Mathiasen Paula, Rovere Adriana E, Premoli Andrea C
Laboratorio Ecotono, Centro Regional Universitario Bariloche, Universidad Nacional del Comahue, Quintral 1250, 8400 Bariloche, Argentina.
Conserv Biol. 2007 Feb;21(1):232-40. doi: 10.1111/j.1523-1739.2006.00565.x.
Deforestation of temperate forests has created landscapes of forest remnants in matrices of intense human use. We studied the genetic effects of fragmentation in southern Chile on Embothrium coccineum J.R. et G. Forster, an early colonizing, bird-pollinated tree. We tested the hypothesis that, because of its self-incompatibility and life-history strategy, E. coccineum is less strongly affected by fragmentation. We studied the effects of reduced population size and increased isolation on population genetic structure and early performance of progeny. Samples were collected from spatially isolated trees and six fragments of differing sizes (small, 1 ha; medium, 20 ha; large, >150 ha). Based on isozyme polymorphisms we estimated parameters of genetic diversity, divergence, and inbreeding for adults and greenhouse-grown progeny. We also measured germination, seedling growth, and outcrossing rates on progeny arrays. Genetic variation of adults did not correlate significantly with population size, as expected, given that fragmentation occurred relatively recently. Weak effects of fragmentation were measured on progeny. Only adults yielded significant inbreeding. Similar total genetic diversity was found in adults and progeny. Low but significant genetic differentiation existed among adult and progeny populations. Seedling growth correlated positively with the effective number of alleles, showing deleterious effects of inbreeding on progeny. Seeds from small fragments had the highest outcrossing rates and germination success, indicating that higher pollinator activity in such fragments reduced selfing, thereby buffering genetic erosion and maintaining adaptive variation. The effects of forest fragmentation were detectable in E. coccineum, but these effects will probably not be detrimental to the viability of remnant populations because small, fragmented populations demonstrated higher levels of gene flow and lower inbreeding than larger stands. Pioneer species that are insensitive to forest clearing may be crucial in recovery plans to facilitate the establishment of species intolerant to such disturbance.
温带森林的砍伐在人类高强度利用的区域形成了森林残余景观。我们研究了智利南部森林碎片化对红苞木（Embothrium coccineum J.R. et G. Forster）的遗传影响，红苞木是一种早期定居、靠鸟类传粉的树木。我们检验了这样一个假设：由于红苞木的自交不亲和性和生活史策略，它受碎片化的影响较小。我们研究了种群规模减小和隔离增加对种群遗传结构及子代早期表现的影响。样本采集自空间隔离的树木以及六个不同大小的片段（小片段，1公顷；中等片段，20公顷；大片段，大于150公顷）。基于同工酶多态性，我们估计了成年植株和温室培育子代的遗传多样性、分化及近亲繁殖参数。我们还测量了子代群体的发芽率、幼苗生长及异交率。正如预期的那样，鉴于碎片化发生时间相对较近，成年植株的遗传变异与种群规模并无显著关联。在子代中检测到碎片化的微弱影响。只有成年植株出现了显著的近亲繁殖。成年植株和子代中发现了相似的总遗传多样性。成年植株和子代群体之间存在低但显著的遗传分化。幼苗生长与有效等位基因数呈正相关，表明近亲繁殖对子代有有害影响。来自小片段的种子异交率和发芽成功率最高，这表明此类片段中较高的传粉者活动减少了自交，从而缓冲了遗传侵蚀并维持了适应性变异。在红苞木中可检测到森林碎片化的影响，但这些影响可能不会对残余种群的生存能力造成不利影响，因为小的碎片化种群显示出比大片段林分更高的基因流水平和更低的近亲繁殖率。对森林砍伐不敏感的先锋物种在恢复计划中可能至关重要，有助于那些不耐受此类干扰的物种的建立。
