Effects of seedling size, El Nino drought, seedling density, and distance to nearest conspecific adult on 6-year survival of Ocotea whitei seedlings in Panama

被引:97
作者
Gilbert, GS
Harms, KE
Hamill, DN
Hubbell, SP
机构
[1] Univ Calif Santa Cruz, Dept Environm Studies, Santa Cruz, CA 95064 USA
[2] Cornell Univ, Dept Nat Resources, Ithaca, NY 14853 USA
[3] Univ Georgia, Dept Bot, Athens, GA 30602 USA
基金
美国国家科学基金会;
关键词
Ocotea whitei; seedling mortality; El Nino-Southern Oscillation; Barro Colorado Island; Janzen-Connell hypothesis;
D O I
10.1007/s004420000616
中图分类号
Q14 [生态学(生物生态学)];
学科分类号
071012 ; 0713 ;
摘要
We present an analysis of the long-term survival of two cohorts of seedlings of the tropical canopy tree Ocotea whitei (Lauraceae) on a 1-ha plot of mature, lowland moist forest on Barro Colorado Island, Panama. In 1980, we counted an even-aged cohort of seedlings that germinated in 1979, then measured and tagged survivors in 1981. We also measured and tagged a second, smaller cohort of seedlings that germinated in 1981. We followed the subsequent survival of all seedlings through 1985, Seedling mortality was phenotypically, temporally, and spatially non-random. Important correlates of nonrandom mortality included: (l)seedling size and age, (2) an El Nino drought, and (3) biotic neighborhood. Larger and older seedlings survived better than smaller and younger seedlings, respectively, and the El Nino-related drought of 1982-1983 was associated with elevated mortality rates. Seedling density, which was strongly correlated with the proximity to the nearest conspecific adult, increased mortality. The observed mortality patterns suggest that processes consistent with the Janzen-Connell hypothesis operate during the recruitment phase of O. whitei population dynamics. However, the processes causing the observed density- and distance-dependent mortality may vary with factors such as total seed number, seedling size, and climatic variation, making it difficult to determine whether time-integrated seedling-to-adult spacing mechanisms other than self-thinning operate on a given plant population. After 6 years in the hectare studied, survivors remained densest and most numerous underneath the adult trees. We conclude that only long-term demographic data, collected at a variety of scales on a variety of species, will ultimately answer the question: do Janzen-Connell effects contribute substantially to structuring tropical forests?.
引用
收藏
页码:509 / 516
页数:8
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