Ackerman J D, Sabat A, Zimmerman J K
Department of Biology, University of Puerto Rico, PO Box 23360, 00931-3360, San Juan, PR, USA.
Terrestrial Ecology Division, University of Puerto Rico, PO Box 363682, 00936-3682, San Juan, PR, USA.
Oecologia. 1996 Apr;106(2):192-198. doi: 10.1007/BF00328598.
Will increased fruit and seed production in a severely pollination-limited orchid stimulate population growth? We tested whether safe sites for germination and seedling establishment are limiting for the twig epiphyte, Tolumnia variegata, by manipulating fruit set and monitoring subsequent seedling establishment for two seasons (1991-1992, 1992-1993). In the Cambalache Forest Reserve of Puerto Rico, we established 36 plots along a transect. Each plot consisted of nine trees. A center tree was designated as the site for attaching Tolumnia and manipulating fruit set. The other eight potential host trees were 1-3 and 3-5 m from the center tree in each of the cardinal directions. A 1-m length of stem 1 m from the ground was monitored for recruits on each of the nine trees of 24 fruit-enhanced plots and 12 controls (23 and 13, respectively for the 1992-1993 season). Fruit enhancement plots were divided among two treatments: one-fruit and five-fruit additions for the 1st year and one to five and more than five fruits for the 2nd year. Availability of suitable host species was not limiting. T. variegata showed little specificity for host tree species, good host trees and shrubs were common, and there was no evidence that the orchid had a preference for small branches, despite possessing the entire suite of characteristics thought to respresent "obligate" twig epiphytes. Fruit enhancement increased seed rain and seedling establishment consistently in only the high-fruit treatment plots. Most recruitment occurred near fruiting plants. Over the 2-year period, mortality was 18% for adults and 85.5% for the 1991-1992 cohort of recruits. Net recruitment was positive for both the treatment (average = 1.74) and control plots (average = 0.67). Seedling establishment at our study site was not microsite-limited. If selection for increased pollinator attraction occurs, then an increase in seed output should result in population growth.
在授粉严重受限的情况下，增加兰花的果实和种子产量会刺激种群增长吗？我们通过控制座果率并在两个季节（1991 - 1992年、1992 - 1993年）监测后续的幼苗建立情况，来测试对于附生在嫩枝上的异色托卢西亚兰来说，用于萌发和幼苗建立的安全地点是否具有限制性。在波多黎各的坎巴拉切森林保护区，我们沿着一条样带设立了36个样地。每个样地由九棵树组成。指定一棵中心树作为附着异色托卢西亚兰并控制座果率的地点。其他八棵潜在的寄主树在中心树的四个主要方向上，距离分别为1 - 3米和3 - 5米。在24个果实增加样地和12个对照样地（1992 - 1993年季节分别为23个和13个）的每棵九棵树上，监测距离地面1米处1米长的茎上的新苗。果实增加样地分为两种处理方式：第一年添加一个果实和五个果实，第二年添加一到五个果实以及五个以上果实。合适寄主物种的可用性并不具有限制性。异色托卢西亚兰对寄主树种几乎没有特异性，优良的寄主树和灌木很常见，并且没有证据表明这种兰花偏好小树枝，尽管它具备被认为代表“专性”嫩枝附生植物的全套特征。果实增加仅在高果实处理样地中持续增加了种子雨和幼苗建立。大多数新苗出现在结果植株附近。在两年期间，成年植株的死亡率为18%，1991 - 1992年新苗群体的死亡率为85.5%。处理样地（平均 = 1.74）和对照样地（平均 = 0.67）的净补充量均为正值。我们研究地点的幼苗建立不受微生境限制。如果选择增加对传粉者的吸引力，那么种子产量的增加应该会导致种群增长。
