Israeli Study Finds Intermediate Conditions Increase Animal Variation Within Populations

A new study from Tel Aviv University reveals that animal populations exhibit the greatest individual variation under intermediate environmental conditions, rather than under extreme or optimal ones. Conducted by doctoral student Eilon Steinberg and led by Dr. Yosef Kiat at the School of Zoology and the Steinhardt Museum of Natural History, the research analyzed data from over 21,000 songbirds across 219 species worldwide. The study, published in Functional Ecology, used birds' feather molting patterns as a biological model to assess how environmental factors influence variation among individuals.

Feathers wear down over time and must be replaced through molting, but the extent of molting varies widely among species and individuals. The researchers found that in harsh conditions, such as limited food or time before migration, most birds conserve energy by molting fewer feathers. Conversely, in very favorable conditions with abundant resources, most birds molt extensively. However, under intermediate conditions, no single molting strategy dominates, resulting in significant variation among individuals within the same population.

Dr. Kiat explained that extreme environments impose a uniform "solution" on most individuals, either conserving or investing heavily in molting. In contrast, intermediate environments allow differences in body condition, food acquisition, and breeding timing to influence individual strategies, fostering diversity. He emphasized that while population averages are often studied, the variation among individuals can be crucial for understanding adaptation.

The researchers suggest these findings extend beyond birds, offering insights into how species adapt to environmental changes, including accelerated climate change. Understanding the factors that increase or reduce variation within populations may explain why some populations are more resilient and flexible in facing changing conditions.