Patterns of niche filling and expansion across the invaded ranges of an Australian lizard

Studies of realized niche shifts in alien species typically ignore the potential effects of intraspecific niche variation and different invaded-range environments on niche lability. We incorporate our detailed knowledge of the native-range source populations and global introduction history of the delicate skink Lampropholis delicata to examine intraspecific variation in realized niche expansion and unfilling, and investigate how alternative niche modelling approaches are affected by that variation. We analyzed the realized niche dynamics of L. delicata using an ordination method, ecological niche models (ENMs), and occurrence records from 1) Australia (native range), 2) New Zealand, 3) Hawaii, 4) the two distinct native-range clades that were the sources for the New Zealand and Hawaii introductions, and 5) the species’ global range (including Lord Howe Island, Australia). We found a gradient of realized niche change across the invaded ranges of L. delicata: niche stasis on Lord Howe Island, niche unfilling in New Zealand (16%), and niche unfilling (87%) and expansion (14%) in Hawaii. ENMs fitted to native-range data generally identified suitable climatic conditions at sites where the species has established non-native populations, whereas ENMs based on native-range source clades and non-native populations had lower spatial transferability. Our results suggest that the extent to which realized niches are maintained during invasion does not depend on species-level traits. When realized niche shifts are predominately due to niche unfilling, fully capturing species’ responses along climatic gradients by basing ENMs on native distributions may be more important for accurate invasion forecasts than incorporating phylogenetic differentiation, or integrating niche changes in the invaded range.

针对外来物种实际生态位（realized niche）偏移的相关研究，通常未考虑种内生态位变异（intraspecific niche variation）以及不同入侵分布区环境对生态位易变性（niche lability）的潜在影响。本研究依托对细石龙子（Lampropholis delicata）原生分布区源种群的详尽认知以及全球引种历史，探究实际生态位扩张与生态位未填充（niche unfilling）的种内变异，并解析不同生态位建模方法如何受该变异影响。
本研究采用排序分析方法、生态位模型（ENMs）以及以下5类出现记录，对细石龙子的实际生态位动态展开分析：1）澳大利亚（原生分布区）；2）新西兰；3）夏威夷；4）作为新西兰与夏威夷引种源的两个独立原生分布区演化支（clades）；5）该物种的全球分布范围（含澳大利亚豪勋爵岛）。
研究结果显示，细石龙子入侵分布区的实际生态位变化呈现梯度特征：豪勋爵岛种群生态位停滞（niche stasis），新西兰种群存在16%的生态位未填充，夏威夷种群则存在87%的生态位未填充与14%的生态位扩张。
基于原生分布区数据拟合的生态位模型，通常可准确识别该物种已建立非原生种群的区域的适宜气候条件；而基于原生分布区源演化支与非原生种群数据构建的生态位模型，其空间转移能力（spatial transferability）相对较低。
本研究结果表明，入侵过程中实际生态位的维持程度并不依赖于物种水平的性状。当实际生态位偏移主要由生态位未填充导致时，相较于纳入系统发育分化信息或整合入侵分布区的生态位变化，以原生分布数据为基础构建生态位模型以全面捕捉物种沿气候梯度的响应，对于开展精准的入侵预测更为关键。