When I was a kid, what passed for phylogenetic trees in the illustrated books I used to read, were drawings showing not just the relationships (often vaguely drawn) between groups, but also their diversity. In such drawings mammals were invariably shown (correctly!) as having increased hugely in diversity after the KT. Reptiles on the other hand, were shown to be in decline after the Mesozoic, and the lines depicting diversity of lizards and snakes were invariably very thin, much more so than those depicting mammals and birds. As an undergraduate student (late) in the previous millennium I was taught that there are a lot of birds, and many mammals, but that amphibians and reptiles are relatively minor groups, with fewer species than in either endotherm class. Ten years ago, when I started studying lizards (i.e., resumed what I used to do as a kid, chasing lizards around, but nowadays calling it a profession) I knew this wasn’t the case. But had I known just how many lizard species are going to be recognized nowadays, I might have despaired and never started. Simply put – reptile taxonomists are running rampant, discovering, splitting, and describing about 200 new species every year: the number of recognized lizard species has increased by 31% since the turn of the century. As a macroecologist I try desperately to keep up.
Who are all these new lizards, which the writers of children’s nature books and the professors who taught me zoology never knew? And why were they described only recently? In a study now published in Journal of Zoology I set out to check.
My first thoughts were to blame eroding species concepts (“taxonomic inflation”), certainly a major cause of elevating subspecies to species level, as well as to recognize new species that older generations of taxonomists would have ranked as mere varieties, or ecotypes within polytypic species. Alternatively, new species may be difficult to detect because they inhabit places that previous generations of herpetologists seldom visited, and have restricted ranges. Likewise, they may have individual-level traits making them difficult to detect: perhaps they are small? Or are active at night? Or below ground (or high in the canopy)?
Some of those hypotheses were already examined in other animal taxa. Using my macroecological database of lizard traits, and data on the distribution of all reptiles we are now finishing to assemble (see http://www.gardinitiative.org/index.html), I now explicitly tested them for the 1323 lizard species described in the 21st century until the beginning of my study (just under a year ago, the number is already 1406 as of April 2016).
If species splitting was the cause, then I would not necessarily reveal many changes in the traits of “new” (i.e., described this century) and “old” species (those described between 1758 and 1999). But I did identify some interesting differences: as is usually the case, newly described species have small distribution ranges. They are also more likely than old species to be threatened with extinction and suffer population declines. New lizards are also small bodied, and often nocturnal (geckos are especially dominant). It seems that the greatest increase in species description rates has occurred in Southeast Asia. This century, new species of lizards have been described in 96 countries, mostly Australia (105 species), Argentina (103), Vietnam (66), Brazil (64), Madagascar (60), Malaysia (58), and the Philippines (48). Africa, however, saw relatively few new descriptions – I assume this reflects geopolitical reasons rather than postulate that we have anywhere near complete lists of African lizards. Similarly, relatively few burrowing species have been described this century – and I think this is likely to reflect our ignorance, rather than a comprehensive knowledge of burrowing forms such as amphisbaenians and dibamids. These assumptions are nearly testable (one can certainly refute them…).
When and at what number of species will this stop? How many species of lizards exist and when will we know them all? Unfortunately, given the accelerating rates of species descriptions, these are questions I cannot answer.
But the species that are being discovered are far from boring, dull, or ugly – some are strikingly beautiful. We need to keep on cataloging them, caring about them, and protecting them.
Tel Aviv University