Flowering synchrony as a trick to enhance species richness in dry meadows

Given the growing consensus on the positive effect of biodiversity on ecosystem functioning (Balvanera et al. 2006; Cardinale et al. 2012), species richness and loss are among the simplest and most used measures of habitats evaluation. Species diversity in a plant community is assumed to be determined by two sets of factors. The first refers to the “species pool”, i.e. the set of propagules able to reach a site. The second comprises local ecological interactions and select species from the pool that are able to coexist. In this ‘community filter’, both abiotic and biotic factors operate. Among biotic factors facilitation may increase the diversity of a community (Stachowicz, 2001). Such enhancement can be produced through facilitation via shared pollinators among co-flowering entomophilous species. We evaluated the role of flowering synchrony in determining species richness and coverage at the community level in dry meadows (Festuco-Brometea) (Habitat 6210). In particular we tested if 1. there is a non-random flowering pattern at the community level; 2. both the presence and percentage cover of different insect-pollinated species are affected by flowering synchrony. The study was carried out in the Euganei Hills district (NE Italy). 45 plots (2x2m) were randomly placed over dry meadows and data on species richness and percentage cover were collected. Flowering phenology of all entomophilous species was monitored every 10 days during the growing season (April, 1st to September, 30th 2013). Flowering was considered started when the first flower opened on an individual plant and terminated when individuals no longer possessed flowers with anthers (Dante et al., 2013). To estimate flowering time overlap at the community level a mean Co-flowering index (V score; Lepš, Šmilauer, 2003) was performed between all possible pairs of monitored species. The significance of flowering overlap pattern was tested using a null model (Gotelli, Graves, 1996). For each plot a Co-flowering index was than computed. Spearman’s rank correlation was used to test for a relationship between the V score and the number (and percentage cover) of insect-pollinated species per plot. Species were classified in six groups according to Müeller’s (1881) classification, which groups nectariferous flowers according to the depth of nectar display. Six classes were recognized as follows: a) pollen flowers, b) flowers with exposed nectar, c) flowers with partly hidden nectar, d) flowers with totally hidden nectar, e) Hymenoptera flowers and f) Lepidoptera flowers. Only rough groups of pollinators are assigned to the first four groups, which differ in length of proboscis, while smaller pollinator range characterizes classes e) and f). A non random flowering pattern has been observed at the community level among entomophilous species (pvalue<0.001). In particular, richness and percentage cover of Hymenoptera flowers turned out to be positive related to Coflowering index (p=0.001 and p=0.02 respectively), while no significant correlations were observed for the other groups of species. In conclusion, our results show that flowering synchrony may play an important role in controlling and enhancing Hymenoptera pollinated species richness in Euganean dry meadows.