Diverse Effects of a Seven-Year Experimental Grassland Fragmentation on Major Invertebrate Groups

Habitat fragmentation is a major driver of biodiversity loss, but observed effects vary and may depend on the group examined. Time since fragmentation may explain some differences between taxonomical groups, as some species and thus species composition respond with a delay to changes in their environment. Impacts of drivers of global change may thus be underestimated in short-term studies. In our study we experimentally fragmented nutrient-poor dry calcareous grasslands and studied the response of species richness, individual density and species composition of various groups of invertebrates (gastropods, ants, ground beetles, rove beetles, orthoptera, spiders, woodlice) in 12 small (1.5 m * 1.5 m) and 12 large (4.5 m * 4.5 m) fragments and their corresponding control plots after 7 years. We further examined responses to fragmentation in relation to body size and habitat preferences. Responses to fragmentation varied between taxonomical groups. While spider species richness and individual density were lower in fragments, the opposite was true for an orthopteran species and woodlice. Species composition and β-diversity differed between fragments and control plots for some groups. However, the interaction treatment*plot size was rarely significant. Species with high occupancy rates in undisturbed control plots responded more negatively to the fragmentation, while species with large body size were relatively more abundant in fragments in some groups. No effect of the fragmentation was found for ants, which may have the longest lag times because of long-lived colonies. However, relationships between abundance and the species’ preferences for environmental factors affected by edge effects indicate that ant diversity too may be affected in the longer-term. Our results show the importance of considering different groups in conservation management in times of widespread fragmentation of landscapes. While species richness may respond slowly, changes in abundance related to habitat preferences or morphology may allow insights into likely long-term changes.

生境破碎化（habitat fragmentation）是生物多样性丧失的主要驱动因子之一，但已观测到的效应存在差异，且可能取决于所研究的生物类群。破碎化发生后的时长或许可以解释不同分类群之间的差异，因为部分物种及其所在的物种群落会对环境变化产生滞后响应。因此，短期研究可能会低估全球变化驱动因子的影响。本研究通过实验对贫瘠营养型干燥石灰质草原（nutrient-poor dry calcareous grasslands）进行破碎化处理，并在7年后调查了12个小型（1.5 m × 1.5 m）、12个大型（4.5 m × 4.5 m）破碎化斑块及其对应的对照样地中，各类无脊椎动物（invertebrates）类群——包括腹足类（gastropods）、蚁类（ants）、步甲科昆虫（ground beetles）、隐翅虫科昆虫（rove beetles）、直翅目昆虫（orthoptera）、蜘蛛（spiders）以及潮虫（woodlice）——的物种丰富度（species richness）、个体密度（individual density）与物种组成（species composition）的响应特征。我们还进一步分析了响应与体型大小和生境偏好的关联。不同分类群对破碎化的响应存在差异：蜘蛛的物种丰富度与个体密度在破碎化斑块中更低，而直翅目类群与潮虫的情况则恰好相反。部分类群的物种组成与β多样性（β-diversity）在破碎化斑块与对照样地间存在显著差异，但“处理×样地大小”的交互作用极少呈现显著性。在未受干扰的对照样地中占据率较高的物种，对破碎化的响应更为负面；而部分类群中体型较大的物种在破碎化斑块中的丰度相对更高。蚁类未表现出显著的破碎化效应，这可能是因为其种群寿命较长，滞后效应最为显著。不过，丰度与物种对受边缘效应（edge effects）影响的环境因子的偏好之间的关联表明，蚁类多样性或许也会在长期尺度上受到影响。本研究结果表明，在景观普遍发生破碎化的当下，保护管理工作中考虑不同生物类群的响应特征至关重要。尽管物种丰富度的响应可能较为缓慢，但与生境偏好或形态特征相关的丰度变化，可为我们预测长期生态变化提供依据。