Chapter Nine

Why are there so many kinds of beetles?

Why study beetle diversity? Beetles are the largest order of animals on earth, their diversity eclipsing other insect orders, even their nearest relatives. Why are beetles, of all groups, so diverse? Is there something about their biology or ecology that has promoted diversification, do they have a longer evolutionary history than other groups, or is the great diversity of beetles simply the outcome of random diversification processes? By investigating some of the proposed explanations for the great diversity of beetles, we can get to grips with the basic logic of setting up comparative analyses to discover why diversity is so unevenly distributed among clades. Exploring beetle diversity is a good way to become familiar with the ways that evidence from phylogenetics, biogeography, and palaeontology can be used to describe patterns and test hypotheses for variation in diversity.

What are the main points?

• Random processes of diversification, in which all lineages have equal probabilities of speciating and going extinct, can produce substantial variation in diversity across a phylogeny.
• Beetles have more species than expected under null models, giving us a reason to postulate and test deterministic hypotheses, such as coevolution between beetles and angiosperms.
• Phylogenetic comparative methods can be used to test for associations between high diversity and the evolution of traits such as phytophagy (plant-feeding).
• Reconstructing the timing of key events in the history of clades can also contribute evidence that can be used to evaluate hypotheses of diversity.

 What techniques are covered?

• Constructing null models to generate expected distributions of diversity and to identify unusually diverse clades
• Using phylogenetic methods to pinpoint shifts in diversification rates on the phylogeny
• Sister-clade comparisons to test associations between diversity and evolution of traits

 What case studies will be included?

• Reconstructing and comparing the relative timing of the beetle and angiosperm radiations

 

Image: H. Zell (CC3.0)