Sonkoly et al. (2016) Journal of Ecology

Sonkoly J., E. Vojtkó A., Tökölyi J., Török P., Sramkó G., Illyés Z., Molnár V. A. (2016): Higher seed number compensates for lower fruit-set in deceptive orchids. – Journal of Ecology DOI 10.1111/1365-2745.12511


Abstract
1. Floral deception is widespread in orchids, with more than one-third of the species being pollinated this way. The evolutionary success of deceptive orchids is puzzling, as species employing this strategy are thought to have low reproductive success (less flowers yielding fruits) because of low pollination rates. However, direct measurements of total seed production in orchids – which is a better measure of reproductive success – are scarce due to the extremely small size of their seeds.
 

2. Here, we quantified seed numbers in 1015 fruits belonging to 48 orchid species from the Pannonian ecoregion (central Europe) and obtained fruit set and thousand-seed weight data for these species from the literature. We used phylogenetic comparative methods to test the hypothesis that deceptive species should compensate for their lower fruit set by having either more flowers, larger seeds or more seeds in a fruit.
 

3. Similarly to previous studies, we found that deceptive orchids have substantially lower fruits-set than nectar-rewarding ones. Also, we found that deceptive species have more seeds in a fruit but not more flowers or larger seeds compared to nectar-rewarding ones. Based on our results, deceptive species compensate for their lower fruit set by having higher seed numbers per fruit. As a consequence, their seed numbers per shoot do not differ from that of nectar-rewarding ones.

4. Together with other benefits of deceptive pollination (e.g. lower energy expenditure due to the lack of nectar production and higher genetic variability due to decreased probability of geitonogamous pollination), our results can explain why deceptive strategies are so widespread in the orchid family.

5. Synthesis. Our results indicate that deceptive orchids can compensate for their lower fruit set by having more (but not larger) seeds in a fruit than rewarding species. These findings highlight possible ways in which plants can increase their reproductive success in face of pollinator limitation. We emphasize that fruit set in itself is an inappropriate measure of the reproductive success of orchids – the total number of seeds per shoot is a much better approximation.


Keywords
deception, nectar reward, Orchidaceae, phylogenetic comparative methods, pollination, reproductive ecology, reproductive success, seed mass, seed number, thousand-seed weight

Kelemen et al. (2016) Applied Vegetation Science

Kelemen, A., Valkó, O., Kröel-Dulay, Gy., Deák, B., Török, P., Tóth, K., Miglécz, T., Tóthmérész, B. (2016): The invasion of common milkweed (Asclepias syriaca L.) in sandy old-fields – Is it a threat to the native flora? Applied Vegetation Science, doi: 10.1111/avsc.12225


Abstract
Questions
Common milkweed (Asclepias syriaca L.) is an invasive ‘super species’ that has invaded extensive areas in Europe, forming novel ecosystems. One study has reported neutral effects of common milkweed on the native flora of sand dune grasslands in Hungary after the removal of invasive pine plantation. However, the effects of common milkweed on native flora more generally are unknown. Focusing on the potential effect of milkweed, we tested the following hypotheses: (1) the cover of native grassland species decreases with increasing cover of common milkweed; and (2) native species with low specific leaf area (SLA), height, seed mass and clonal spreading ability (i.e. low competitive ability) are more likely suppressed by milkweed compared with natives with high competitive ability.

Location
Late successional sandy old-fields invaded by milkweed in the Great Hungarian Plain (Kiskunság, central Hungary).

Methods
We recorded the cover of vascular plants in seven old-fields; in each old-field we sampled 12 plots including plots with different milkweed cover and control plots without milkweed. We used linear mixed effect models for exploring the effects of milkweed on the species richness and cover of native grassland species. To identify the common traits of the most affected native species, we used trait-based analyses; we studied leaf–height–seed traits and clonal spreading ability.

Results
We detected no effect of common milkweed on total species richness, but it had a negative effect on the cover of grassland species. The negative effect of common milkweed was most pronounced on the cover of species with low SLA, low seed mass and low clonal spreading ability.

Conclusions
Our results suggest that native, late successional sandy grasslands invaded by common milkweed form undesirable novel ecosystems because of significant negative impacts on the cover of native grassland species, especially those species with low competitive ability. For these species, management of milkweed might be needed to ensure their persistence in sandy grasslands in this landscape.

Keywords
Clonal spreading, Competition, Functional traits, Novel ecosystem, Old-field, Plant invasion, Sandy vegetation, Seed mass, Specific leaf area