Pollination Mutualism Research Articles

Geographic variations of floral traits and pollinator guilds in a specialized pollination mutualism, Kadsura longipedunculata and gall midges

AbstractFloral traits exhibit variations in response to both biotic and abiotic factors, potentially leading to dynamic interactions between plants and pollinators. Little is known about whether these geographic variations in floral traits influence species–specific interactions in obligate mutualisms. In this study, variations in flower morphology, color and scent were investigated within and among Kadsura longipedunculata populations. Local midge pollinators across three populations were sampled to examine the plant‐insect dynamics at the geographic scale. Our results suggested dimorphism in androecium color within and among populations. Floral scent analyses suggested quantitative differences in major compounds (terpenes) among populations and between individuals with differing colors, but similar composition of volatile compounds between different color morphs. Stamen chamber size did not differ between different color morphs within the Xinning population. However, it was significantly larger in the Xinning population compared to the Hengshan population. Totally, four pollinating and ovipositing gall midge species were identified in these three populations with shared Resseliella kadsura between the Xinning and Hengshan population and shared Resseliella sp. between the Xinning and Lushan population. The variations in floral traits and pollinator guilds provide new empirical evidence for the dynamic interactions at geographic scales within specialized pollination mutualisms, potentially supporting the geographic mosaic theory of coevolution.

When is lethal deceptive pollination maintained? A population dynamics approach.

Not all plant-pollinator interactions are mutualistic, and in fact, deceptive pollination systems are widespread in nature. The genus Arisaema has a pollination system known as lethal deceptive pollination, in which plants not only attract pollinating insects without providing any rewards, but also trap them until they die. Many Arisaema species are endangered from various disturbances including reduction in forest habitat, modification of the forest understory owing to increasing deer abundance, and plant theft for horticultural cultivation. We aimed to theoretically investigate how lethal deceptive pollination can be maintained from a demographic perspective and how plant and pollinator populations respond to different types of disturbance. We developed and analysed a mathematical model to describe the population dynamics of a deceptive plant species and its victim pollinator. Calibrating the model based on empirical data, we assessed the conditions under which plants and pollinators could coexist, while manipulating relevant key parameters. The model exhibited qualitatively distinct behaviours depending on certain parameters. The plant becomes extinct when it has a low capability for vegetative reproduction and slow transition from male to female, and plant-insect co-extinction occurs especially when the plant is highly attractive to male insects. Increasing deer abundance has both positive and negative effects because of removal of other competitive plants and diminishing pollinators, respectively. Theft for horticultural cultivation can readily threaten plants whether male or female plants are frequently collected. The impact of forest habitat reduction may be limited compared to that of other disturbance types. Our results have emphasised that the demographic vulnerability of lethal deceptive pollination systems would differ qualitatively from that of general mutualistic pollination systems. It is therefore important to consider the demographics of both victim pollinators and deceptive plants to estimate how endangered Arisaema populations respond to various disturbances.

The specialised buzz pollination syndrome poses a partial barrier to plant invasions

Abstract Plants that exhibit generalised pollination syndromes have been hypothesised to become invasive more easily compared with specialists, yet the degree to which specialised pollination traits inhibit plant invasions is unknown. One such specialisation is the buzz pollination syndrome, which encompasses specialised floral traits that restrict pollen access (typically poricidal anthers) and benefits from specialised insect behaviour for pollen extraction. We reviewed the literature on buzz pollination of invasive plants to assess whether: (1) plant species exhibiting specialised pollination syndromes are underrepresented as invasive species, and (2) species with specialised pollination syndromes that have become invasive can reproduce in the absence of specialist buzzing pollinators. Synthesis. We found 2.5% (117/4630) of invasive angiosperms have poricidal anthers, which is an underrepresentation of the proportion of global angiosperms that are estimated to have poricidal anthers (6%–10%). Most invasive buzz‐pollinated plants are genetically self‐compatible (97%), but only 43% can set fruit in the absence of a pollinator. Our findings highlight the importance of establishing new pollinator mutualisms for sexual reproduction. However, we identified six non‐buzzing behaviours used to extract pollen from plants with poricidal anthers, which is important where buzzing pollinators may be absent or not attracted to newly introduced plant species.

Chemical imitation of yeast fermentation by the drosophilid-pollinated deceptive trap-flower Aristolochia baetica (Aristolochiaceae)

Deceptive flowers, unlike in mutualistic pollination systems, mislead their pollinators by advertising rewards which ultimately are not provided. Although our understanding of deceptive pollination systems increased in recent years, the attractive signals and deceptive strategies in the majority of species remain unknown. This is also true for the genus Aristolochia, famous for its deceptive and fly-pollinated trap flowers. Representatives of this genus were generally assumed to be oviposition-site mimics, imitating vertebrate carrion or mushrooms. However, recent studies found a broader spectrum of strategies, including kleptomyiophily and imitation of invertebrate carrion. A different deceptive strategy is presented here for the western Mediterranean Aristolochia baetica L. We found that this species is mostly pollinated by drosophilid flies (Drosophilidae, mostly Drosophila spp.), which typically feed on fermenting fruit infested by yeasts. The flowers of A. baetica emitted mostly typical yeast volatiles, predominantly the aliphatic compounds acetoin and 2,3-butandiol, and derived acetates, as well as the aromatic compound 2-phenylethanol. Analyses of the absolute configurations of the chiral volatiles revealed weakly (acetoin, 2,3-butanediol) to strongly (mono- and diacetates) biased stereoisomer-ratios. Electrophysiological (GC-EAD) experiments and lab bioassays demonstrated that most of the floral volatiles, although not all stereoisomers of chiral compounds, were physiologically active and attractive in drosophilid pollinators; a synthetic mixture thereof successfully attracted them in field and lab bioassays. We conclude that A. baetica chemically mimics yeast fermentation to deceive its pollinators. This deceptive strategy (scent chemistry, pollinators, trapping function) is also known from more distantly related plants, such as Arum palaestinum Boiss. (Araceae) and Ceropegia spp. (Apocynaceae), suggesting convergent evolution. In contrast to other studies working on floral scents in plants imitating breeding sites, the present study considered the absolute configuration of chiral compounds.

The Effect of Ficus semicordata Fig Quality on the Sex Ratio of Its Pollinating Wasp Ceratosolen gravelyi

The interaction between fig wasps and their host fig trees (Ficus spp.) is a striking example of an obligate pollination mutualism. Male and female fig wasps are confined within their natal patch instead of panmictic; under this circumstance, mating only occurs between individuals of the same patch. This is known as a local mate competition (LMC). It pays foundresses to invest mainly in daughters and to only produce enough sons to ensure that all female offspring can be fertilized, but in nature, pollinating fig wasps may face many problems with host quality, such as limitation of oviposition sites and the nutrition deficiency of the host fig. The sex ratio of wasps can determine the stability of fig–fig wasp mutualistic system and, thus, the stability of other species associated with it. In this study, we controlled the quality of host figs in three ways. The results showed that the host fig age can influence the sex ratio of pollinator offspring, while the foundress numbers and the presence of pollen have no significant effect on it. A compelling explanation for this result is that the sex-dependent mortality occurs. This is a novel finding of how host quality influences the interaction of fig and fig wasps, which can also help us understand the evolution and stability mechanism of this symbiotic system.

Who holds the reins? Context-dependent resource allocation in the mutualism between fig trees and their fig wasp pollinators.

Mutualisms are consumer-resource interactions, in which goods and services are exchanged. Biological market theory states that exchanges should be regulated by both partners. However, most studies on mutualisms are one-sided, focusing on the control exercised by host organisms on their symbionts. In the brood-site pollination mutualism between fig trees and their symbiont wasp pollinators, galled flowers are development sites for pollinator larvae and are exchanged for pollination services. We determined if pollinator galls influenced resource allocation to fig inflorescences called syconia and considered feedbacks from the host tree. We experimentally produced syconia containing only seeds (S), only pollinator galls (G) or seeds and galls (SG) with varying number of introduced female pollinator wasps, i.e., foundress wasps. Biomass allocation to syconia was affected by foundress numbers and treatment groups; SG treatments received highest biomass allocation at low foundress numbers, and both G and SG treatments at high foundress numbers. Seeds are important determinants of allocation at low foundress numbers; galls are likely more influential at high foundress numbers. Most allocation in the G and SG treatment was to the syconium wall, likely as protection from parasitoids and temperature/humidity fluctuations. Dry mass of individual seeds and wasps (except at low foundress numbers) was unchanged between treatment groups, indicating seeds and wasps regulate resource flow into them, with lower flow into galls containing the smaller males compared to females commensurate with sexual dimorphism. We demonstrate the importance of considering the direct role of symbionts in accessing resources and controlling exchanges within mutualisms.

Back from the dead: A fungus gnat pollinator turns Arisaema lethal trap into nursery

Societal Impact StatementThe research explores the complex interaction between flowering plants and their pollinators, specifically focusing on the genus Arisaema. Unlike most plants, Arisaema has a distinctive trait in which killing pollinators can be beneficial. Traditionally, this interaction has been viewed as highly antagonistic because it appears to favor the plants at the expense of the pollinators. However, new evidence reveals that a pollinator uses the lethal floral trap of Arisaema thunbergii as a nursery. Remarkably, some individuals probably even escape from the trap after laying eggs. This finding challenges the prevailing notion that deceptive pollination is the sole outcome in Arisaema, a genus known for its intricate lethal pollination mechanisms.Summary While many flowering plants engage in mutualistic relationships with their pollinators, flower‐insect interactions are not always mutually beneficial. Some plants exploit their pollinators by deceptively promising rewards without delivering them. Among such plants, the genus Arisaema (Araceae) is notable for its antagonistic behavior towards pollinators, as female plants invariably entrap them with lethal effects. Here we tested the hypothesis that the succulent appendix of some Arisaema species, such as Arisaema thunbergii, may serve as a food source for pollinator larvae, leading to the possibility of nursery pollination. To investigate this, we retrieved adult insect corpses trapped within the spathes of A. thunbergii. Subsequently, we incubated the spathes after collecting the corpses to determine if conspecific insects emerged from them. We present novel evidence that one of the main pollinating fungus gnats, Leia ishitanii, uses the lethal floral trap of A. thunbergii inflorescences as a nursery. Astonishingly, some L. ishitanii individuals may even succeed in escaping from the female spathe after depositing their eggs. These findings challenge the conventional understanding that deceptive pollination is the norm within the genus Arisaema. The interaction between A. thunbergii and L. ishitanii, in which a significant portion of female adults die inside but still reproduction seems successful, suggests an intermediate stage between brood‐site deception and nursery pollination mutualism.

Local ecological factors, not interference competition, drive the foundress number of two species of fig wasp sharing Ficus septica figs.

Recent studies have challenged assumptions about the classic fig-fig wasp pollination mutualism model, suggesting that further investigation into the receptive phase of fig development is needed. This study assessed the pollination mechanisms of Ficus septica in southern Taiwan and identified two species of wasps as the primary pollinators. Machine learning was used to identify and rank the factors that explain the relative abundance of these wasps. The two wasp species showed the highest level of cohabitation ever reported in the literature, with three-quarters of the figs containing multiple foundresses. The study also reported re-emerged foundresses and a 10% ratio of pollinated figs without foundresses. Local factors, such as the sampling period and tree identity, were the best predictors of the presence and number of each foundress species, with fig size also affecting the number of foundresses. The study highlights the variability in pollinator abundance between figs, crops, and trees. It also shows that the local environment of the trees and the availability of figs are crucial factors in determining which figs the pollinator wasps choose. These findings challenge assumptions about the classic mutualism model and suggest that long-term surveys are needed to estimate the relative contributions of each partner and provide data for evolutionary and ecological models. This study also provides valuable insights into the factors that affect the abundance and interactions of pollinator wasps during the receptive phase of fig development, with implications for understanding the behaviour of pollinating wasps and advancing our knowledge of population dynamics in Ficus species.

The conspicuously large bracts influence reproductive success in Thunia alba (Orchidaceae)

Abstract In angiosperms, diverse floral traits are adaptations to various selective pressures and ecological functions. So far, studies on floral traits in orchids have focused primarily on the labellum but never on bracts. A bumblebee-pollinated and rewarding terrestrial or epiphytic herb, Thunia alba (Lindley) H. G. Reichenbach (Orchidaceae), has conspicuously large and curly bracts that enclose the spur and pedicel of flowers. We hypothesized that these large bracts could protect spurs against nectar robbers. To confirm this hypothesis, we experimentally removed the bracts to record the changes in visiting behavior of mutualistic pollinators and antagonistic nectar robbers and evaluated their effects on reproduction success. Our result revealed that Bombus breviceps, the only pollinator of T. alba, shifted to nectar robbery when the bracts were removed, and the proportion of robbed flowers also significantly increased. Thunia alba was found to be pollinator limited regardless of whether in intact treatment or removed bract treatment. Removal of bracts had no effect on the visiting frequency of B. breviceps, but it reduced male and female reproductive success. These findings indicate that, under complex environmental pressures with limited pollination, large bracts can protect against nectar robbers and enhance the fitness of T. alba.

Phenological overlap between crop and pollinators: Contrasting influence of native and non‐native bees on raspberry fruits over the flowering season

Abstract Phenological overlap between crop flowering and pollinators is a crucial trait for the pollination of more than 75% of the world's crops. However, crop management rarely considers the seasonal aspect of plant–pollinator mutualism. Here, we investigate the phenological overlap between crops and pollinators and how it affects pollination and fruit production. We measured the abundance and richness of native and non‐native pollinators visiting raspberry flowers at two different times during the flowering season (i.e. early and late flowering periods) and examined their effects on crop yield in 16 fields. The community of pollinators foraging on raspberry flowers was more diverse and dominated by native pollinators during the early flowering period when most native plant species were flowering. Later in the season, when native flower resources declined in the surrounding environment, raspberry flowers were visited mainly by two non‐native bees: managed honeybees and the invasive bumblebee Bombus terrestris. Pollinator contribution to raspberry yield was twice as high in the early flowering period compared to the late period (61% vs. 31% increase in drupelet set respectively). Flower damage caused by extremely high visitation frequencies by non‐native bees in the late period was six times higher than in the early flowering period (30% vs. 5% of damaged flowers respectively). Synthesis and applications. Providing sufficient pollen and nectar resources to support wild pollinators over extended periods in agricultural landscapes can contribute to crop pollination and ensure high fruit weight and quality. This can be achieved by restoring natural and semi‐natural areas near crop fields with native, long‐flowering plant species. Growers and crop breeding programmes should consider selecting flowering times that coincide with periods of high diversity or abundance of native pollinators to reduce dependence on managed pollinators.

Phylogenomics illuminates the phylogeny of flower weevils (Curculioninae) and reveals ten independent origins of brood-site pollination mutualism in true weevils.

Weevils are an unusually species-rich group of phytophagous insects for which there is increasing evidence of frequent involvement in brood-site pollination. This study examines phylogenetic patterns in the emergence of brood-site pollination mutualism among one of the most speciose beetle groups, the flower weevils (subfamily Curculioninae). We analysed a novel phylogenomic dataset consisting of 214 nuclear loci for 202 weevil species, with a sampling that mainly includes flower weevils as well as representatives of all major lineages of true weevils (Curculionidae). Our phylogenomic analyses establish a uniquely comprehensive phylogenetic framework for Curculioninae and provide new insights into the relationships among lineages of true weevils. Based on this phylogeny, statistical reconstruction of ancestral character states revealed at least 10 independent origins of brood-site pollination in higher weevils through transitions from ancestral associations with reproductive structures in the larval stage. Broadly, our results illuminate the unexpected frequency with which true weevils-typically specialized phytophages and hence antagonists of plants-have evolved mutualistic interactions of ecological significance that are key to both weevil and plant evolutionary fitness and thus a component of their deeply intertwined macroevolutionary success.

While Prosopanche (Hydnoraceae) flowers gently heat: mutualistic pollination relationships among the perianth-bearing Piperales

Abstract Flowers of most Piperales do not reward pollinators. However, a few mutualistic pollination relationships have been proposed among the perianth-bearing species. To test the hypothesis of a mutualistic relationship between Prosopanche and beetle pollinators, we studied the pollination biology of three species (P. americana, P. bonacinae, P. panguanensis). For all three species, we recorded flower visitors and flower volatile organic compounds (VOCSs). In addition, for P. americana we investigated flower phases, thermogenesis, visitors’ behaviour, and viability of transported pollen. Using a behavioural experiment, we identified the role of flower heat and fragrance in pollinator attraction. We recorded Neopocadius nitiduloides and Lasiodactylus sp. sap beetles (Nitidulidae) as main pollinators and Hydnorobius hydnorae and H. helleri weevils (Belidae) as occasional pollinators. Thermogenic female flowers heat up to 8°C above the ambient temperature. Flowers only trap the small-sized sap beetles. Methyl-3-methyl-2-butenoate dominated the VOC profile. This was a powerful attractant for sap beetles in controlled bioassays. We conclude that pollination in Prosopanche is mutualistic. This was observed through a pollinator-size-based access limit to the stigmatic chamber and a strong olfactory attractant. Mutualism in Prosopanche therefore contrasts with that of most perianth-bearing Piperales, suggesting it is a novel pollination relationship in early-diverging angiosperms.

The genetic structuring in pollinating wasps of Ficus hispida in continental Asia.

The interaction between figs and fig wasps provides a striking example of obligate brood site pollination mutualism. Monoecious figs, constituting independent radiations in each tropical biome, are present in significant proportions worldwide, but in continental Asia, dioecious figs have diverged into various niches, making the region's assemblage remarkably diverse. However, the reproductive success of figs and fig wasps largely depends on the fig wasp dispersal process. Monoecious fig pollinators in continental Asian tropical rain forests exhibit high gene flow of the plant, while many dioecious fig pollinators have a more restricted gene flow. However, there are limited studies on the genetic structure of dioecious Ficus pollinators that pollinate figs with intermediate gene flow. Here, we used molecular methods to investigate the genetic structure of pollinating wasps of the widely distributed dioecious Ficus hispida in China and Southeast Asia. Sequence data from two gene regions were used: the mitochondrial protein-coding gene cytochrome c oxidase subunit I (COI) and the nuclear 28S genes. Both molecular and morphological results support two fig wasp species at our sampling sites. Our findings suggest that for widely sympatric Ficus species in continental Asia, monoecious figs presenting long gene glow have the fewest fig wasp species, followed by dioecious figs presenting intermediate gene flow, and dioecious figs presenting local gene flow have the most fig wasp species.

Plants are the drivers of geographic variation of floral odours in brood site pollination mutualisms: A case study of Ficus hirta

Plant odours are central for pollinator attraction. This is particularly true in obligate brood site pollination mutualisms. However, we know little about the evolution of olfactory signalling in these mutualisms. Here, we investigate geographic variation of floral odour in the obligate host-specific brood site pollination mutualism between Ficus hirta and its specialised pollinators. Floral scent samples from nine locations in China were collected using head-space adsorption and were analysed by gas chromatography-mass spectrometry. We evidence progressive geographic divergence of floral odours. The pattern of variation fits plant genetic structure for neutral genes but differs from pollinating insect structuring into species and populations. In our study system, the geographic variation of receptive floral odour presents a pattern that is not distinguishable from neutral drift. The variation is not canalised by the insects. We propose that this pattern characterises obligate brood site pollination mutualisms in which pollinators are host specific and dispersal of plant and insect is limited. Insects with their short generation times and large population sizes rapidly track any chance variation in host receptive inflorescence odours. Plants are the drivers and insects the followers. The source of the geographic variation in floral odours can be genetic or phenotypic in response to local conditions. Strict sense plant-insect co-evolution is not involved. In contrast, previous results on another Ficus-pollinating wasp association suggest that stabilising selection could be at work in more dispersive systems.

Assisted Species Migration of Joshua Trees

The Joshua tree evolved in a complex way with its environment, pollinator, and seed dispersers over millions of years. Its survival as a species is now imminently threatened by climate change. Many factors prevent it from migrating to a cooler range quickly enough to keep up with the planet’s current rate of warming. This paper explores the viability of assisted migration for the Joshua tree, where humans help it move to escape extinction. Several studies are examined. One persuasively shows that the Joshua tree had a range contraction when the climate warmed at the end of the Ice Age and that present warming will cause a similar, drastic range reduction. Other studies look at factors such as soil, CO2, pollinator mutualism, and seed longevity to determine if assisted migration would be successful. The ethics of assisted migration is also explored. This paper concludes that humans must try to assist the Joshua tree to migrate but that it will be difficult given the complexities of its evolution, its relationship to its environment, and a migration lag that is not completely understood.

Parallel developments in floral adaptations to obligate moth pollination mutualism in tribe Phyllantheae (Phyllanthaceae).

Several groups within tribe Phyllantheae (Phyllanthaceae) formed, independently, an (obligate) pollination mutualism with Epicephala moths, which originally had been parasitic. In this pollination system, female moths actively collect pollen from staminate flowers and deposit it on the stigma of pistillate flowers, after which they place at least one egg in or against the ovary. The high pollination rate makes the system beneficial for the plants, whereas the larvae are provided with food (part of the developing seeds) and some protection against predation. Qualitative comparisons are made between non-moth-pollinated lineages, used as outgroups and various, independently moth-pollinated Phyllantheae clades, used as ingroups, thereby looking for parallel developments. The flowers of both sexes of various groups display similar, convergent morphological adaptations to the pollination system, likely to secure the obligate relationship and to improve efficiency. Sepals in both sexes, free or partly to highly connate, are commonly upright and form a narrow tube. The staminate flowers often have united, vertical stamens with the anthers along the androphore or on top of the androphore. Pistillate flowers generally reduce the stigmatic surface, either by making the stigmas shorter or by uniting them into a cone with a small opening at the top for pollen deposition. Less obvious is the reduction of the stigmatic papillae; these are often present in non-moth-pollinated taxa, but absent in the moth-pollinated species. The most diverging, parallel adaptations to moth pollination are currently found in the Palaeotropics, whereas in the Neotropics, some groups continue to also be pollinated by other insect groups and are morphologically less changed.

Responses of floral traits to water limitation across soil types and along climatic gradients

Understanding how environmental changes affect plant-pollinator interactions is of increasing importance given that new environmental extremes continue to be reached. Drought may be a particularly destabilizing force for plant-pollinator interactions because moisture availability can affect floral trait expression. Past work has found variability in how some floral traits respond to moisture limitation, motivating work on the potential drivers of the variability in responses. Here we asked how flower size and nectar provisioning to pollinators change with moisture limitation, and if seed provenance mediates trait responses. Specifically, we conducted a greenhouse common garden using seeds of the serpentine-tolerant annual Antirrhinum vexillocalyculatum collected from pairs of populations on and off drought-prone serpentine soil and along moisture and temperature gradients. We experimentally quantified responses to two moisture treatments, and we found no evidence that seeds from different soil types vary in drought responses. However, plants from seeds from different temperature regimes varied in the way that water limitation affected nectar volume, and those from different precipitation regimes varied in the way that water limitation affected flower size. Water limitation reduced floral display and reward for plants from some populations but increased trait means in other populations. This suggests that drought will reduce floral resources for pollinators overall, but plants from some environments may continue to invest in pollination mutualisms under moisture limitation.

Active pollination in a functionally dioecious Ficus species: An interplay between pollinator behaviour and floral morphology

Active pollination has evolved four times in brood site pollination mutualisms. When pollination is active, the pollinator's behaviour specifically evolves to ensure flower fertilisation. In functionally dioecious Ficus species, the male figs host pollinating wasp larvae, while wasps cannot breed in the female figs because the styles are longer than the wasp ovipositor. Here we investigate the dioecious Ficus hispida. We show that in male figs, every time the wasp has laid an egg into a pistillate flower, it removes one pollen grain from its pollen pockets and places it on the hypopygium. When the wasp inserts its ovipositor into the next flower, the pollen grain is deposited deep within the style. Each ovipositor insertion results in flower pollination and insect oviposition. Because of systematic pollination of the flowers into which the eggs are laid, the wasp larvae benefit from feeding on fertilised endosperm while no seed are produced. In female figs, after probing a flower, the wasp presents pollination behaviour only every five visits. However, if it does occur, this behaviour lasts longer than in male figs and results in the deposition of on average 10 pollen grains on the hypopygium. The exposed sticky papillae on the stigmatic surface collect pollen from the hypopygium and pollen tubes may grow to neighbouring stigmas, ensuring secondary dispersal and efficient ovule fertilisation. Overall, our study demonstrates that the floral morphology of male figs facilitates precise pollen deposition, beneficial for the wasp progeny, while the floral morphology of female figs compensates for wasp pollination behaviour that is not selected in those figs. We conclude that the morphology of the arena in which interactions with its pollinator are played out is the result of selection on the plant to maximize its male and female fitness. Incidentally, this morphology stabilises the mutualistic interaction.

Plant spatial aggregation modulates the interplay between plant competition and pollinator attraction with contrasting outcomes of plant fitness

Abstract. Ecosystem functions such as seed production are the result of a complex interplay between competitive plant–plant interactions and mutualistic pollinator–plant interactions. In this interplay, spatial plant aggregation could work in two different directions: it could increase hetero- and conspecific competition, thus reducing seed production; but it could also attract pollinators, increasing plant fitness. To shed light on how plant spatial arrangement modulates this balance, we conducted a field study in a Mediterranean annual grassland with three focal plant species with different phenology, Chamaemelum fuscatum (early phenology), Leontodon maroccanus (middle phenology) and Pulicaria paludosa (late phenology), and a diverse guild of pollinators (flies, bees, beetles and butterflies). All three species showed spatial aggregation of conspecific individuals. Additionally, we found that the two mechanisms were working simultaneously: crowded neighborhoods reduced individual seed production via plant–plant competition, but they also made individual plants more attractive for some pollinator guilds, increasing visitation rates and plant fitness. The balance between these two forces varied depending on the focal species and the spatial scale considered. Therefore, our results indicate that mutualistic interactions do not always effectively compensate for competitive interactions in situations of spatial aggregation of flowering plants, at least in our study system. We highlight the importance of explicitly considering the spatial structure at different spatial scales of multitrophic interactions to better understand individual plant fitness and community dynamics.

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (SYMP 14) Organized at ESA + CSEE 2022 Joint Meeting

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (<scp>SYMP</scp> 14) Organized at <scp>ESA</scp> + <scp>CSEE</scp> 2022 Joint Meeting