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1. The natural history of luck: A synthesis study of structured population models

   https://doi.org/10.1111/ele.14390  

   Hernández, Christina M; Ellner, Stephen P; Snyder, Robin E; Hooker, Giles (March 2024, Ecology Letters)

   Heino, Mikko (Ed.)

   Abstract: Chance pervades life. In turn, life histories are described by probabilities (e.g. survival and breeding) and averages across individuals (e.g. mean growth rate and age at maturity). In this study, we explored patterns of luck in lifetime outcomes by analysing structured population models for a wide array of plant and animal species. We calculated four response variables: variance and skewness in both lifespan and lifetime reproductive output (LRO), and partitioned them into contributions from different forms of luck. We examined relationships among response variables and a variety of life history traits. We found that variance in lifespan and variance in LRO were positively correlated across taxa, but that variance and skewness were negatively correlated for both lifespan and LRO. The most important life history trait was longevity, which shaped variance and skew in LRO through its effects on variance in lifespan. We found that luck in survival, growth, and fecundity all contributed to variance in LRO, but skew in LRO was overwhelmingly due to survival luck. Rapidly growing populations have larger variances in LRO and lifespan than shrinking populations. Our results indicate that luck‐induced genetic drift may be most severe in recovering populations of species with long mature lifespan and high iteroparity. 

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2. Time and Chance: Using Age Partitioning to Understand How Luck Drives Variation in Reproductive Success

   https://doi.org/10.1086/712874  

   Snyder, Robin E.; Ellner, Stephen P.; Hooker, Giles (February 2021, The American Naturalist)

   null (Ed.)

   Over the course of individual lifetimes, luck usually explains a large fraction of the between-individual variation in life span or lifetime reproductive output (LRO) within a population, while variation in individual traits or “quality” explains much less. To understand how, where in the life cycle, and through which demographic processes luck trumps trait variation, we show how to partition by age the contributions of luck and trait variation to LRO variance and how to quantify three distinct components of luck. We apply these tools to several empirical case studies. We find that luck swamps effects of trait variation at all ages, primarily because of randomness in individual state dynamics (“state trajectory luck”). Luck early in life is most important. Very early state trajectory luck generally determines whether an individual ever breeds, likely by ensuring that they are not dead or doomed quickly. Less early luck drives variation in success among those breeding at least once. Consequently, the importance of luck often has a sharp peak early in life or it has two peaks. We suggest that ages or stages where the importance luck peaks are potential targets for interventions to benefit a population of concern, different from those identified by eigenvalue elasticity analysis. 

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3. 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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4. Shifting ocean conditions influence temporal variation in the fecundity of California Current rockfishes ( Sebastes spp.)

   https://doi.org/10.1139/cjfas-2023-0253  

   Beyer, Sabrina G; Sogard, Susan M; Stafford, David M; Kashef, Neosha S; Rodriguez, Abel; Alonzo, Suzanne H; Field, John C (June 2024, Canadian Journal of Fisheries and Aquatic Sciences)

   Successful reproduction is critical to the growth and persistence of marine fish populations, yet how changes in the environment influence reproduction remains largely unknown. We explored how shifting ocean conditions influenced larval production in four species of long-lived, live-bearing rockfish (Sebastes spp.) in the California Current. Brood fecundity, body size, and environmental information were analyzed from the mid-1980s through 2020. Interannual variation in brood fecundity was greater than 50% in the single-brooding yellowtail rockfish (S. flavidus) and widow rockfish (S. entomelas). Brood fecundity varied less in chilipepper (S. goodei) and bocaccio (S. paucispinis), two species capable of multiple broods per year. In these two species, interannual fecundity variability is more likely to depend on the number of broods produced than on brood size alone. In all four species, brood fecundity was positively correlated with maternal length and body condition. Variable ocean conditions influenced the strength of maternal size effects by year. These results provide evidence for reproductive plasticity and environmental effects on fecundity, with implications for changes in population reproductive potential with climate change. 

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5. Born this way: individuality is seeded before birth and robust to environmental stress

   https://doi.org/10.32942/X2ZH27  

   Gallagher, James; Perkes, Ammon; Chang, Chia-Chen; Chirila, Emma; Kacevas, Karen; Laskowski, Kate (September 2025, EcoEvoRxiv)

   Consistent individual differences in behavior, known as behavioral individuality, are pervasive across the animal world and have major ecological and evolutionary consequences. Nevertheless, we still have a limited understanding of what drives individuality and how it emerges during ontogeny. Here, we subjected clonal individuals to a ubiquitous yet critical environmental challenge—the threat of predation—to disentangle the developmental mechanisms of individuality. Under such a salient environmental stressor, among-individual differences may collapse or expand depending on whether there is a single or multiple optimal strategies, demonstrating that individuality itself is a developmentally plastic trait. If, however, the environment does not impact among-individual variation, this suggests that individuality is determined before birth. We continuously tracked the behavior of genetically identical fish (Amazon mollies, Poecilia formosa), reared with or without predation stress, from birth through their first month of life. Predation shifted mean-level behaviors, with predator-exposed individuals swimming more slowly and spending more time near their refuges. However, the magnitude of individuality (as evidenced by repeatability) increased similarly over development in both treatments, indicating that individuality crystallizes robustly over time, even under stress and in a vacuum of genetic variation. Predator-reared fish also exhibited greater within-individual variability in refuge use, suggesting increased behavioral flexibility or disrupted developmental canalization in response to stress. Surprisingly, maternal identity, but not maternal behavior, was the strongest predictor of swimming speed, pointing to non-behavioral maternal effects as a key pre-birth source of behavioral variation. Refuge use however was not at all predicted by maternal identity, indicating that major fitness-related behaviors can have entirely different developmental mechanisms. Collectively, we show that individuality persists despite environmental stress and is seeded before birth through non-genetic factors. Even in the face of a shared environmental challenge, the behavioral trajectories of individuals are unique. 

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