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Theoretical models suggest that species abundance plays a crucial role in mutualism; high densities can lead to overexploitation. Additionally, mutualistic benefits are expected to increase under abiotic stress. We investigated the interplay between density dependence and abiotic factors in conditional mutualism, focussing on the interactions between yellow‐necked mice (Apodemus flavicollis) and common oaks (Quercus robur) across 3 years. We controlled for seed abundance, while mouse densities varied. Our approach included monitoring mouse abundance, measuring seed removal, determining the fate of harvested seeds and conducting seedling emergence trials to assess the advantages of seeds caching. We found that mouse abundance exerted a strong influence on all studied aspects of seed dispersal. Higher densities led to increased seed removal and greater dispersal distances. However, they also decreased the probability of seed caching and increased seed consumption, degrading dispersal quality and shifting the interaction towards antagonism. Furthermore, the reliance of seedling recruitment on burial varied over time, likely becoming more critical during dry conditions. This indicates that plants face the worst conditions when high abundance of mice coincides with abiotic stress. Synthesis: Our results supports the notion that increased rodent abundance reduces plant recruitment, revealing the conflicting interests of the interacting species. However, the dynamics of rodent–oak interactions are shaped not only by the density‐dependent foraging decisions of rodents, but also by the benefits of seed burial under stress. These findings illustrate how the interplay between population density and abiotic factors jointly dictate the costs and benefits of mutualistic interactions. [ABSTRACT FROM AUTHOR]

Intraspecific variation plays a pivotal role in shaping ecological dynamics. As the dispersal of seeds of most woody plants is mediated by animals, individual variation within the animal dispersers holds considerable implications for plant population and ecology.We explored how individual traits (such as sex, body mass and exploration levels) of yellow‐necked mice (Apodemus flavicollis) impact the dispersal of common oak (Quercus robur) acorns. Over 3 years, we collected data on seed fate and the specific mice responsible for their dispersal.The relationship between individual traits and seed dispersal was not static, but influenced by yearly environmental conditions. Heavier individuals tended to carry seeds farther, yet contrary to our expectations, sex had no effect on the distance of seed dispersal. Moreover, the exploration rate showed an inconsistent association with seed consumption and dispersal distance, while it positively impacted the distance of dispersal from the nearest tree.Synthesis. Our findings suggest a more nuanced role of individual traits in seed dispersal than often assumed, with noticeable annual variation significantly influencing these impacts. Consequently, it appears there is no single, universally beneficial individual type to ensure maximal benefits to plants. Rather, the traits conferring advantages in seed dispersal are dynamic, subject to change over time in response to environmental context. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Seeds produced by individual plants often vary substantially in size. Typically, larger seeds produce seedlings that have higher chances of establishment and survival relative to seedlings produced by smaller seeds. However, larger seeds are also preferred by granivores due to larger caloric content. While choosing the patch to forage, granivores might avoid the ones with smaller, less preferred seeds. We tested a novel hypothesis that the production of different size seeds by a plant may be a strategy to decrease predation by granivores. We conducted a 3-year seed removal experiment. We presented Quercus robur acorns in forests in three configurations: large acorns alone, medium acorns alone, and large acorns mixed with small ones. The impact of seed size on seed survival was inconsistent: in the first year of the study, survival probability for seeds in the mixed treatment was significantly higher than survival probability of large seeds alone, supporting our hypothesis. However, in the following years, results were non-significant, probably because of reduced granivore selectivity in poor seed crop years. Our study demonstrated that the impact of neighbourhood of different size seeds seed survival varied over time in Q. robur. This provides limited evidence that intraspecific variation in seed size could evolve to shift the interaction between trees and scatter hoarders away from predation and towards mutualism. [ABSTRACT FROM AUTHOR]

Predator satiation is the most commonly tested hypothesis that explains the evolutionary advantages of masting. It proposes that masting benefits plant reproduction by reducing the proportion of seed crop that is consumed by predators. This hypothesis is widely accepted, but many theoretical notions about predator satiation have not been subjected to a robust evaluation. To address this issue, we conducted a meta-analysis of studies that quantified seed predation in relation to mast seeding. We found evidence of both numerical (starvation between mast years) and functional (satiation during mast years) response of consumers to masting. These two effects reinforced each other. Masting satiated invertebrate but not vertebrate seed predators. Satiation was more pronounced at higher, temperate, and boreal latitudes, perhaps because masting is more effective in reducing seed losses when plant communities are less diverse. The effectiveness of masting in satiating invertebrate consumers declined over time (1972 to 2018), probably reflecting the impact of climate change on the frequency and intensity of masting. If masting ceases to reduce seed losses, a crucial advantage of this reproductive strategy will be lost, and sustainability of many tree populations will decline. [ABSTRACT FROM AUTHOR]

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long‐lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time‐series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population‐level time‐series from 974 species in 66 countries. The mean and median time‐series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well‐studied species, MASTREE+ includes extensive replication of time‐series across geographical and climatic gradients. Here we describe the open‐access data set, available as a.csv file, and we introduce an associated web‐based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long‐lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics. [ABSTRACT FROM AUTHOR]