2026-06-25 ミシガン大学
Tree swallows are uniquely suited for a study like this because they will return to nesting sites that researchers have set up for them. Researchers can also peek into nests to count eggs and band chicks without the parents abandoning the nest. Image credit: Sherri and Brock Fenton
＜関連情報＞
- https://news.umich.edu/crashing-insect-populations-have-resulted-in-smaller-tree-swallows-that-reproduce-less/
- https://www.pnas.org/doi/10.1073/pnas.2607714123
資源の減少は気候変動に対する生物季節学的および形態学的反応を左右する Resource declines shape phenological and morphological responses to climate change
Charlotte M. Probst, Scott Yanco, Isaiah Clark, +4 , and Brian C. Weeks
Proceedings of the National Academy of Sciences Published:June 24, 2026
DOI:https://doi.org/10.1073/pnas.2607714123
Significance
Shrinking body size and advancing phenology are two widespread responses to climate change. However, they are rarely considered in the context of co-occurring biodiversity declines. Using a half-century of data on an insectivorous bird species, we find declines in insect abundance altered birds’ body size and phenology. Years with low insect abundance led to smaller nestlings and adults. Although mismatch between peak insect abundance and bird breeding dates increased through time, decreasing insect abundance eroded the benefit of synchronizing breeding with the insect peak, with mismatch becoming advantageous in some years. Our results suggest resource declines may contribute to responses typically attributed to climate change alone and emphasize the importance of considering trophic interactions when interpreting responses to global change.
Abstract
Biodiversity is declining, with cascading effects of defaunation expected across trophic levels. Widespread population declines may drive general biotic responses to global change and determine their fitness effects. We find that a 62% decrease in insect biomass over a half-century altered the morphology, survival, and breeding phenology of an aerial insectivore, the tree swallow (Tachycineta bicolor). Low-insect years resulted in decreased tree swallow body mass, with the fitness landscape shifting to favor smaller individuals. Earlier, more temporally variable, and less-pronounced peaks in insect abundance eroded the benefits of phenological synchronization across trophic levels. This phenomenon—which we term trophic decay—led to advantageous phenological mismatch in low-insect years. Our results suggest classic responses to climate change must be evaluated within the context of widespread resource declines.
