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Author(s): Jeremiah Marsicek (corresponding author) [1]; Bryan N. Shuman [1]; Patrick J. Bartlein [2]; Sarah L. Shafer [3]; Simon Brewer [4] Cooling during most of the past two millennia has [...]

Patterns of jack pine (Pinus banksiana Lambert) pollen cone production are of interest because they may help explain jack pine budworm (Choristoneura pinus pinus Freeman) outbreak patterns. We used generalized linear mixed models to analyze pollen cone production in 180 permanent plots in Ontario, Canada between 1992 and 2008. Pollen cone production increased with stand age, and large trees in sparsely-populated stands produced more pollen cones. Defoliation decreased the propensity of trees to produce pollen cones for at least two years. We also identified important patterns that are not explained by defoliation and stand characteristics. Pollen cone production is spatially synchronized among years, trees in central Ontario produced more pollen cones than trees in northwestern Ontario, and background cone production increased over time in the central region but not in more northwestern plots. Synchronized reproduction is common among tree species, but has not previously been noted for jack pine pollen cones. Increasing cone production in central Ontario may be evidence of changing forest and (or) climatic conditions and deserves further investigation. Our model can be used to quantitatively predict pollen cone production and assess the risk of jack pine budworm defoliation. Key words: Choristoneura pinus pinus, Pinus banksiana, population dynamics, spatial synchrony, insect plant interactions. Resume: Les profils de production de cones males chez le pin gris (Pinus banksiana Lambert) presentent un interet parce qu'ils pourraient contribuer a expliquer le comportement des epidemies de tordeuse du pin gris (Choristoneura pinus pinus Freeman). Nous avons utilise des modeles lineaires mixtes generalises pour analyser la production de cones males dans 180 placettes permanentes en Ontario, au Canada, entre 1992 et 2008. La production de cones males augmentait avec l'age du peuplement et les gros arbres dans les peuplements clairsemes produisaient plus de cones males. La defoliation reduisait la propension des arbres a produire des cones males pendant au moins deux ans. Nous avons aussi identifie des profils importants qui ne sont pas expliques par la defoliation ni par les caracteristiques du peuplement. La production de cones males est spatialement synchronisee d'une annee a l'autre: les arbres produisaient plus de cones males dans le centre que dans le nord-ouest de l'Ontario, et la production historique de cones males a augmente avec le temps dans la region centrale mais pas dans les placettes les plus eloignees vers le nord-ouest. La reproduction synchrone est courante parmi les especes d'arbre mais n'avait pas jusqu'ici ete observee chez les cones males du pin gris. La production accrue de cones males dans le centre de l'Ontario pourrait etre un indice que les conditions climatiques et la foret changent et merite d'etre davantage etudiee. Notre modele peut etre utilise pour predire de facon qualitative la production de cones males et evaluer le risque de defoliation par la tordeuse du pin gris. [Traduit par la Redaction] Mots-cles: Choristoneura pinus, Pinus banksiana, dynamique des populations, synchronisme spatial, interactions entre les plantes et les insects., Introduction Many animal populations undergo large, spatially synchronized changes in abundance over time, and determining the causes of these patterns is a central topic in population ecology (Bjornstad and Grenfell [...]

Xyridaceae are a predominantly tropical family of five genera that exhibit two pollen morphologies often considered to be of taxonomic importance. Xyris comprises about 95% of the species and is characterized by medium to large, elliptic, sulcate pollen grains. The other pollen class is spheroidal grains without an evident aperture. Many of the species with spheroidal grains have remarkably large and ornamented pollen found to be species specific in earlier research. A scanning electron microscopy investigation of 23 taxa representing all genera with spheroidal pollen revealed new data to further distinguish the genera based on pollen characters. Reliable specific pollen characters need to be evaluated in a statistical study. Keywords Clypeate * Inaperturate * Omniaperturate * Scanning electron microscopy, Xyridaceae (Poales) are a predominantly tropical and subtropical family of five genera and about 415 species (Kral, 1998; Campbell, 2004a; 2008). The family is most speciose in South America where [...]

Self-incompatibility (SI)--intraspecific pollen recognition systems that allow plants to avoid inbreeding--in the Solanaceae (the nightshade family) is controlled by a polymorphic S locus where 'self' pollen is rejected on pistils with matching S alleles. In contrast, unilateral interspecific incompatibility (UI) prevents hybridization between related species, most commonly when the pollen donor is self-compatible (SC) and the recipient is SI. We observed that in Solanum, a pollen-expressed Cullin1 gene with high similarity to Petunio SI factors interacts genetically with a gene at or near the S locus to control UI. Cultivated tomato and related red- or orange-fruited species (all SC) exhibit the same loss-of-function mutation in this gene, whereas the green-fruited species (mostly SI) contain a functional allele; hence, similar biochemical mechanisms underlie the rejection of both 'self' and interspecific pollen. 10.1126/science.1197908

Pollen is unique among floral rewards in functioning as both a carrier of gametes and an attractant and nutritious resource for floral visitors. Animals that collect pollen without pollinating (pollen thieves) could reduce siring success of thieved plants and cause pollen limitation of seed set at the population level; however, such impacts on plant reproduction have not been demonstrated experimentally. To test these effects we added hives of native honey bees (Apis mellifera scutellata) to populations of a primarily bird-pollinated plant, Aloe maculata, in eastern South Africa. In field and aviary trials, bee addition increased pollen removal from anthers but decreased pollen deposition on stigmas, and so reduced both male and female pollination components. Further, total seed production decreased with hive addition in the aviary experiment and in three of four field populations, indicating that population-level pollen theft can also compromise reproductive success. In the field, naturally occurring allodapine bees also seemed to act as pollen thieves, outweighing the effect of honey bee hive addition at one of the four aloe populations. Our results highlight the importance of social bees as pollen thieves, even of plants that have evolved in their presence, and the role of dichogamy in promoting pollen theft. Given the commonness of both social bees and dichogamy, pollen theft is likely a much more common influence on floral ecology and evolution than suggested by the sparse literature. Key words. Aloe maculata; antagonist: Apis mellifera scutellata; cheating: honey bee; pollen theft; pollination efficiency; South Africa; sunbirds.

Soybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures > 35[degrees]C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50[degrees]C at 5[degrees]C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 [micro]m). Mean cardinal temperatures ([T.sub.min], [T.sub.opt], and [T.sub.max]) were 13.2, 30.2, and 47.2[degrees]C for PG and 12.1, 36.1, and 47.0[degrees]C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum ([T.sub.max]), minimum ([T.sub.min]), and optimum ([T.sub.opt]) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat-tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30[degrees]C) compared with heat-intermediate (PI 471938) and heat-sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumellae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88-5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [C[O.sub.2]] did not modify reproductive parameters or CTRI. The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature-tulerant genotypes and temperature-dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.

Ergot (caused predominantly by Claviceps africana Freder., Mantle & De Milliano) is a disease of sorghum (Sorghum bicolor L. Moench), with pollen trails reported to be associated with resistance. This study investigated the genetic architecture and the role of pollen quantity (PQ) and pollen viability (PV) in ergot resistance in an F5 recombinant inbred line (RIL) sorghum population developed from the cross between an elite germplasm line, 31945-2-2 from Australia, and a recently reported putatively resistance source line, IS8525. Percentage ergot infection (PCERGOT) in IS8525 was very low, while in contrast, 31945-2-2 was heavily infected at all inoculation dates of the two field trials conducted under artificial epiphytotic conditions during 2001 and 2002. The distribution of the predicted means for PCERGOT, PQ, and PV was normal, suggesting that the traits are polygenic in nature. Genetic correlations between the two pollen traits and PCERGOT were moderately negative, indicating that there might be some common genetic factors controlling these traits. However, low [R.sup.2] values of PQ (11%) and PV (9%) suggest that only a small part of the total variability in ergot resistance in this population was due In the variability in PQ and PV. Correlations between ergot scores for different sampling dates (SDATEs) and years were moderate to high, indicating relatively low levels of genotype x environment interaction. Genetic variance and broad sense heritability were also high, indicating that ergot resistance is likely to respond well to conventional selection.

Self-incompatibility (SI) prevents inbreeding through specific recognition and rejection of incompatible pollen. In incompatible Papaver rhoeas pollen, SI triggers a [Ca.sup.2+] signaling cascade, resulting in the inhibition of tip growth, actin depolymerization, and programmed cell death (PCD). We investigated whether actin dynamics were implicated in regulating PCD. Using the actin-stabilizing and depolymerizing drugs jasplakinolide (Jasp) and latrunculin B, we demonstrate that changes in actin filament levels or dynamics play a functional role in initiating PCD in P. rhoeas pollen, triggering a caspase-3--like activity. Significantly, SI-induced PCD in incompatible pollen was alleviated by pretreatment with Jasp. This represents the first account of a specific causal link between actin polymerization status and initiation of PCD in a plant cell and significantly advances our understanding of the mechanisms involved in SI.

The antigenic profile of Olea europaea pollen from different Mediterranean cultivars was obtained by MALDI mass spectrometry. A simple procedure of chemical fractionation of the whole antigen extract was developed, whereby less complex, or pure, fractions of antigen candidate were obtained prior to mass spectrometric analysis. Some of the features of protein structure and distribution probably depend on cultivar adaptation to the environment. The profilings of pollen proteins thus obtained allow the distinction of the analyzed cultivars into three distinct groups: (i) those characterized by a low Ole e 1 content; (ii) those over-enriched in Ole e 1 and (iii) that containing Ole e 3 and Ole e 7 only. The latter consists of at least four isoforms differing by the degree of glycosilation. These results demonstrate that the proposed experimental procedure, can supply valuable information on the antigens' micro heterogeneity.

Brasenia is a monotypic genus sporadically distributed throughout the Americas, Asia, Australia, and Africa. It is one of eight genera that comprise the two families of Nymphaeales, or water lilies: Cabombaceae (Brasenia, Cabomba) and Nymphaeaceae (Victoria, Euryale, Nymphaea, Ondinea, Barclaya, Nuphar). Evidence from a range of studies indicates that Nymphaeales are among the most primitive angiosperms. Despite their phylogenetic utility, pollen developmental characters are not well known in Brasenia. This paper is the first to describe the complete pollen developmental sequence in Brasenia schreberi. Anthers at the microspore mother cell, tetrad, free microspore, and mature pollen grain stages were studied using combined scanning electron, transmission electron, and light microscopy. Both tetragonal and decussate tetrads have been identified in Brasenia, indicating successive microsporogenesis. The exine is tectate-columellate. The tetrad stage proceeds rapidly, and the infratectal columellae are the first exine elements to form. Development of the tectum and the foot layer is initiated later during the tetrad stage, with the tectum forming discontinuously. The endexine lamellae form during the free microspore stage, and their development varies in the apertural and non-apertural regions of the pollen wall. Degradation of the secretory tapetum also occurs during the free microspore stage. Unlike other water lilies, Brasenia is wind-pollinated, and several pollen characters appear to be correlated with this pollination syndrome. The adaptive significance of these characters, in contrast to those of the fly-pollinated genus Cabomba, has been considered. Brasenia does not produce pollenkitt nor develop tectal microchannels as does Cabomba. Instead, the discontinuity of the tectum reduces the amount of sporopollenin in the wall, which may allow for more effective wind dispersal. The importance of reassessing palynological characters in light of new ontogenetic data and the phylogenetic implications of this reevaluation are also discussed. Key words: anther; Brasenia; Cabombaceae; development; Nymphaeales; ontogeny; pollen; ultrastructure.

The Velay sequence (France) provides a unique, continuous, palynological record spanning the last four climatic cycles. A pollen-based reconstruction of temperature and precipitation displays marked climatic cycles. An analysis of the climate and vegetation changes during the interglacial periods reveals comparable features and identical major vegetation successions. Although Marine Isotope Stage (MIS) 11.3 and the Holocene had similar earth precessional variations, their correspondence in terms of vegetation dynamics is low. MIS 9.5, 7.5, and especially 5.5 display closer correlation to the Holocene than MIS 11.3. Ecological factors, such as the distribution and composition of glacial refugia or postglacial migration patterns, may explain these discrepancies. Comparison of ecosystem dynamics during the past five interglacials suggests that vegetation development in the current interglacial has no analogue from the past 500,000 years. climatic cycles | interglacials | pollen records

A procedure to experimentally simulate pollen coronas is discussed. Observed coronas are due to pine and birch pollen having different geometries. Using computer simulations, two-dimensional projections of a large number of pollenlike objects with adjustable shapes, with or without preferential orientation and statistical or regular spatial distribution, are generated. The photograph of the printout allows samples with typical sizes between 20 and 200 [micro]m. Their diffraction patterns can closely resemble the ones observed in nature and predicted by theory. OCIS codes: 010.1290, 010.1310.

A method was developed for the analysis of the UV-absorbing sporopollenin monomers p-coumaric acid and ferulic acid in very low numbers of pollen. This enables the analysis of pollen or spores from cultured plants, from herbarium collections, and from sediment, soil, and peat cores. The method involves thermally assisted hydrolysis and methylation using tetramethylammonium hydroxide combined with gas chromatography and mass spectrometry. Pyrolysis, gas chromatographic, and mass spectrometric conditions were optimized for the analysis of minimal amounts of pollen. The method has a detection limit of 460 fresh pollen of Alnus glutinosa and a relative standard deviation of ~10% between 100 and 600 pollen.

Records of abnormal gymnosperm pollen morphotypes from coeval localities in Russia and NW China provide independent and unique evidence of deteriorating atmospheric conditions at the close of the Permian. Although at similar palaeolatitude, the Vologda region of European Russia and the Junggar Basin of Xinjiang Province, China, were thousands of kilometres apart and on different tectonic plates. The co-occurrence of the megaspore Otynisporites eotriassicus Fuglewicz 1977, and its restricted distribution elsewhere in marine sections with either Late Permian ammonoids or the basal Triassic conodont marker Hindeodus parvus, confirms the age range, and correlation of the Russian and NW Chinese sections. In three Chinese sections, rapid changes in carbon isotopic ([[sigma].sup.13][C.sub.org]) composition of between 4 and 10 [per thousand] occur over the intervals showing abnormal pollen. These patterns reflect bioclastic facies contributions responding to local environmental changes. They are nevertheless coincident with global perturbations in the atmosphere, caused by extensive volcanic activity around the Permian-Triassic boundary. Keywords: Permian, Triassic, pollen, carbon isotopes, palaeoclimate.

High-resolution analyses of a late Holocene core from Kettle Lake in North Dakota reveal coeval fluctuations in loss-on-ignition carbonate content, percentage of grass pollen, and charcoal flux. These oscillations are indicative of climate-fuel-fire cycles that have prevailed on the Northern Great Plains (NGP) for most of the late Holocene. High charcoal flux occurred during past moist intervals when grass cover was extensive and fuel loads were high, whereas reduced charcoal flux characterized the intervening droughts when grass cover, and hence fuel loads, decreased, illustrating that fire is not a universal feature of the NGP through time but oscillates with climate. Spectral and wavelet analyses reveal that the cycles have a periodicity of [approximately equal to] 160 yr, although secular trends in the cycles are difficult to identify for the entire Holocene because the periodicity in the early Holocene ranged between 80 and 160 yr. Although the cycles are evident for most of the last 4,500 yr, their occasional muting adds further to the overall climatic complexity of the plains. These findings clearly show that the continental interior of North America has experienced short-term climatic cycles accompanied by a marked landscape response for several millennia, regularly alternating between dual landscape modes. The documentation of cycles of similar duration at other sites in the NGP, western North America, and Greenland suggests some degree of regional coherence to climatic forcing. Accordingly, the effects of global warming from increasing greenhouse gases will be superimposed on this natural variability of drought. charcoal | Holocene | Northern Great Plains | pollen | aridity cycles

Pollen collected from snow samples on the Quelccaya Ice Cap in 2000 and 2001 reveals significant interannual variability in pollen assemblage, concentration, and provenance. Samples from 2000, a La Nina year, contain high pollen concentrations and resemble samples from the Andean forests (Yungas) to the east. Samples from 2001, an El Nino year, contain fewer pollen and resemble those from the Altiplano. We suggest that varying wind patterns under different El Nino/Southern Oscillation (ENSO) conditions may affect the processes of pollen transport over the Altiplano and on the ice cap, although confounding variables such as flowering phenology and sublimation should also be considered Key Words: biogeography, ice-core palynology, Peru, pollen dispersal, Quelccaya ice cap.

The inheritance and compatibility behavior of two spontaneous homostyled mutants is determined for exploring the genetic architecture of distyly in Turnera spp. Pollen competition result in aberrant segregation ratios among some crosses and the inheritance of distyly in Turnera is underlied by a linked gene complex.

It is usually assumed that pollen availability does not limit reproduction in wind-pollinated plants. Little evidence either supporting or contradicting this assumption exists, despite the importance of seed production to population persistence and growth. We investigated the role of pollen limitation in an invasive estuarine grass (Spartina alterniflora), with a manipulative pollen supplementation and exclusion experiment in areas of high population density and at the low-density leading edge of the invasion. We also quantified pollen deposition rates on stigmas and pollen traps along a windward to leeward gradient. We found pollen impoverishment at the low-density leading edge of a large invasion, causing an 8-fold reduction in seed set. We found 9-fold more pollen on stigmas of high-density plants than on those of low-density plants. Pollen deposition rates on stigmas and traps did not increase downwind of low-density plants but did increase downwind of high-density plants and dropped off precipitously across a gap that lacked pollen donors. The delay of appreciable numbers of seed caused by pollen limitation persists for decades until vegetative growth coalesces plants into continuous meadows, and this Allee effect has slowed the rate of spread of the invasion.

Determining whether seed production is pollen limited has been an area of intensive empirical study over the last two decades. Yet current evidence does not allow satisfactory assessment of the causes or consequences of pollen limitation. Here, we critically evaluate existing theory and issues concerning pollen limitation. Our main conclusion is that a change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen-resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation. We formalize and extend D. Haig and M. Westoby's conceptual model, and illustrate its use in guiding research on the evolutionary consequences of pollen limitation, i.e., whether plants evolve or have evolved to ameliorate pollen limitation. This synthesis also reveals that we are only beginning to understand when and how pollen limitation at the plant level translates into effects on plant population dynamics. We highlight the need for both theoretical and empirical approaches to gain a deeper understanding of the importance of life-history characters, Allee effects, and environmental perturbations in population declines mediated by pollen limitation. Lastly, our synthesis identities a critical need for research on potential effects of pollen limitation at the community and ecosystem levels. Key words: elasticities; hand pollination; plant demography, pollen; pollen limitation, causes and consequences; pollinators; seed set; supplemental pollination.

A quantitative annual mean temperature reconstruction from an annually laminated lake-sediment sequence in Estonia, eastern Europe, shows a distinct cold period at 8400-8080 yr B.P. (= before A.D. 2000); the timing is consistent with that seen in the Greenland ice-core data and various high-resolution records from western Europe. During maximal cooling at 8250-8150 yr B.P., the annual mean temperature in Estonia was ~2.0 [degrees]C colder than prior to and ~3.0 [degrees]C colder than after the cooling. The pollen-stratigraphic and sedimentological data suggest especially cold and snowy winter conditions. The duration and amplitude of the cold event agree with the modeled impact of a sudden freshening of the North Atlantic surface water and subsequent perturbation of the thermohanne circulation. Provided that the cold event was caused by a pulse of freshwater--from the melting Laurentide Ice Sheet--to the North Atlantic, the results indicate a strong teleconnection between the North Atlantic oceanic forcing and the east European climate at least up to long 26[degrees]E, mediated probably by the changing intensity of the zonal atmospheric circulation. Keywords: varve chronology, pollen, oxygen isotopes, 8200 yr B.P. cold event, thermohaline circulation, Estonia.

Reproductive genes and traits evolve rapidly in many organisms, including mollusks, algae, and primates. Previously we demonstrated that a family of glycine-rich pollen surface proteins (GRPs) from Arabidopsis thaliana and Brassica oleracea had diverged substantially, making identification of homologous genes impossible despite a separation of only 20 million years. Here we address the molecular genetic mechanisms behind these changes, sequencing the eight members of the GRP cluster, along with 11 neighboring genes in four related species, Arabidopsis arenosa, Olimarabidopsis pumila, Capsella rubella, and Sisymbrium irio. We found that GRP genes change more rapidly than their neighbors; they are more repetitive and have undergone substantially more insertion/ deletion events while preserving repeat amino acid composition. Genes flanking the GRP cluster had an average [K.sub.a]/[K.sub.s] [approximately equal to] 0.2, indicating strong purifying selection. This ratio rose to [approximately equal to] 0.5 in the first GRP exon, indicating relaxed selective constraints. The repetitive nature of the second GRP exon makes alignment difficult; even so, [K.sub.a]/[K.sub.s] within the Arabidopsis genus demonstrated an increase that correlated with exon length. We conclude that rapid GRP evolution is primarily due to duplication, deletion, and divergence of repetitive sequences. GRPs may mediate pollen recognition and hydration by female cells, and divergence of these genes could correlate with of even promote speciation. We tested cross-species interactions, showing that the ability of A. arenosa stigmas to hydrate pollen correlated with GRP divergence and identifying A. arenosa as a model for future studies of pollen recognition.

Pollen fecundity is crucial to crop productivity and also to biodiversity in general. Pollen development is supported by the tapetum, a metabolically active sporophytic nurse layer that devotes itself to this process. The tapetum in cereals and a vast majority of other plants is of the nonamoeboid type. Unable to reach out to microspores, it secretes nutrients into the anther locule where the microspores reside and develop. Orbicules (Ubisch bodies), studied in various plants since their discovery [approxiametly equal to] 140 years ago, are a hallmark of the secretory tapetum. Their significance to tapetal or pollen development has not been established. We have identified in wheat and rice an anther-specific single-copy gene (per haploid genome equivalent) whose suppression in rice by RNA interference nearly eliminated the seed set. The flowers in the transgenics were normal for female functions, but the pollen collapsed and became less viable. Further characterization of the gene product, named RAFTIN, in wheat has shown that it is present in pro-orbicule bodies and it is accumulated in Ubisch bodies. Furthermore, it is targeted to microspore exine. Although the carboxyl portion of RAFTINs shares short, dispersed amino acid sequences (BURP domain) in common with a variety of proteins of disparate biological contexts, the occurrence RAFTIN per se is limited to cereals; neither the Arabidopsis genome nor the vast collection of ESTs suggests any obvious dicot homologs. Furthermore, our results show that RAFTIN is essential for the late phase of pollen development in cereals.

Pollen movement within and among plants affects levels of inbreeding and plant fitness as well as the spatial scale of genetic differentiation. Pollen movement has primarily been studied as a function of the direct relationships between plants and pollinators; however, nonpollinating floral visitors; such as some nectar robbers, may have indirect effects on pollen dispersal by altering plant--pollinator interactions. Theory predicts that nectar robbing should have indirect positive effects on plants by increasing pollen dispersal distance and reducing self-pollen transfer (geitonogamy) and inbreeding through changes in pollinator behavior associated with reduced nectar rewards. Here I xperimentally tested the indirect effects of the nectar-robbing bumble bee, Bombus occidentalis, on the distance of pollen movement among plants and levels of pollen movement within plants (estimated using powdered fluorescent dyes as pollen analogues) using the self-incompatible, hummingbird-pollinated host, Ipomopsis aggregata. Empirical results did not fully support the theoretical predictions. Heavy levels of nectar (>80% of available flowers robbed) had no effect on the mean and mean-squared distance of dye dispersal within populations. However, hummingbird pollinators were 50% more likely to depart from a population after visiting a plant with low robbing relative to a plant with high robbing, suggesting that pollen dispersal among populations might be reduced in plants with high robbing relative to plants with low robbing. Heavy nectar robbing reduced levels of self-dye transfer by one-half. However, when I manipulated robbing levels and access to self-pollen, the costs associated with increased robbing and reduced pollinator visitation (e.g., reduced seed production) outweighed any advantages associated with reduced geitonogamy. Taken together, these results suggest that the negative indirect effects of robbing on plant reproduction through decreased pollinator visitation and changes in pollinator departure from plants far exceed any positive effects associated with decreased geitonogamy. Given the widespread nature of plant attack by nectar robbers, these indirect effects are likely common phenomena structuring natural plant populations. Key words: Bombus occidentalis; geitonogamy; indirect effects; Ipomopsis aggregata; nectar robbing; plant reproductive success; pollen dispersal.