No abstract

Because of the flower morphology and high number of insect visitors, plants of the family Apiaceae are regarded as generalists in terms of pollination systems. Recent studies however showed some degree of, at least, ecological specialization in some members of this taxonomical group and indicated interesting patterns of insect visitor behavior: discrimination between umbel sexual phases. To test whether this is true in case of other members of the family, over two years we studied the pollination biology of a common European umbellifer, Angelica sylvestris, a species considered by some authors as a supergeneralist. Although its flowers were visited by over 70 species of insects grouped in 10 morphospecies, only a relatively narrow assemblage of muscoid and syrphid flies, rather constant in both study years, contributed to pollination. These insects did not exhibit any preferences toward plant sexual phases. Based on our results and available literature, we discuss the concept of specialization/generalization of the A. sylvestris pollination system, especially in the context of the ''unspecialized'' floral morphology characteristic for members of the Carrot family.

The majority of flowering plants, including many rare and threatened species, are pollinated by animals, but little is known of pollination and breeding systems of many endangered species. Polemonium caeruleum (Polemoniaceae) is a red-listed species and is regarded as dichogamous, self-compatible and bee pollinated. However, some studies show that it is visited by a vast assemblage of anthophilous insects from many taxonomic orders and that breeding systems vary greatly between closely related taxa of this genus. Over a period of 3 years we investigated breeding system, dichogamy, nectar secretion and composition, insect visitations and pollen loads in flowers of P. caeruleum in north-eastern Poland to determine whether the reproductive biology of the plant explains its rarity. Contrary to published data, our study plants were self-incompatible and showed a high degree of outcrossing. Our experimental work confirmed the occurrence of protandry in this species, revealed that nectar is sucrose-dominant and proline-rich and, for the first time for Polemoniaceae, that nectar secretion and nectar sugar concentration in flowers of P. caeruleum is female-biased. Although flowers were visited by at least 39 species of insects from five taxonomic orders, overall the plant exhibited many characters associated with bee pollination, and analysis of insect performance showed that bumblebees and honeybees are the key pollinators; occasionally hoverflies and butterflies may also be involved. We conclude that, in terms of pollination system, P. caeruleum demonstrates high apparent generalization, but low realized generalization, and is a functional specialist, as most pollinators belong to a single functional group (guild). Its conservation status, at least in our study population, cannot be explained in terms of the biological properties of its breeding or pollination systems; rather, the present decline of the species is caused by habitat loss. However, if this process and bumblebee decline in Europe continue, P. caeruleum populations may diminish in numbers and density and, owing to the self-incompatibility of the species, quickly become severely pollen-limited, thereby accelerating further local extinctions.

On the basis of theoretical predictions, pollination networks seem to be resilient to random node elimination but sensitive to targeted exclusion. However, such predictions have a very weak empirical basis. In order to test the robustness of the pollination network to shortterm disturbances, we removed inflorescences of the most connected species occurring in a lowland meadow network using the before-after approach and compared the result with that obtained by network modelling. The manipulated network showed no significant differences for the most commonly used metrics, but was more generalized than control networks, owing to a change in the preferences of pollinators. Furthermore, no secondary extinctions (emigrations) were found, owing to the considerable natural variation found among insect species assemblages. Following elimination of the most linked plant species, a new hub was detected in the experimental meadow, the hub node being a plant species with a similar inflorescence to that removed, and formerly playing the role of a peripheral node. We conclude that exclusion of the main food source forced insects to change their specialized preferences to other plant species that were available. Mostly, these had inflorescences similar to those that were removed.

For 4 years we studied pollination biology and breeding system of the critically endangered, Red List plant Fritillaria meleagris L. (Liliaceae), in the larger of the two remaining populations of the plant in SE Poland. Our observations indicated that, contrary to literature data, the species is not dichogamous nor is it obligatorily out-crossing. Selfing, although rare in natural populations, results in fully developed seeds. Flowers are visited by several insect species, mostly social and solitary bees. In spite of extremely low visitation rates to this early spring-flowering plant, the species is not pollen limited. Although the largest pollen loads are transferred by solitary bees, the key pollinators are bumblebees (mostly the most common species, Bombus terrestris and B. lapidarius) due to their seasonal and floral constancy, and tolerance of bad weather conditions. The current decline of the studied population seems not to be related to the species' pollination or breeding systems but to plant habitat loss. It is suggested, however, that in smaller populations, the species' dependence on generally rare pollinators and largely out-crossed breeding system may accelerate local extinction.

Plant species and their pollinators are linked by their mutualistic interactions, which form the basis of pollination networks. The use of a network approach allows one to take into account all interactions between a group of plants and its animal pollinators, and to reveal the structure of these connections. We analysed pollination interactions for urban habitat fragments located within the Warsaw city environment. We compared two similar, ruderal communities (phytosociological order Onopordetalia acanthii) located in distant parts of the city of Warsaw (Poland) that differed with the surrounding ecosystems. The aim of this study was to define the structures and properties of flower-visitor (visitation) and pollen transport networks (based on analysis of pollen loads carried by insects) and to assess the differences between the studied sites. Although the sites differed in insect relative abundance (Diptera dominated one study site, whereas Hymenoptera dominated the other), network size and structure were similar for both communities. In both cases, networks contained moderately specialized species (based on H 2 0 index); however, networks were dominated by apparently ecologically generalized insect taxa as well as those represented by a single specimen. Networks based on pollen transport indicated greater generality of insect species (more links) than those based on our samples of visitation. The most highly linked plant species represented were either the most abundant (Fabaceae) or phenotypically generalized taxa (Daucus carota). We conclude that plantpollinator interactions in such highly disturbed and isolated habitats are composed mostly of ecologically generalised species. Moreover, we stress the usefulness of pollen load analysis in the development and verification of visitation data.

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Angelica sylvestris is morphologically well adapted to ecological generalization, and there is little evidence that the surveyed populations represent distinct pollination ecotypes. Most likely, the observed variation in floral characters can be interpreted as 'adaptive wandering'. Specialization in this family seems possible only under very special circumstances, for example when the pollinator community comprises insect visitor groups that clearly differ in their pollination capacity (e.g. due to differences in their functional morphology) and/or have different perceptional biases (e.g. for colour or scent). However, the barrier to the evolution of morphological adaptations resulting in the fine-tuning of the flower towards particular pollinator types may arise from the architectural constraints on the floral bauplan that make umbellifers so uniform in their floral displays and so successful in attracting large numbers of pollinators.