Monotypic species and extinction risk: looking at lagomorphs

Abstract

news and update ISSN 1948-6596 commentary Monotypic species and extinction risk: looking at lagomorphs Innovative perspectives in meta-analyses, like the study of lagomorph diversity produced by Verde Arregoitia et al. (2013), are clarifying the poorly understood relationship between biodiversity and ecosystem function. As a result, maintaining cur- rent ecosystem function relies on the preservation of as much biodiversity as possible, especially for rare or unusual clades that may have specialized roles in their environments. Species-poor verte- brate clades are more common than predicted to occur by chance (Ricklefs et al. 2007), suggesting that non-random mechanisms promote the persis- tence of relict species, members of once-large clades that rarely generate new species (Fig. 1). These species-poor clades, which have low net diversification, are thought to be at greater extinc- tion risk in the anthropogenic world because of their propensity to contain species with marginal, specialized niches (Verde Arregoitia et al. 2015; Ricklefs et al. 2007). Loss of these clades would disproportionately impact global biodiversity, due to their evolutionary uniqueness, and potentially ecosystem function if evolutionary uniqueness is also related to both unusual and important func- tional characteristics (Hampe and Petit 2005). In Lagomorpha, unlike other mammalian orders (such as Rodentia), there is a direct correla- tion between genus size and extinction risk, where species-poor clades are more likely to include threatened species (Verde Arregoitia et al. 2013). This correlation may explain why an unusually high proportion of lagomorphs overall is under threat of extinction. In a follow-up study, Verde Arregoitia et al. (2015) seek to explain the poten- tial underlying causes of this pattern. They find that lagomorph diversity tends to be low in bioti- cally diverse areas like the tropics, and high in are- as with low richness of other mammal species. They find that lagomorphs are most diverse in temperate latitudes, opposing the latitudinal di- versity gradient that predominates in most taxa. Sensitivity to high temperatures restricts the geo- graphic ranges of many of these species (Rolland et al. 2014). Verde Arregoitia et al. (2015) also find that evolutionary distinctiveness does not corre- late with biogeographic patterns like range size. These counterintuitive results may also have im- plications for niche breadth, which is often related to range size. Classic ecological studies of species and their habitats offer snapshots of species’ current niches. However, they may not provide broad- enough information about a species’ extinction risk or whether relatives should be expected to share similar risks. In conjunction with fossils and paleoenvironmental data, phylogenetics can be used to reconstruct within-clade evolutionary re- lationships, providing historical and evolutionary insight into potential threats (Cavender-Bares et al. 2012). Measures of extinction risk can often be informed by study of processes that have driven extinction in a clade in the past or through analy- sis of risk to related species by highlighting ecolog- ical, biogeographic, and evolutionary similarities and differences between family members (Ricklefs Contrary to expectations, Verde Arregoitia et al. (2015) found that there may not be a direct relationship between evolutionary distance and extinction risk for species-poor lagomorph genera. Rather (p.9), “...threatened and species-poor gen- era... occur in productive megadiverse areas that currently experience strong habitat degrada- tion...” and increasing anthropogenic pressure, whereas species in more diverse genera tend to live in harsher environments that have much low- er overall mammalian diversity. Thus, the correla- tion between genus size and extinction risk is driv- en by a relationship between genus size and habi- tat quality, in which high-productivity and at-risk habitats contain a disproportionately large num- ber of species-poor lagomorph genera. Further work is necessary to determine whether this rela- tionship is due to lagomorphs’ ability to exploit nutrient-poor habitats (Hirakawa 2002 Hacklander et al. 2008), or due to neutral processes. This relationship between genus size and habitat quality contradicts a common explanation frontiers of biogeography 7.2, 2015 — © 2015 the authors; journal compilation © 2015 The International Biogeography Society