Wetland Suitability and Connectivity for Trans-Saharan Migratory Waterbirds

To complete their life cycle waterbirds rely on patchily distributed and often ephemeral wetlands along their migration route in a vast unsuitable matrix. However, further loss and degradation of remaining wetland habitats might lead to a configuration and size of stopovers that is no longer sufficient to ensure long-term survival of waterbird populations. By identifying optimal conservation targets to maintain overall habitat availability en route, we can accommodate an as yet absent functional connectivity component in larger management frameworks for migratory waterbirds, such as the Ramsar Convention and the EU Natura 2000 Network. Using a graph-based habitat availability metric (Equivalent Connected Area) we determine the functional connectivity of wetland networks for seven migratory waterbirds with divergent habitat requirements. Analyses are performed at two spatial extents both spanning the Mediterranean Sea and centered around Greece (Balkan-Cyrenaica and Greece-Cyrenaica). We create species-specific suitable habitat maps and account for human disturbance by species-specific disturbance buffers, based on expert estimates of Flight Initiation Distances. At both spatial extents we quantitatively determine the habitat networks’ overall functional connectivity and identify wetland sites that are crucial for maintaining a well-connected network. We show that the wetland networks for both spatial extents are relatively well connected and identify several wetland sites in Greece and Libya as important for maintaining connectivity. The application of disturbance buffers results in wetland site-specific reduction of suitable habitat area (0.90–7.36%) and an overall decrease of the network’s connectivity (0.65–6.82%). In addition, we show that the habitat networks of a limited set of species can be combined into a single network which accounts for their autoecological requirements. We conclude that targeted management in few but specific wetland complexes could benefit migratory waterbird populations. Deterioration of these vital wetland sites in Greece and Libya will have disproportionate consequences to the waterbird populations they support.

迁徙水鸟为完成其生命周期，需在广袤的不适宜生境基质中，依赖其迁徙沿线呈斑块状分布且往往短暂存在的湿地。然而，剩余湿地生境的进一步丧失与退化，可能会使中途停歇地的配置与规模不再足以保障水鸟种群的长期存续。通过识别最优保护目标以维持迁徙沿线整体生境可用性，我们可在针对迁徙水鸟的大型管理框架（如拉姆萨尔公约（Ramsar Convention）与欧盟自然2000网络（EU Natura 2000 Network））中纳入目前尚未涵盖的功能连通性要素。
本研究采用基于图论的生境可用性指标（等效连通面积（Equivalent Connected Area）），针对7种生境需求各异的迁徙水鸟，对其湿地网络的功能连通性进行测算。分析在两个横跨地中海且以希腊为中心的空间尺度下开展，分别为巴尔干-昔兰尼加与希腊-昔兰尼加。本研究基于专家估算的惊飞距离（Flight Initiation Distances），构建了物种专属的适宜生境分布图，并通过物种专属干扰缓冲区纳入人为干扰因素。在两个空间尺度下，本研究均定量测算生境网络的整体功能连通性，并识别出对维持连通良好的网络至关重要的湿地点位。
研究结果显示，两个空间尺度下的湿地网络均具备较好的连通性，同时识别出希腊与利比亚境内的多处湿地点位对维持连通性具有关键作用。干扰缓冲区的应用使得各湿地点位的适宜生境面积出现不同程度缩减（0.90%~7.36%），同时导致网络整体连通性下降（0.65%~6.82%）。此外，本研究证实，可将少量物种的生境网络整合为单一网络，以兼顾它们的个体生态需求。
本研究得出结论：对少数特定湿地综合体开展针对性管理，即可为迁徙水鸟种群带来显著益处。希腊与利比亚境内这些关键湿地点位的退化，将对其承载的水鸟种群产生不成比例的严重影响。