Facilitation beyond species richness

Abstract

Facilitation studies have previously focused on the effects of plant–plant interactions on species richness and, more recently, on functional traits or phylogenetic aspects. Little is known, however, about the simultaneous effects that facilitation have on overall biodiversity, jointly considering taxonomic, functional and phylogenetic diversity. In this study, we investigated shrub facilitation on herb communities in a Mediterranean grassland over a 9‐year period (2007–2015), each year representing different water availability conditions. Taxonomic, functional and phylogenetic diversity indices were estimated using generalised Hill numbers within the integrated framework of attribute diversity. We used generalised linear mixed models to analyse the effect of shrub cover on the different diversity indices along a water availability gradient. Shrub cover had a positive effect on all attribute diversity indices, yet greater for abundant species. Shrubs also favoured survival of certain species (26.5% of total species), but above all they affected relative abundances of common species, filtering growth of dominant species (e.g., Poa bulbosa) and promoting evenness. Diversity indices accounting only for abundant (i.e., high coverage) species showed the strongest facilitation effects that peaked at mid‐range water availability conditions. Synthesis. Our results suggest that shrubs are key in the maintenance of all three dimensions of biodiversity in the Mediterranean grasslands, promoting more even communities, and to a lower extent, also species richness. We show that shrub facilitation on taxonomic, functional and phylogenetic diversity of herbaceous communities is maximum for abundant species at mid‐range values of water availability, in accordance with the humped‐back model. This study illustrates the need to evaluate different biodiversity dimensions from an integrated perspective, such as attribute diversity, to disentangle the role of facilitation in community assembly.

Plant–plant facilitation increases with reduced phylogenetic relatedness along an elevation gradient

“…Our results highlight the inescapable relationship between the ecological and evolutionary factors determining the frequency of facilitating interactions (Verdú and Valiente‐Banuet 2011). There is consensus about the importance of facilitation in shaping different facets of biodiversity, including taxonomic, functional and phylogenetic diversity (Hacker and Gaines 1997, Cavieres and Badano 2009, Soliveres et al 2012b, Navarro‐Cano et al 2016, Vega‐Álvarez et al 2019). Understanding how these components are altered along elevation gradients may be determinant to conserve vulnerable and threatened communities facing new climatic scenarios, such as those located in Mediterranean ecosystems (Duarte et al 2019).…”

“…Competition and facilitation are ecological interactions of opposite sign that mainly modulate the structure of plant communities (Bertness and Callaway 1994, Callaway 1995, Lortie et al 2004). While competition has traditionally been the most studied interaction, in the last two decades facilitation is receiving increasing attention, with theoretical models and experiments demonstrating its importance to plant diversity in terms of functional traits diversity (Spasojevic and Suding 2012, Schöb et al 2013, Madrigal‐González et al 2020), taxonomic richness (Cavieres et al 2002a, 2014, Cavieres and Badano 2009, Sklenář 2009) as well as phylogenetic diversity (Bruno et al 2003, Valiente‐Banuet and Verdú 2007, Butterfield et al 2013, Pistón et al 2015, Vega‐Álvarez et al 2019). Facilitation, by assembling phylogenetically and functional diverse communities, ultimately promotes diverse ecosystem functions (Navarro‐Cano et al 2014, 2016).…”

Ecotone formation through ecological niche construction: the role of biodiversity and species interactions

“…In this case, ecosystem engineers indirectly facilitate other species through environmental modification. Facilitation has been shown to occur, particularly under harsh environmental conditions, such as in arid ecosystems (Soliveres and Maestre, 2014;Vega-Álvarez et al, 2018;Armas and Pugnaire, 2005) or in cold environments (Choler et al, 2001;Callaway et al, 2002). When an engineer facilitates another species, it can be considered as a "nurse species" (Niering et al, 1963) that modifies the environment and allows the growth of species that would not have the ability to grow otherwise.…”

Taxonomic, Phylogenetic, and Functional Diversity of Ferns at Three Differently Disturbed Sites in Longnan County, China

“…(4) Taxonomic, phylogenetic, and functional diversity through Hill numbers (q) are unified standardization methods to quantify the diversity of different communities [73][74][75][76][77][78]. The equivalent diversity indices linked to Hill numbers of order q = 0, 1, 2 are listed in Table 2.…”

“…Accordingly, different diversity measurements do not always show consistent patterns with each other [12,33,70,71]. The reinterpretation of diversity around the Hill numbers [72] is a powerful tool for unifying the comparisons between habitats and scales [73][74][75][76][77][78]. Therefore, it is better to select multiple diversity elements together to evaluate overall fern biodiversity [12,71,79,80].…”