Flower constancy in pollinators: a bouquet of agendas shape interactions among mutualistic partners

Plant-pollinator interactions have become a major research area due to their impact on important ecosystem services that are driven by the outcomes of these mutualistic interactions. One pollinator behaviour of particular importance is flower constancy, i.e. the tendency of pollinators to temporarily specialise on one flower species during a foraging trip, thereby promoting cross-pollination. The costs and benefits of flower constancy for both plants and pollinators are varied, complex and far from understood. This review aims to synthesise and interpret studies spanning the last decades, from both plant and pollinator perspectives. Flower constancy is often viewed as an epiphenomenon of pollinator cognition, but there is increasing recognition that pollinators show remarkable behavioural flexibility in their flower choice, often in response to ecological and social factors. Plants usually benefit from flower constancy, which reduces pollen loss and interspecific pollen transfer. However, in some situations, pollinator inconstancy can be advantageous due to increased visits from pollinators shared with co-flowering plants. The fitness consequences of pollinator behaviour for rare or invasive plants is not well understood, which is blind spot for plant conservation. Rather than seeing flower constancy as a strategy imposed on pollinators by cognitive constraints, this review emphasises that plants and pollinators pursue varied agendas depending on their ecological context and lifestyle.