The intimacy between sexual traits and Grime’s CSR strategies for orchids coexisting in semi-natural calcareous grassland at the Olive Lawn

Abstract

The diversity of orchid species in seminatural calcareous grassland is thought to depend on floral variability. However, differences in primary lifehistory strategy, or the overall suite of functional traits, could also affect coexistence. Both primary strategy (affecting day-to-day survival) and reproductive traits (representing periodic events) have been hypothesized to contribute to a general mechanism regulating the local persistence and relative abundance of species. We recorded species identity at 8,000 points at the centimetre scale along sixteen 5-m long transects at the Olive Lawn, a xeric sand calcareous grassland near Lecco, Italy. Transects allowed the relative abundance and spatial aggregation of Grime's competitor, stresstolerator, ruderal (CSR) strategies to be quantified. Orchid flowering and fruiting phenology was recorded alongside the phenology of graminoid growth. Seven orchid species were present and exhibited a spectrum of strategies spanning two extremes, (1) small earlyflowering ruderals (R/CR-selected), and (2) largerleaved competitors (C/CR) flowering later as dominant graminoids attained maximum height. These orchids, and other subordinate species in the community, exhibited random spatial distributions amongst dominant graminoids that exhibited a high degree of spatial aggregation and similar, but non-identical, stresstolerator (S) strategies. The reproductive phenology of meadow orchids is an intimate component of their CSR strategies, and appears to promote coexistence by allowing segregation between temporal niches and the exploitation of opportunities between clumps of dominant species. Only for closely related species with identical CSR strategies, such as Ophrys benacensis and Ophrys sphegodes, could specific floral differences alone explain coexistence.

A global method for calculating plant CSR ecological strategies applied across biomes world‐wide

“…For example, microsite differences and niche partitioning between contrasting CSR strategies have been invoked as a mechanism of coexistence and local biodiversity creation on Brazilian coastal Atlantic forest inselbergs (de Paula et al 2015). Similarly, xeric sand calcareous grasslands in Europe include a mixture of relatively abundant stress-tolerator graminoids and larger numbers of infrequent ruderal or competitive-ruderal herbs, and CSR strategies are thus markedly different between dominant and subordinate plants at the centimetre scale (Pierce et al 2014b). Future application of CSR analysis in further bio-geographical and ecological contexts world-wide will allow general conclusions with regard to how the equilibrium between dominant and subordinate species may change in response to environmental perturbation and with regard to the precise relationships between microsite factors and particular plant species.…”

Are endemic species necessarily ecological specialists? Functional variability and niche differentiation of two threatened Dianthus species in the montane steppes of northeastern Iran

“…For species coexisting within plant communities, quantification and comparison of CSR strategies provide a theoretical framework for understanding functional variability that can expand interpretation beyond the variability evident for single traits 4 . Although co-occurring plant species may exhibit conspicuous convergence in CSR strategies, some studies also demonstrate fine-scale CSR strategy divergence and niche differentiation that appear to underpin coexistence 10 . Indeed, when investigated over a wide range of plant communities, CSR strategy convergence (ecological specialization) and limited species richness are evident at extremes of productivity, with high richness associated with divergence in CSR strategies at intermediate productivities 11 .…”

Ontogenetic shifts in plant ecological strategies

“…As strategies determine the suites of traits functioning in concert to affect fitness, their quantification provides an overall metric of plant functioning in the same way that "net photosynthetic rate" represents the sum of single traits such as CO 2 uptake and respiration rates. Grime's system has proven useful to represent and compare functional strategies and community assembly across different ecological scales, from that of species (Pierce, Vagge, Brusa, & Cerabolini, 2014), populations (May, Warner, & Wingler, 2017), habitats (Negreiros, Le Stradic, Fernandes, & Rennó, 2014;Rosado & de Mattos, 2017), successional stages (Caccianiga, Luzzaro, Pierce, Ceriani, & Cerabolini, 2006) and biomes (Pierce et al, 2017). The most recent, globally-calibrated, CSR analysis method (Pierce et al, 2017) is supported experimentally (Li & Shipley, 2017).…”