Howe Henry F, Richter Wayne M
Department of Zoology, University of Iowa, 52242, Iowa City, Iowa, USA.
Oecologia. 1982 Jun;53(3):347-351. doi: 10.1007/BF00389011.
We conducted a greenhouse study of the effects of initial seed mass on seedling characteristics in a Panamanian population of Virola surinamensis, a canopy tree in which mean seed mass of different individuals ranges from 1.34 to 4.04g. The system is of particular interest because birds preferentially eat fruits of small-seeded plants, leaving seedlings of large-seeded individuals under conditions of potentially severe sibling competition (Howe and Vande Kerckhove 1980).Effects of differences of mean seed mass between trees are explored using an analysis of variance, while effects of seed-mass variation within crops are demonstrated with a regression analysis. A two-way analysis of variance decisively shows effects of parental source and light condition on seedling height, leaf length, and dry shoot mass (all P<0.0001). A posteriori tests show that differences in seedling characteristics reflect differences in initial seed mass, with especially strong differences apparent in shoot mass. Regression of seedling characteristics on initial seed mass shows that variation of seed size within a crop is sufficient to influence shoot mass at 15 weeks (P<0.0001).Effects of size differences of seeds that land adjacent to each other, either under the parent or in monkey droppings, are documented with growth of pairs of seedlings in pots. Differences in shoot height and mass at 15 weeks are evident when seeds of average size differ by only 0.2 g, and dramatic differences are evident when paired seeds differ by an average of 1.5 g. Seedlings grow more when isolated than when planted with conspecifics.These experimental results offer indirect support for the hypothesis that small-seeded Virola parents secure an advantage in reproduction through differential dispersal, while large-seeded plants produce more competitive seedlings under their own crowns - an advantage most likely to be of importance when frugivores are scarce.
我们对巴拿马苏里南肉豆蔻（Virola surinamensis）种群中初始种子质量对幼苗特征的影响进行了一项温室研究，苏里南肉豆蔻是一种树冠层树木，不同个体的平均种子质量在1.34至4.04克之间。该系统特别值得关注，因为鸟类优先食用小种子植物的果实，使得大种子个体的幼苗处于潜在的激烈同胞竞争条件下（豪和范德·克尔霍夫，1980年）。我们使用方差分析来探究树木之间平均种子质量差异的影响，同时通过回归分析来证明作物内部种子质量变化的影响。双向方差分析明确显示了亲本来源和光照条件对幼苗高度、叶片长度和干茎质量的影响（所有P<0.0001）。事后检验表明，幼苗特征的差异反映了初始种子质量的差异，茎质量方面的差异尤为明显。幼苗特征对初始种子质量的回归分析表明，作物内部种子大小的变化足以影响15周时的茎质量（P<0.0001）。通过盆栽中成对幼苗的生长情况记录了相邻落地种子大小差异的影响，这些种子要么在母树下，要么在猴子粪便中。当平均大小的种子仅相差0.2克时，15周时茎高度和质量的差异就很明显，而当成对种子平均相差1.5克时，差异则更为显著。幼苗单独生长时比与同种植物一起种植时长得更好。这些实验结果为以下假设提供了间接支持：小种子的苏里南肉豆蔻亲本通过差异传播在繁殖中获得优势，而大种子植物在其自身树冠下产生更具竞争力的幼苗——当食果动物稀缺时，这一优势可能最为重要。
