Body Size, Extinction Risk and Knowledge Bias in New World Snakes

Citation: Vilela B, Villalobos F, Rodrguez MA , Terribile LC ( Body Size, Extinction Risk and Knowledge Bias in New World Snakes Bruno Vilela 0 Fabricio Villalobos 0 Miguel A ngel Rodrguez 0 Levi Carina Terribile 0 Sergio A. Lambertucci, INIBIOMA (Universidad Nacional del Comahue-CONICET), Argentina 0 1 Departamento de Ecologia, Instituto de Ciencias Biol o gicas, Universidade Federal de Goia s , Goiania, Goia s, Brazil , 2 Departamento de Ciencias de la Vida, Universidad de Alcala , Madrid, Spain, 3 Laborato rio de Macroecologia , Universidade Federal de Goia s - Campus Jata , Jata , Goia s , Brazil Extinction risk and body size have been found to be related in various vertebrate groups, with larger species being more at risk than smaller ones. We checked whether this was also the case for snakes by investigating extinction risk-body size relationships in the New World's Colubroidea species. We used the IUCN Red List risk categories to assign each species to one of two broad levels of threat (Threatened and Non-Threatened) or to identify it as either Data Deficient or NotEvaluated by the IUCN. We also included the year of description of each species in our analysis as this could affect the level of threat assigned to it (earlier described species had more time to gather information about them, which might have facilitated their evaluation). Also, species detectability could be a function of body size, with larger species tending to be described earlier, which could have an impact in extinction risk-body size relationships. We found a negative relationship between body size and description year, with large-bodied species being described earlier. Description year also varied among risk categories, with Non-Threatened species being described earlier than Threatened species and both species groups earlier than Data Deficient species. On average, Data Deficient species also presented smaller body sizes, while no size differences were detected between Threatened and Non-Threatened species. So it seems that smaller body sizes are related with species detectability, thus potentially affecting both when a species is described (smaller species tend to be described more recently) as well as the amount of information gathered about it (Data Deficient species tend to be smaller). Our data also indicated that if Data Deficient species were to be categorized as Threatened in the future, snake body size and extinction risk would be negatively related, contrasting with the opposite pattern commonly observed in other vertebrate groups. - Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by the Spanish Ministry of Economy and Competitiveness (grant: CGL2010-22119), Conselho Nacional de Desenvolvimento Cientfico e Tecnol ogico (Process n. 473788/2009-8) (http://www.cnpq.br/), and Coordenacao de Aperfeicoamento de Pessoal de Nvel Superior (http://www. capes.gov.br/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. A general attribute that can be easily measured in every species on earth is its body size. Understanding how to make ecological predictions based on body size remains an important research goal in ecology since, in general, it is easier to measure morphological traits than to directly assess ecological aspects [1,2]. For instance, a major question is whether ecological features correlated with body size can render any size class more or less susceptible to extinction. In other words, are small- or large-bodied species (or any size class in between) more vulnerable to extinction? Analyses based on species conservation statuses, such as those included in the IUCN Red List of Threatened Species [3], have shown that Threatened vertebrate species tend to be larger than Non-Threatened ones, at least for mammals [4,5], birds [6,7], frogs [8], and marine fishes [9]. Therefore, some ecological implications of body size may be causing large-bodied species to become more vulnerable to extinction. For instance, large-bodied species tend to have lower local abundances and, hence, are more likely to suffer from endogamy and loss of genetic diversity from stochastic processes [10]. Also, larger species are often more prone to be targeted by human hunters, fishermen or for general commercialization [9,11,12], or to suffer from habitat loss [4] owing to their greater energetic demands and their consequent need for larger home ranges [13]. Finally, large-bodied species typically reproduce at lower rates and have smaller litters than small-bodied species, thus being less able to recover from population decline [8,14]. Generalizing the above explanations to all taxa is challenging owing to different or unknown body size-ecology relationships in poorly known taxa. For example, one could argue that large body size does not necessarily imply higher energetic demands because metabolic rate also depends on behavior [15], or that large-bodied species do not always show low local abundances [e.g. 16]. Additionally, extinction risk related to large body size may be undermined by other species traits conveying less vulnerability to local threats, such as large geographic ranges and high dispersal capability [17]. Moreover, exceptions to the large specieshigher vulnerability pattern have been found, for example, in Australian Elapidae snakes [18], freshwater fishes [9], and fossil bivalves [19]. Another caveat in generalizing the large species-vulnerability pattern is its dependence on conservation status assessments based on available information. Red Lists provide summarized information on species threats, population trends, and conservation status, but are not free of biases as they depend on data availability [20,21]. Thus, it is possible that small-bodied species are poorly studied owing to their more cryptic nature, narrow ranges and less charismatic appeal. Indeed, such characteristics of small-bodied species make them hard to discover and thus tend to be scientifically described more recently [22], resulting in less time for their study and, possibly, for accumulating relevant information to establish their level of threat. Overall, this could result in more small-sized species being assigned a conservation status related to uncertainty (i.e. categorized as Data Deficient) or not even being evaluated in comparison with larger species, which means that conclusions about the large species-vulnerability pattern could be misleading when based solely on species categorized as Threatened or Non-Threatened. Here we focus on the New Worlds snakes (superfamily Colubroidea) for which we first asked (1) how species distribute within major IUCN extinction risk ca (...truncated)