Game, (fruit) set, match: Pollinator rules, pollen donor/receiver matching, and fruit set in simulated wild blueberry agroecosystems
Fruits are important reproductive organs for many plants, yet low fruit set is common in many (perhaps most) populations. Many factors are known to influence fruit set, but how they ultimately interact is poorly understood. Additionally, we lack an explanation for why low fruit set occurs even under seemingly “ideal” conditions in many systems. Simulation modeling can permit manipulations that would be difficult in the “real world,” revealing where our hypotheses or data need supplementation. An agent-based model, coded in R language, is described that simulates pollination and fruit set in a virtual Maine wild blueberry (Vaccinium angustifolium) agroecosystem; low fruit set is typical in these systems even when agricultural production inputs are high. A field is produced, populated with blueberry individuals that differ in fecundity, and bees of several taxa with differing behavioral rules are allowed to forage within the field. Several pertinent questions are asked, including: 1) How sensitive is fruit set to the flower/pollinator ratio, as well as to the movement and pollination rules of the pollinators? 2) Given what is known about this system, what parameters must change to achieve a higher fruit set? and 3) How will climate change impact blueberry pollination?
Blueberry fruit set was responsive to the flower/pollinator ratio in simulations, although the nature of this relationship was very different for different pollinator types. For example, while adding more virtual “honey bees” (Apis mellifera) beyond usual densities did not generally increase fruit set, adding more “small native bees” (modeled after Osmia and Andrena spp.) did in some cases. More generally, outcomes were very sensitive to the types of pollinators included and to the assumptions made about how their behaviors differ. For example, “bumble bees” (Bombus spp.) were more efficient pollinators per individual than “honey bees” were; this was at least partially because they were modeled to deposit more pollen per flower visit on average. However, other differences, such as the bees’ differing sensitivities to weather conditions, were also important. The model suggests climate change could have substantial and surprising impacts on wild blueberry pollination; for example, predicted decreases in average weather quality during bloom were demonstrated to actually increase fruit set in some circumstances. Experiments in simulated systems (“virtual ecology”) represent an exciting new way to combine disparate data and hypotheses to study the interplay between factors influencing important and complex natural phenomena, such as fruit set.