Managing multiple threats: Evaluating the efficacy of broad-scale introduced predator management in improving native mammal resilience to fire

Preventing further biodiversity loss requires understanding which processes threaten biodiversity and the effectiveness of management actions in mitigating them. Threatening processes can interact in complex and unexpected ways, but different threats are often managed independently. Here, we develop a conceptual model to identify the conditions needed for management of a single threat to achieve a net conservation benefit in systems with multiple interacting threats, and demonstrate its relevance in a replicated case-study experiment. In Australia, introduced red foxes (Vulpes vulpes) and feral cats (Felis catus) may hunt vulnerable native mammals more effectively after fire, due to loss of understory vegetation. However, the efficacy of broad-scale control of introduced predators in improving native mammal resilience to fire has not been quantified. Moreover, many studies assessing the impacts of prescribed fire on species rely on a much smaller number of independent replicates. Using a natural before-after control-impact experiment with 14 prescribed fires, each > 200 ha, we tested whether existing landscape-scale fox baiting programs influenced the immediate effects of prescribed fire on these two introduced predators and five medium-sized native mammals, including the threatened long-nosed potoroo (Potorous tridactylus) and southern brown bandicoot (Isoodon obesulus). Fox occupancy increased across both treatments post-fire, but baiting reduced the magnitude of increase. In contrast, mean feral cat occupancy remained constant in unbaited areas post-fire, but nearly doubled in fox-controlled areas, possibly due to a mesopredator release. Existing landscape-scale fox control programs did not clearly improve the short-term resilience of native mammals to prescribed fire (at least under the current fire and fox management regimes in our study landscapes). These results likely emphasise the need to integrate fire and predator management strategies for threatened faunal conservation iIn the presence of acute disturbances such as fire, threatened native mammals may require more intensive and integrated management of fire and introduced predators, such as (e.g., through more intensive targeted predator controlbaiting around fire events, or intensive protection usingthrough natural or artificial refuges).防止生物多样性进一步丧失，需明确哪些过程对生物多样性构成威胁，以及各类管理行动在缓解这些威胁方面的有效性。威胁过程往往会以复杂且难以预料的方式相互作用，但不同威胁的管理工作通常独立开展。为此，本文构建了一套概念模型，用以识别在多交互威胁的生态系统中，对单一威胁实施管理并实现净保护收益所需的条件，并通过重复案例研究实验验证了该模型的适用性。在澳大利亚，由于下层植被遭到破坏，火灾后引入的赤狐（red fox, *Vulpes vulpes*）与野猫（feral cat, *Felis catus*）可能会更高效地捕猎脆弱的本土哺乳动物。然而，大规模管控引入捕食者能否提升本土哺乳动物应对火灾的恢复力，目前尚未得到量化验证。此外，诸多评估计划火烧（prescribed fire）对物种影响的研究，其独立重复样本量往往偏少。本研究依托一项涵盖14场规模均超200公顷的计划火烧的自然前后对照影响（Before-After Control-Impact, BACI）实验，检验现有景观尺度赤狐诱饵投放项目，是否会影响计划火烧对这两种引入捕食者，以及5种中型本土哺乳动物的即时效应——其中包括受威胁的长鼻鼠袋鼠（long-nosed potoroo, *Potorous tridactylus*）与南方棕袋狸（southern brown bandicoot, *Isoodon obesulus*）。实验结果显示：火灾后，两组处理样地的赤狐占用率均有所上升，但诱饵投放抑制了其上升幅度。与之相反，未开展诱饵投放的样地中，野猫平均占用率在火灾后保持稳定，而在赤狐被管控的样地中，野猫占用率几乎翻倍，这可能源于中捕食者释放（mesopredator release）效应。现有景观尺度的赤狐管控项目，并未显著提升本土哺乳动物应对计划火烧的短期恢复力（至少在本研究样地当前的火与狐管理方案下）。上述结果凸显出，在受威胁动物群落的保护工作中，亟需整合火与捕食者管理策略。在火灾这类急性扰动发生时，受威胁的本土哺乳动物可能需要更精细化、一体化的火与引入捕食者管理措施，例如：在火灾事件周边实施更高强度的针对性捕食者管控与诱饵投放，或是借助自然或人工庇护所开展强化保护。