A latitudinal gradient in species richness is the Earth’s predominant biodiversity pattern, yet how and why this gradient arose remains unresolved. Biotic interactions play a key role in many of the hypotheses that have been put forward to explain the latitudinal diversity gradient (LDG). In my introductory talk to the session on “Latitudinal gradients in consumer-resource interactions”, I will summarize the evidence for the LDG, showing that the gradient is both ancient and pervasive. I will then discuss the general classes of hypotheses that have been put forward to explain the LDG, highlighting those in which biotic interactions play a major role. Lastly, I will present the results of a recent literature review that asks, "Is there a latitudinal gradient in the importance of biotic interactions".
Results/Conclusions
Our literature review complied data on 39 subcategories of biotic interactions and we found that low latitudes have stronger biotic interactions in 30 (77%) of the cases, compared to 9 cases with no geographic difference. In no case did a class of biotic interactions appear stronger at high latitudes. These results support the hypothesis that biotic interactions are more important in the tropics and may contribute to the origin and maintenance of the LDG. However, the quality of the studies comprising our review is uneven and much more work is needed to answer the question of whether the strength of biotic interactions varies across geographical gradients. In particular, standardized experiments that span a broad range of latitude are extremely rare, as are studies that compare the strength of competitive interactions across latitude. I conclude by outlining several possible directions for further research, setting the stage for the talks that follow.