热带森林的低密度种及其形成与维持机制

低密度种指在热带森林中存在的成年个体密度很低的物种，是热带森林中树种的主要存在形式。对低密度种的认识和保护是热带森林生物多样性保育的关键之一。与稀有种相比，低密度种的含义更为广阔，它还包括那些密度低、分布范围广和绝对个体数量大的物种。低密度种形成的主要原因是母树附近的幼苗和种子的存活率较低，密度制约和有限更新也是低密度种形成的重要原因。维持低密度种最重要的外部原因是昆虫较强的飞行能力和传粉能力，而其最重要的内部原因是低密度种的生殖特性。

Low-density species and the mechanism of their formation and maintenance in tropical forests

Low -density species are species that occur with a low density of mature individuals. They are the most common species in tropical forests. Knowledge and protection of low density species are key tobiodiversity conservation in tropical forests. The meanings of low density species is broader than that of rare species. Low density species also include species that have low density, wide distribution range and a huge number of mature individuals. Low survivorship of seeds and seedlings near the parent individual is an important mechanism of creation of low density species. Low density species probably arise from intraspecific density dependent effects and limited population recruitment. The possible mechanisms of maintenance of low density species lie in both external factors, such as capacities of insect pollinating, and inner factors, including flower number and flowering duration of tropical plants. Some tropical species are self fertilized, compensating for the decline in opportunity for cross breeding due to extreme low density. Up to now, few studies have been carried out in this field. We should design more detailed research in combination with research on the properties of tropical forests, so that we can provide a theoretical basis and practical advice for biodiversity conservation in tropical forests of our country.