Theoretical Evolutionary Ecology Group, Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Wurzburg, Germany.
Field Station Fabrikschleichach, University of Würzburg, Wurzburg, Germany.
J Anim Ecol. 2019 Jan;88(1):178-188. doi: 10.1111/1365-2656.12908. Epub 2018 Oct 26.
Empirical studies of annual eusocial insects in agricultural landscapes report contrasting findings with regard to colony responses to mass-flowering of crops such as oilseed rape. In particular, total sexual production is often unaffected by such events, whereas worker number responds with a prominent increase. To resolve these conflicting observations, we model-using an established approach-the expected change in worker and sexual numbers in response to an increased worker productivity induced by mass-flowering events at different times of the season. We find that the predicted response pattern is mainly shaped by the degree to which individual worker productivity is reduced by an increasing number of workers in the colony. Different environmental conditions and colony characteristics result in different levels of interference of workers, for example, during foraging or nest construction. Reduction in individual productivity is low, when worker interference is negligible ("weak limitation") and high when an increasing number of workers substantially decreases per-capita efficiency ("strong limitation"). For weak limitation, any mass-flowering event that ends before the production of sexuals starts has a strong multiplicative impact on both worker and sexual numbers. The magnitude of the effect is quite independent of the precise timing of such an event. After the onset of sexual production, mass-flowering has a weaker effect, as the added resource supply is only linearly transferred into production of additional sexuals. For colonies under strong limitation, the predicted impact of mass-flowering events is generally weaker, especially on the production of sexuals, and the timing of mass-flowering events becomes more influential: Production of sexuals profits more from late than from early mass-flowering events. Consequently, early mass-flowering events are predicted to have a prominent effect on worker numbers but a negligible one on the output of sexuals. The model presented provides a mechanistic explanation of why increased worker abundances do not necessarily translate into increased production of sexuals. The model is also applicable to other eusocial insects such as paper wasps whenever brief pulses of massive resource availability shortly elevate resource intake rates above the "normal" levels.
农业景观中年度群居昆虫的实证研究报告称，关于群体对作物如油菜大规模开花的反应存在相互矛盾的发现。特别是，这种事件通常不会影响总生殖产量，而工蜂数量则会显著增加。为了解决这些相互矛盾的观察结果，我们使用一种既定的方法——模型——来预测在季节的不同时间，由于大规模开花事件导致的工蜂生产力增加，工蜂和有性生殖数量的预期变化。我们发现，预测的反应模式主要取决于个体工蜂生产力因群体中工蜂数量的增加而降低的程度。不同的环境条件和群体特征导致工蜂的干扰程度不同，例如，在觅食或巢建设期间。当个体生产力的降低程度较低，即工蜂干扰可以忽略不计（“弱限制”）时，或者当越来越多的工蜂大大降低人均效率时（“强限制”），降低个体生产力的程度较高。对于弱限制，任何在有性生殖开始之前结束的大规模开花事件都会对工蜂和有性生殖数量产生强烈的乘法影响。这种影响的幅度与这种事件的精确时间相当独立。在有性生殖开始后，大规模开花的影响较弱，因为增加的资源供应仅线性转化为额外有性生殖的产生。对于处于强限制下的群体，大规模开花事件的预测影响通常较弱，尤其是对有性生殖的产生，大规模开花事件的时间变得更加重要：有性生殖从晚期的大规模开花事件中获益更多，而不是从早期的大规模开花事件中获益。因此，早期的大规模开花事件预计会对工蜂数量产生显著影响，但对有性生殖的产量影响可以忽略不计。所提出的模型提供了一个机制解释，说明为什么增加的工蜂数量不一定转化为有性生殖产量的增加。该模型也适用于其他群居昆虫，如纸蜂，只要大量资源的短暂脉冲会使资源摄入率短暂升高到“正常”水平之上。
