Describing patterns of biodiversity and identifying their underlying causes have been at the core of ecology for decades and have gained momentum since this knowledge is necessary for better diagnoses and preparation for ongoing biodiversity changes. Here, I review the different factors that have been tested to explain large-scale patterns in reef fish richness, particularly the underlying mechanisms of proposed hypotheses. Evidence regarding biodiversity drivers is unclear about the relative roles of variables related to habitat area, isolation, temperature, and the mid-domain effect. In turn, some agreement exists over the relatively minor role of environmental stability and the nullification of Rapoport's rule. Several caveats in available data prevent a better understanding of biodiversity patterns in reef fishes. Yet, evidence is sufficient to suggest that ongoing human-induced environmental changes have the capacity to reshape large-scale biodiversity patterns. The extent to which humanity will become the main driver will depend on how soon such stressors are ameliorated.

Describing and revealing the underlying causes of biodiversity patterns (here referred to as patterns in species richness or the number of species) have been long-standing goals in ecology [620, 2599]. These goals have gained recent interest as such knowledge provides the basis for effective allocation of limited available resources in biodiversity conservation [2123] and scientific grounds for the mitigation of stressors more likely to impact biodiversity (e.g. climate change, habitat loss, etc.) [198, 200, 1191]. Given the human dependency on biodiversity goods and services, understanding the drivers of biodiversity is also critical to assessing how potential changes in biodiversity, arising from ongoing environmental change, could impact societies [492, 1744, 1750].

For coral reef fishes, the general outline of their global pattern of species richness is relatively well documented and accepted. For these taxa, the number of species declines steadily from a peak of high diversity in the “Coral Triangle” (i.e. the area between Indonesia, Philippines, and Papua New Guinea) towards the margins of the Indian and Pacific Oceans (Figure 9.1A) [40, 193, 1733, 1923, 2123].