When Grinnellian generalist species seem to be more sensitive to altered habitats than specialists: the case of Orthoptera communities settled in coastal dunes

Numerous examples documented that species generalists for habitats are less sensitive to altered environment than specialists. However, in arid environments, an example indicated an opposite trend due to special adaptive features of organisms. We tested this hypothesis in the case of grasshopper communities, settled in the coastal dunes of northeast Algeria, as several aspects of dunes constitute stressful conditions resembling those of deserts. To define the dune-specific grasshoppers (specialists) and the dune non-specific ones (generalists), we applied the indicator value index to monthly samplings conducted in four coastal dune sites and 12 other sites of grasslands, fallow lands and scrublands in the same area. The degree of disturbance of each coastal dune site was deduced from the alteration of plant cover and richness. We investigated the relation between the specialist and generalist richness and abundance with the degree of perturbation using linear regressions. Results showed contrasting patterns for specialist and generalist grasshoppers: both abundance and richness of the generalists significantly decrease with an increasing degree of perturbation, while specialists show little to no changes. The higher resistance of specialist grasshoppers over generalists toward disturbance was not linked to the plant dune-specialists or generalists. This study is one of very few illustrating the relative resistance of specialized species toward disturbance.

已有大量研究证实，生境广适物种（habitat generalist）对环境变化的敏感度低于生境特化物种（habitat specialist）。然而在干旱环境中，已有案例呈现出相反的趋势，这源于生物的特殊适应性特征。本研究以栖息于阿尔及利亚东北部沿海沙丘中的蝗虫群落为研究对象，对该假说展开验证——由于沙丘的多项环境特征构成了类似荒漠的胁迫生境。为界定沙丘专属性蝗虫（特化种）与非沙丘专属性蝗虫（广适种），我们对该区域内4个沿海沙丘样地以及12个草地、休耕地和灌丛样地开展的月度采样数据应用了指示值指数（indicator value index）。我们通过植被盖度与物种丰富度的变化情况，推导得到每个沿海沙丘样地的受干扰程度。我们采用线性回归分析，探究了特化种与广适种的丰富度、多度与干扰程度之间的关联。研究结果显示，蝗虫特化种与广适种呈现出截然相反的变化模式：随着干扰程度加剧，广适种的多度与丰富度均显著下降，而特化种则几乎无显著变化。蝗虫特化种相较于广适种所具备的更高抗干扰能力，与沙丘专性植物或非沙丘专性植物并无关联。本研究是少数几例阐明特化物种相对抗干扰能力的学术研究之一。