Phylogenetic structure of understorey annual and perennial plant species reveals opposing responses to aridity in a Mediterranean biodiversity hotspot

Convergent evolution of the annual life history syndrome from perennial ancestors

“…In studies of species community assemblages in specific environments, it has been suggested that phylogenetic overdispersion of species (i.e., species are less related than expected by chance) is the result of independent convergent evolution, whereas constraints and/or conservation of functional traits through parallel mechanisms would lead to non-random clustering of annual species (Cavender-Bares et al, 2009). Recently, some studies of community assemblages in arid environments have taken phylogeny into account (Garcıá-Camacho et al, 2017;Massante et al, 2021). Massante et al (2021) studied species richness and relatedness across a climate gradient of the arid Mediterranean and found lower species richness in more arid regions for perennial, but not annual, species.…”

“…Recently, some studies of community assemblages in arid environments have taken phylogeny into account (Garcıá-Camacho et al, 2017;Massante et al, 2021). Massante et al (2021) studied species richness and relatedness across a climate gradient of the arid Mediterranean and found lower species richness in more arid regions for perennial, but not annual, species. Furthermore, they found that perennial species showed overdispersion across an aridity gradient in the Mediterranean, indicating independently converged traits, whereas annuals were phylogenetically clustered at different phylogenetic scales in 1 Exact numbers and phylogenetic distribution depend how exactly 'annuals' have been defined.…”

“…Part of this advantage comes from the fact that a successful annual seedbank depends on dry storage conditions and that annuals have an enhanced ability to outcompete already established perennials under drought conditions during germination and seedling growth ( Corbin and D'Antonio, 2004 ; Monroe et al., 2019 ). Annual species likely also become more competitive under seasonally stressful and high disturbance conditions – such as drought, heat, flooding, grazing, and erosion – which, unlike perennials that need to invest in persistence, annuals can escape as seed ( Whyte, 1977 ; Pettit et al., 1995 ; Tofts, 2004 ; Evans et al., 2005 ; Kadereit et al., 2006 ; Cruz-Mazo et al., 2009 ; Nunes et al., 2019 ; Massante et al., 2021 ). Although most studies indicate that annuals are frequent in areas with predictable drought, we are still in need of large empirical studies to test the generality of these results.…”

“…Although most studies indicate that annuals are frequent in areas with predictable drought, we are still in need of large empirical studies to test the generality of these results. Interestingly, high-latitude winters, which are among the most stressful seasonal environments for plants, do not appear to have selected for increased annuality ( Lindberg et al., 2020 ; Massante et al., 2021 ). One explanation for this is that lower growth rates at cold temperatures can limit a plant’s ability to complete its life cycle during the short growing season ( Körner and Larcher, 1988 ; Ogburn and Edwards, 2015 ).…”

“…Recently, some studies of community assemblages in arid environments have taken phylogeny into account ( García-Camacho et al., 2017 ; Massante et al., 2021 ). Massante et al. (2021) studied species richness and relatedness across a climate gradient of the arid Mediterranean and found lower species richness in more arid regions for perennial, but not annual, species.…”