Floral antagonists counteract pollinator-mediated selection on attractiveness traits in the hummingbird-pollinated Collaea cipoensis (Fabaceae)

Pollinator-mediated selection towards larger and abundant flowers is common in naturally pollen-limited populations. However, floral antagonists may counteract this effect, maintaining smaller- and few-flowered individuals within populations. We quantified pollinator and antagonist visit rates and determined a multiplicative female fitness component from attacked and non-attacked flowers of the Brazilian hummingbird-pollinated shrub Collaea cipoensis to determine the selective effects of pollinators and floral antagonists on flower size and number. We predicted that floral antagonists reduce the female fitness component and thus exert negative selective pressures on flower size and number, counteracting the positive effects of pollinators. Pollinators, mainly hummingbirds, comprised 4% of total floral visitation, whereas antagonist ants and bees accounted for 90% of visitation. Nectar-robbers involved about 99% of floral antagonist visit rates, whereas florivores comprised the remaining...在自然花粉限制种群中，由传粉者（pollinator）介导的对更大、更多花的选择作用普遍存在。然而，花部拮抗生物（floral antagonist）可能会抵消这一选择效应，使得种群中保留花更小、数量更少的个体。本研究量化了传粉者与拮抗生物的访花频率（visit rate），并以巴西蜂鸟传粉灌木Collaea cipoensis的受损伤与未受损伤花朵为材料，测定了乘性雌性适合度组分（multiplicative female fitness component），以此明确传粉者与花部拮抗生物对花大小及花数量的选择效应。我们提出假说：花部拮抗生物会降低雌性适合度组分，进而对花大小与花数量施加负向选择压力，抵消传粉者带来的正向选择效应。传粉者（主要为蜂鸟）仅占总访花量（floral visitation）的4%，而作为拮抗生物的蚂蚁与蜜蜂则占总访花量的90%。盗蜜者（nectar-robber）约占花部拮抗生物访花总量的99%，剩余部分则为食花者（florivore）……