Ecological and life-history traits predict temporal trends in biomass of boreal moths

Dramatic insect declines, and their consequences for ecosystems globally, have received considerable attention recently. Yet, it is still poorly known if ecological and life-history traits can explain declines and whether insect decline occurs also at high latitudes. Insects’ diversity and abundance are dramatically lower at high latitudes compared to the tropics, and insects might benefit from climate warming in high-latitude environments. 

We adopted a trait- and biomass-based approach to estimate temporal change between 1993 and 2019 in Finnish macro-moth communities by using data from 85 long-running light traps. We analysed spatio-temporal variation in biomass of moth functional groups with Joint Dynamic Species Distribution Models while accounting for environmental variables. 

We did not detect any declining trends in total moth biomass of moth functional groups, and most groups were stable over time. Moreover, biomass increased for species using coniferous trees, lichens, or mushrooms as hosts, multivoltine species, as well as monophagous and oligophagous species feeding on trees. We found that length and temperature of the growing season, winter climatic conditions, and habitat structure all partially explained variation in moth biomass.

Although boreal moth communities are rapidly changing due to species turnover, in terms of total biomass they seem to contradict the trend of dramatic insect declines observed globally. This may lessen the immediate possibility of negative bottom-up trophic cascades in boreal food webs.

昆虫种群的大幅衰减及其对全球生态系统的连锁影响，近期已受到学界广泛关注。然而，目前仍不甚明晰：生态与生活史特征能否解释昆虫衰减的成因，以及高纬度地区是否同样存在昆虫种群衰减现象。相较于热带地区，高纬度地区的昆虫多样性与种群丰度本就显著偏低，且该区域昆虫或可从气候变暖中获益。

本研究采用基于特征与生物量的研究方法，依托85台长期运行的灯光诱捕器采集的数据，估算了1993年至2019年间芬兰大型蛾类群落的时间动态变化。我们通过联合动态物种分布模型（Joint Dynamic Species Distribution Models）分析了蛾类功能群生物量的时空变异特征，并纳入环境变量进行校正。

研究未在蛾类功能群的总生物量中检测到显著衰减趋势，多数功能群的生物量随时间保持稳定。此外，以针叶树、地衣或真菌为寄主的物种、多化性物种，以及取食树木的单食性与寡食性物种，其生物量均呈现上升趋势。我们发现，生长季时长与温度、冬季气候条件以及生境结构，均可部分解释蛾类生物量的变异。

尽管受物种周转影响，北方针叶林带蛾类群落正经历快速变化，但就总生物量而言，其趋势与全球观测到的昆虫大幅衰减现象相悖。这或可降低北方针叶林食物网中出现负面上行营养级联效应的即时风险。