Data from: Mechanism matters: the cause of fluctuations in boom-bust populations governs optimal habitat restoration strategy

Many populations exhibit boom-bust dynamics in which abundance fluctuates dramatically over time. Past research has focused on identifying whether the cause of fluctuations is primarily exogenous, e.g., environmental stochasticity coupled with weak density dependence, or endogenous, e.g., over-compensatory density dependence. Far fewer studies have addressed whether the mechanism responsible for boom-bust dynamics matters with respect to at-risk species management. Here, we ask whether the best strategy for restoring habitat across a landscape differs under exogenously versus endogenously driven boom-bust dynamics. We used spatially explicit individual-based models to assess how butterfly populations governed by the two mechanisms would respond to habitat restoration strategies that varied in the level of resource patchiness – from a single large patch to multiple patches spaced at different distances. Our models showed that the restoration strategy that minimized extinction risk and boom-bust dynamics would be markedly different depending on the governing mechanism. Exogenously governed populations fared best in a single large habitat patch, whereas for endogenously driven populations, boom-bust dynamics were dampened and extinction risk declined when the total restored area was split into multiple patches with low to moderate inter-patch spacing. Adding environmental stochasticity to the endogenous model did not alter this result. Habitat fragmentation lowered extinction risk in the endogenously driven populations by reducing their growth rate, precluding both “boom” phases and, more importantly, “bust” phases. Our findings suggest that: 1) successful restoration will depend on understanding the causes of fluctuations in at-risk populations; 2) the level and pattern of spatiotemporal environmental heterogeneity will also affect the ideal management approach; and 3) counter-intuitively, for at-risk species with endogenously governed boom-bust dynamics, lowering the intrinsic population growth rate may decrease extinction risk.诸多种群均存在盛衰循环动态（boom-bust dynamics），其种群丰度随时间发生剧烈波动。既往研究多聚焦于甄别种群波动的主导诱因：是外源性因素（如结合弱密度制约的环境随机性），还是内源性因素（如过度补偿型密度制约）。而针对盛衰循环动态的作用机制是否会影响受威胁物种管理的研究则相对匮乏。本研究旨在探讨：在外源性与内源性驱动的盛衰循环动态下，跨景观尺度的栖息地恢复最优策略是否存在差异。我们采用空间显式个体模型（spatially explicit individual-based models），评估受两种调控机制作用的蝴蝶种群，对资源斑块性水平各异的栖息地恢复策略的响应——恢复策略覆盖从单个大型斑块，到以不同间距布设的多个斑块的多种场景。模型结果表明，能够同时最小化灭绝风险与盛衰循环动态的恢复策略，会因种群调控机制的不同而呈现显著差异。受外源性机制调控的种群，在单个大型栖息地斑块中表现最优；而对于内源性驱动的种群，当总恢复面积被分割为斑块间距处于低至中等水平的多个斑块时，其盛衰循环动态会得到缓解，灭绝风险也会降低。向内源性模型中加入环境随机性后，该结论并未发生改变。栖息地破碎化通过降低种群增长率，同时抑制了内源性驱动种群的“盛”期与“衰”期，其中遏制“衰”期的效果更为关键，进而降低了其灭绝风险。本研究结果显示：其一，成功的栖息地恢复有赖于明晰受威胁种群波动的成因；其二，时空环境异质性的水平与格局同样会影响理想的管理方案；其三，与直觉相悖的是，对于受内源性盛衰循环动态调控的受威胁物种，降低种群内在增长率或许能够降低其灭绝风险。