Highly variable, synchronized seed production, called masting, is a widespread reproductive strategy in plants. Resource dynamics, pollination success, and, as described here, environmental veto, are possible proximate mechanisms of masting. We extended the resource budget model of masting with correlated and uncorrelated reproductive failure, and ran this model across its parameters space. Next, we parametrized the model based on a 16-year seed production data for red (Quercus rubra) and white (Q. alba) oaks. Simulations showed that resource dynamics and reproduction failure produce masting even in the absence of pollen coupling. In concordance, in both species, among-year variation in resource gain and correlated reproductive failure were necessary and sufficient to produce masting.Environmental variation is a form of reproduction failure caused by environmental veto that may drive large-scale synchronization without density-dependent pollen limitation. Reproductive-inhibiting weather events are prevalent in ecosystems, suggesting that these described mechanisms likely operate in many masting systems.

Scatterhoarding rodents often place caches in the open where pilferage rates are reduced, suggesting that they tradeoff higher risks of predation for more secure cache sites. We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities (GUDs) at known cache sites and other sites for comparison. Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds. In the first experiment, we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels (Sciurus carolinensis) and then measured GUDs at: (i) these caches; (ii) comparable points along logs and rocks where rodent activity was assumed highest; and (iii) a set of random points. We found that GUDs and, presumably, predation risks, were higher at both cache and random points than those with cover. At the second site, we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites, where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest. These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent, and that the landscape of fear, now so well documented in the literature, could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.

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.

Variable, synchronized seed production, called masting, is a widespread reproductive strategy in plants. Resource dynamics, pollination success, and, as described here, environmental veto are possible proximate mechanisms driving masting. We explored the environmental veto hypothesis, which assumes that reproductive synchrony is driven by external factors preventing reproduction in some years, by extending the resource budget model of masting with correlated reproductive failure. We ran this model across its parameter space to explore how key parameters interact to drive seeding dynamics. Next, we parameterized the model based on 16 yr of seed production data for populations of red (Quercus rubra) and white (Quercus alba) oaks. We used these empirical models to simulate seeding dynamics, and compared simulated time series with patterns observed in the field. Simulations showed that resource dynamics and reproduction failure can produce masting even in the absence of pollen coupling. In concordance with this, in both oaks, among-year variation in resource gain and correlated reproductive failure were necessary and sufficient to reproduce masting, whereas pollen coupling, although present, was not necessary. Reproductive failure caused by environmental veto may drive large-scale synchronization without density-dependent pollen limitation. Reproduction-inhibiting weather events are prevalent in ecosystems, making described mechanisms likely to operate in many systems.

The predator satiation hypothesis posits that masting helps plants escape seed predation through starvation of predators in lean years, followed by satiation of predators in mast years. Importantly, successful satiation requires sufficiently delayed bottom-up effects of seed availability on seed consumers. However, some seed consumers may be capable of quick aggregative and reproductive responses to masting, which may jeopardize positive density dependence of seed survival. We used a 17-yr data set on seed production and insect (Curculio weevils) infestation of three North American oaks species (northern red Quercus rubra, white Q. alba, and chestnut oak Q. montana) to test predictions of the predation satiation hypothesis. Furthermore, we tested for the unlagged numerical response of Curculio to acorn production. We found that masting results in a bottom-up effect on the insect population; both through increased reproductive output and aggregation at seed-rich trees. Consequently, mast seeding in two out of three studied oaks (white and chestnut oak) did not help to escape insect seed predation, whereas, in the red oak, the escape depended on the synchronization of mast crops within the population. Bottom-up effects of masting on seed consumer populations are assumed to be delayed, and therefore to have negligible effects on seed survival in mast years. Our research suggests that insect populations may be able to mount rapid reproductive and aggregative responses when seed availability increases, possibly hindering satiation effects of masting. Many insect species are able to quickly benefit from pulsed resources, making mechanisms described here potentially relevant in many other systems.