Data from: Climate, invasive species and land use drive population dynamics of a cold-water specialist

Climate change is an additional stressor in a complex suite of threats facing freshwater biodiversity, particularly for cold-water fishes. Research addressing the consequences of climate change on cold-water fish has generally focused on temperature limits defining spatial distributions, largely ignoring how climatic variation influences population dynamics in the context of other existing stressors.
We used long-term data from 92 populations of bull trout Salvelinus confluentus – one of North America's most cold-adapted fishes – to quantify additive and interactive effects of climate, invasive species and land use on population dynamics (abundance, variability and growth rate).
Populations were generally depressed, more variable and declining where spawning and rearing stream habitat was limited, invasive species and land use were prevalent and stream temperatures were highest. Increasing stream temperature acted additively and independently, whereas land use and invasive species had additive and interactive effects (i.e. the impact of one stressor depended on exposure to the other stressor).
Most (58%–78%) of the explained variation in population dynamics was attributed to the presence of invasive species, differences in life history and management actions in foraging habitats in rivers, lakes and reservoirs. Although invasive fishes had strong negative effects on populations in foraging habitats, proactive control programmes appeared to effectively temper their negative impact.
Synthesis and applications. Long-term demographic data emphasize that climate warming will exacerbate imperilment of cold-water specialists like bull trout, yet other stressors – especially invasive fishes – are immediate threats that can be addressed by proactive management actions. Therefore, climate-adaptation strategies for freshwater biodiversity should consider existing abiotic and biotic stressors, some of which provide potential and realized opportunity for conservation of freshwater biodiversity in a warming world.

气候变化是淡水生物多样性所面临的一系列复杂威胁中的额外胁迫因子，对于冷水性鱼类而言尤甚。以往针对气候变化对冷水鱼类影响的研究，大多聚焦于决定其空间分布的温度阈值，却在很大程度上忽略了在其他现存胁迫因子的背景下，气候变异如何影响种群动态。
本研究采用北美适应性最强的冷水性鱼类之一——牛鳟（*Salvelinus confluentus*）的92个种群的长期监测数据，以量化气候、入侵物种与土地利用对种群动态（种群丰度、波动幅度与增长率）的加性效应与交互效应。
在产卵与育幼溪流生境受限、入侵物种与土地利用压力普遍存在且溪流水温最高的区域，种群普遍呈现丰度降低、波动加剧且数量衰减的态势。溪流水温升高表现出独立的加性效应，而土地利用与入侵物种则同时存在加性效应与交互效应（即某一胁迫因子的影响程度取决于种群是否暴露于另一胁迫因子）。
种群动态中可解释的变异约有58%~78%可归因于入侵物种的存在、河流、湖泊与水库索饵生境中的生活史特征差异以及管理措施。尽管入侵鱼类对索饵生境中的种群具有显著的负面影响，但主动防控计划似乎能够有效缓和其负面效应。
综合与应用：长期种群动态数据表明，气候变暖将加剧牛鳟等冷水性特有物种的濒危程度，而其他胁迫因子——尤其是入侵鱼类——则是可通过主动管理措施加以应对的即时威胁。因此，淡水生物多样性的气候适应策略应兼顾现存的非生物与生物胁迫因子，其中部分胁迫因子可为变暖世界中的淡水生物多样性保护提供潜在且已可落地的机遇。