Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands

Abstract

Aim Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory. Location Canary Islands, Spain. Major taxa studied Spermatophytes. Time period Present day. Methods We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non‐endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non‐endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients. Results Trait space of endemic and non‐endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non‐endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups. Main conclusions We found that endemic and non‐endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.

Links to rare climates do not translate into distinct traits for island endemics

“…We would expect species with distinct traits to occupy the peripheries of trait space but our results show considerable overlap of the species groups. This may reflect specialisation and niche packing (Hanz et al, 2022), particularly considering that endemics occupy a wide range of climate space overall (Figure 3). Therefore, it is possible that endemics are experiencing selection without it driving them into novel areas of trait space.…”

“…Thus, a number of distinct characteristics, often referred to as island syndromes (Burns, 2019), are typical for island species-a wellknown example being the evolution of secondary woodiness in plants (Lens et al, 2013;Zizka et al, 2022). Given the unique circumstances under which oceanic island biotas are shaped and the distinctive qualities of island endemic species, we might expect to see distinct combinations of functional traits (Hanz et al, 2022;Keppel et al, 2018;Ottaviani et al, 2020;Veron et al, 2021). On the other hand, speciation on islands may not always be driven by strong adaptation.…”

Are plant communities on the Canary Islands resistant to plant invasion?

“…Finally, in a recent analysis that contrasts plant traits of six native and six non‐native plants along an elevational gradient on Tenerife, Kuhn et al (2021) show that the trait space occupied by the six non‐native plants only covers a subset of and is fully nested within the trait space occupied by the six native plants, a fact that would support this hypothesis, extending the list of vaccine species to several more not here preliminary considered, such as Forsskaolea angustifolia or Fagonia cretica . However, Hanz et al (2022) using data from ca. 45% of the Canarian flora argues that invasive species can strongly increase the trait space occupied, highlighting that plant strategies of native and non‐natives through the lens of functional traits provide a distinct and important opportunity of future research (see also Schrader et al, 2021).…”

Projecting the futures of plant traits across habitats in Central Europe

“…However, trait differences between natives and non-natives have mostly been assessed independently of the environmental contexts (e.g., Divíšek et al, 2018; Mathakutha et al, 2019; van Kleunen et al, 2010). In contrast, studies that compare how native and non-native traits shift along environmental gradients and therefore allow extrapolating trait differences into different environmental conditions remain scarce (Gross et al 2013; Hanz et al, 2022; Henn et al, 2019; Knapp & Kühn, 2012; Sandel & Low, 2019; Westerband et al, 2020). This highlights a mismatch between the trait-based research on native species, which strongly focuses on environmental filtering and adaptation, and that on non-native species, which often insufficiently considers environmental gradients and thus provides only a limited ability to identify the circumstances under which non-natives functionally diverge from or converge with natives.…”