Trapline foraging by bumble bees: III. Temporal patterns of visitation and foraging success at single plants

We analyzed the temporal structure of visitation by bumble beeworkers to a single Penstemon strictus plant growing in an arrayof conspecifics. When tested against a null distribution usinga randomization model, the observed pattern of arrivals forthe whole group of bees was random, but departures were clusteredin time. Certain individuals visited the plant repeatedly andfrequently throughout the day. These showed significantly regulararrival and departure schedules, which were likely producedby traplining. We explored whether these more frequent and regularforagers gained a higher reward than random or incidental plantvisitors. Using an analytical model, Possingham predicted thata dominating forager that visited a simple, renewing resourcein a regular pattern would garner higher and less variable rewardsthan random visitors. Inspired by these results, but interestedin plant-level visitation, we constructed a simulation modelof resource dynamics for a multiflowered plant with high visitation.The model incorporates the observed visitation schedules ofall bees and independent reward dynamics for each flower onthe plant. We calculated the rewards that observed bees wouldhave collected given a range of resource-renewal parameters.More frequent visitors did not return to the plant when whole-plantresource levels were higher, but these visitors did get greaterrewards. Their increased reward resulted from greater foragingefficiency, primarily through selecting (on average) more rewardingflowers than those selected by less frequent, random visitors.     

Trapline foraging by bumblebees: I. Persistence of flight-path geometry

By setting out arrays of potted plants of Penstemon strictus,I tested whether freely foraging bumblebee (Bombus spp. ) workerswould establish regular foraging routes that reflected the geometryof the array. They did, passing through an asymmetrical arrayin a pattern that minimized interplant flight distances. Afterthe array was changed to a symmetrical pattern, however, theexperienced bees continued to show their previous asymmetricalflight patterns. New bees without experience on the asymmetricalarray showed no asymmetry on the symmetrical array. I term thispersistence of flight-path geometry "trapline holdover, " anddiscuss its implications for the study of animals' learningand foraging behavior.     

Plant quality and predation risk mediated by plant ontogeny: consequences for herbivores and plants

Bottom‐up and top‐down impacts on herbivores can be influenced by plant productivity, structural complexity, vigor and size. Although these traits are likely to vary with plant development, the influence of plant ontogeny on the relative importance of plant quality (i.e. bottom‐up forces) and predation risk (i.e. top‐down forces) has been the focus of little previous investigation. We evaluated the role of plant ontogeny for the relative importance of bottom‐up and top‐down forces on insect herbivore abundance, species richness, and species diversity attacking the tropical tree Casearia nitida. We also quantified the cascading effects on herbivory, growth and reproduction of this plant species. Plant quality traits (nitrogen and phenolic compounds) were assessed in saplings and reproductive trees. Bottom‐up forces were manipulated by fertilizing plants from both ontogenetic stages. Top‐down forces were manipulated by excluding insectivorous birds from saplings and reproductive trees. Plant ontogeny influenced foliage quality in terms of total phenolics, which were in greater concentration in reproductive trees than in saplings; however, it did not influence bottom‐up forces as modified by fertilization. Bird exclusion increased herbivore density with the same magnitude on both stages. Ontogeny influenced species diversity, which was greater in reproductive trees than in saplings, and also influenced treatment impacts on species richness and diversity. Although top‐down forces increased herbivory equally on plants of each ontogenetic stage, the two stages showed different overcompensation responses to increased damage: caged saplings produced greater leaf biomass than non‐caged saplings, whereas caged trees increased in height proportionally more than non‐caged trees. In sum, plant ontogeny influenced the impact of bird predation on herbivore density, species richness, and species diversity, and the growth variables affected by increased damage in caged plants. We suggest that plant ontogeny can contribute to some extent to the influence of plant quality and the third trophic level on herbivores in this system.     

Adaptive foraging behaviour of individual pollinators and the coexistence of co-flowering plants

Although pollinators can play a central role in determining the structure and stability of plant communities, little is known about how their adaptive foraging behaviours at the individual level, e.g. flower constancy, structure these interactions. Here, we construct a mathematical model that integrates individual adaptive foraging behaviour and population dynamics of a community consisting of two plant species and a pollinator species. We find that adaptive foraging at the individual level, as a complementary mechanism to adaptive foraging at the species level, can further enhance the coexistence of plant species through niche partitioning between conspecific pollinators. The stabilizing effect is stronger than that of unbiased generalists when there is also strong competition between plant species over other resources, but less so than that of multiple specialist species. This suggests that adaptive foraging in mutualistic interactions can have a very different impact on the plant community structure from that in predator–prey interactions. In addition, the adaptive behaviour of individual pollinators may cause a sharp regime shift for invading plant species. These results indicate the importance of integrating individual adaptive behaviour and population dynamics for the conservation of native plant communities.     

Personality-dependent dispersal: characterization, ontogeny and consequences for spatially structured populations

Dispersal is one of the most fundamental components of ecology, and affects processes as diverse as population growth, metapopulation dynamics, gene flow and adaptation. Although the act of moving from one habitat to another entails major costs to the disperser, empirical and theoretical studies suggest that these costs can be reduced by having morphological, physiological or behavioural specializations for dispersal. A few recent studies on different systems showed that individuals exhibit personality-dependent dispersal, meaning that dispersal tendency is associated with boldness, sociability or aggressiveness. Indeed, in several species, dispersers not only develop behavioural differences at the onset of dispersal, but display these behavioural characteristics through their life cycle. While personality-dependent dispersal has been demonstrated in only a few species, we believe that it is a widespread phenomenon with important ecological consequences. Here, we review the evidence for behavioural differences between dispersers and residents, to what extent they constitute personalities. We also examine how a link between personality traits and dispersal behaviours can be produced and how personality-dependent dispersal affects the dynamics of metapopulations and biological invasions. Finally, we suggest future research directions for population biologists, behavioural ecologists and conservation biologists such as how the direction and the strength of the relationship between personality traits and dispersal vary with ecological contexts.     

Trapline foraging by bumble bees: IV. Optimization of route geometry in the absence of competition

Foraging on resources that are fixed in space but that replenishover time, such as floral nectar and pollen, presents animalswith the problem of selecting a foraging route. What can flowervisitors such as bees do to optimize their foraging routes,that is, reduce return time or route distance? Some repeatedlyvisit a set of plants in a significantly predictable sequence(so-called "trapline foraging"), which may also enhance theirforaging efficiency. A moderate level of optimization and repetitionof foraging routes can be reached by following simple movementrules for choosing the distances and turning angles of successiveflights, without the use of spatial memory. If pollinators canlearn the locations of patches and choose among possible foragingroutes or paths, however, even better performance may be achieved.We tested whether and how bumble bees can optimize and repeattheir foraging routes in laboratory experiments with artificialflowers that secreted nectar at a constant rate. With increasingexperience, foraging routes of bees became more repeatable andefficient than expected from a combination of simple movementrules between successive flowers. We suggest that trapline foragingis a more sophisticated pattern of spatial use than searchingand is based on memory. On the other hand, certain spatial configurationsof flowers hampered optimization by the bees; bees preferredto choose short distances over straight moves and showed littleplasticity in this regard. Developing an efficient trapline,therefore, may require prior selection of a set of plants withan appropriate spatial configuration.     

Optimal foraging and ontogeny; food selection by Haplochromis piceatus

Summary We examined the influence of satiation level, prey density and light intensity on food uptake rate through the ontogeny of Haplochromis piceatus. Prey handling in the buccal cavity was found to be the main factor limiting prey uptake rate under light circumstances and at a sufficiently high prey density. Food uptake rate per unit body weight of different sizes of H. piceatus was equal when feeding on Chaoborus but decreased with increasing fish size when feeding on Daphnia magna. In choice experiments with Chaoborus and D. magna, prey selection by H. piceatus of all sizes was according to the predictions based on Charnov's 1976 model.     

Cryptic bumblebee species: consequences for conservation and the trade in greenhouse pollinators

Commercial greenhouse growers in both Japan and China are increasingly using reared orange-tailed bumblebees known previously as Bombus hypocrita Pérez as pollinators. Phylogenetic analysis of the DNA (COI) barcodes with Bayesian methods shows that this "species" is a long-standing confusion of two cryptic species. We find that the orange-tailed bumblebees in North China are actually part of the widespread Russian (otherwise white-tailed) B. patagiatus Nylander (as B. patagiatus ganjsuensis Skorikov, n. comb.), whereas the orange-tailed bees in Japan are true B. hypocrita. This situation has been further complicated because two other cryptic species from North China that were previously confused with the Russian B. patagiatus are now recognised as separate: B. lantschouensis Vogt n. stat. and B. minshanensis Bischoff n. stat.. As demand for pollination services by greenhouse growers inevitably increases, these bees are more likely to be transported between countries. In order to conserve genetic resources of pollinator species for their option value for future food security, we advocate preventing trade and movement of B. patagiatus from China into Japan and of B. hypocrita from Japan into China.     

Absorption of air pollution by plants, and consequences for growth

There is now great concern that air pollutants (especially sulfur dioxide, ozone, and oxides of nitrogen) can alter the physiological processes of plants, thereby affecting patterns of growth. Air pollutants cause damage to leaf cuticles and affect stomatal conductance. They can also have direct effects on photosynthetic systems, leaf longevity, and patterns of carbon allocation within plants. Pollutants interact with other environmental factors, and may alter plant-environment relationships on a regional scale. In this article, Winner and Atkinson summarize current knowledge of the effects of air pollutants on plant growth and physiology, and indicate the new directions of research now under way in North America and Europe.     

Oviposition by mutualistic seed-parasitic pollinators and its effects on annual fitness of single- and multi-flowered host plants

The balance of intimate relationships between plants and seed-eating pollinators can depend on pollinator behaviour in relation to floral characters, such as flower size and flower number. Here, we examined how pollinator oviposition in relation to these traits affected annual fitness (seed output) of single- and multi-flowered Trollius europaeus along altitudinal gradients in subarctic Sweden and the French Alps. Small flies (Chiastocheta spp.) pollinate T. europaeus and their larvae feed on developing seeds. Assuming that late flowers in multi-flowered plants attracted flies to the earliest flower on the same plant, we expected more eggs and higher seed predation in early multiple flowers than in single flowers. Relative seed predation would thereby increase with flower number. Both in Sweden and the Alps, more eggs were placed on large flowers. Early multiple flowers were slightly larger than single flowers, and about twice the size of secondary flowers. As a result, and possibly combined with the effects of secondary flowers, early multiple flowers attracted more ovipositing flies and experienced relatively higher seed predation. However, this did not generally result in higher seed predation of multi-flowered hosts. Multiple flowers had greater seed output than single flowers at all altitudes, also in the high alpine and subarctic sites, where single flowers were more abundant. We hypothesise that the distribution of multiple flowers generally is enforced by environmental factors, rather than by fly-host plant interactions, because only very rarely (in triple-flowered alpine plants) was seed predation disproportionate, and the relationship skewed to the disadvantage of the host. The outcome of the mutualistic interaction was often similar in alpine and subarctic populations, but the underlying factors were different. Subarctic flowers had high abortion and low predation rates, while alpine flowers experienced the reversed situation. The higher fly abundance in the Alps suggests a more intense mutualistic interaction than in Sweden. Despite varying ecological and environmental conditions at these sites, the mutualistic relationship was generally in balance. However, when it was unbalanced, this could be explained by fly behaviour in response to floral traits, and by differences in fly abundance. Received: 4 January 1999 / Accepted: 5 May 1999     

On the economics of sit-and-wait foraging: site selection and assessment

We present two models of optimal resource exploitation for sit-and-waitforagers. The first model assumes immediate recognition of sitequality and that site quality does not change over time. Thismodel predicts a forager's minimum acceptable site quality.We present a graphical analysis to show how (1) the distributionof site qualities, (2) the travel time between sites, (3) costof search, and (4) expected duration of the foraging processinfluence the minimum acceptable rate. Our second model allowssite qualities to change and relaxes the assumption of immediaterecognition. This model defines conditions of (1) state duration,(2) recognition time, (3) site abundance, and (4) cost of searchwhere the optimal policy is to stay put in a site regardlessof experience. We discuss the implications of these models forthe design and interpretation of field experiments of site useand habitat selection.     

Reconnecting plants and pollinators: challenges in the restoration of pollination mutualisms

Ecological restoration of plant-pollinator interactions has received surprisingly little attention, despite animal-mediated pollination underpinning reproduction of the majority of higher plants. Here, we offer a conceptual and practical framework for the ecological restoration of pollination mutualisms. Through the use of targeted restoration plantings to attract and sustain pollinators and increased knowledge of the ecological requirements of pollinators, we propose that pollination could be successfully restored in degraded ecosystems. The challenge for pollination biologists is to integrate their findings with those of plant restoration ecologists to ensure sustainable pollination in restored ecosystems.     

毛乌素沙地固沙植物披针叶黄华主要传粉昆虫及其访花行为

披针叶黄华(Thermopsis lanceolata)是我国西部地区早春重要野生蜜源植物,也是一种重要的固沙植物,然而对其繁殖特性的研究甚少.本文在系统调查披针叶黄华的访花昆虫基础上,确定其主要传粉昆虫种类、访花行为、传粉过程以及日活动规律,以期揭示主要访花者行为对其有性繁殖的影响.作者在内蒙古毛乌素沙地设置1个10m×10 m的样方,于2010和2011年在披针叶黄华盛花期,采用目测、拍照和摄像等方式对传粉昆虫进行观测,记录样方内主要访花昆虫种类、数量、访花行为及日活动规律.研究表明,大和切叶蜂(Megachile japonica)和戎拟孔蜂(Hoplitis princeps)是披针叶黄华的主要传粉者,但两种昆虫的访花频率存在显著差异;晴天时,大和切叶蜂在19:00-13:00和16:00-18:00出现两个活动高峰,而戎拟孔蜂只在11:30-16:30出现1个活动高峰,两种蜂的访花活动高峰期存在互补关系.大和切叶蜂访花同时具有盗蜜行为,但其盗蜜行为对披针叶黄华的结籽率没有显著影响.根据种群数量、访花频率综合判断,大和切叶蜂是披针叶黄华优势传粉蜂.     

Behavioural consequences of hunting by expectation: A simulation study of foraging tactics

Foraging behaviour has been simulated using a model that predicts the path taken by an animal foraging for particulate food, the path being defined by the animal's remembrance of its previous foraging success. This is represented in the model by a two-dimensional vector with its modulus encoding an exponentially smoothed average of the animal's feeding rate and its orientation encoding the average direction of travel. As food is ingested the amount ingested and its position are used to update the remembrance, and the animal turns in the adjusted direction travelling at a speed inversely proportional to the average feeding rate. Foraging paths simulated in a patchy environment are shown to have the following properties: (i) They tend to avoid crossing the boundaries of patches from the inside. (ii) They tend to avoid intersecting themselves. (iii) When they do intersect themselves they usually do so more or less at right angles. (iv) They ascend gradients of density of food.