Global biodiversity patterns are characterized by increasing species richness from the poles to the tropics. Although the underlying mechanisms of this biogeographic pattern have not been fully elucidated, the biotic interactions hypothesis has strong evolutionary roots and suggests that biological interactions, such as competition and predation, serve to maintain tropical biodiversity. Despite the potentially strong effects of competition in shaping natural communities, few empirical data exist to demonstrate latitudinal interaction patterns. Intransitive competition, defined as competitive networks lacking hierarchy, may be common in nature and enhance coexistence even when species compete strongly. However, the role of intransitivity in structuring communities and the relative importance of other factors, such as predation, influencing these competition networks remains unclear. Using standardized settlement panels in nearshore habitats across three biogeographic regions spanning 47 degrees of latitude, we quantified competitive intransitivity among sessile marine invertebrate communities and tested whether predation influences intransitivity.
Results/Conclusions
We found that mid- and low-latitude communities were characterized by intransitive networks, while high latitude communities were not strongly influenced by competition, likely driven by a greater sensitivity of these communities to abiotic factors than to competition. Despite theoretical predictions to the contrary, predation had no discernable effect on intransitivity. However, intransitivity decreased during later stages of community development, indicating shifts in competitive networks over time. This work furthers our understanding of species interactions and biodiversity across global biogeographic gradients.