Alberta Biodiversity Monitoring Institute, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
Department of Biology, University of British Columbia, Kelowna, British Columbia, Canada V1V 1V7.
Proc Biol Sci. 2021 Jan 27;288(1943):20202811. doi: 10.1098/rspb.2020.2811. Epub 2021 Jan 20.
Changes in primary productivity have the potential to substantially alter food webs, with positive outcomes for some species and negative outcomes for others. Understanding the environmental context and species traits that give rise to these divergent outcomes is a major challenge to the generality of both theoretical and applied ecology. In aquatic systems, nutrient-mediated eutrophication has led to major declines in species diversity, motivating us to seek terrestrial analogues using a large-mammal system across 598 000 km of the Canadian boreal forest. These forests are undergoing some of the most rapid rates of land-use change on Earth and are home to declining caribou () populations. Using satellite-derived estimates of primary productivity, coupled with estimates of moose () and wolf () abundance, we used path analyses to discriminate among hypotheses explaining how habitat alteration can affect caribou population growth. Hypotheses included food limitation, resource dominance by moose over caribou, and apparent competition with predators shared between moose and caribou. Results support apparent competition and yield estimates of wolf densities (1.8 individuals 1000 km) above which caribou populations decline. Our multi-trophic analysis provides insight into the cascading effects of habitat alteration from forest cutting that destabilize terrestrial predator-prey dynamics. Finally, the path analysis highlights why conservation actions directed at the proximate cause of caribou decline have been more successful in the near term than those directed further along the trophic chain.
初级生产力的变化有可能极大地改变食物网，对一些物种产生积极的结果，而对另一些物种则产生消极的结果。了解导致这些不同结果的环境背景和物种特征，是对理论和应用生态学的普遍性的一个重大挑战。在水生系统中，营养物质引起的富营养化导致物种多样性的大幅下降，这促使我们在加拿大北方森林的 598000 平方公里范围内，利用大型哺乳动物系统寻找陆地类似物。这些森林正经历着地球上最快的土地利用变化速度，也是正在减少的驯鹿（）种群的家园。我们使用卫星衍生的初级生产力估计值，并结合驼鹿（）和狼（）丰度的估计值，使用路径分析来区分解释栖息地变化如何影响驯鹿种群增长的假设。假设包括食物限制、驼鹿对驯鹿的资源优势，以及与驼鹿和驯鹿共享的捕食者之间的明显竞争。结果支持明显的竞争，并对狼密度（每 1000 平方公里 1.8 只）产生估计，超过这个密度驯鹿种群就会减少。我们的多营养层分析深入了解了森林砍伐导致的栖息地改变对陆地捕食者-猎物动态的级联效应。最后，路径分析突出了为什么直接针对驯鹿减少的近因采取的保护行动在短期内比沿着食物链进一步采取的保护行动更成功。
