Data from: Forest fragmentation and loss reduce richness, availability, and specialization in tropical hummingbird communities

Hummingbirds are important pollinators of many native Neotropical plants but their abundance and diversity in landscapes dominated by intensive human uses such as agriculture have rarely been examined, despite such land-uses prevailing in the tropics. We examined how tropical deforestation affects hummingbird community structure in premontane forest patches embedded in a tropical countryside of Coto Brus Canton, Costa Rica. We captured hummingbirds in fourteen landscapes representing a gradient in patch size and forest amount, and tested for the effects of these variables on (1) hummingbird captures at flowers (pollinator availability); (2) species richness; and (3) filtering of functional traits. After accounting for sampling effects, both hummingbird availability and species richness declined by 40% and 50%, respectively, across the gradient in deforestation that we observed (9–66% forest within 1000 m). Focal patch size was the strongest predictor, even after statistically accounting for the amount of forest and matrix composition of landscapes. These reductions in availability and richness were well predicted by functional traits; morphologically specialized species with the capacity to transport long-distance outcrossed pollen and low functional redundancy within the pollinator network showed the greatest sensitivity to landscape change. We hypothesize that declines in hummingbird availability, diversity, and functional traits are important mechanisms driving the observed pollen limitation of ornithophilous flowers in fragmented tropical landscapes. Efforts to conserve large forest patches and enhance matrix permeability are critical for maintaining forest hummingbird communities and pollination services under current and predicted deforestation regimes.蜂鸟是众多本土新热带植物（Neotropical plants）的重要传粉者（pollinators），但在以农业等高强度人类土地利用为主的热带景观中，其种群丰度与物种多样性却鲜有研究——尽管这类土地利用模式在热带地区极为普遍。本研究以哥斯达黎加科托布拉斯县（Coto Brus Canton）热带乡村景观中嵌入的山地前带森林斑块为研究对象，探讨热带森林砍伐如何影响蜂鸟群落结构。我们在14个代表斑块面积与森林占比梯度的景观样地中捕捉蜂鸟，并检验了两类变量对以下三项指标的影响：（1）花朵上的蜂鸟捕获量（即传粉者可及性（pollinator availability））；（2）物种丰富度；（3）功能性状（functional traits）过滤效应。在控制抽样效应（sampling effects）后，我们观测到的森林砍伐梯度（1000米范围内森林覆盖率为9%至66%）中，蜂鸟可及性与物种丰富度分别下降了40%与50%。即使在统计上控制森林面积与景观基质组成后，目标斑块面积仍是最强的预测因子。传粉者可及性与物种丰富度的下降可通过功能性状得到良好预测：那些具备长距离异交花粉（outcrossed pollen）传播能力、且在传粉网络中功能冗余度（functional redundancy）较低的形态特化物种，对景观变化的敏感性最高。我们提出假说：蜂鸟可及性、物种多样性与功能性状的下降，是破碎化热带景观中观测到的鸟媒花（ornithophilous flowers）花粉限制现象的重要驱动机制。在当前及未来的森林砍伐格局下，保护大型森林斑块并提升景观基质渗透性（matrix permeability），对维持森林蜂鸟群落与传粉服务至关重要。