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

本文研究了生长在墨西哥东南部维拉克鲁斯州Los Tuxtlas热带雨林中两种最丰富的先锋树种（Cecropia obtusifolia和Heliocarpus appendiculatus）在殖民过程中的重要性。同时考虑了森林的斑块动态和各树种种子种群动态。使用人口统计工具来实现这一目标，并处理以下问题：-缝隙形成的时空格局是什么？以及Los Tuxtlas森林中不同类型斑块的过渡概率是多少？2.-塔克斯特拉斯地区地面黄柏和尾果种子雨的时空格局？3.-不同类型森林斑块中各物种的种子捕食、萌发和生理死亡对物种土壤种子动态有何影响？4.-在间隙定殖过程中，各物种的斑块动态和种子种群动态如何影响其种子的相对丰度？5.-种子种群动态对决定它们的生态变量的变化有多敏感？6.繁殖体的相对有效性如何决定在特定间隙中每个物种在苗期和幼期的未来相对成功？这些问题的答案将有助于理解控制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.