Despite a large number of hypotheses, a wealth of empirical work and an increasing number of theoretical models, the processes that generate and maintain latitudinal gradients in species richness remain poorly understood. The biggest impediment to progress on this question may not be the lack of information but the way we approach the problem. Starting with the early naturalists such as Humboldt and Wallace and continuing to this day, individual hypotheses highlight either the role of ecological (e.g. the role of contemporary climate) or evolutionary (e.g. differential speciation/extinction) dynamics in producing this gradient even though both are undoubtedly involved. In contrast, recent theoretical models have revealed the importance of a more integrative approach, taking into account both historical and contemporary dynamics together. Such an approach is particularly relevant for testing the role of biotic interactions in generating the latitudinal diversity gradient where separating cause and effect has proven to be difficult. In the introductory talk for this session on "Latitudinal gradients in consumer-resource interactions" I will suggest that integrating ecological and evolutionary processes into a general model of latitudinal diversity gradient also requires a shift from the traditional species-focused approach to a more trait-based one.
Results/Conclusions
A recent review of the literature shows that like species richness, the strength of biotic interactions tends to decrease with increasing latitude but the information available is insufficient to distinguish between whether interactions contribute to the generation and maintenance of latitudinal differences in richness or whether they are simply a consequence of changing richness. Testing these alternatives would be difficult without information about how the traits involved in interactions influence patterns of speciation and extinction. Similarly, geographic distributions of traits involved in interactions also remain poorly quantified even though latitudinal differences in relative frequency of such traits can be informative about the role of niche conservatism (or alternatively niche evolution) in generating the latitudinal differences in diversity. I will provide specific examples of how a trait-based approach can provide better insights about the role of biotic interactions in generating and maintaining the latitudinal diversity gradient and thus set the stage for the other talks in this session.
