Special Issue "Plant-Pollinator Interactions in Mediterranean-Type Ecosystems"

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Ecology".

Deadline for manuscript submissions: closed (30 September 2020).

Special Issue Editor

Dr. Tamar Keasar
E-Mail Website
Guest Editor
Department of Biology, University of Haifa - Oranim, 36006 Tivon, Israel
Interests: pollination ecology; host–parasitoid interactions; bees; parasitoid wasps; agroecology
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Mediterranean-climate ecosystems exist in five different parts of the world: the Mediterranean Basin, Southwest Australia, California, Central Chile, and South Africa's Cape region. They are characterized by cool, rainy winters and hot arid summers and experience periodic outbreaks of wildfires. Many Mediterranean-type ecosystems (MTEs) have been exposed to long-term anthropogenic disturbances, including livestock grazing, logging, and conversion of natural habitats into croplands.

Such selective pressures have resulted in floras that are species-rich, evolve rapidly, and display high levels of plant endemism. Diverse assemblages of co-evolved insects, primarily bees, play a key role as pollinators in MTEs.

The MEDECOS (International Mediterranean Ecosystems) series of conferences, established in 1971, focuses on convergences in the structure and function of MTEs around the globe. The meetings cover a diverse set of topics, including patterns of biodiversity, fire regimes, effects of climate change, and plant and animal phylogenies in MTEs. This Special Issue of Plants will specifically focus on the interactions between plant and insect pollinators in Mediterranean-climate areas. Contributions on the pollination biology of specific plant species, as well as community-level interactions with pollinators, are welcome. The scope of the Special Issue will also include anthropogenic effects on Mediterranean-type pollination systems and the interplay between pollination and other ecosystem-level processes.

Dr. Tamar Keasar
Guest Editor

Manuscript Submission Information

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Keywords

  • Mediterranean climate
  • plant community
  • pollination syndrome
  • flower traits
  • plant–pollinator coevolution
  • bees
  • plant conservation
  • pollinator conservation

Published Papers (5 papers)

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Research

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Article
Extreme Drought Affects Visitation and Seed Set in a Plant Species in the Central Chilean Andes Heavily Dependent on Hummingbird Pollination
Plants 2020, 9(11), 1553; https://doi.org/10.3390/plants9111553 - 12 Nov 2020
Cited by 4 | Viewed by 617
Abstract
Rising temperatures and increasing drought in Mediterranean-type climate areas are expected to affect plant–pollinator interactions, especially in plant species with specialised pollination. Central Chile experienced a mega drought between 2010 and 2020 which reached an extreme in the austral summer of 2019–2020. Based [...] Read more.
Rising temperatures and increasing drought in Mediterranean-type climate areas are expected to affect plant–pollinator interactions, especially in plant species with specialised pollination. Central Chile experienced a mega drought between 2010 and 2020 which reached an extreme in the austral summer of 2019–2020. Based on intensive pollinator sampling and floral studies we show that the subalpine form of Mutisia subulata (Asteraceae) is a specialised hummingbird-pollinated species. In a two-year study which included the severest drought year, we quantified visitation frequency, flower-head density, flower-head visitation rates, two measures of floral longevity, nectar characteristics and seed set and monitored climatic variables to detect direct and indirect climate-related effects on pollinator visitation. Flower-head density, nectar standing crop and seed set were significantly reduced in the severest drought year while nectar concentration increased. The best model to explain visitation frequency included flower-head density, relative humidity, temperature, and nectar standing crop with highly significant effects of the first three variables. Results for flower-head density suggest hummingbirds were able to associate visual signals with reduced resource availability and/or were less abundant. The negative effect of lower relative humidity suggests the birds were able to perceive differences in nectar concentration. Reduced seed set per flower-head together with the availability of far fewer ovules in the 2019–2020 austral summer would have resulted in a major reduction in seed set. Longer and more intense droughts in this century could threaten local population persistence in M. subulata. Full article
(This article belongs to the Special Issue Plant-Pollinator Interactions in Mediterranean-Type Ecosystems)
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Article
Floral Complexity Traits as Predictors of Plant-Bee Interactions in a Mediterranean Pollination Web
Plants 2020, 9(11), 1432; https://doi.org/10.3390/plants9111432 - 24 Oct 2020
Viewed by 689
Abstract
Despite intensive research, predicting pairwise species associations in pollination networks remains a challenge. The morphological fit between flowers and pollinators acts as a filter that allows only some species within the network to interact. Previous studies emphasized the depth of floral tubes as [...] Read more.
Despite intensive research, predicting pairwise species associations in pollination networks remains a challenge. The morphological fit between flowers and pollinators acts as a filter that allows only some species within the network to interact. Previous studies emphasized the depth of floral tubes as a key shape trait that explains the composition of their animal visitors. Yet, additional shape-related parameters, related to the handling difficulty of flowers, may be important as well. We analyzed a dataset of 2288 visits by six bee genera to 53 flowering species in a Mediterranean plant community. We characterized the plant species by five discrete shape parameters, which potentially affect their accessibility to insects: floral shape class, tube depth, symmetry, corolla segmentation and type of reproductive unit. We then trained a random forest machine-learning model to predict visitor identities, based on the shape traits. The model’s predictor variables also included the Julian date on which each bee visit was observed and the year of observation, as proxies for within- and between-season variation in flower and bee abundance. The model attained a classification accuracy of 0.86 (AUC = 0.96). Using only shape parameters as predictors reduced its classification accuracy to 0.76 (AUC = 0.86), while using only the date and year variables resulted in a prediction accuracy of 0.69 (AUC = 0.80). Among the shape-related variables considered, flower shape class was the most important predictor of visitor identity in a logistic regression model. Our study demonstrates the power of machine-learning algorithms for understanding pollination interactions in a species-rich plant community, based on multiple features of flower morphology. Full article
(This article belongs to the Special Issue Plant-Pollinator Interactions in Mediterranean-Type Ecosystems)
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Article
Enhanced UV-Reflection Facilitated a Shift in the Pollination System of the Red Poppy, Papaver rhoeas (Papaveraceae)
Plants 2020, 9(8), 927; https://doi.org/10.3390/plants9080927 - 22 Jul 2020
Cited by 4 | Viewed by 1022
Abstract
Evolutionary change is considered a major factor influencing the invasion of new habitats by plants. Yet, evidence on how such modifications promote range expansion remains rather limited. Here we investigated flower color modifications in the red poppy, Papaver rhoeas (Papaveraceae), as a result [...] Read more.
Evolutionary change is considered a major factor influencing the invasion of new habitats by plants. Yet, evidence on how such modifications promote range expansion remains rather limited. Here we investigated flower color modifications in the red poppy, Papaver rhoeas (Papaveraceae), as a result of its introduction into Central Europe and the impact of those modifications on its interactions with pollinators. We found that while flowers of Eastern Mediterranean poppies reflect exclusively in the red part of the spectrum, those of Central European poppies reflect both red and ultraviolet (UV) light. This change coincides with a shift from pollination by glaphyrid beetles (Glaphyridae) to bees. Glaphyrids have red-sensitive photoreceptors that are absent in bees, which therefore will not be attracted by colors of exclusively red-reflecting flowers. However, UV-reflecting flowers are easily detectable by bees, as revealed by visual modeling. In the North Mediterranean, flowers with low and high UV reflectance occur sympatrically. We hypothesize that Central European populations of P. rhoeas were initially polymorphic with respect to their flower color and that UV reflection drove a shift in the pollination system of P. rhoeas that facilitated its spread across Europe. Full article
(This article belongs to the Special Issue Plant-Pollinator Interactions in Mediterranean-Type Ecosystems)
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Article
Flower Colour Polymorphism, Pollination Modes, Breeding System and Gene Flow in Anemone coronaria
Plants 2020, 9(3), 397; https://doi.org/10.3390/plants9030397 - 23 Mar 2020
Cited by 5 | Viewed by 1396
Abstract
The flower colour of Anemone coronaria (Ranunculaceae) is a genetically inherited trait. Such intra-specific flower colour polymorphism might be driven by pollinators, other non-pollinating agents, or by abiotic factors. We investigated the genetic relations among red, white and purple-blue flower colour morphs growing [...] Read more.
The flower colour of Anemone coronaria (Ranunculaceae) is a genetically inherited trait. Such intra-specific flower colour polymorphism might be driven by pollinators, other non-pollinating agents, or by abiotic factors. We investigated the genetic relations among red, white and purple-blue flower colour morphs growing in 10 populations of A. coronaria in Israel, in relation to their breeding system, pollination modes, differential perception by bees and visitors’ behaviour. Flowers of these three morphs differed in their reflectance that could be perceived by bees. Honeybees, solitary bees and flies demonstrated only partial preferences for the different colour morphs. No spontaneous self-pollination was found; however, fruit set under nets, excluding insects but allowing wind pollination, was not significantly lower than that of natural free pollinated flowers, indicating a potential role of wind pollination. Anemone coronaria flowers were visited by various insects, honeybees and Andrena sp. preferred the white and purple-blue morphs, while the syrphid flies preferred the white flowers. Thus, visitor behaviour can only partially explain the evolution or maintenance of the colour polymorphism. No significant genetic differences were found among the populations or colour morphs. Wind pollination, causing random gene flow, may explain why no significant genetic divergence was found among all studied populations and their colour morphs. The existence of monomorphic red populations, along other polymorphic populations, might be explained by linked resistance to aridity and/or grazing. Full article
(This article belongs to the Special Issue Plant-Pollinator Interactions in Mediterranean-Type Ecosystems)
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Review

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Review
Evolutionary and Ecological Considerations on Nectar-Mediated Tripartite Interactions in Angiosperms and Their Relevance in the Mediterranean Basin
Plants 2021, 10(3), 507; https://doi.org/10.3390/plants10030507 - 09 Mar 2021
Viewed by 449
Abstract
The Mediterranean basin hosts a high diversity of plants and bees, and it is considered one of the world’s biodiversity hotspots. Insect pollination, i.e., pollen transfer from male reproductive structures to conspecific female ones, was classically thought to be a mutualistic relationship that [...] Read more.
The Mediterranean basin hosts a high diversity of plants and bees, and it is considered one of the world’s biodiversity hotspots. Insect pollination, i.e., pollen transfer from male reproductive structures to conspecific female ones, was classically thought to be a mutualistic relationship that links these two groups of organisms, giving rise to an admirable and complex network of interactions. Although nectar is often involved in mediating these interactions, relatively little is known about modifications in its chemical traits during the evolution of plants. Here, we examine how the current sucrose-dominated floral nectar of most Mediterranean plants could have arisen in the course of evolution of angiosperms. The transition from hexose-rich to sucrose-rich nectar secretion was probably triggered by increasing temperature and aridity during the Cretaceous period, when most angiosperms were radiating. This transition may have opened new ecological niches for new groups of insects that were co-diversifying with angiosperms and for specific nectar-dwelling yeasts that originated later (i.e., Metschnikowiaceae). Our hypothesis embeds recent discoveries in nectar biology, such as the involvement of nectar microbiota and nectar secondary metabolites in shaping interactions with pollinators, and it suggests a complex, multifaceted ecological and evolutionary scenario that we are just beginning to discover. Full article
(This article belongs to the Special Issue Plant-Pollinator Interactions in Mediterranean-Type Ecosystems)
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