Testing effects of water stresses and herbivory on habitat differentiation among diverse willow communities in central Minnesota

The co-existence of closely-related species has long intrigued ecologists since they are likely to require similar resources and therefore compete with each other severely. Here we use the highly diverse willow and poplar communities in central Minnesota as a model system to test if differentiation of functional attributes could facilitate habitat differentiation among closely-related species. Using a series of common garden experiments, we examined tolerance to water stresses and resistance to insect herbivory among 14 species of willow and poplar. Data collected so far shown that survival rate respond differently to water table depth among species, suggesting these species might have different water-logging tolerance and spring flood could be one factor influencing species distribution along water table depth gradient. We also found differential susceptibility to insect herbivores among species, suggesting potential difference in defense to herbivory. This study could provide empirical example of how differentiation of functional traits related to biotic and abiotic factors together promote habitat differentiation among closely-related species.