Birds and insects respond differently to combinations of semi-natural features in farm landscapes

Semi-natural features among farmland have a key role in maintaining wildlife in rural landscapes. Practical conservation requires knowledge of which combinations of features are of greatest value and whether this differs among faunal groups. We used a 'landscape' approach to investigate the relative importance to birds and insects (bees, flies, wasps) of combinations of three wooded features typical of farmland in south-eastern Australia: scattered trees, wooded roadsides and wooded streamside vegetation. We selected 44 landscapes (1 km diameter) representing four combinations: a) landscapes with all three features present, b) landscapes lacking scattered trees, c) lacking wooded roadsides, and d) lacking wooded streamsides. We surveyed birds and selected insects, and compared mean alpha (α, site), beta (β, between site) and gamma (γ, landscape) diversity for each taxon between landscape types; and gamma (γ) diversity of bird species displaying breeding activity. Mean α-diversity of birds was reduced in landscapes lacking wooded roadsides or streams, relative to those with all three wooded features; while species differentiation (β-diversity) increased in these landscapes. Loss of streamside vegetation had the greatest landscape-scale impact, reducing γ-diversity by ~33% for all land-birds and ~50% for woodland birds. Bird breeding activity declined by ~50% in landscapes lacking wooded streamsides. In contrast, insects showed little response, except bees for which mean α-diversity was greater in more-open landscapes lacking scattered trees or wooded roadsides, compared with those containing all wooded features. This did not lead to differences in landscape-level (γ) diversity. Synthesis and applications. Marked differences in how birds and insects respond to different combinations of semi-natural features mean that a 'one size fits all' approach to nature conservation is insufficient. Wooded features, especially streamside vegetation, are critical for maintaining diversity and breeding activity of woodland birds. In the absence of adequate knowledge of many insect groups in southern Australia, a prudent approach is to foster a diverse farmland mosaic comprising semi-natural habitats together with floristically rich, modified features that provide temporally dynamic resources. Small semi-natural features have disproportionate value for conservation, relative to their area, while also benefitting farm productivity and supporting ecosystem services.

农田中的半自然景观要素（semi-natural features）在维系乡村景观野生动物种群存续方面发挥着核心作用。务实的保护实践需要明确哪些景观要素组合的保育价值最高，且该价值是否会因动物类群的不同而存在差异。本研究采用景观尺度研究方法（landscape approach），探究澳大利亚东南部农田中三类典型林木景观要素——散生树木、路边林带、溪流沿岸林木植被——的组合对鸟类与昆虫（蜂类、蝇类、胡蜂类）的相对重要性。我们共选取44个直径为1千米的研究样区，涵盖四类景观要素组合模式：a）同时具备三类林木景观要素的样区；b）缺失散生树木的样区；c）缺失路边林带的样区；d）缺失溪流沿岸林木植被的样区。我们对鸟类与目标昆虫类群开展了调查，对比了不同景观类型下各动物类群的平均α多样性（alpha diversity，样点尺度）、β多样性（beta diversity，样点间尺度）与γ多样性（gamma diversity，景观尺度），同时分析了具有繁殖活动的鸟类类群的γ多样性差异。相较于同时具备三类林木景观要素的样区，缺失路边林带或溪流沿岸植被的样区中，鸟类的平均α多样性有所降低；而此类样区的鸟类物种分化程度（β多样性）则有所提升。溪流沿岸林木植被的丧失对景观尺度的生物多样性影响最为显著：全陆栖鸟类的γ多样性降低约33%，林栖鸟类的γ多样性降低约50%。在缺失溪流沿岸林木植被的样区中，鸟类的繁殖活动强度下降约50%。与之形成鲜明对比的是，昆虫类群几乎未表现出显著响应；仅蜂类例外：相较于同时具备三类林木景观要素的样区，在缺失散生树木或路边林带的开阔样区中，蜂类的平均α多样性更高，但该差异并未导致景观尺度（γ多样性）的物种多样性出现显著变化。研究综合与应用启示：鸟类与昆虫对半自然景观要素不同组合的响应模式存在显著差异，这意味着采用‘一刀切’的自然保护策略并不足以实现有效的保育目标。林木景观要素，尤其是溪流沿岸林木植被，对维持林栖鸟类的物种多样性与繁殖活动至关重要。鉴于澳大利亚南部多数昆虫类群的相关研究数据仍较为匮乏，审慎的保护策略应推动构建多样化的农田镶嵌生境：既保留半自然生境，也辅以植物区系丰富的人工改造型景观要素，以提供具有时间动态变化的资源供给。小型半自然景观要素的保育价值与其面积不成正比，具有极高的相对保育效益；同时还可提升农田生产效率并支撑生态系统服务功能。