Pascoe Penelope P, Bartlett Mitchell, Shaw Justine, Trebilco Rowan, Weldrick Christine K, Jones Holly P
University of Tasmania Institute for Marine and Antarctic Studies, Ecology and Biodiversity, Hobart, Tasmania, Australia.
Independent Contractor, Nelson, New Zealand.
Ecol Appl. 2025 Jun;35(4):e70030. doi: 10.1002/eap.70030.
Invasive mammal eradications are commonplace in island conservation. However, post-eradication monitoring beyond the confirmation of target species removal is rarer. Seabirds are ecosystem engineers on islands and are negatively affected by invasive mammals. Following an invasive mammal eradication, the recovery of seabird populations can be necessary for wider ecosystem recovery. Seabirds fertilize islands with isotopically heavy nitrogen, which means that nitrogen stable isotope analysis (δN) could provide a useful means for assessing corresponding change in ecosystem function. We quantified decadal changes in δN on eight temperate New Zealand islands subject in pairs to distinct mammal invasion and seabird restoration histories: invaded, never-invaded, invader-eradicated, and undergoing active seabird restoration. First, we investigated long-term changes in δN values on individual islands. Second, we used a space-for-time analysis to determine whether δN levels on islands from which invaders had been removed eventually recovered to values typical of never-invaded islands. On each island, soil, plants (Coprosma repens, Coprosma robusta, and Myrsine australis), and spiders (Porrhothelidae) were sampled in 2006/2007 and 2022, allowing δN change on individual islands over 16 years to be assessed. Combined, the samples from invader-eradicated islands provided a 7- to32-year post-eradication dataset. Change in δN was only detected on one island across the study period, following the unexpected recolonization of seabirds to an invaded island. Invader-eradicated islands generally had higher δN values than invaded islands; however, they were still lower than never-invaded islands, and there was no trend in δN with time since eradication. This, and the measurable increase in δN following seabird recolonization on one island, may suggest that δN change occurs rapidly following invader eradication but then slows, with δN values staying relatively constant in the time period studied here. Isotope and seabird population studies need to be coupled to ascertain whether plateauing in δN reflects a slowing of seabird population growth and subsequent basal nutrient input or whether the baseline nutrients are entering the ecosystem but then not propagating up the food web.
在岛屿保护中，根除入侵哺乳动物是常见做法。然而，在确认目标物种被清除之后进行的根除后监测却较为少见。海鸟是岛屿生态系统的工程师，会受到入侵哺乳动物的负面影响。在根除入侵哺乳动物之后，海鸟种群的恢复对于更广泛的生态系统恢复可能是必要的。海鸟用同位素重氮给岛屿施肥，这意味着氮稳定同位素分析（δN）可以为评估生态系统功能的相应变化提供一种有用的方法。我们对新西兰八个温带岛屿的δN年代际变化进行了量化，这些岛屿成对呈现出不同的哺乳动物入侵和海鸟恢复历史：被入侵、从未被入侵、入侵者已被根除以及正在积极进行海鸟恢复。首先，我们研究了各个岛屿上δN值的长期变化。其次，我们采用时空分析来确定已清除入侵者的岛屿上的δN水平最终是否恢复到从未被入侵岛屿的典型值。在2006/2007年和2022年，对每个岛屿的土壤、植物（匍匐滨藜、粗壮滨藜和南方铁仔）以及蜘蛛（拟壁钱科）进行了采样，从而能够评估各个岛屿在16年里的δN变化。综合来看，来自入侵者已被根除岛屿的样本提供了一个根除后7至32年的数据集。在整个研究期间，仅在一个岛屿上检测到了δN的变化，原因是海鸟意外重新回到了一个被入侵的岛屿。入侵者已被根除的岛屿的δN值通常高于被入侵岛屿；然而，它们仍然低于从未被入侵的岛屿，并且自根除以来δN没有随时间变化的趋势。这一点，以及一个岛屿上出现海鸟重新定居后δN的可测量增加，可能表明在根除入侵者之后δN变化迅速，但随后放缓，在此处研究的时间段内δN值保持相对稳定。需要将同位素研究和海鸟种群研究结合起来，以确定δN的稳定是否反映了海鸟种群增长放缓以及随后基础养分输入的减少，或者基线养分是否正在进入生态系统但随后没有在食物网中向上传播。
