Dissertation Research: Seed Population Dynamics and the Coexistence of Pioneer Tree Species in Tropical Forests

对生长在墨西哥东南部韦拉克鲁斯洛斯塔克特拉斯热带雨林的两个最丰富的先锋树种(Cecropia obtusifolia和Heliucpus appendulatus)共存的重要性进行了研究。同时考虑了森林的斑块动态和每个物种的种子种群动态。人口统计学工具被用来实现这一目标，并解决了以下问题：1.-差距形成的时间和空间模式是什么？洛斯塔特拉斯森林中不同类型斑块的过渡概率是多少？2.-洛斯塔特拉斯地面上的天牛和香果种子雨的时空格局是什么？3.-种子捕食如何，萌发和生理性死亡影响不同类型森林斑块中各物种的土壤种子动态？4.各物种的斑块动态和种子种群动态在林隙定居过程中如何影响其种子的相对丰度？5.种子种群动态对生态变量的变化有多敏感？6.繁殖体的相对可用性如何决定每个物种在苗期和幼年阶段，特别是林隙中未来的相对成功？对这些问题的回答将有助于理解热带地区如此多树种共存的一些机制。

A study is proposed of the importance of the colonization process in the coexistence of the two most abundant pioneer tree species (Cecropia obtusifolia and Heliocarpus appendiculatus) growing in the tropical rain forest of Los Tuxtlas, Veracruz (Southeast Mexico). Both the patch dynamics of the forest and the seed population dynamics of each species are considered. Demographic tools are used to fulfill this objective and the following questions are addressed: 1.-What is the temporal and spatial pattern of gap formation? and what are the transition probabilities of the different types of patches in the forest of Los Tuxtlas? 2.-What is the spatial and temporal pattern of seed rain of Cecropia obtusifolia and Heliocarpus appendiculatus at ground level in Los Tuxtlas? 3.-How does seed predation, germination and physiological death affect the species soil seed dynamics of each species in different types of forest patches? 4.-How does the patch dynamics and the seed population dynamics of each species affect their relative abundance of seeds during the process of gap colonization? 5.-How sensitive are the seed population dynamics to alterations of the ecological variables that determine them? 6.-How does the relative availability of propagules determine the future relative success of each species at the seedling and juvenile stage in particular gaps? Answers to these questions will contribute to understanding some of the mechanisms governing the coexistence of so many tree species in the tropics.