Data from: Speciation and the latitudinal diversity gradient: insights from the global distribution of endemic fish

The nearly universal pattern that species richness increases from the
poles to the equator (the latitudinal diversity gradient [LDG]) has been
of intense interest since its discovery by early natural-history
explorers. Among the many hypotheses proposed to explain the LDG,
latitudinal variation in (1) productivity, (2) time and area available for
diversification, and (3) speciation and/or extinction rates have recently
received the most attention. Because tropical regions are older and were
formerly more widespread, these factors are often intertwined, hampering
efforts to distinguish their relative contributions to the LDG. Here we
examine the global distribution of endemic lake fishes to determine how
lake age, area, and latitude each affect the probability of speciation and
the extent of diversification occurring within a lake. We analyzed the
distribution of endemic fishes worldwide (1,933 species and subspecies
from 47 families in 2,746 lakes) and find that the probability of a lake
containing an endemic species and the total number of endemics per lake
increase with lake age and area and decrease with latitude. Moreover, the
geographic locations of endemics in 34 of 41 families are found at lower
latitudes than those of nonendemics. We propose that the greater
diversification of fish at low latitudes may be driven in part by
ecological opportunities promoted by tropical climates and by the
coevolution of species interactions.