Effects of sex-ratio selection on the demography of an annual plant: challenging the seed-centric view of population dynamics

性别比选择对一年生植物种群统计的影响：挑战以种子为中心的种群动态观点

• 批准号: NE/G003203/1
• 负责人: John Pannell
• 金额: $ 41.49万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG003203%2F1
• 关键词: Effects; sex; ratio; selection; demography

The distribution and the abundance of organisms depend on both the persistence of species locally as well as on their regional persistence through a balance between colonisation of available habitat and local extinctions. Both local and regional processes depend on the density-dependent regulation of population growth rates and the fecundity of their constituent individuals. Population growth decreases with population density as a result of reduced individual survivorship and fecundity through competition for resources and microsites for germination (negative density dependence); and population growth increases with density below some critical threshold if, for example, mating opportunities are limited at low density (positive density dependence, or the 'Allee effect'). Negative density-dependent interactions are expected to regulate populations as they grow towards their local equilibrium; positive density-dependent reproduction prohibits the survival of populations that are too small and may limit colonisation success, thus limiting the regional persistence of a species. In plants positive density dependence can most likely occur in dioecious species, where seed production may be limited; in addition, there is a trade-off between male and female function that will be expected to severely constrain seed production. Here we propose for the first time to test the roles of these in determining population dynamics. The novel contribution of our study will be in the challenge it poses to the 'seed-centred view' of plant demography. We draw a link between plant population dynamics at local and regional scales, which depends fundamentally on seed production, and natural selection on a plant's sex allocation, which diverts up to half a population's reproductive resources away from seed production towards male function in outcrossing species. Because selection on sex allocation compromises seed production so greatly, we expect it to affect a species local and regional dynamics. Surprisingly, this link does not appear to have been made before. Our study will address questions about the way in which selection on sex allocation affects both the negative and positive density-dependent regulations of plant populations. Using a series of manipulative experiments under controlled conditions, we will assess the extent to which the presence of males in hermaphroditic populations of the species Mercurialis annua compromises population seed production, thus reducing a population's intrinsic rate of growth at different densities. This species is particularly useful for our purposes because it displays striking variation in its reproductive system, with populations comprising either only hermaphrodites, males with females, or males with hermaphrodites. By studying populations with different sexual systems, we will determine how the allocation of resources to male function affects the regulation of plant populations through competition, and through the colonisation of new patches or populations by seed dispersal. We will also establish a large field experiment in which we will test the hypothesis that the establishment of dioecious populations (comprising only males and females) will be more severely compromised at low densities (because of pollen limitation on seed set) than self-fertile hermaphroditic populations. We will experimentally assess the extent to which seed-bank dynamics may contribute to the local and regional dynamics of populations. Finally, we will use experimental mating arrays under controlled conditions to determine the relationship between density (i.e., interplant distance) and seed set for dioecious and hermaphroditic populations. The results of these experimental studies will be used to parameterise models that link sex allocation with the local and regional regulation of plant populations through both positive and negative density dependence.

生物的分布和丰度取决于物种在当地的持久性以及它们通过现有栖息地的殖民化和当地保护之间的平衡而在区域上的持久性。地方和区域进程都依赖于人口增长率的密度依赖性调节及其组成个体的繁殖力。人口增长随着人口密度的下降，作为减少个人的生存和繁殖力的结果，通过竞争资源和微网站的发芽（负密度依赖）;和人口增长增加密度低于一些临界阈值，如果，例如，交配机会是有限的，在低密度（正密度依赖，或“阿利效应”）。负的密度依赖的相互作用，预计将调节人口，因为他们朝着他们的本地平衡增长;正的密度依赖的繁殖禁止生存的人口太小，可能会限制殖民成功，从而限制了区域持久性的一个物种。在植物中，正密度依赖性最有可能发生在雌雄异株的物种中，其中种子产量可能有限;此外，雄性和雌性功能之间存在权衡，预计将严重限制种子产量。在这里，我们建议第一次测试这些在确定人口动态的作用。我们的研究的新贡献将是它对植物人口学的“种子中心观点”提出的挑战。我们绘制了植物种群动态之间的联系，在当地和区域尺度上，这从根本上取决于种子生产，和自然选择对植物的性别分配，这转移了一半人口的生殖资源远离种子生产对男性功能的异交物种。由于性别分配的选择妥协种子生产如此之大，我们预计它会影响一个物种的地方和区域动态。令人惊讶的是，这种联系似乎以前没有出现过。我们的研究将解决的问题，在选择性别分配的方式影响植物种群的负和正的密度依赖性法规。在受控条件下使用一系列的操纵实验，我们将评估在何种程度上存在的男性在雌雄同体的种群中的物种一年生汞妥协人口种子生产，从而降低人口的内在增长率在不同的密度。这个物种对我们的目的特别有用，因为它的生殖系统显示出惊人的变化，种群要么只包括雌雄同体，雄性与雌性，或雄性与雌雄同体。通过研究具有不同性系统的种群，我们将确定资源分配给雄性功能如何通过竞争影响植物种群的调节，以及通过种子传播新斑块或种群的殖民化。我们还将建立一个大型的田间实验，我们将测试的假设，雌雄异株的人口（只包括男性和女性）的建立将更严重地损害在低密度（因为花粉限制在种子集）比自育雌雄同体的人口。我们将通过实验评估种子库的动态可能有助于当地和区域的人口动态的程度。最后，我们将在受控条件下使用实验交配阵列来确定密度（即，株间距离）和结实率。这些实验研究的结果将被用来参数化模型，通过积极和消极的密度依赖性的性别分配与植物种群的地方和区域监管。