The demographic consequences of mutualism: ants increase host-plant fruit production but not population growth
The demographic consequences of mutualism: ants increase host-plant fruit production but not population growth
复制标题
互利共生的人口后果：蚂蚁增加了寄主植物的果实产量，但没有增加人口增长
作者：
K. Ford;J. Ness;J. Bronstein;W. Morris
互助主义者对伴侣人口统计学的影响取决于他们如何影响伴侣的多重生命率，以及这些生命率如何反过来影响人口增长。然而，互惠共生研究很少测量对多个生命率的影响或将其整合以评估对人口增长的最终影响。我们使用生命率数据，人口模型和模拟的长期人口动态，以量化的人口影响的一个公会的蚂蚁物种的植物Ferocactus wislizeni。蚂蚁以植物的花外蜜腺为食，并攻击试图消耗生殖器官的食草动物。蚂蚁守卫的植物产生了更多的果实，但蚂蚁对个体的生长或存活没有显着影响。整合蚂蚁的影响，在这些重要的利率，我们发现，预计人口增长之间没有显着不同的无人看守和蚂蚁看守的植物，因为人口增长只有微弱的影响，在水果产量的差异（虽然强烈影响个体生长和生存的差异）。然而，模拟表明，蚂蚁可以通过在罕见但重要的事件（食草动物爆发，减少生存或多年的高幼苗招募与丰富的降水）提供服务，积极影响长期的植物种群动态。因此，在这个看似明显的互利共生的例子中，这种相互作用实际上可能对植物种群的增长没有明显的好处，或者如果有，也可能只是通过蚂蚁在罕见事件中的行动来实现的。这些见解证明了采用人口统计学方法研究互利共生后果的价值。
The impact of mutualists on a partner’s demography depends on how they affect the partner’s multiple vital rates and how those vital rates, in turn, affect population growth. However, mutualism studies rarely measure effects on multiple vital rates or integrate them to assess the ultimate impact on population growth. We used vital rate data, population models and simulations of long-term population dynamics to quantify the demographic impact of a guild of ant species on the plant Ferocactus wislizeni. The ants feed at the plant’s extrafloral nectaries and attack herbivores attempting to consume reproductive organs. Ant-guarded plants produced significantly more fruit, but ants had no significant effect on individual growth or survival. After integrating ant effects across these vital rates, we found that projected population growth was not significantly different between unguarded and ant-guarded plants because population growth was only weakly influenced by differences in fruit production (though strongly influenced by differences in individual growth and survival). However, simulations showed that ants could positively affect long-term plant population dynamics through services provided during rare but important events (herbivore outbreaks that reduce survival or years of high seedling recruitment associated with abundant precipitation). Thus, in this seemingly clear example of mutualism, the interaction may actually yield no clear benefit to plant population growth, or if it does, may only do so through the actions of the ants during rare events. These insights demonstrate the value of taking a demographic approach to studying the consequences of mutualism.