montane ‘sky islands’ (Smith & Young, 1987; Warshall, 1995; Gehrke & Linder, 2014), parallels which have intrigued evolutionary biologists ever since Carlquist’s (1965, 1974) classical studies of island biology
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