Μεσογειακά οσμοτοπία: ο ρόλος των αρωμάτων των φυτών στα επικονιαστικά δίκτυα

At present, overexploitation of species, aggressive agricultural practices, land-use changes, biological invasions, pollution, and climate change represent, in descending order of magnitude, the main global-scale threats to biodiversity. Given that the majority of these phenomena represent threats also to plant–pollinator interactions worldwide, intensive research efforts across the world are focusing on disentangling the dynamics and structure of the p–p interactions, so that prevention, conservation, and restoration strategies can be effectively designed and implemented. In this context, this thesis focuses on the sensory ecology of pollination, in particular, on the role of floral signals as perceived by pollinating insects in structuring the pollination network of a natural community. I first find an unprecedented fine-tuning of floral scent and color implying a community-wide floral phenotypic integration according to the sensory systems of pollinators, especially bees. Next, by using innovative methods to analyze the pollination network of the same phryganic community, I find that network cohesiveness relates to floral scent and floral color as perceived by pollinators. Results suggest a hypothesis on the role of the profuse emissions of aromatic plants in mediterranean-type scrublands, and highlight the fundamental connection between bees and floral cues in this ecosystem. Floral sensory diversity emerges as an important component of functional diversity that could help designate influential plants in the community, to be used in targeted restoration practices for maintaining network dynamics and facilitative effects. Then, I analyze the network of associations between the insects and the volatile organic compounds of the plants in the community, as a new methodology for studying chemically-mediated plant–arthropod interactions. Finally, I focus on plant volatile compounds as natural products, and I built a geo-database of the chemical diversity of plants in Greece, by combining data published in the last 25 years. This approach allowed the development of the first chemodiversity maps, as a special case of natural product maps.Η βιοτική επικονίαση είναι μία οικοσυστημική λειτουργία-κλειδί για τη διατήρηση της φύσης και της παγκόσμιας πρωτογενούς παραγωγής. H διατήρηση καθώς και η εξέλιξη της χερσαίας βιοποικιλότητας της Γης εξαρτώνται από την ποιότητα και την αποτελεσματικότητα των αλληλεπιδράσεων αμοιβαιότητας μεταξύ ανθοφόρων φυτών και επικονιαστών. Επιπλέον, η επιβίωση των ανθρώπων βασίζεται, επίσης σε μεγάλο βαθμό, στους επικονιαστές, δεδομένου ότι περισσότερα από 1500 καλλιεργούμενα είδη φυτών παγκοσμίως επικονιάζονται από ζώα, κυρίως έντομα. Στις μέρες μας, όπου οι κύριες απειλές κατά της βιοποικιλότητας σε παγκόσμια κλίμακα αποδεδειγμένα δρουν και ενάντια στις επικονιαστικές σχέσεις, έρευνες σε όλον τον κόσμο επικεντρώνονται ολοένα και συχνότερα στην κατανόηση της δομής και της δυναμικής των αλληλεπιδράσεων φυτών–επικονιαστών, προκειμένου οι πρακτικές οικολογικής διατήρησης και αποκατάστασης να σχεδιάζονται και να εφαρμόζονται αποτελεσματικά. Η παρούσα διδακτορική διατριβή επικεντρώνεται στην αισθητηριακή οικολογία (sensory ecology) της επικονίασης, ειδικότερα στον τρόπο με τον οποίο τα σήματα που εκπέμπονται από τα άνθη και στοχεύουν στα αισθητηριακά συστήματα των επικονιαστών (όραση και όσφρηση) σχετίζονται με την πραγματοποιούμενη ανθική επισκεψιμότητα. Τα ανθικά σήματα, οπτικά και οσφρητικά, με την τεράστια ποικιλία χρωμάτων, σχημάτων και αρωμάτων, έχοντας ως πρωταρχική λειτουργία τη διαμεσολάβηση στην επικοινωνία μεταξύ φυτών και επικονιαστών, αναμένεται να επιδρούν στη δομή των δικτύων φυτών–επικονιαστών και, συνακόλουθα, στη δομή της βιοκοινότητας. Αρχικά, διερευνάται το ανθικό αισθητηριακό τοπίο μιας φρυγανικής βιοκοινότητας στη Λέσβο. Τα ευρήματα αποκαλύπτουν μία ενδιαφέρουσα φαινοτυπική συνδιακύμανση του ανθικού αρώματος και χρώματος όπως το αντιλαμβάνονται οι επικονιαστές. Στη συνέχεια, τα δεδομένα αυτά συνθεωρούνται στην ανάλυση του δικτύου φυτών–επικονιαστών της μελετώμενης βιοκοινότητας και τα αποτελέσματα καταδεικνύουν σαφή συσχέτιση των ανθικών χαρακτήρων με τη συμπεριφορά, δηλ. τον λειτουργικό ρόλο των φυτών στο δίκτυο αλληλεπιδράσεων. Τα ευρήματα επιτρέπουν τον μελλοντικό σχεδιασμό στοχευμένων πρακτικών οικολογικής διατήρησης και αποκατάστασης βιοκοινοτήτων με βάση την αισθητηριακή ποικιλότητα της αρχικής βιοκοινότητας και εφαρμόζοντας στοχευμένες επιλογές ειδών-κλειδιών για την προσέλκυση συγκεκριμένων ομάδων εντόμων. Ακολούθως, εφαρμόζοντας τη μεθοδολογία ανάλυσης δικτύων, παρουσιάζεται το πρώτο δίκτυο εντόμων–ανθικών αρωμάτων συντεθειμένο από (α) τα δεδομένα του δικτύου ανθικής επισκεψιμότητας από έντομα-επικονιαστές, και (β) από τα χημικά δεδομένα του ανθικού αρώματος των φυτών που έχουν συλλεγεί στη βιοκοινότητα μελέτης. Τα αποτελέσματα καθιστούν τα διμερή δίκτυα ειδών–μεταβολιτών ένα νέο εργαλείο μελέτης της χημικής επικοινωνίας φυτών και αρθροπόδων. Τέλος, το ερευνητικό ενδιαφέρον εστιάζεται στην αξία των φυτικών αρωμάτων ως φυσικά προϊόντα, αναπτύσσοντας μία γεω-βάση δεδομένων της χημικής ποικιλότητας των φυτικών αρωμάτων στην Ελλάδα με την οποία μελετάται η κατανομή και οι ιδιότητες των πτητικών οργανικών ενώσεων των φυτών, και καθίσταται δυνατή η παραγωγή χαρτών χημικής ποικιλότητας ως μια ειδική περίπτωση χαρτογράφησης φυσικών πόρων

Reduced fecundity in large populations of a Mediterranean orchid - Evidence for pollinator limitation

Increased anthropogenic influence is expected to reduce the size of natural populations, which may decrease individual fecundity and long-term survival. However, it is unclear whether populations of a species that occur in a variety of habitats will suffer decreased fecundity similarly. Certain habitats, such as those in agricultural landscapes that used to undergo traditional management, may be altered more than others and therefore individuals within such populations may be more prone to decreased fecundity. This is particularly important to quantify in Mediterranean landscapes, where habitat change is a major threat to biodiversity. We examined the fecundity of 88 populations of the orchid Spiranthes spiralis, across multiple habitats on the Greek island of Lesvos. In each population we recorded both the habitat and geological substrate. At the end of the flowering season, population size was quantified in each population by counting the number of fruiting plants and the percentage fruit set was determined. To test whether seed set was reduced due to pollination limitation we performed a pollen supplementation experiment. Large populations had significantly lower fruit set than small populations, and this effect was most pronounced in olive groves. Pollen supplementation showed that S. spiralis may suffer reduced seed set due to pollen limitation. The results of this study show that larger olive grove populations may be pollinator-limited and there may be two reasons for this: first, olive groves are less favourable sites for honeybees - the major and more efficient pollinators of S. spiralis on Lesvos; second, such populations have been suffering severe management changes in recent years (e.g. chemical treatments, chopping) and are most vulnerable to reductions in reproductive output

Global change and plant-pollinator communities in Mediterranean biomes

AimOccurring in five distinct global regions, Mediterranean-type ecosystems (MTEs) include both centres of agricultural production and hotspots of extratropical biodiversity - particularly for plants and bees. Considerable research has addressed the persistence of highly diverse biological communities within MTEs, despite their typically long histories of anthropogenic and natural disturbance. However, important questions remain, especially regarding the limits of ecological resilience in the face of accelerating environmental change. Here, we explore current knowledge regarding the effects of disturbance on MTE plant-pollinator communities.LocationMediterranean Basin, California, Cape Province in South Africa, Central Chile and Southern South-Western Australia.Taxa StudiedFlowering plants and pollinators (insects, birds and mammals).MethodsWe reviewed the available literature about MTE plant-pollinator communities via a systematic search that yielded 234 case studies. We analysed this dataset to quantify research efforts across regions and taxonomic groups, the proportion of surveys addressing ecological interactions (i.e. rather than only taxonomic diversity) and the availability of work addressing community responses to specific stressors (viz. climate change, landscape alteration, fire, farming, grazing, urbanization and species introductions).ResultsCurrent knowledge on MTE plant-pollinator communities is dominated by work from the northern Mediterranean Basin, while the Southern Hemisphere and California are markedly understudied by comparison. Taxonomic coverage is similarly uneven, with 58% of studies focusing only on a single pollinator group. Furthermore, less than half of the surveys address ecological networks. Finally, despite some pioneering work addressing fire, climate and species introductions, only 13% focus on the impact of stressors on interaction networks.OutlookBased on our findings, we identify a need for coordinated international research efforts focusing on (i) community-level studies, observational and experimental, (ii) ecological networks, (iii) functional traits mediating post-disturbance recovery and (iv) impacts of combined/synergistic stressors. Progress in these areas will facilitate predictions about the long-term impacts of global change on MTE plant-pollinator communities.ISSN:1466-822XISSN:1466-823

High species turnover and unique plant-pollinator interactions make a hyperdiverse mountain

We studied α- and β-diversity of pollinators, flowering plants and plant–pollinator interactions along the altitudinal gradient of Mt. Olympus, a legendary mountain and biodiversity hotspot in Central Greece. We explored 10 study sites located on the north-eastern slope of the mountain, from 327 to 2596 m a.s.l. Insect surveys were conducted once a month using hand netting (years 2013, 2014 and 2016), and they were combined with recordings of flowering plant diversity (species richness and flower cover). We then calculated α- and β-diversity of pollinators, plants in flower and plant–pollinator interactions, and explored their demographic response along the altitudinal gradient. Alpha diversity of pollinators, plants and plant–pollinator interactions were altitude dependent; α-diversity of all pollinators, bees, non-bumblebee bees, bee flies and butterflies showed linear declines with altitude, whereas those of hoverflies and bumblebees showed unimodal patterns. Beta diversity and its turnover component of all pollinators, hoverflies, bees, bumblebees, non-bumblebee bees, butterflies and plants showed linear increases, whereas those of bee flies and of plant–pollinator interactions varied independently from the pairwise altitudinal difference. The high dissimilarity and uniqueness of pollination networks, which is probably a result of the high biodiversity and endemism of Mt. Olympus, is driven by species turnover and the formation of new interactions between new species. Contrasting to the monotonic decline of the remaining groups, the unimodal patterns of hoverfly and bumblebee α-diversity are probably the effect of a higher tolerance of these groups to high-altitude environmental conditions. Our findings highlight that the high turnover of species and of pollination interactions along the altitudinal gradient are the mainstay of hyperdiverse mountains, a fact that conveys important historical, ecological and conservational implications.ISSN:0021-8790ISSN:1365-265

Bumblebee diversity and pollination networks along the elevation gradient of Mount Olympus, Greece

Aim We studied bumblebee diversity and bumblebee pollination networks along the altitudinal gradient of Mt. Olympus, a legendary mountain in Central Greece, also known for its exceptional flora. Location Mt. Olympus, Central Greece. Taxon Bombus (Latreille, 1802). Methods We explored 10 study sites located on the north‐eastern slope of the mountain, from 327 to 2,596 m a. s. l. Bumblebee surveys were carried out on a monthly basis using pan traps (years 2013 and 2014) and random transect observations assisted by hand netting (years 2013, 2014, and 2016); visited flowering plants and their diversity were recorded during the transect observations. Results With a total of 22 recorded bumblebee species and one species complex, Mt. Olympus is one of the richest mountains in Mediterranean Europe regarding bumblebee diversity. Bombus quadricolor was recorded as a new species for Greece, whereas four species were recorded at their southernmost distribution limit, therefore possibly vulnerable to climate change. Species richness of both bumblebees and plants in flower followed a unimodal pattern along the altitudinal gradient, the former peaking at high altitudes (1,900–2,200 m a.s.l.), the latter at lower to intermediate altitudes (500–1,500 m a.s.l.). Bumblebee–plant visitation networks were larger, more diverse and more generalized in the between intermediate altitudes (1,500–1,800 m a.s.l.), while nestedness peaked at low and high altitudes. Main conclusions Our results disclose the differential significance of the altitudinal zones of Mt. Olympus for the conservation of the diversity of bumblebees and their host plants, as well as of the interactions among them. Furthermore, they highlight the importance of this mountain, because of its South‐European location, regarding climate change impacts on the bumblebee fauna of Europe. All in all, they point towards more reinforced conservation measures to be taken including the expansion of the protection status to the entire mountain.ISSN:1366-9516ISSN:1472-464

Recent fire in a Mediterranean ecosystem strengthens hoverfly populations and their interaction networks with plants

Fire affects many critical ecological processes, including pollination, and effects of climate change on fire regimes may have profound consequences that are difficult to predict. Considerable work has examined effects of fire on pollinator diversity, but relatively few studies have examined these effects on interaction networks including those of pollinators other than bees. We examined the effects of a severe wildfire on hoverfly pollinators in a Mediterranean island system. Using data collected over 3 consecutive years at burnt and unburnt sites, we documented differences in species diversity, abundance, and functional traits, as well as hoverfly interactions with flowering plants. Hoverfly abundance and species richness peaked during the first post-fire flowering season (year 1), which coincided with the presence of many opportunistic species. Also in year 1, hoverfly pollination networks were larger, less specialized, more nested, and less modular at burnt (vs. unburnt) sites; furthermore, these networks exhibited higher phylogenetic host-plant diversity. These effects declined over the next 2 years, with burnt and unburnt sites converging in similarity to hoverfly communities and interaction networks. While data obtained over 3 years provide a clear timeline of initial post-fire recovery, we emphasize the importance of longer-term monitoring for understanding the responses of natural communities to wildfires, which are projected to become more frequent and more destructive in the future.ISSN:2045-775

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

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

Recent fire in a Mediterranean ecosystem strengthens hoverfly populations and their interaction networks with plants

Abstract Fire affects many critical ecological processes, including pollination, and effects of climate change on fire regimes may have profound consequences that are difficult to predict. Considerable work has examined effects of fire on pollinator diversity, but relatively few studies have examined these effects on interaction networks including those of pollinators other than bees. We examined the effects of a severe wildfire on hoverfly pollinators in a Mediterranean island system. Using data collected over 3 consecutive years at burnt and unburnt sites, we documented differences in species diversity, abundance, and functional traits, as well as hoverfly interactions with flowering plants. Hoverfly abundance and species richness peaked during the first post‐fire flowering season (year 1), which coincided with the presence of many opportunistic species. Also in year 1, hoverfly pollination networks were larger, less specialized, more nested, and less modular at burnt (vs. unburnt) sites; furthermore, these networks exhibited higher phylogenetic host‐plant diversity. These effects declined over the next 2 years, with burnt and unburnt sites converging in similarity to hoverfly communities and interaction networks. While data obtained over 3 years provide a clear timeline of initial post‐fire recovery, we emphasize the importance of longer‐term monitoring for understanding the responses of natural communities to wildfires, which are projected to become more frequent and more destructive in the future