Image_1_Differential Effects of Climate Warming on the Nectar Secretion of Early- and Late-Flowering Mediterranean Plants.PDF

<p>Floral nectar is a vital resource for pollinators, thus having a very important role in ecosystem functioning. Ongoing climate warming could have a negative effect on nectar secretion, particularly in the Mediterranean, where a strong temperature rise is expected. In turn, decreased nectar secretion, together with shifts in flowering phenology can disrupt plant–pollinator interactions and consequently affect the entire ecosystem. Under fully controlled conditions, we tested how temperature influenced nectar secretion (through nectar volume, sugar concentration, sugar content, and number of flowers produced) in six Mediterranean plant species flowering from winter to summer (viz. Asphodelus ramosus, Ballota acetabulosa, Echium plantagineum, Lavandula stoechas, Rosmarinus officinalis, and Teucrium divaricatum). We compared the changes in nectar secretion under temperatures expected by the end of the century and estimated the effect of climate warming on nectar secretion of plants flowering in different seasons. We found a significant effect of temperature on nectar secretion, with a negative effect of very high temperatures in all species. Optimal temperatures for nectar secretion were similar to the mean temperatures in the recent past (1958–2001) during the respective flowering time of each species. Increasing temperatures, however, will affect differently the early-flowering (blooming in winter and early spring) and late-flowering species (blooming in late spring and early summer). Temperature rise expected by the end of the century will shift the average temperature beyond the optimal range for flower production and the sugar produced per plant in late-flowering species. Therefore, we expect a future decrease in nectar secretion of late-flowering species, which could reduce the amount of nectar resources available for their pollinators. Early-flowering plants will be less affected (optimal temperatures were not significantly different from the future projected temperatures), and may in some cases even benefit from rising temperatures. However, as many earlier studies have found that early-flowering species are more prone to shifts in phenology, the plant–pollinator interactions could instead become affected in a different manner. Consequently, climate warming will likely have a distinctive effect on both plant and pollinator populations and their interactions across different seasons.</p

The Floral Complexity Index (FCI) values distributed across the Greek rare and threatened plants’ phylogeny.

<p>Grey bars indicate the relative magnitude of the FCI (highest value: 3.25, lowest: 1.15). Red rectangles mark the “more threatened” (CR, EN or EX) taxa.</p

Weights of the floral variables used in the Floral Complexity Index. For details on the estimation of the variable level values see S1 Text.

<p>^aBased on a scale of 1–3 (for floral depth, symmetry, corolla segmentation and functional reproductive unit) or a scale of 1–5 (for floral shape). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138414#pone.0138414.s002" target="_blank">S1 Text</a>.</p><p>^bResulting from the floral variable weight (<i>w</i>) multiplied by the variable level’s value (<i>V</i>).</p><p>All terms are explained in the text.</p

Lessons from Red Data Books: Plant Vulnerability Increases with Floral Complexity

<div><p>The architectural complexity of flower structures (hereafter referred to as floral complexity) may be linked to pollination by specialized pollinators that can increase the probability of successful seed set. As plant—pollinator systems become fragile, a loss of such specialized pollinators could presumably result in an increased likelihood of pollination failure. This is an issue likely to be particularly evident in plants that are currently rare. Using a novel index describing floral complexity we explored whether this aspect of the structure of flowers could be used to predict vulnerability of plant species to extinction. To do this we defined plant vulnerability using the Red Data Book of Rare and Threatened Plants of Greece, a Mediterranean biodiversity hotspot. We also tested whether other intrinsic (e.g. life form, asexual reproduction) or extrinsic (e.g. habitat, altitude, range-restrictedness) factors could affect plant vulnerability. We found that plants with high floral complexity scores were significantly more likely to be vulnerable to extinction. Among all the floral complexity components only floral symmetry was found to have a significant effect, with radial-flower plants appearing to be less vulnerable. Life form was also a predictor of vulnerability, with woody perennial plants having significantly lower risk of extinction. Among the extrinsic factors, both habitat and maximum range were significantly associated with plant vulnerability (coastal plants and narrow-ranged plants are more likely to face higher risk). Although extrinsic and in particular anthropogenic factors determine plant extinction risk, intrinsic traits can indicate a plant’s proneness to vulnerability. This raises the potential threat of declining global pollinator diversity interacting with floral complexity to increase the vulnerability of individual plant species. There is potential scope for using plant—pollinator specializations to identify plant species particularly at risk and so target conservation efforts towards them.</p></div

Results of the best fitting (based on AIC) GLM showing the effects of the intrinsic and extrinsic variables on the Greek rare and threatened plants’ vulnerability.

<p>Results of the best fitting (based on AIC) GLM showing the effects of the intrinsic and extrinsic variables on the Greek rare and threatened plants’ vulnerability.</p

Extrinsic vulnerability factors of the Greek rare and threatened plants.

<p>The effects of the extrinsic variables on plant vulnerability as included in the best fitted logistic GLM based on the backward AIC selection process. (a) Mean maximal distance (±SE); (b) mean minimum altitude (±SE); and (c) habitat. The variation of the latter is presented in a spinogram. The width of the columns corresponds to the relative frequency of the “more threatened” and “less threatened” plants in the dataset; the height of the cells represents the relative frequency of the response variable in every type of habitat. Colored cells denote statistical significance of the respective level (**: ≤ 0.01, ***: ≤ 0.001).</p

GuildDryad

Degree and d' for each insect species in the study network

SummaryNetLevelDryad

Network-level characteristics for the 33 study network

StandardNetwDryad

Network-level characteristics for the standardized network

Data from "Disentangling the role of floral sensory stimuli to pollination networks"

<div><b>Supplementary Data 1:</b> The weighted plant-pollinator interactions network including 41 plant and 168 insect species, recorded in a Mediterranean scrubland (phrygana) in Lesvos Island, Greece.<br></div><div><b>Supplementary Data 2: </b>Inflorescence volatile compounds of the plant species studied.</div