Data from: Local biodiversity erosion in South Brazilian grasslands under moderate levels of landscape habitat loss

1.Habitat loss is one of the greatest threats to biodiversity, exerting negative effects on the ecological viability of natural vegetation remnants. The South Brazilian grasslands belong to one of the largest temperate grassland regions in the world, but have lost 50% of their natural extent in the past 35 years. To date, there is no empirical evidence for the effects of habitat loss on these grasslands’ biological diversity, undermining their conservation.

2.Using data from a large-scale biodiversity survey, we asked if local plant communities respond to levels of habitat loss representative of the entire region (≤50%). Vegetation in grassland remnants was sampled in 24 landscapes at three localities each, using 9 plots per locality. To investigate whether species losses were a consequence of stochastic or nonrandom local extinctions and whether plant communities became more homogenized, we evaluated species richness, beta-diversity components (spatial turnover and nestedness), and phylogenetic diversity, in respect to landscape change. In part of the landscapes, arthropods were sampled to investigate if loss of plant diversity had a cascading effect on other trophic levels. We evaluated generic richness of ants, an omnivore group with high levels of plant associations, in respect to a plant community's phylogenetic diversity.

3.Local plant communities in landscapes with less grassland cover had fewer species, less spatial turnover, increased nestedness and lower phylogenetic diversity. Our results suggest that the observed species loss can be linked to taxonomic homogenization and is nonrandom, decreasing evolutionary diversity within the community. Furthermore, ant richness declined by 50% in plant communities with the lowest phylogenetic diversity, suggesting that effects of habitat loss propagate to higher trophic levels.

4.Policy implications. We conclude that the biological diversity of South Brazilian grasslands, at the producer and consumer level, is at risk under the current rate of land use conversion, even at habitat losses below 50%. To avoid substantial biodiversity loss, conservation and more restrictive policies for conversion of native grasslands to different land uses in South Brazil are urgent.

1. 生境丧失 (habitat loss) 是威胁生物多样性 (biodiversity) 的首要因素之一，会对自然植被残存斑块的生态存续产生负面影响。巴西南部草原属于全球规模最大的温带草原 (temperate grassland) 区域之一，但在过去35年间已丧失了50%的原生分布范围。截至目前，尚无关于生境丧失对该类草原生物多样性影响的实证研究证据，极大阻碍了其保护工作的推进。
2. 本研究依托大规模生物多样性调查获取的数据，旨在探究本地植物群落对符合全区域典型水平（≤50%）的生境丧失程度的响应模式。研究于24个景观单元内开展植被采样，每个景观包含3个调查点位，每个点位设置9个样方。为明确物种丧失是随机还是非随机的局域灭绝过程所致，同时探究植物群落是否出现均质化趋势，我们针对景观变化梯度，分别评估了物种丰富度、β多样性 (beta-diversity) 组分（空间周转 (spatial turnover) 与嵌套性 (nestedness)）以及系统发育多样性 (phylogenetic diversity)。在部分景观单元中，我们同时采样了节肢动物 (arthropods)，以验证植物多样性丧失是否会对其他营养级 (trophic levels) 产生级联效应；针对与植物关联度极高的杂食性类群——蚂蚁，我们基于植物群落的系统发育多样性评估了其属级丰富度变化。
3. 生境覆盖度较低的景观中的本地植物群落，其物种丰富度更低、空间周转程度更弱、嵌套性更高且系统发育多样性更低。研究结果表明，观测到的物种丧失与分类学均质化存在关联，且该过程并非随机，而是降低了群落内的进化多样性。此外，在系统发育多样性最低的植物群落中，蚂蚁的属级丰富度下降了50%，这说明生境丧失的影响可传递至更高营养级。
4. 政策启示：本研究得出结论，即便生境丧失程度低于50%，按照当前的土地利用转换速率，巴西南部草原生产者与消费者层级的生物多样性均面临威胁。为避免出现大规模生物多样性丧失，巴西南部地区亟需出台针对原生草原向其他土地利用类型转换的保护政策与更为严格的管控措施。