Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, Ex-Hacienda de San José de la Huerta, 58190, Morelia, Michoacán, Mexico.
Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, Coyoacán, 04510, Mexico City, Mexico.
Ecol Appl. 2020 Mar;30(2):e02033. doi: 10.1002/eap.2033. Epub 2019 Dec 2.
Land-use change modifies the spatial structure of tropical landscapes, shaping global biodiversity patterns. Yet, it remains unknown how key ecological processes, such as seed dispersal, can be affected by changes in landscape patterns, and whether such effects differ among regions with different climate and disturbance intensity. We assessed the effect of five landscape metrics (forest cover, matrix openness, forest edge density, forest fragmentation, and interpatch distance) on the seed rain recorded in two Mexican fragmented regions (20 forest sites per region): the more deforested, defaunated, and windy Los Tuxtlas rainforest (LTX), and the better-preserved Lacandona rainforest (LAC). We quantified the proportions of dispersed tree species and their seeds, separately evaluating wind- and animal-dispersed species. Our findings support the hypothesis that forest loss is more important than fragmentation per se, negatively impacting the seed rain in both regions. As expected, landscape patterns were comparatively more important for wind-dispersed seeds in LTX, probably because of stronger wind events in this region. Specifically, proportions of wind-dispersed seeds and species decreased with increasing edge density, suggesting that forest edges prevent dispersal of wind-dispersed species, which may occur if edges create physical barriers that limit wind flow. This pattern can also be caused by source limitation in landscapes with more forest edges, as tree mortality rates usually increase at forest edges. The wind-dispersed seed rain was also positively related to matrix openness, especially in LTX, where wind flow can be favored by the dominance of treeless anthropogenic matrices. Surprisingly, the proportion of animal-dispersed seeds in LTX was positively related to matrix openness and patch isolation, suggesting that seed dispersers in more deforested regions may be forced to concentrate in isolated patches and use the available habitat more intensively. Yet, as expected, patch isolation limited wind-dispersed seeds in LAC. Therefore, dispersal (and potentially regeneration) of wind-dispersed trees is favored in regions exposed to stronger wind events, especially in landscapes dominated by regularly shaped patches surrounded by open areas. Conversely, animal-dispersed seeds are primarily favored by increasing forest cover. Preventing forest loss is therefore critical to promote animal seed dispersal and forest recovery in human-modified rainforests.
土地利用变化改变了热带景观的空间结构，塑造了全球生物多样性格局。然而，人们仍然不清楚关键的生态过程，如种子传播，如何受到景观格局变化的影响，以及这种影响是否因不同气候和干扰强度的地区而有所不同。我们评估了五个景观指标（森林覆盖率、基质开阔度、森林边缘密度、森林破碎化和斑块间距离）对记录在两个墨西哥破碎化区域（每个区域 20 个森林样地）的种子雨的影响：森林砍伐、动物灭绝和多风的 Los Tuxtlas 雨林（LTX），以及保存较好的 Lacandona 雨林（LAC）。我们分别评估了风传播和动物传播的物种，量化了分散树种及其种子的比例。我们的研究结果支持了这样一种假设，即森林损失比破碎化本身更为重要，对两个地区的种子雨都产生了负面影响。正如预期的那样，景观格局对 LTX 中风传播种子的影响相对更大，这可能是因为该地区风事件更强。具体来说，随着边缘密度的增加，风传播种子和物种的比例下降，这表明森林边缘阻止了风传播物种的传播，如果边缘形成限制风流动的物理障碍，可能会发生这种情况。这种模式也可能是由于边缘有更多森林的景观中源限制造成的，因为树木死亡率通常会在森林边缘增加。风传播的种子雨也与基质开阔度呈正相关，特别是在 LTX，那里的风流动可以得益于无树的人为基质的主导地位。令人惊讶的是，LTX 中动物传播种子的比例与基质开阔度和斑块隔离呈正相关，这表明在森林砍伐更严重的地区，种子传播者可能被迫集中在孤立的斑块中，并更密集地利用可用栖息地。然而，正如预期的那样，斑块隔离限制了 LAC 中风传播的种子。因此，在易受强风事件影响的地区，风传播树木的扩散（和潜在的再生）受到青睐，尤其是在由规则形状的斑块组成、周围有开阔区域的景观中。相反，动物传播的种子主要受到森林覆盖率增加的影响。因此，防止森林损失对于促进人类改造后的热带雨林中的动物种子传播和森林恢复至关重要。
