What types of long-standing natural barriers are cited as features that shape the modern genetic landscape across North American populations?
Major mountain ranges or large river systems
Analyzing the genetic variation across the widespread range of species like the yellow sac spider in North America helps reveal the history of their movement and isolation. When gene flow is not uniform across the continent, it implies that certain geographic features have acted as physical impediments, preventing interbreeding between distant populations. These significant, stable geographical features, such as large mountain ranges or extensive river systems, act as long-standing natural barriers. They function as selective filters, effectively isolating populations and allowing localized adaptation to proceed without being interrupted by gene flow from other regions, thus maintaining distinct substructures within the overall species distribution.
