Connectivity increases trophic subsidies in fragmented landscapes

Landscape corridors mitigate the negative effects of habitat fragmentation by increasing dispersal. Corridors also increase biodiversity in connected habitat fragments, suggestive of metacommunity dynamics. What is unknown in this case is the mechanisms through which metacommunity dynamics act. Working in a large-scale fragmentation experiment, we tested the effect of corridors on the movement of prey species and subsequent effects on predator nutrition (which we call trophic subsidies). We enriched plants of central patches with 15N, then measured 15N in green lynx spiders, the most abundant insect predator, in patches that were either connected to or isolated from the enriched patch. We found that corridors increased prey movement, as they increased spider 15N by 40% in connected patches. Corridors also improved spider body condition, increasing nitrogen relative to carbon. We suggest a novel mechanism, trophic subsidies, through which corridors may increase the stability or size of populations in connected landscapes.

景观廊道（Landscape corridors）通过提升生物扩散能力，缓解生境破碎化带来的负面影响。同时，廊道可提升连通生境斑块内的生物多样性，这暗示了集合群落动态（metacommunity dynamics）的调控作用。但目前尚未明确集合群落动态发挥功能的具体机制。本研究依托一项大型生境破碎化控制实验，探究了廊道对猎物物种移动的影响，以及由此对捕食者营养状况产生的后续效应——我们将该效应命名为营养补贴（trophic subsidies）。我们以15N同位素标记中心斑块内的植物，随后在与标记斑块连通或隔离的斑块中，检测了优势昆虫捕食者绿猫蛛（green lynx spiders）体内的15N含量。结果发现，廊道促进了猎物移动：连通斑块内绿猫蛛的15N含量提升了40%，这一结果佐证了该结论。此外，廊道还改善了绿猫蛛的身体状况，提升了其体内氮元素相对于碳元素的比值。我们提出了营养补贴（trophic subsidies）这一全新机制，用以解释廊道如何提升连通景观中种群的稳定性与种群规模。