Niche segregation allows competing species to capture resources in contrasting ways so they can co-exist and maintain diversity, yet global change is simplifying ecosystems and associated niche diversity. Whether climate perturbations alter niche occupancy among co-occurring species and affect species diversity is a key, but unanswered question. Using CO₂ vents as natural analogues of ocean acidification, we show that competing fish species with overlapping diets are partially segregated across microhabitat niches and differently-orientated substrata under ambient CO₂ conditions. Under elevated CO₂, benthic microhabitats experienced a significant increase in non-calcifying turf and fleshy algae but a sharp reduction in calcareous algae. The increased availability of turf and fleshy algae supported increased densities of a competitively dominant species, whilst the reduction in calcifying algal microhabitats decreased densities of several subordinate species. The change in microhabitat availability also drove an increased overlap in microhabitat use among competing fishes at the vents, associated with a reduced fish species richness on horizontal substrates. We conclude that loss of preferred microhabitat niches, exacerbated by population proliferation of competitively dominant species, can drive population losses of less common and subordinate species, and reduce local species richness. The indirect effects of ocean acidification on microhabitat availability can therefore impair maintenance of species populations, and drive changes in local community and biodiversity patterns.

生态位隔离使竞争物种能够以相反的方式捕获资源，因此它们可以共存并维持多样性，而全球变化正在简化生态系统和相关的生态位多样性。气候扰动是否会改变同生物种之间的生态位占有率并影响物种多样性，这是一个关键但尚未得到解答的问题。使用CO ₂排放口作为海洋酸化的天然类似物，我们显示，在环境CO ₂条件下，饮食重叠的竞争鱼类在微生境和不同方向的基质中部分隔离。在CO ₂升高的情况下，底栖微生境的非钙化草皮和肉质藻类显着增加，但底栖生物的急剧减少。钙质藻类。草坪和肉质藻类的可利用性增加，支持了竞争优势种的密度增加，而钙化微生境的减少降低了几种下属物种的密度。微生境可利用性的变化也促使在出风口竞争的鱼类之间的微生境使用重叠增加，这与鱼类减少有关水平底物上的物种丰富度。我们得出结论，竞争优势物种的种群扩散加剧了首选微生境生态位的丧失，可以驱使较少见的和从属物种的种群丧失，并降低本地物种的丰富度。因此，海洋酸化对微生境可用性的间接影响会损害物种种群的维持，并推动当地社区和生物多样性格局的变化。