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Summary Post‐dispersal seed predators contribute substantially to seed loss across many ecosystems. Most research has focused on understanding sources of variation in seed loss, without appreciating the implications of seed predation for plant coexistence, community assembly and broader community theory. Meanwhile, research aimed at understanding coexistence and community assembly processes in plant communities has focused on axes of dispersal and resource competition and the traits influencing these processes, without accounting for the role of generalist seed predators. We review the unique features of post‐dispersal seed predation and assess the implications of seed loss on three critical components of plant community organization – coexistence, community structure and plant invasions – pointing to both important gaps in theory and empirical knowledge. We highlight how understanding fundamental controls on plant recruitment is central to determining how seed predation affects plant recruitment and coexistence. We discuss how accounting for seed predator foraging strategies may shift trait‐based inferences of community assembly. Synthesis. We argue that seed predation by generalist consumers, which is pervasive in temperate communities, should be better incorporated into plant community theory. Experiments that specifically incorporate the presence and attributes of the seed predator community and that follow seed fate would fill important knowledge gaps. Particularly needed are studies focused on strengthening the connections between seed removal and plant establishment and linking selective and density‐dependent foraging strategies to plant traits. Advancing our understanding of the processes regulating plant coexistence and community assembly requires that future research not only acknowledge but also incorporate generalist consumers’ effects on plant communities. A lay summary is available for this article. Lay Summary

1. Both seed predators and herbivores can have profound effects on individual plant growth, reproduction and survival, but their population-level effects are less well understood. While most plants interact with a suite of seed predators and herbivores over their life cycle, few studies incorporate the effects of multiple interacting partners and multiple life stages on plant population growth. 2. We constructed a matrix model using 6 years of data from a rare, seed-producing population of American chestnut (Castanea dentata). We combined field demographic data with published experimental results on the effects of pre-dispersal seed predators (weevils) and post-dispersal seed predators (scatter-hoarding vertebrates) and incorporated the effect of vertebrate herbivores estimated from the field data. We explored the impact of these three different animal interactions for short-term (transient) and long-term (asymptotic) tree population growth. In addition, we used the model to explore the conditions under which scatter hoarding would function as a mutualism. 3. Seed predators had greater effect on both short- and long-term population growth than herbivores. Although weevil infestation can greatly reduce the probability of germination, pre-dispersal seed predators had smaller effects on both short- or long-term population growth than post-dispersal predators. The elasticities of weevil-related parameters were also small. The effect of browsers on both the shortand long-term population growth rate were the smallest of the effects studied. Post-dispersal seed predation affected population growth the most in the interactions studied. The probability of seed removal was among the largest elasticities, similar in magnitude to survival of large trees. 4. Synthesis. Our results indicate that neither weevils nor the intensity of browse damage observed at our study site are likely to hinder tree regeneration or reintroduction, although both reduced population growth. Although researchers and forest managers often assume that seeds are unimportant for long-lived tree populations, our test of this assumption shows that scatterhoarders and other post-dispersal seed consumers can significantly limit natural regeneration. Forest management that alters scatterhoarder behaviour could have significant effects on tree population dynamics that are largely unexplored.

1. Local plant community assembly is influenced by a series of filters that affect the recruitment and establishment of species. These filters include regional factors that limit seeds of any given species from reaching a local site as well as local interactions such as post-dispersal seed predation and disturbance, which dictate what species actually establish. How these filters interact to influence recruitment into local assemblages, and whether they act differentially on individual species based on traits such as seed size or their provenance (i.e. native vs. exotic), has not been well examined. Such studies, however, are crucial for understanding community assembly and for making predictions about what species might be favoured under specific ecological circumstances. 2. We added 20 native and 19 exotic species that varied in seed size to undisturbed or experimentally disturbed subplots in and out of larger rodent exclusion plots at ten grassland sites across the Blackfoot River drainage in western Montana, USA. 3. Individually, exclusion of rodent seed predators and disturbance substantially increased cumulative (summed across all species) seedling recruitment. Exclusion of rodent seed predators enhanced recruitment to a greater extent in disturbed rather than undisturbed plots and for native species compared with exotics, while disturbance enhanced recruitment to a greater extent for exotics compared with natives. Examination of individual species responses indicated that results were generalizable across species within each group and not driven by the response of a few species. 4. Seed size mediated these patterns. Notably, the positive effect of rodent exclusion on recruitment was greater for large- versus small-seeded species, while the impact of disturbance on recruitment was more pronounced for small-seeded exotics relative to other groups. 5. Synthesis. These results reveal that local 'filters' such as post-dispersal seed predation and disturbance can individually and collectively impose strong limitation on seedling recruitment into local assemblages. Seed size importantly predicts how strongly individual species are influenced by these local filters. Interestingly, in situ community filters have differential effects on native versus exotic species, suggesting that processes that limit native recruitment may not have the same inhibitory influence on exotics.

• Annually variable and synchronous seed production by plant populations, or masting, is a widespread reproductive strategy in long-lived plants. Masting is thought to be selectively beneficial because interannual variability and synchrony increase the fitness of plants through economies of scale that decrease the cost of reproduction per surviving offspring. Predator satiation is believed to be a key economy of scale, but whether it can drive phenotypic evolution for masting in plants has been rarely explored. • We used data from seven plant species (Quercus humilis, Quercus ilex, Quercus rubra, Quercus alba, Quercus montana, Sorbus aucuparia and Pinus pinea) to determine whether predispersal seed predation selects for plant phenotypes that mast. • Predation selected for interannual variability in Mediterranean oaks (Q. humilis and Q. ilex), for synchrony in Q. rubra, and for both interannual variability and reproductive synchrony in S. aucuparia and P. pinea. Predation never selected for negative temporal autocorrelation of seed production. • Predation by invertebrates appears to select for only some aspects of masting, most importantly high coefficient of variation, supporting individual-level benefits of the population-level phenomenon of mast seeding. Determining the selective benefits of masting is complex because of interactions with other seed predators, which may impose contradictory selective pressures.

1. A central focus of ecology is to understand the conditions under which biotic interactions affect species' abundance and distribution. Classic and recent studies have shown that biotic interactions can strongly impact local or regional patterns of species abundance, but two fundamental questions remain largely unaddressed for non-competitive biotic interactions. First, do the effects of these interactions on population performance change predictably with environmental context? Second, to what extent do population-scale effects contribute to limiting species' geographic distributions? 2. To address these questions, we experimentally assessed the extent to which pollen limitation and insect seed predators affected the fecundity and projected population growth rate (λ) of the native forb Astragalus utahensis. We studied populations at the centre and northern edge of the latitudinal range of A. utahensis that occur across a gradient in abiotic harshness characterized primarily by declining mean annual precipitation. 3. Supplementing pollen and suppressing pre-dispersal seed predators increased seed production similarly within A. utahensis populations at the centre and northern edge of the range. Integral projection population models revealed that relaxing these checks on seed production tended to increase in most populations, regardless of their location within the range. 4. Synthesis. Our results suggest that pollen limitation and insect herbivores limit population growth in A. utahensis similarly across the centre-to-north portion of its latitudinal distribution. However, because A. utahensis population growth barely reaches the level of replacement at the northern range edge, the reduction in resulting from these interactions may contribute to limiting expansion at the northern edge of A. utahensis' latitudinal range.

Seed ecologists have often stated that they expect larger-seeded species to have lower survivorship through postdispersal seed predation than smaller-seeded species. Similar predictions can be made for the relationship between survivorship through predispersal seed predation and seed mass. In order to test these predictions, we gathered data regarding survivorship through 24 hours of exposure to postdispersal seed predators for 81 Australian species, and survivorship through predispersal seed predation for 170 Australian species. These species came from an arid environment, a subalpine environment, and a temperate coastal environment. We also gathered data from the published literature (global) on survivorship through postdispersal seed predation for 280 species and survivorship through predispersal seed predation for 174 species. We found a weak positive correlation between seed mass and the percentage of seeds remaining after 24 hours of exposure to postdispersal seed predators at two of three field sites in Australia, and no significant relationship across 280 species from the global literature, or at the remaining field site. There was no significant relationship between seed mass and survivorship through predispersal seed predation either cross-species or across phylogenetic divergences in any of the vegetation types, or in the compilation of data from the literature. Postdispersal seed removal was responsible for a greater percentage of seed loss in our field studies than was predispersal seed predation. On average, 83% of diaspores remained after 24 hours of exposure to postdispersal seed removers, whereas 87% of seeds survived all predispersal seed predation that occurred between seed formation and seed maturity. Mean seed survival was higher in the field studies than in the literature compilations, and species showing 100% survival were heavily underrepresented in the literature. These differences may be due to biases in species selection or publication bias. Seed defensive tissue mass increased isometrically with seed mass, but there was no significant relationship between the amount of defensive tissue per gram of seed reserve mass and survivorship through postdispersal seed predation.

Variation in insect herbivory can drive variation in plant fitness and population dynamics. However, our ability to predict the ecological contexts in which insect herbivores will reduce plant fitness or population growth is limited. In theory, populations at the periphery of a plant species' biogeographic range are expected to experience reduced herbivory. Further, in montane landscapes, elevation is expected to drive variation in abiotic conditions and variation in plant–insect interactions. Specifically, less insect herbivory may occur at cooler, higher elevations. To examine these predictions, we quantified effects of inflorescence‐ and seed‐feeding insect herbivores in populations of the short‐lived, monocarpic, perennial forb Cirsium canescens (Platte thistle) in montane grasslands in Colorado, USA. We asked: (1) Does insect flower head herbivory and pre‐dispersal seed predation limit Platte thistle lifetime seed production? (2) Does this insect herbivory limit seedling recruitment? (3) Does ecological context, including spatial—especially elevational—and temporal variation, affect the outcome of these interactions? We conducted insect exclusion experiments in three years at five sites over 52% of Platte thistle's elevation range in our region. We compared both lifetime viable seed production and seedlings recruited between plants with ambient versus insecticide‐reduced levels of flower head herbivory. Insect herbivory on flower heads significantly reduced Platte thistle lifetime viable seed production at all sites, independent of elevation. Unexpectedly, however, increasing seed by reducing herbivory did not lead to a proportional increase in seedling recruitment. The relationship between viable seed production and seedling recruitment per plant was non‐linear, decelerating across the range of seed production achieved by both plants exposed to and protected from flower head herbivory. While elevation altered Platte thistle flowering phenology, it did not influence insect damage, viable seed production, or seedling recruitment. These results show that flower head‐ and seed‐feeding insect herbivores strongly reduced Platte thistle lifetime viable seed production, a key component of maternal fitness, in these peripheral populations. Yet, the herbivory did not determine population recruitment, suggesting post‐dispersal processes limit recruitment here. Further, elevation did not drive context‐dependent variation in the insect herbivore outcomes.

Determining how climate affects biotic interactions can improve understanding of drivers of context-dependence and inform predictions of how interactions may influence plants under future climates. In arid environments, the communitylevel impacts of seed predators may depend strongly on aridity; yet, long-term studies documenting impacts of granivores on plant communities over variable climate conditions remain scarce. We evaluated how rodent exclusion interacted with climate to influence grassland and shrubland forb communities and the community-scale distribution of seed mass over 15 years in the climatically variable northern Chihuahuan Desert. In this dynamic system, two seasonally distinct plant community phases occur annually, one in spring and the other during the summer monsoon. Rodent exclusion significantly altered the community composition of monsoon season plant communities in both grassland and shrubland, but did not affect spring plant composition. Rodents suppressed the abundance of larger-seeded forb species and promoted smaller-seeded species. As a consequence, rodent exclusion increased community seed mass (CWM) in monsoon forb communities, most strongly in grassland. The magnitude of impacts of rodents on seed mass varied substantially from year-to-year, tracking variation in climate. Specifically, rodent exclusion increased community mean seed mass the most in dry years (grassland) or in years following dry years (shrubland). Rodent exclusion had relatively weak effects on plant species diversity and richness. Our results indicate that climate interacts with the presence of rodents to structure not only the composition but also the traits of desert plant communities.

Plants often face chronic seed loss from predispersal seed predation by insects. Although many studies have documented the rates of seed loss for single species in different communities, it is unclear how rates of predispersal seed predation vary among co‐occurring species within the same community. If interspecific asymmetries in seed loss are great, this common interaction could have important implications for coexistence. Species traits, such as seed size or seed nitrogen and carbon, might correlate with interspecific variation in predispersal seed predation among co‐occurring grassland forb species. We collected infructescences from 13 co‐occurring forb species from each of four western Montana grasslands over 2 years. We quantified the magnitude of seed loss due to predispersal seed predation by insects. The average level of seed loss was 15.8%. Larger seeded species suffered significantly higher levels of predispersal seed predation than smaller seeded species, and seed size predicted seed loss more than seed nitrogen or carbon. Although large‐seeded species often have greater proportional recruitment and early survival than small‐seeded species, our study suggests that these advantages are partially counterbalanced by greater predispersal seed loss for larger versus smaller seeded species. Asymmetries in predispersal seed predation may importantly affect coexistence among these species.

Ambrosia artemisiifolia has turned into a noxious weed species in agricultural fields and landscapes in Europe. Durable control options are still needed to limit the abundance of this species. Weed seed consumption by naturally occurring seed predators is a key ecosystem service in agricultural areas. Seed predation levels of common ragweed were examined in wheat and maize fields and adjacent semi-natural habitats (SNHs). To evaluate the weed seeds’ exposure to invertebrate seed predators, 20 cards each were set on the soil surface inside the crop field and in SNHs with four replications. Twenty seeds of ragweed were attached to sandpaper. Seed removal was assessed every 24 h of exposure for 5 days in June and November 2019, October 2020, and June 2021. The seed consumption level was measured according to the number of removed seeds from the seed cards. High consumption rates of ragweed seeds were found in all sampling rounds in both seasons and habitats. The seed predation rates in 2019 were stronger within crop fields in summer than in autumn with a slight difference between SNHs and inside fields. Our results demonstrate the possibility of seed predation contributing to Integrated Plant Protection (IPM) of common ragweed in rural areas.