Structural changes within trophic levels are constrained by within-family assembly rules at lower trophic levels

Background/Question/Methods

Historical contingency broadly refers to the proposition that even random historical events can constrain the evolutionary pathways of organisms and that of entire ecological communities. Focusing on communities, these pathways can be reflected into structural changes across trophic levels---how species affect each other---which has important consequences for species coexistence. Using the registry of the last 2000 years of plant introductions and their novel herbivores encountered in Central Europe, we test the extent to which the order of plant arrivals can explain structural changes observed among competing herbivore species.

Results/Conclusions

The data have revealed a positive trend of resource partitioning within the herbivore trophic level over 2000 years. This trend was highly unlikely to be reproduced by a random arrival of plant species and it is not dependent on community size. We find that the order of arrival of closely-related (but not of distantly-related) plant species constrains this trend of structural changes within the trophic level formed by herbivore species as it was observed across time. Because it is difficult for field and lab experiments to be conducted over hundreds of years to record and replay the assembly history of a community, our study provides an alternative to understand how structural changes have occurred across extensive periods of time.