Abstract
Although dispersal is critical to plant life history, the relationships between seed traits and dispersal success in animal-dispersed plants remain unclear due to complex interactions among the effects of seed traits, habitat structure, and disperser behavior. We propose that in plants dispersed by scatter-hoarding granivores, seed trait evolution may have been driven by selective pressures that arise from interactions between seedling shade intolerance and predator-mediated caching behavior. Using an optimal foraging model that accounts for cache concealment, hoarder memory, and perceived predation risk, we show that hoarders can obtain cache-recovery advantages by placing caches in moderately risky locations that force potential pilferers to engage in high levels of vigilance. Our model also demonstrates that the level of risk needed to optimally protect a cache increases with the value of the cached food item. If hoarders perceive less sheltered, high-light conditions to be more risky and use this information to protect their caches, then shade-intolerant plants may increase their fitness by producing seeds with traits valued by hoarders. Consistent with this hypothesis, shade tolerance in scatter-hoarded tree species is inversely related to the value of their seeds as perceived by a scatter-hoarding rodent.
Highlights
The seed-seedling transition represents a critical juncture in plant life history and a central theme in plant demography, community ecology, and evolution, as well as ecosystem management and conservation [1], [2]
We propose that the evolution of one common seed dispersal syndrome—dispersal by scatter-hoarding granivorous birds and rodents—may have been shaped by the joint selective pressures generated by three interacting ecological processes: shade effects on seedling competitiveness and growth, pilferage-avoidance by scatter-hoarding, granivorous animals, and habitat-mediated anti-predator behavior among those animals
Through a series of modelling exercises, we show that acting in concert, these processes can incentivize hoarders to direct highly valued seeds toward favorable seedling habitats, and that this behavior can create selective pressures to express seed traits that are useful to hoarders
Summary
The seed-seedling transition represents a critical juncture in plant life history and a central theme in plant demography, community ecology, and evolution, as well as ecosystem management and conservation [1] (and citations therein), [2]. Seeds are killed by inhospitable abiotic conditions (e.g., desiccation, freezing), pathogens, and predation by granivorous insects, birds, or mammals [6,7], and further mortality is caused at the seedling stage by arrival in inhospitable locations [4]. Given these pressures, researchers dating back to Darwin [8] have considered selection for successful dispersal to be the principle driver of diversification in seed morphology and chemistry [9,10]. Our understanding of the functional ecology and evolution of seed traits
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