Elevational Ranges of Montane Birds and Deforestation in the Western Andes of Colombia

Deforestation causes habitat loss, fragmentation, degradation, and can ultimately cause extinction of the remnant species. Tropical montane birds face these threats with the added natural vulnerability of narrower elevational ranges and higher specialization than lowland species. Recent studies assess the impact of present and future global climate change on species’ ranges, but only a few of these evaluate the potentially confounding effect of lowland deforestation on species elevational distributions. In the Western Andes of Colombia, an important biodiversity hotspot, we evaluated the effects of deforestation on the elevational ranges of montane birds along altitudinal transects. Using point counts and mist-nets, we surveyed six altitudinal transects spanning 2200 to 2800m. Three transects were forested from 2200 to 2800m, and three were partially deforested with forest cover only above 2400m. We compared abundance-weighted mean elevation, minimum elevation, and elevational range width. In addition to analysing the effect of deforestation on 134 species, we tested its impact within trophic guilds and habitat preference groups. Abundance-weighted mean and minimum elevations were not significantly different between forested and partially deforested transects. Range width was marginally different: as expected, ranges were larger in forested transects. Species in different trophic guilds and habitat preference categories showed different trends. These results suggest that deforestation may affect species’ elevational ranges, even within the forest that remains. Climate change will likely exacerbate harmful impacts of deforestation on species’ elevational distributions. Future conservation strategies need to account for this by protecting connected forest tracts across a wide range of elevations.

森林砍伐会引发栖息地丧失、破碎化与退化，最终甚至可能导致残存物种走向灭绝。热带山地鸟类不仅面临上述威胁，还相较于低地物种具备额外的天然脆弱性：其海拔分布范围更窄，生态特化程度更高。现有研究多聚焦当前及未来全球气候变化对物种分布范围的影响，但仅有少数研究探讨了低地森林砍伐对物种海拔分布的潜在混淆效应（confounding effect）。作为重要的生物多样性热点（biodiversity hotspot）区域，哥伦比亚西部安第斯山脉为本研究的开展场地。我们沿海拔样带（altitudinal transects）评估了森林砍伐对山地鸟类海拔分布范围的影响。本研究采用点样计数（point counts）与雾网（mist-nets）法，对6条海拔跨度为2200米至2800米的样带开展了野外调查。其中3条样带在2200米至2800米范围内均维持完整森林覆盖，剩余3条样带则遭到部分砍伐，仅在2400米以上区域保留森林植被。我们对比了三类核心指标：个体数加权平均海拔、最低海拔以及海拔分布范围宽度。除了分析森林砍伐对134个物种的整体影响外，我们还针对不同营养类群（trophic guilds）与栖息地偏好类群分别检验了该干扰的效应。在完全森林覆盖与部分砍伐的样带之间，个体数加权平均海拔与最低海拔均未呈现显著差异。而海拔分布范围宽度则呈现边缘显著（marginally significant）差异：正如预期，完全森林覆盖样带内的鸟类分布范围更广。不同营养类群与栖息地偏好类群的物种，其响应趋势存在显著分化。上述结果表明，即便在现存的森林区域内，森林砍伐仍可能对物种的海拔分布范围产生影响。全球气候变化或进一步加剧森林砍伐对物种海拔分布的有害影响。未来的保护策略需兼顾该问题，即保护跨多海拔梯度的连通性森林斑块（connected forest tracts）。