James D. Thomson

University of Toronto | U of T · Department of Ecology and Evolutionary Biology

•Widespread reports of declining populations of pollinators have raised concerns that plant populations may be incurring increasing shortfalls in pollination, but few studies have measured pollination deficits over enough seasons to detect such changes. I have conducted pollen‐supplementation experiments in a wild population of the glacier lily (Er...

Background and aims: If two plant species share pollinators, it has been proposed that the interaction between them may range from competitive to facilitative, depending on the way in which they intermingle. In particular, the presence of a rewarding plant species may increase the rate of pollinator visitation to a less rewarding species in its vi...

Across angiosperm species, the longevity of individual flowers can range from fixed to highly plastic. The orchid family is noteworthy for frequent reports of species in which flower lifespans are greatly prolonged if flowers are not pollinated. Less dramatic cases of pollination-induced senescence of anthesis have been reported for various species...

Geographical variation in pollinators visiting a plant can produce plant populations adapted to local pollinator environments. We documented two markedly different pollinator climates for the spring ephemeral wildflower Claytonia virginica: in more northern populations, the pollen-specialist bee Andrena erigeniae dominated, but in more southern pop...

Table S1. Intra – and interspecific sexual organ reciprocity of experimental plants and plants from natural Swiss populations of P. elatior and P. vulgaris. Table S2. Results of generalized linear mixed‐effects models testing whether anther–stigma distance and pollen transfer differ between pollen transfer types and organ levels. Table S3. Result...

Exploratory behavior—an individual’s response to novel environments, resources, or objects—should vary with the associated benefits, including new sources of food and reduced levels of competition, and the costs, such as predation pressure. Using guppies from multiple streams and rivers in Trinidad, we compared guppies from high- and low-predation...

Shifts in the timing of life history events have become an important source of information about how organisms are responding to climate change. Phenological data have generally been treated as purely temporal, with scant attention to the inherent spatial aspects of such data. However, phenological data are tied to a specific location, and consider...

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains une...

Plant species can influence the pollination and reproductive success of coflowering neighbors that share pollinators. Because some individual pollinators habitually forage in particular areas, it is also possible that plant species could influence the pollination of neighbors that bloom later. When flowers of a preferred forage plant decline in an...

Pollinators that collect pollen – and specifically, pollen-specialist bees – are often considered to be the best pollinators of a (host) plant. Although pollen collectors and pollen specialists often benefit host plants, especially in the pollen that they deliver (their pollination “effectiveness”), they can also exact substantial costs because the...

Surveys of bumble bees and the plants they visit, carried out in 1974 near the Rocky Mountain Biological Laboratory in Colorado, were repeated in 2007, thus permiting the testing of hypotheses arising from observed climate change over the intervening 33-yr period. As expected, given an increase in average air temperature with climate warming and a...

Miller-Struttmann et al. (2015) suggest that, in a North American alpine ecosystem, reduced flower abundance due to climate change has driven the evolution of shorter tongues in two bumble bee species. We accept the evidence that tongue length has decreased, but are unconvinced by the adaptive explanation offered. It posits foraging responses and c...

Plants might be under selection for both attracting efficient pollinators and deterring wasteful visitors. Particular floral traits can act as exploitation barriers by discouraging the unwelcome visitors. In the genus Penstemon, evolutionary shifts from insect pollination to more efficient hummingbird pollination have occurred repeatedly, resulting...

Differences in the pollinator performance of flower visitor sexes are rarely considered. In bumble bees, males differ from workers in morphology and behaviour in ways that may affect their contribution to pollination. We compared the abundance, foraging behaviour, and pollen transfer ability of worker and male bumble bees on late-blooming Gentiana...

Female bees store scattered pollens grains from their bodies for transport by different modes of grooming and pollen packing. Species with corbiculae, such as honey or bumble bees, compress grains into dense pellets borne on the hind tibiae. Other species sweep grains into local concentrations of hairs (scopae), typically around the legs (in Halict...

Floral nectar functions to attract insects, so the inclusion of toxic compounds calls for explanation. Recent work shows that honeybees prefer nectars with low concentrations of caffeine and nicotine, and that associative learning by honeybees is enhanced by caffeine, prompting speculation that pollination service could be enhanced. We directly tes...

Background/Question/Methods The community of floral visitors for a plant species often shows extensive variation across the plants’ geographic range, and this variation may influence the value of each pollinator to plant reproductive success. Claytonia virginica is visited by a pollen-specialist bee Andrena erigeniae and a bombyliid fly Bombylius...

Different strategies to reduce selfing and promote outcrossing have evolved in hermaphroditic flowers. Heterostyly, a complex floral polymorphism that occurs in at least 27 families of angiosperms, is hypothesized to achieve both goals by optimizing cross-pollination (via disassortative pollen transfer) and restricting gamete wastage to autogamy (v...

Understanding the interaction between reward-seeking flower feeding animals and plants requires consideration of the dynamic nature of nectar secretion. Studies on several plants suggest that nectar secretion may increase in response to its removal, but it is not clear whether the phenomenon is widespread. We determined whether 11 species of Colora...

Abstract Ants on flowers can disrupt pollination by consuming rewards or harassing pollinators, but it is difficult to disentangle the effects of these exploitative and interference forms of competition on pollinator behavior. Using highly rewarding and quickly replenishing artificial flowers that simulate male or female function, we allowed bumble...

Individuals of some pollinator species, including bumble bees, commonly revisit small areas habitually to forage on a favorite plant species. However, it is unknown how such individual area-fidelity can impact plant pollination. When a bumble bee’s favorite forage plant goes out of bloom in an area, because of this tendency towards area-fidelity, i...

Background/Question/Methods The nature of interspecific relationships can be context-dependent, and relationships between plants and floral visitors are no exception. Floral visitors can increase plant fitness by acting as pollinators, or may lower plant fitness by acting as nectar or pollen thieves. The same insect may act as a mutualist in some...

Background/Question/Methods Pollinators must make decisions about where to forage in landscapes where floral resources are patchy at many spatial scales. These foraging decisions are expected to be economical, for example, pollinators may prefer to forage in large and less isolated flower patches. These resulting foraging decisions can influence p...

Animals collecting food from renewable resource patches scattered in space often establish small foraging areas to which they return faithfully. Such area fidelity offers foraging advantages through selection of profitable patches, route minimization, and regular circuit visits to these patches (“trapline foraging”). Resource distribution under fie...

Trapline foraging (repeated sequential visits to a series of feeding locations) has often been observed in animals collecting floral resources. Past experiments have shown that bumble bees cannot always develop accurate (i.e., repeatable) traplines to a sufficient level, despite their economic advantages in many situations. The bees' preference for...

Surveys in 1974 of bumble bee species distributions along elevational gradients (Pyke 1982) were revisited to reevaluate the original conclusion that coexistence of bumble bee species can be ascribed to niche differentiation, primarily on the basis of proboscis lengths and the associated corolla lengths of visited flowers. Each bee species largely...

The capacity to discriminate between choice options is crucial for a decision-maker to avoid unprofitable options. The physical properties of rewards are presumed to be represented on context-dependent, nonlinear cognitive scales that may systematically influence reward expectation and thus choice behavior. In this study, we investigated the discri...

Pollinators must make decisions about where to forage in landscapes where floral resources are patchy at many spatial scales. The resulting foraging decisions can influence plant pollination and reproductive success. Despite this importance, we still have a poor understanding of how pollinators use patches which vary in floral abundance and isolati...

1. The primary function of secondary plant metabolites is thought to be defence against herbivores. The frequent occurrence of these same noxious compounds in floral nectar, which functions primarily to attract pollinators, has been seen as paradoxical. 2. Although these compounds may have an adaptive purpose in nectar, they may also occur as a non...

We developed novel artificial flowers that dispense and receive powdered food dyes as pollen analogues while their nectar is replenished by capillary action. Dye receipt, which can be measured colourimetrically, is a direct surrogate for pollen receipt or female reproductive success, but can also serve to compare pollen donation (male reproductive...

1. Although competition for pollination is often invoked as a driver of broad-scale evolutionary and ecological patterns, we still lack a clear understanding of the mechanics of such competition. When flower visitors alternate between two species of flower, heterospecific pollen transfer takes place. The impact of these mixed loads on the female re...

Female bumble bee workers are the most recognised bumble bee caste to act as pollinators of wild plants. However, male bumble bees can be common on flowers in the late summer and fall, and they differ from worker bees in both morphology and behaviour, so may differ as pollinators for plants. For instance, male bumble bees may retain more pollen tha...

One possible effect of climate change is the generation of a mismatch in the seasonal timing of interacting organisms, owing to species-specific shifts in phenology. Despite concerns that plants and pollinators might be at risk of such decoupling, there have been few attempts to test this hypothesis using detailed phenological data on insect emerge...

1. We revisited bumble bee survey data collected by Pyke in 1974 (Pyke, Ecology, 63, 555–573, 1982) to evaluate seasonal changes in abundances of bumble bees and their floral resources, diel patterns of bumble bee activity, and elevation effects on plant and bumble bee phenology. 2. Bumble bee abundance increased during summer as spring queens foun...

Background and Aims In sub-alpine habitats, patchiness in snowpack produces marked, small-scale variation in flowering phenology. Plants in early- and late-melting patches are therefore likely to experience very different conditions during their flowering periods. Mertensia fusiformis is an early-flowering perennial that varies conspicuously in sty...

Pollinator exclusion bags for small herbaceous plants are much more convenient to apply and remove if their bottom edge is made in the form of a cloth tunnel loaded with sand to conform to the terrain. Damage and inadvertent selfing of flowers are minimized.

Two free-foraging colonies of Bombus terricola Kirby were stressed, on alternate days, by removing either their honey or their pollen stores. The amount of pollen taken into the colonies by foragers was significantly greater under pollen stress than under honey stress. This effect was not due to an increase in the number of foraging trips but rathe...

In field experiments, the nectar and pollen levels of Aralia hispida inflorescences were independently manipulated. In the absence of Vespula spp., Bombus spp. workers (the primary pollinators) appeared to prefer nectar-enriched inflorescences, learning their locations and visiting them at a higher rate, but did not respond to variation in pollen....

To determine whether interspecific pollen transfer could reduce seed production by two sympatric lilies, Erythronium albidum and Erythronium americanum, we hand-pollinated flowers with mixtures of conspecific and heterospecific pollen. These species exhibited typical unilateral interspecific incompatibility, i.e., pollen tubes from the self-inferti...

Exposure-cage trials in spruce–fir forest near Doaktown, N.B., Canada, showed that Matacil aminocarb insecticide, applied for control of spruce budworm, increased mortality rates of several types of solitary bees and syrphid flies, although previous studies had found no effect on bumblebees. Of two plant species predominantly pollinated by the sens...

Many plant species rely on female bumble bee workers for pollen transfer. However, male bumble bees, which differ both behaviourally and morphologically from female workers, also visit many species of flowering plants and may transfer pollen differently. Males can outnumber workers on some plants, particularly those that flower late in the season....

Spatio-temporal patterns of snowmelt and flowering times affect fruiting success in Erythronium grandiflorum Pursh (Liliaceae) in subalpine western Colorado, USA. From 1990 to 1995, I measured the consistency across years of snowmelt patterns and flowering times along a permanent transect. In most years since 1993, I have monitored fruit set in tem...

Background/Question/Methods In generalist pollination systems, what role do individual pollinator species play in plant reproductive success? Compared to generalist pollinators, oligolectic pollinators are abundant, efficient foragers, and can provide dependable pollination services to their host plant. However, they also can excel at pollen remov...

One floral characteristic associated with bat pollination (chiropterophily) is copious pollen production, a pattern we confirmed in a local comparison of hummingbird- and bat-adapted flowers from a cloud forest site in Ecuador. Previous authors have suggested that wasteful pollen transfer by bats accounted for the pattern. Here we propose and test...

Nectar-feeding animals have served as the subjects of many experimental studies and theoretical models of foraging. Their willingness to visit artificial feeders renders many species amenable to controlled experiments using mechanical “flowers” that replenish nectar automatically. However, the structural complexity of such feeders and the lack of a...

Climate change is expected to alter patterns of species co-occurrence, in both space and time. Species-specific shifts in reproductive phenology may alter the assemblages of plant species in flower at any given time during the growing season. Temporal overlap in the flowering periods (co-flowering) of animal-pollinated species may influence reprodu...

Climate change is causing many plants to flower earlier in spring, exposing them to novel selection pressures, including-potentially-pollinator shortages. Over 2 years that contrasted in timing of flowering onset, we studied reproductive strategies, pollen limitation, and selection on flowering time in Mertensia fusiformis, a self-incompatible, spr...

Diet has a significant effect on pathogen infections in animals and the consumption of secondary metabolites can either enhance or mitigate infection intensity. Secondary metabolites, which are commonly associated with herbivore defense, are also frequently found in floral nectar. One hypothesized function of this so-called toxic nectar is that it...

Background/Question/Methods There are concerns that species-specific shifts in phenology in response to climate warming may lead to temporal mismatches between interacting species. As yet, there have been few empirical data to evaluate whether (or which) plant-pollinator interactions might be vulnerable to phenological disjunctions brought about b...

Abstract 1. Secondary metabolites have acute or chronic post-ingestive effects on animals, ranging from death to growth inhibition to reduced nutrient assimilation. 2. Although characterised as toxic, the nectar of Gelsemium sempervirens is not lethal to pollinators, even when the concentration of the nectar alkaloid gelsemine is very high. However...

Flowers adapted for hummingbird pollination are typically red. This correlation is usually explained by the assertion that nectar- or pollen-stealing bees are "blind" to red flowers. However, laboratory studies have shown that bees are capable of locating artificial red flowers and often show no innate preference for blue over red. We hypothesised...

In many nectarless flowering plants, pollen serves as both the carrier of male gametes and as food for pollinators. This can generate an evolutionary conflict if the use of pollen as food by pollinators reduces the number of gametes available for cross-fertilization. Heteranthery, the production of two or more stamen types by individual flowers red...

Trapline foraging (repeated sequential visits to a series of feeding locations) has been often observed in pollinators collecting nectar or pollen from flowers. Although field studies on bumble-bees and hummingbirds have clarified fundamental aspects of this behaviour, trapline foraging still poses several difficult questions from the perspectives...

In a hypothesis that has remained controversial since its inception, Darwin suggested that long-tubed flowers and long-tongued pollinators evolved together in a coevolutionary race, with each selecting for increasing length in the other. Although the selective pressures that flowers impose on tongue length are relatively straightforward, in that lo...

Environmental changes, such as current climate warming, can exert directional selection on reproductive phenology. In plants, evolution of earlier flowering requires that the individuals bearing genes for early flowering successfully reproduce; for non-selfing, zoophilous species, this means that early flowering individuals must be visited by polli...

A number of different types of flower-visiting animals coexist in any given habitat. What evolutionary and ecological factors influence the subset of these that a given plant relies on for its pollination? Addressing this question requires a mechanistic understanding of the importance of different potential pollinators in terms of visitation rate (...

Background/Question/Methods Climate change is expected to alter patterns of species co-occurrence, in both space and time. Species-specific shifts in reproductive phenology may produce changes in the assemblages of plant species in flower at any given time during the growing season. Temporal overlap in the flowering periods (co-flowering) of anim...

The sensitivity of our diffusion model to variation in parameter estimates. In each panel, we show how variation in a single parameter affects the predicted prevalence of C. bombi during late summer (t = 14 weeks in the model), relative to the distance from the source (greenhouse). We explore a range of decay rates (μ in d−1, panel A), pathogen pro...

Experimental parameter estimates (0.06 MB DOC)

Parameter estimates from the literature (0.07 MB DOC)

Temporal decline in the infectivity of pathogenic C. bombi cells deposited at flowers. Each point represents a single bumble bee's (n = 76) predicted probability of infection from the logistic regression including bee size and dose as covariates (see Materials and Methods). The solid line, indicating the time-dependent decrease in infectivity, is a...

(0.04 MB DOC)

The conservation of insect pollinators is drawing attention because of reported declines in bee species and the 'ecosystem services' they provide. This issue has been brought to a head by recent devastating losses of honey bees throughout North America (so called, 'Colony Collapse Disorder'); yet, we still have little understanding of the cause(s)...

Animals collecting resources that are fixed in space but replenish over time, such as floral nectar and pollen, often establish small foraging areas to which they return faithfully. Some repeatedly visit a set of patches in a significantly predictable sequence (so-called "trapline foraging"), which may allow them to focus on more profitable patches...

Early-flowering species may be especially susceptible to occasional pollen limitation and, therefore, may benefit from a mixed-mating strategy that provides reproductive assurance. We studied cleistogamous (CL) and chasmogamous (CH) fruit set of spring-flowering Viola praemorso Dougl. ex Lindl. along an elevational gradient in the Rocky Mountains,...

In certain angiosperm genera, closely related species have diverged from one another to converge on different pollination syndromes, whereas species with intermediate phenotypes are rare or absent. Convergent conformity to syndromes implies the existence of ''evolutionary attractors'' toward which phenotypes are drawn; divergent breaks from conform...

In socially living animals, individuals interact through complex networks of contact that may influence the spread of disease. Whereas traditional epidemiological models typically assume no social structure, network theory suggests that an individual's location in the network determines its risk of infection. Empirical, especially experimental, stu...

A new yeast species, Candida gelsemii, is described to accommodate three isolates recovered in Georgia, USA, from the toxic nectar of the Carolina jessamine (Gelsemium sempervirens). The species resembles other members of the Metschnikowiaceae clade that have been recovered from nectar, but differs in a number of morphological and physiological cha...

Secondary compounds may benefit plants by deterring herbivores, but the presence of these defensive chemicals in floral nectar may also deter beneficial pollinators. This trade-off between sexual reproduction and defense has received minimal study. We determined whether the pollinator-deterring effects of a nectar alkaloid found in the perennial vi...

In the clade of Penstemon and segregate genera, pollination syndromes are well defined among the 284 species. Most display combinations of floral characters associated with pollination by Hymenoptera, the ancestral mode of pollination for this clade. Forty-one species present characters associated with hummingbird pollination, although some of thes...

Pollen removal and deposition to two crop species are measured as a preliminary screening tool to compare pollination by two commercially available bee species. The ratio of pollen deposited to pollen removed offers a rough estimate of pollinator effectiveness per visit. Differences among pollinators in these measures can help direct future study....

Despite broad consensus on the power of experiments, correlational studies are still important in ecology, and may become more so as spatial studies proliferate. Conventional correlation analysis, however, (1) fundamentally conflicts with the basic ecological concept of limiting factors, and (2) ignores spatial structure in data, which can produce...

Isolated bumblebee workers, Bombus impatiens Cresson 1863, developed their ovaries to produce laying-sized eggs in 11 days, but did so 5 days faster in queenless groups of 2-12 that they came to dominate. In groups larger than pairs, reproductive dominance (as measured by oocyte length) was distributed continuously in a graded hierarchy, rather tha...

Patch departure was studied in experimentally naive, laboratory-reared bumble bees, Bombus impatiens (Cresson 1863) foraging from artificial umbels (rings of eight wells in blocks of Plexiglas, each well containing 0-4 μL of 30% sucrose solution). Bees from three colonies probed an average of about ten wells (all available wells plus two revisits t...

Foraging on resources that are fixed in space but that replenish over time, such as floral nectar and pollen, presents animals with the problem of selecting a foraging route. What can flower visitors such as bees do to optimize their foraging routes, that is, reduce return time or route distance? Some repeatedly visit a set of plants in a significa...

The success of a pathogen depends not only on its transmission to new hosts, but also on its ability to colonize and persist within its current host. Studies of within-host dynamics have focused on only a few diseases of humans, whereas little is known about the factors that influence pathogen populations as they develop inside non-human hosts. Her...

The basic tenet of sex allocation theory is that an organism's reproductive success, through either male or female function, can be represented as a sex-specific, monotonic, increasing function of the organism's investment of resources in that function. The shapes of these curves determine what patterns of resource allocation can be evolutionarily...

Parasitic infection can influence a variety of behavioural mechanisms in animals, but little is known about the effects of infection on the cognitive processes underlying ecologically relevant behaviours. Here, we examined whether parasitic infection alters cognitive aspects of foraging in a social insect, the bumble-bee (Bombus impatiens). In cont...

When pollen from Hieracium floribundum Wimmer and Grab. (Compositae) was applied to stigmas of Diervilla lonicera Mill. (Caprifoliaceae) in mixtures with Diervilla pollen, Diervilla fecundity was strongly depressed. While this phenomenon is unlikely to be of importance to Diervilla under field conditions, this property of Hieracium pollen may have...