The effect of past defaunation on ranges, niches, and future biodiversity forecasts

Humans have reshaped the distribution of biodiversity across the globe, extirpating species from regions otherwise suitable and restricting populations to a subset of their original ranges. Here, we ask if anthropogenic range contractions since the Late Pleistocene led to an under‐representation of the realized niches for megafauna, an emblematic group of taxa often targeted for restoration actions. Using reconstructions of past geographic distributions (i.e., natural ranges) for 146 extant terrestrial large‐bodied (>44 kg) mammals, we estimate their climatic niches as if they had retained their original distributions and evaluate their observed niche dynamics. We found that range contractions led to a sizeable under‐representation of their realized niches (i.e., niche unfilling). For 29 species, more than 10% of the environmental space once seen in their natural ranges has been lost due to anthropogenic activity, with at least 12 species undergoing reductions of more than 50% of the..., To evaluate the effect of shifted baselines on estimates of sensitivity to future climate change—measured in terms of potential distribution variation—we used ecological niche models based on different assumptions. The first scenario assumes that species’ distributions are in equilibrium with the environmental conditions across their ranges today and uses climatic information solely from species’ current ranges to calibrate ecological niche models, which we call current‐based models. The second scenario relies on climatic information from species’ natural ranges, that is, simulating a scenario where species have never experienced heavy anthropogenic stressors (Faurby & Svenning, 2015). The latter considers that fundamental niches tend to be conserved over time (Peterson, 2011) so that occurrence records from different periods should provide additional information on species’ climatic tolerances from environments without contemporary counterparts (Faurby & Araújo, 2018; Lima‐Ribe..., File List: 1) Current_based_future_binary.rar maps of species' future potential distribution, calibrated with environmental information from species' current ranges (available as Current_PHYLACINE.rar) 2) Current_PHYLACINE.rar maps of species' current realized distribution, obtained from PHYLACINE dataset 3) Present_natural_future_binary.rar maps of species' future potential distribution, calibrated with environmental information from species' present natural ranges (available as Present_natural_PHYLACINE.rar) 4)Present_natural_PHYLACINE.rar maps of species' present natural distribution, obtained from PHYLACINE dataset Relationship between files: Present natural ranges depict the locations species might have occupied in the present, had they not been affected by human presence. Current ranges depict the locations species are known to occupy in the present.人类重塑了全球生物多样性的分布格局，将物种从原本适宜的栖息地中局部移除，并将种群限制在其原始分布范围的子集之中。本研究旨在探究：晚更新世（Late Pleistocene）以来人类活动引发的分布范围收缩，是否导致巨型动物群（megafauna，一类常被列为修复行动重点的标志性类群）的实际生态位（realized niche）出现表征不足的情况。 本研究依托146种现存陆生大型哺乳动物（体重＞44千克）的历史地理分布（即原生分布范围）重建数据，模拟若这些物种保留其原始分布范围时的气候生态位，并评估其实际观测到的生态位动态。研究结果显示，分布范围收缩显著造成了其实际生态位的表征不足（即生态位填充缺失）。其中29个物种因人类活动丢失了其原生分布范围内曾占据的10%以上的环境空间，至少12个物种的环境空间缩减幅度超过50%…… 为评估基准偏移对未来气候变化敏感性评估（以潜在分布变化量为衡量指标）的影响，本研究采用基于不同假设的生态位模型开展分析。第一种假设场景假定：当前物种分布与其分布区内的环境条件处于平衡状态，且仅利用物种当前分布范围内的气候信息校准生态位模型，本研究将此类模型称为基于当前分布的模型。第二种场景则依托物种原生分布范围的气候信息，即模拟物种从未遭受强烈人类活动胁迫的情景（Faurby & Svenning, 2015）。后一种场景假定基础生态位（fundamental niche）通常会随时间保持保守（Peterson, 2011），因此不同时期的物种出现记录，能够提供物种在无现代对应环境下的气候耐受度相关额外信息（Faurby & Araújo, 2018; Lima-Ribe…… 文件列表： 1) Current_based_future_binary.rar：基于物种当前分布范围的环境信息校准得到的物种未来潜在分布分布图（配套数据可通过Current_PHYLACINE.rar获取） 2) Current_PHYLACINE.rar：来自PHYLACINE数据集的物种当前实际分布分布图 3) Present_natural_future_binary.rar：基于物种当前原生分布范围的环境信息校准得到的物种未来潜在分布分布图（配套数据可通过Present_natural_PHYLACINE.rar获取） 4) Present_natural_PHYLACINE.rar：来自PHYLACINE数据集的物种当前原生分布分布图 文件关联说明：当前原生分布范围指假设未受人类活动影响时，物种当前理论上应占据的栖息地；当前实际分布范围则指当前已观测到的物种实际占据的栖息地。