A test of the effect of floral color change on pollination effectiveness using artificial inflorescences visited by bumblebees

Floral color change has been recognized as a pollination strategy, but its relative effectiveness has been evaluated insufficiently with respect to other floral traits. In this study, effects of floral color change on the visitation pattern of bumblebees were empirically assessed using artificial flowers. Four inflorescence types were postulated as strategies of flowering behavior: type 1 has no retention of old flowers, resulting in a small display size; type 2 retains old flowers without nectar production; type 3 retains old flowers with nectar; and type 4 retains color-changed old flowers without nectar. Effects of these treatments varied depending on both the total display size (single versus multiple inflorescences) and the pattern of flower-opening. In the single inflorescence experiment, a large floral display due to the retention of old flowers (types 2–4) enhanced pollinator attraction, and the number of flower visits per stay decreased with color change (type 4), suggesting a decrease in geitonogamous pollination. Type-4 plants also reduced the foraging time of bees in comparison with type-2 plants. In the multiple inflorescence experiment, the retention of old flowers did not contribute to pollinator attraction. When flowering occurred sequentially within inflorescences, type-4 plants successfully decreased the number of visits and the foraging time in comparison with type-2 plants. In contrast, floral color change did not influence the number of visits, and it extended the foraging time when flowering occurred simultaneously within inflorescences but the opening of inflorescences progressed sequentially within a plant. Therefore, the effectiveness of floral color change is highly susceptible to the display size and flowering pattern within plants, and this may limit the versatility of the color change strategy in nature.     

Habitat structure and animal movement: the behaviour of bumble bees in uniform and random spatial resource distributions

Foraging organisms (like bumble bees) move between resource points (like flowers) whose natural distributions vary enormously: from hyperdispersed to random to clumped. These differences in habitat structure may significantly influence the fitness of both plant and pollinator. To examine the effect of habitat structure on pollinator movement and fitness, we observed captive worker bumble bees collecting nectar from artificial flowers containing equal volumes of reward and arranged in two spatial configurations: a hexagonal array with constant distances between flowers (“constant”), and an “exploded hexagonal” array, with variable distances between flowers (“variable”). The mean nearest-neighbour distance was the same in both arrays, as was the general hexagonal appearance. The experiment therefore compares how resource dispersion, independent of nearest-neighbour distance, influences bee behaviour. Bees in the variable array showed decreased directionality, higher revisitation frequencies, and greater inter-flower flight distances than shown in the constant array. As a consequence, bees in the variable array had a 19% lower gross rate of nectar collection. Our results suggest that wild-foraging bees should prefer regularly spaced flowers (when all else, including mean nearest-neighbour distance, is equal), and that plants can decrease self-pollination by regular spacing between flowers, inflorescences, or individuals. Received: 16 January 1996 / Accepted: 30 June 1997     

Spatial and temporal dynamics of the male effective population size in bumblebees (Hymenoptera: Apidae)

Eusociality and male haploidy of bumblebees (Bombus spp.) enhance the deleterious effects of population decline and aggravate the degeneration of population fitness compared to solitary and diploid species. The highly dispersive male sex may be the prime driver to connect otherwise isolated populations. We therefore studied the temporal and spatial structure of the male population of Bombus terrestris (Linnaeus 1758) and Bombus lapidarius (Linnaeus 1758) using microsatellite DNA markers. We found that the majority of the males in a 1000 m2 sampling area originated from colonies located outside of the workers foraging range, which was consistent with the genetic distances among colonies. The analyses of temporal population sub-structure based on both colony detection rate over time and the clustering software STRUCTURE consistently suggested one large and temporally unstructured male population. Our results indicate an extended male flight distance for both species. Though the range of queen dispersal remains to be studied, the effective size (N _e) of bumblebees is increased by extended male mating flight ranges (A _m ) exceeding worker foraging distance by factor 1.66 (A _m  = 69.75 km²) and 1.74 (A _m  = 13.41 km²), B. terrestris and B. lapidarius, respectively. Thus this behaviour may counteract genetic deprivation and its effects. All populations were genetically highly diverse and showed no signs of inbreeding. We discuss the implications of our findings in context of bumblebee population dynamics and conservation. We also highlight the effects and benefits of sampling both workers and males for population genetic studies.     

Effect of local spatial plant distribution and conspecific density on bumble bee foraging behaviour

1. Size variations in pollinator populations may modify competitive interactions among foragers. Competition among pollinators has been shown to lead to one of two contrasting behaviours: either specialisation to the most profitable plant species or generalisation to several species. When foraging, pollinators are also confronted with heterogeneity in the spatial distribution of plant resources. Because variations in both the forager density and plant spatial distribution can affect pollinator behaviour, focus was on the interactive effect of these two factors. 2. Bumble bee (Bombus terrestris L.) individuals were trained on a focal species (Lotus corniculatus L.) and experimentally tested whether variations in the forager density (two or six bumble bees foraging together), plant community spatial distribution (two plant species: L. corniculatus and Medicago sativa, which were either patchily or randomly distributed), and their interaction modified bumble bee foraging behaviour. 3. It was shown that when confronted with a high forager density, bumble bees focused their visits towards the most familiar species, especially when foraging under a random plant distribution. These modifications affected the fruiting of the focal plant species, with a significantly lower reproductive success under low density/patchy conditions. 4. This study demonstrates that the foraging decisions of bumble bees are influenced by variations in both the conspecific density and plant spatial distribution. Given the increasing impact of human activities on plant‐pollinator communities, this raises the question of the potential implications of these results for plant communities in natural conditions when confronted with variations in the pollinator density and spatial distribution of plants.     

安氏薮羚的性二型对采食行为的影响(英文)

安氏薮羚(Tragelaphus angasii)是具有性别体二型的动物,其体型大小的差异可能对采食行为和生境选择有显著影响.利用连续行为取样法检测了雌雄个体在生境和植物利用上的差异,记录采食植物种类和采食高度并进行了性别间比较.在每个采食周期末,采用点中心方形样方法(PCQ)对植被进行一次调查,利用判别函数分析鉴别雌雄个体之间在种类和高度上是否存在差异.雌羚在三类生境中花费的采食时间相似,但雄羚表现出对砂地林的偏好.另外,在同一生境内雄羚利用更多的木本种类且采食较高的部位,而雌羚喜欢采食低层草本植物.安氏薮羚雌雄个体在生境内具有食性(采食种类)和空间(生境斑块)上的分离.我们认为这是由性二型引起的性别间营养与能量需求差异和不同繁殖策略造成的,最终使得精食者动物在具有复杂结构空间异质性的生境内表现为空间性别分离     

The pollination efficiency of a pollinator depends on its foraging strategy,flowering phenology,and the flower characteristics of a plant species

Honey bees and stingless bees are generalist visitors of several wild and cultivated plants. They forage with a high degree of floral fidelity and thereby help in the pollination services of those plants. We hypothesized that pollination efficiency might be influenced by flowering phenology, floral characteristics, and resource collection modes of the worker bees. In this paper, we surveyed the foraging strategies of honey bees (Apis cerana, Apis dorsata, and Apis florea) and stingless bees (Tetragonula iridipennis) concerning their pollination efficiencies. Bees showed different resource gathering strategies, including legitimate (helping in pollination as mixed foragers and specialized foragers) and illegitimate (serving as nectar robbers and pollen thieves) types of flower visitation patterns. Foraging strategies are influenced by the shape of flowers, the timing of the visitation, floral richness, and bee species. Honey bees and stingless bees mainly acted as legitimate visitors in most plants studied. Sometimes honey bees served as nectar robbers in tubular flowers and stingless bees as pollen thieves in large-sized flowers. Among the legitimate categories, mixed foragers have a comparatively lower flower visitation rate than the specialized nectar and pollen foragers. However, mixed foragers have greater abundance and higher values of the single-visit pollination efficiency index (PEi) than nectar and pollen foragers. The value of the combined parameter ‘importance in pollination (PI)’ was thus higher in mixed foragers than in nectar and pollen foragers.     

Effects of floral traits and plant genetic composition on pollinator behavior

Pollinator-mediated selection plays a major role in floral evolution and speciation. Floral traits that influence animal pollinator behavior are the target of pollinator-mediated selection, but can only evolve if floral phenotypes have underlying genetic variation. Thus, understanding the genetic basis of a floral trait is a crucial step in studying pollinator-mediated selection. In this study I tested the effect of quantitative trait loci (QTL) underlying floral traits on pollinator behavior in recombinant inbred lines (RILs) in the common sunflower, Helianthus annuus L. and its crop relative. The indirect effects of QTL on pollinator behavior, mediated by floral phenotypes, were analyzed for six insect visitor types using structural equation modeling (SEM) and path analysis. For three of the six visitor types (large and small bees and non-bee insects) valid models were revealed when all three levels (QTL, floral traits, and pollinator behavior) were incorporated. Nested model without genetics were validated for five of the six visitor types. The results suggest that insect behavior as a reaction to floral phenotypes is affected by the genetic architecture of floral traits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: Heikki Hokkanen     

The relationship between the abundances of bumblebees and honeybees in a native habitat

Abstract. 1. The western honeybee, Apis mellifera, has been introduced to many parts of the world and is sometimes purported to be detrimental to native bees because it reduces their food base. It is seldom viewed in this light in Europe; however, when beekeepers maintain very high bee densities, the species could also be displacing insects in its native European range by reducing the resource base. 2. In England, populations of bumblebees (Bombus Latr. Hym.) have been decreasing both in terms of diversity and abundance, mainly because of a loss of habitat resulting from agricultural intensification. The impact of competition from other flower feeders is largely unknown. 3. Nineteen dry lowland heaths in southern England were sampled once for honeybees and bumblebees. Honeybee abundance varied from 4 to 81 bees per 100 m² (mean = 30.89, median = 23), whereas bumblebees varied from 2 to 17 individuals per 100 m² (mean = 8.26, median = 7), belonging to between one and five species. There was a negative association between honeybee and bumblebee abundance but there was no apparent relationship between honeybee abundance and bumblebee diversity. 4. The Bray–Curtis coefficient was used to compare the similarity in honeybee and bumblebee floral host breadth at these 19 sites. The coefficient was negatively associated with honeybee abundance: thus where honeybees were most abundant, bumblebees were fewer and/or foraged on different flower species. 5. Foraging host breadth was also examined at four heathlands over a field season (April to September). No association between honeybee abundance and foraging host breadth was found for short‐tongued bees, although there was some evidence for a change in floral host breadth for long‐tongued bees. 6. It is concluded that the impact of honeybees on bumblebees is complex. Although competition between the two species cannot be ruled out, it is perhaps equally likely that bumblebees decline in response to other factors, and that honeybees move independently of this decline.     

Effects of flowering plant's patch size on species composition of pollinator communities,foraging strategies,and resource partitioning in bumblebees (Hymenoptera: Apidae)

Summary In 4 common Middle-European mainly bumblebee-pollinated plant species (Impatiens glandulifera, Echium vulgare, Aconitum napellus, Symphytum officinale) the influence of patch size on species composition of the pollinator community was studied. Short-tongued species were most dominant in large patches, while small patches were frequented by middle- and long-tongued bumblebees. This phenomenon was extremely obvious in Symphytum officinale and Aconitum napellus, where short-tongued species had bitten a hole in nearly every flower of large patches. Long-tongued species were forced to small patches, where nectarrobbing occurred only exceptionally. In small patches visitationrate (Number of visits per flower per hour) was not lower but either equal or even higher then in large patches. Nectar measurements in Echium vulgare showed, that not only the mean quantity of nectar but also the variance was lower in small patches. As a result, the possible gain can be predicted much more precisely in a small patch than in a large one, and bumblebees have less difficulties in making the right foraging decisions. According to this, foraging strategies depend on patch size. This was confirmed by a computer simulation. The conclusion can be drawn, that many bumblebee species are able to share the same resource by using different patch sizes. Since large flower patches occur mainly in man-made habitats, the dominance of short-tongued species in many bumblebee communities studied by other authors may be unnatural.Supported by the Landesgraduiertenförderung Baden-Württemberg     

Effects of habitat isolation on pollinator communities and seed set

Destruction and fragmentation of natural habitats is the major reason for the decreasing biodiversity in the agricultural landscape. Loss of populations may negatively affect biotic interactions and ecosystem stability. Here we tested the hypothesis that habitat fragmentation affects bee populations and thereby disrupts plant-pollinator interactions. We experimentally established small ”habitat islands” of two self-incompatible, annual crucifers on eight calcareous grasslands and in the intensively managed agricultural landscape at increasing distances (up to 1000 m) from these species-rich grasslands to measure effects of isolation on both pollinator guilds and seed set, independently from patch size and density, resource availability and genetic erosion of plant populations. Each habitat island consisted of four pots each with one plant of mustard (Sinapis arvensis) and radish (Raphanus sativus). Increasing isolation of the small habitat islands resulted in both decreased abundance and species richness of flower-visiting bees (Hymenoptera: Apoidea). Mean body size of flower-visiting wild bees was larger on isolated than on nonisolated habitat islands emphasizing the positive correlation of body size and foraging distance. Abundance of flower-visiting honeybees depended on the distance from the nearest apiary. Abundance of other flower visitors such as hover flies did not change with increasing isolation. Number of seeds per fruit and per plant decreased significantly with increasing distance from the nearest grassland for both mustard and radish. Mean seed set per plant was halved at a distance of approximately 1000 m for mustard and at 250 m for radish. In accordance with expectations, seed set per plant was positively correlated with the number of flower-visiting bees. We found no evidence for resource limitation in the case of mustard and only marginal effects for radish. We conclude that habitat connectivity is essential to maintain not only abundant and diverse bee communities, but also plant-pollinator interactions in economically important crops and endangered wild plants. Received: 7 May 1999 / Accepted: 19 July 1999     

The relative importance of prey availability and intruder pressure in feeding territory size regulation by harriers,Circus cyaneus

Summary The relative importance of prey availability and intruder pressure in the regulation of harrier (Circus cyaneus) territory size was investigated over two years using analytical methods chosen to permit comparison with Myers et al. (1979) study of sanderlings (Calidris alba). Relationships between territory area and two variables, prey type (mice; large, medium, and small birds) and intruder type (conspecific neighbors, conspecific floaters, and heterospecific floaters), and the consistency of these relationships between years, also were examined. Individual harrier territory areas were highly variable, ranging from 7.8 to 1249 ha in 1984/1985, and 3.9 to 71.3 ha in 1985/1986. Of the prey variables, only mouse availability was significantly inversely correlated with territory area in both years, and slopes resulting from correlations between the logarithms of these two variables did not differ significantly from — 1, the expected result if harriers were adjusting mouse availabilities. The abundance of mice in conjunction with their greater ease of capture relative to birds made them functionally more available, and hence harriers' primary prey. This may explain why mice, rather than birds, were apparently the defended resource. Of the intruder variables, neighbor variables were most strongly inversely cortelatd with territory area. Partial correlation analyses to determine the relative importance of intruder pressure and prey availability in regulating territory size revealed that in 1984/1985, mouse availability and intruder pressure were relatively independent and each explained some variation in territory area, whereas in 1985/1986, mouse availability, rather than intruder pressure, significantly explained all variation in territory area. Possible explanations for why territory sizes of harriers appear to be regulated more closely by food density, whereas territory sizes of sanderlings appear to be regulated more closely by intruder pressure, are based upon differences in 1) neighbor effects, 2) environmental ronmental variability, and 3) accuracy of resource assessment by intruders. The variation in intruder rates and prey availabilities observed between years suggests the need to conduct studies over several years in order to assess accurately the relative importance of these variables in territory-size regulation.     

The relative influence of density and kinship on dispersal in the common lizard

We experimentally investigated the relative role of kinshipand density on juvenile dispersal in the common lizard. A fewdays after birth, juveniles were introduced into seminaturalendosures, where they experienced different social environmentsin the first experiment we varied the density of unrelated adults(males or females) within the enclosure (0, 1, or 2 adults),and in the second experiment, we varied the level of kinshipand familiarity between juveniles and adults. Each enclosurewas connected to a second enclosure by small holes which allowedonly juveniles to move between enclosures. Juvenile movementswere monitored during 14 days after birth, as juvenile dispersalis mainly completed within 10 days after birth under naturalconditions. Most juveniles did not return to the first enclosure.Sex had no effect on juvenile dispersal. Adult densityand kinshipwith adults both affected dispersal. Adult female density increasedjuvenile dispersal whatever the level of kinship and familiaritywith the females. Dispersers had better body condition thannondispersers at high female densit and this difference wassignificantly greater when the mother and the familiar femalewere present in the enclosure. Furthermore, body condition ofmothers and familiar females was positively correlated withjuvenile dispersal, whereas there was no such correlation inthe case of unfamiliar and unrelated females. These resultsstrongly suggest that adult female density is a major factorpromoting dispersal in this species and that both intraspecificand kin competition motivate dispersal.     

The effect of climatic variation on abundance and diversity of bumblebees: a ten years survey in a mountain hotspot

Even if climates play an evident role in the bumblebees distribution, at the present time, no research has been performed to test whether climatic parameters actually affect their abundance and diversity. For more than one decade (1999–2009), we monitored the bumblebee fauna of a mountain hotspot in the Eastern Pyrenees. We sampled each year, in July, the same hayfield habitat, resulting in the sampling of 28 species. We computed the correlation of the yearly abundance of the main species with several climatic parameters concerning temperature and precipitation. We separated the parameters measured during the bumblebee solitary phase and those measured during their social phase. Bumblebee fauna composition varied significantly over years. In the 13 species considered, the abundance of 9 was correlated with at least one climatic parameter. The lowest abundance of bumblebees was correlated with hot and dry conditions during the month of August the year before sampling (the nuptial time of the founders). The highest overall abundance of bumblebees was observed during the social phase in the rainy months. Across years, climatic parameters seem to have strongly affected the composition of bumblebee fauna. Our results seem to indicate that hot and dry weather represent serious threat for most bumblebee species. The potential effects of Global Warming are discussed: they may cause a severe reduction of the mountain bumblebee diversity.     

The influence of food supply on foraging behaviour in a desert spider

We tested the alternative hypotheses that foraging effort will increase (energy maximizer model) or decrease (due to increased costs or risks) when food supply increased, using a Namib desert burrowing spider, Seothyra henscheli (Eresidae), which feeds mainly on ants. The web of S. henscheli has a simple geometrical configuration, comprising a horizontal mat on the sand surface, with a variable number of lobes lined with sticky silk. The sticky silk is renewed daily after being covered by wind-blown sand. In a field experiment, we supplemented the spiders' natural prey with one ant on each day that spiders had active webs and determined the response to an increase in prey. We compared the foraging activity and web geometry of prey-supplemented spiders to non-supplemented controls. We compared the same parameters in fooddeprived and supplemented spiders in captivity. The results support the costs of foraging hypothesis. Supplemented spiders reduced their foraging activity and web dimensions. They moulted at least once and grew rapidly, more than doubling their mass in 6 weeks. By contrast, food-deprived spiders increased foraging effort by enlarging the diameter of the capture web. We suggest that digestive constraints prevented supplemented spiders from fully utilizing the available prey. By reducing foraging activities on the surface, spiders in a prey-rich habitat can reduce the risk of predation. However, early maturation resulting from a higher growth rate provides no advantage to S. henscheli owing to the fact that the timing of mating and dispersal are fixed by climatic factors (wind and temperature). Instead, large female body size will increase fitness by increasing the investiment in young during the period of extended maternal care.     

Effects of floral herbivory on foraging behaviour of bumblebees and female reproductive success in Pedicularis gruina (Orobanchaceae)

The effects of floral herbivores on floral traits may result in alterations in pollinator foraging behaviour and subsequently influence plant reproductive success. Fed-upon plants may have evolved mechanisms to compensate for herbivore-related decreased fecundity. We conducted a series of field experiments to determine the relative contribution of floral herbivores and pollinators to female reproductive success in an alpine herb, Pedicularis gruina, in two natural populations over two consecutive years. Experimental manipulations included bagging, hand supplemental, geitonogamous pollination, and simulated floral herbivory. Bumblebees not only avoided damaged flowers and plants but also decreased successive visits of flowers in damaged plants, and the latter may reduce the level of geitonogamy. Although seed set per fruit within damaged plants was higher than that in intact plants, total seed number in damaged plants was less than that in intact plants, since floral herbivory-mediated pollinator limitation led to a sharp reduction of fruit set. Overall, the results suggest that resource reallocation within inflorescences of damaged plants may partially compensate for a reduction in seed production. Additionally, a novel finding was the decrease in successive within-plant bumblebee visits following floral herbivory. This may increase seed quantity and quality of P. gruina since self-compatible species exhibit inbreeding depression. The patterns of compensation of herbivory and its consequences reported in this study give an insight into the combined effects of interactions between floral herbivory and pollination on plant reproductive fitness.     

The influence of light quality on the development of the brown algae Petalonia and Scytosiphon

Petalonia fascia (O. F. Müll.) Kuntze, P. zosterifolia (Reinke) Kuntze and Scytosiphon lomentaria (Lyngb.) J. Ag. have been cultured in white, blue and red light of equal quantum irradiance at 15°C. Hairs, knot-filaments and Ralfsia-like crusts were formed only in blue light, whereas the prostrate system of red-grown plants consisted entirely of sparingly-branched and mostly uniseriate filaments. The production of erect thalli from the prostrate system was controlled or stimulated by red light, but these erect thalli became fertile only in the presence of blue light. All three species exhibited all of these types of response, although specific differences in the degree of certain types of response were observed.