Protected areas and compositional diversity of fish from Serranias Costeiras of the Ribeira de Iguape River basin, Southeast Brazil

Abstract The Serranias Costeiras of the Ribeira de Iguape River basin comprise landscapes with steep slopes, where many streams are contained in protected areas. We evaluated the importance of these protected areas for stream fish diversity. We sampled the ichthyofauna during the dry season of 2010, 2018 and 2019 in 36 stream stretches. We used beta diversity measures and estimated species richness and dark diversity in streams from two types of protected areas (full protection, FP and sustainable use, SU) and outside (Out). The altitude-width and velocity gradient of the streams explained the species turnover. The PA type promoted the richness difference, with FP streams having less species richness than SU and outside. Streams from FP presented lower species richness and dark diversity. These results indicate that the few species in FPs are well protected. The FP streams contain a relevant proportion of the regional species pool and, therefore, are essential for conserving fish stream diversity in the study region. On the other hand, streams from SU or Out have higher species richness, but their fish fauna is more vulnerable. Due to longitudinal stream connectivity, we highlight the importance of rethinking the limits of protected areas.

摘要
伊瓜佩河（Ribeira de Iguape）流域的沿海塞拉尼亚斯山区（Serranias Costeiras）为陡峭坡地地貌，区内多条溪流均处于保护区范围内。本研究评估了此类保护区对溪流鱼类多样性的重要性。我们于2010年、2018年及2019年的旱季，对36处溪流河段的鱼类区系（ichthyofauna）进行了采样调查。采用β多样性（beta diversity）测度方法，对两类保护区：严格保护（full protection, FP）、可持续利用（sustainable use, SU），以及保护区外（Out）的溪流的物种丰富度与暗多样性（dark diversity）进行了估算。
溪流的海拔-宽度比与流速梯度可解释物种更替现象；保护区类型会导致物种丰富度的差异：严格保护河段的物种丰富度低于可持续利用河段与保护区外河段。严格保护河段的物种丰富度与暗多样性均更低，这表明该区域内的少量物种得到了有效保护。严格保护河段涵盖了区域物种库中相当比例的物种，因此对本研究区域的溪流鱼类多样性保护至关重要。
与之相对，可持续利用河段与保护区外河段的物种丰富度更高，但其鱼类区系却更为脆弱。鉴于溪流的纵向连通性（longitudinal stream connectivity），我们强调重新审视保护区边界划定的重要性。