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1. Does masting scale with plant size? High reproductive variability and low synchrony in small and unproductive individuals

   https://doi.org/10.1093/aob/mcaa118  

   Bogdziewicz, Michał; Szymkowiak, Jakub; Calama, Rafael; Crone, Elizabeth E; Espelta, Josep M; Lesica, Peter; Marino, Shealyn; Steele, Michael A; Tenhumberg, Brigitte; Tyre, Andrew; et al (June 2020, Annals of Botany)

   null (Ed.)

   Abstract Background and Aims In a range of plant species, the distribution of individual mean fecundity is skewed and dominated by a few highly fecund individuals. Larger plants produce greater seed crops, but the exact nature of the relationship between size and reproductive patterns is poorly understood. This is especially clear in plants that reproduce by exhibiting synchronized quasi-periodic variation in fruit production, a process called masting. Methods We investigated covariation of plant size and fecundity with individual-plant-level masting patterns and seed predation in 12 mast-seeding species: Pinus pinea, Astragalus scaphoides, Sorbus aucuparia, Quercus ilex, Q. humilis, Q. rubra, Q. alba, Q. montana, Chionochloa pallens, C. macra, Celmisia lyallii and Phormium tenax. Key Results Fecundity was non-linearly related to masting patterns. Small and unproductive plants frequently failed to produce any seeds, which elevated their annual variation and decreased synchrony. Above a low fecundity threshold, plants had similar variability and synchrony, regardless of their size and productivity. Conclusions Our study shows that within-species variation in masting patterns is correlated with variation in fecundity, which in turn is related to plant size. Low synchrony of low-fertility plants shows that the failure years were idiosyncratic to each small plant, which in turn implies that the small plants fail to reproduce because of plant-specific factors (e.g. internal resource limits). Thus, the behaviour of these sub-producers is apparently the result of trade-offs in resource allocation and environmental limits with which the small plants cannot cope. Plant size and especially fecundity and propensity for mast failure years play a major role in determining the variability and synchrony of reproduction in plants. 

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2. Incorporating the effects of generalist seed predators into plant community theory

   https://doi.org/10.1111/1365-2435.12905  

   Larios, Loralee; Pearson, Dean E.; Maron, John L. (January 2017, Functional Ecology)

   1. 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. 2. 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. 3. 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. 

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3. Predation risk and personality influence seed predation and dispersal by a scatter‐hoarding small mammal

   https://doi.org/10.1002/ecs2.4377  

   Merz, Margaret R.; Boone, Sara R.; Mortelliti, Alessio (January 2023, Ecosphere)

   Small mammals are key scatter hoarders in forest ecosystems, acting as both seed predators and dispersers. The outcome of their interactions (i.e., predation vs. dispersal) is determined by a series of decisions made by small mammals, such as the choice of seed, whether the seed is immediately consumed or cached, and where it is cached. These decisions are influenced by a variety of factors, including the intrinsic traits of the seed, the individual personality of the scatter hoarder, and the perceived risk of predation while foraging. Furthermore, these factors may all interact to dictate the fate of the seed, with consequences for forest regeneration. Nevertheless, the ways in which perceived predation risk and personality interact to affect the seed dispersal decisions of scatter hoarders are still poorly understood. To contribute in filling this knowledge gap, we tested the hypotheses that southern red‐backed voles (Myodes gapperi), an important scatter hoarder in forest ecosystems, would exhibit personality‐mediated foraging and that predation risk would alter associations between personality and seed dispersal. We conducted a large‐scale field experiment, offering seed trays at stations with altered risk levels and recorded foraging decisions of free‐ranging voles with known personalities. We found that personality and perceived predation risk influenced decisions made by foraging voles. Specifically, docility, and boldness predicted foraging site selection, boldness predicted seed species selection and the number of seeds individuals selected, and the tendency to explore of an individual predicted whether voles would remove or consume seeds. Predation risk, mediated by the amount of cover at a site and by moon illumination, affected which foraging site individuals chose, seed species selection, and the probability of removal versus consumption. We did not find support for an interaction between personality and predation risk in predicting foraging decisions. These findings highlight the importance of scatter hoarder personality and perceived predation risk in affecting foraging decisions, with important consequences for seed dispersal and implications for altered patterns of forest regeneration in areas with different small mammal personality distributions or landscapes of fear. 

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4. Cone characteristics and insect predation levels vary across years in mast seeding white spruce

   https://doi.org/10.1139/cjfr-2020-0442  

   Leeper, Abigail C.; LaMontagne, Jalene M. (October 2021, Canadian Journal of Forest Research)

   Populations of many tree species exhibit synchronous and highly temporally variable seed crops across years. This is called mast seeding, and there are two predominant hypotheses for this pattern of reproduction: pollination efficiency and seed-predator satiation. Mast seeding studies typically involve records of population-level reproduction, with less information on the characteristics of reproductive structures. Here, we use data across 6 years (2012–2017), spanning a range of population-level cone conditions, to characterize (i) white spruce (Picea glauca (Moench) Voss) cone lengths and seeds per cone, and (ii) levels of seed predation. We quantified population-level cone production and collected 1399 cones from a total of 38 trees in the Huron Mountains, Michigan, USA. Linear mixed models showed that mean and minimum cone lengths varied significantly across years; both being longest during the greatest cone production year. Larger cones had more seeds and the slopes of the relationships as well as the intercepts varied significantly across years. Generalized linear mixed models and Akaike’s information criterion model selection showed that cones with insect predation damage was greatest when population-level reproduction was the lowest, with a mean proportion of cones damaged 0.82 in that year. Our findings show that white spruce cone characteristics and losses to insect seed predation vary temporally, and follow expectations based on mast seeding hypotheses. 

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5. Post-fire seed dispersal of a wind-dispersed shrub declined with distance to seed source, yet had high levels of unexplained variation

   https://doi.org/10.1093/aobpla/plac045  

   Applestein, Cara; Caughlin, T Trevor; Germino, Matthew J (November 2022, AoB PLANTS)

   Auge, Gabriela (Ed.)

   Abstract Plant-population recovery across large disturbance areas is often seed-limited. An understanding of seed dispersal patterns is fundamental for determining natural-regeneration potential. However, forecasting seed dispersal rates across heterogeneous landscapes remains a challenge. Our objectives were to determine (i) the landscape patterning of post-disturbance seed dispersal, and underlying sources of variation and the scale at which they operate, and (ii) how the natural seed dispersal patterns relate to a seed augmentation strategy. Vertical seed trapping experiments were replicated across 2 years and five burned and/or managed landscapes in sagebrush steppe. Multi-scale sampling and hierarchical Bayesian models were used to determine the scale of spatial variation in seed dispersal. We then integrated an empirical and mechanistic dispersal kernel for wind-dispersed species to project rates of seed dispersal and compared natural seed arrival to typical post-fire aerial seeding rates. Seeds were captured across the range of tested dispersal distances, up to a maximum distance of 26 m from seed-source plants, although dispersal to the furthest traps was variable. Seed dispersal was better explained by transect heterogeneity than by patch or site heterogeneity (transects were nested within patch within site). The number of seeds captured varied from a modelled mean of ~13 m−2 adjacent to patches of seed-producing plants, to nearly none at 10 m from patches, standardized over a 49-day period. Maximum seed dispersal distances on average were estimated to be 16 m according to a novel modelling approach using a ‘latent’ variable for dispersal distance based on seed trapping heights. Surprisingly, statistical representation of wind did not improve model fit and seed rain was not related to the large variation in total available seed of adjacent patches. The models predicted severe seed limitations were likely on typical burned areas, especially compared to the mean 95–250 seeds per m2 that previous literature suggested were required to generate sagebrush recovery. More broadly, our Bayesian data fusion approach could be applied to other cases that require quantitative estimates of long-distance seed dispersal across heterogeneous landscapes. 

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