ENDEMISM: ORIGINS AND IMPLICATIONS A Myers, S de Grave To cite this version: A Myers, S de Grave. ENDEMISM: ORIGINS AND IMPLICATIONS. Vie et Milieu / Life & Envi- ronment, Observatoire Océanologique - Laboratoire Arago, 2000, pp.195-203. hal-03186913 HAL Id: hal-03186913 https://hal.sorbonne-universite.fr/hal-03186913 Submitted on 31 Mar 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. VIE ET MILIEU, 2000, 50 (4) : 195-204 ENDEMISM: ORIGINS AND IMPLICATIONS A.A. MYERS* S. DE GRAVE** * Department of Zoology and Animal Ecology, National University of Ireland Cork, Lee Maltings, Prospect Row, Cork, Ireland ** Oxford University Muséum of Natural History, Parks Road, Oxford, 0X1 3PW, U.K. ENDEMISM ABSTRACT. - Ail taxa are endémie and occur in nested distributions at a range CLADISTICS of spatial scales. Distinguishing endémies as either neoendemics or palaeoende- mics may not be of practical value in analytical biogeography, but distinguishing extinction mediated endémies (cryptoendemics) from endémies which never had a significantly wider range (euendemics) would be useful for interpreting the histo- ry of géographie areas. Only cladistic phylogeny provides a tool for distinguis- hing thèse two types of endémie. ENDÉMISME RÉSUMÉ. - Tous les taxons sont endémiques et présentent des répartitions em- CLADISTIQUE boîtées selon les échelles spatiales considérées. La distinction de néoendémiques et de paléoendémiques parmi les endémiques peut ne pas avoir de valeur pratique en biogéographie analytique; en revanche, distinguer les endémiques dus à des ex- tinctions (cryptoendémiques) par rapport aux endémiques qui n'ont jamais pré- senté de distribution significativement plus large (euendémiques) pourrait être utile pour interpréter l'histoire des aires géographiques. Seule, la phylogénie cla- distique fournit un outil permettant de distinguer ces deux types d'endémiques. ENDEMISM IN BIOGEOGRAPHY the Guianan lowlands of South America. When considered globally, this is not a disjunct distribu- tion. Within the Guianan lowlands, however, the Endemism has long been a central thème in species are separated into four major basins, the biogeography, but it is often misinterpreted as re- Orinoco basin, the Essequibo-Cuyuni basin, the ferring only to "narrow" distributions, inferring Atlantic basin and the Amazon basin (Rodriguez that only some taxa are endémie. Hengeveld & Campos 1998), a clearly disjunct distribution. (1990) for example notes "it is hard to distinguish Disjunction can corne about either through a between endémie species and "wides"...". Lincoln vicariant event, or through jump dispersai. et al. (1982) define an endémie as "restricted to a Vicariance may resuit from tectonic activity (plate particular geographical région", a définition which movement, or orogeny), from eustasy or from lo- can be seen to apply, quite correctly, to ail organ- cal climate changes (often linked to tectonic and isms. eustatic events). Jump dispersai occurs when Since ail taxa are endémie, it becomes neces- propagules cross an intervening uninhabitable ter- sary to catégorise them on the basis of their range rain to colonise a new area. This is difficult to dis- (extensive or restricted) and of their disjunction. cern as a naturally occurring event due to its rela- Both range and disjunction are continua and dé- tive rareness coupled with the short period of time pend upon the spatial scale (Table I, Fig. 1). The over which scientific records have been kept. It ranges of taxa vary from cosmopolitan through may also be obscured by the frequency of human continental or océan basin scales, to single sites. mediated transport (anthropochore dispersai). They ail show some degree of disjunction, since Endémies then, can be classified hierarchically, populations, species and higher taxa are ail sepa- consisting of a séries of nested sets of areas of oc- rated from one another at some spatial scale. A cupancy by taxa, the largest set of which, under taxon occurring uniquely in a local area might not current knowledge, is the entire world. If the be considered to have a disjunct distribution at a biogeographic patterns resulting from multiple global scale. On the other hand it clearly could be nested distributions can be shown to be statisti- considered to have a disjunct distribution on a lo- cally non-random, they demand a biogeographic cal spatial scale. The decapod crustacean genus interprétation. Some areas can be shown to have Fredius Pretzman, for example, is found only in greater densities of species which are endémie to 196 MYERS A., DE GRAVE S. Table I. - Classification of endémies with examples. Range Characteristics Explanation Example Global Unlimited biogeographically, Taxon with good powers of dispersai Gnathophyllum (Holendemic) limited only by ecological and colonisation (high compétitive (Fig. 1) and physiological tolérances. advantage) and with sufficient time for establishment Conjunct broad Broad, more or less continuons Taxon expanding or contracting ils Periclimenella (Euryendemic) or contiguous distribution, limited range(s), or in quasi stasis or régressive (Fig. 2) by biogeographic barriers (aging) taxon beginning to contract its range(s), or in quasi stasis Conjunct narrow Restricted more or less continuous Progressive taxon recently evolved Macrohectopus (Stenoendemic) or contiguous distribution limited yet to expand its range, or evolved (Fig. 2) by biogeographic barriers in situ (phylogenesis) from a clade constrained historically by biogeographic barrier(s), or relict (old) taxon. Disjunct Two or more widely disjunct 1. Vicariated taxon (Rhoendemic) distributions. a) Euendemics, isolated by tectonic Globosolembos francanni Reid changes in geography Amphiatlantic (Cape Verde and Florida) b) Cryptendemics, isolated by Iguanidae extintion of intervening populations New World + Madagascar/Fiji or taxa Extinet in Africa 2. Taxon jump-dispersed across a biogeographic barrier. a) Natural Bubulcus ibis (L.) jump dispersed from Africa to South America in 1920's b) Anthropochore Elminius modestus Darwin Spread in 20* century from New Zealand, ? Australia to Europe and South Africa Stenoendemic Euryendemic (suturing) iflà i Vicariance X 1 Rhoendemics * A Jump dispersai T Euryendemic Stenoendemic Fig. 1. - Schematic représentation of the formation of endémie types. ENDEMISM 197 themselves than have others. Thèse have been de- and vicariance. The use of cladistic methodology to scribed as "areas of endemism" and have formed answer biogeographic questions has been further the nucleus of much biogeographic classification. developed in récent years by several authors, nota- Areas of endemism are interpreted as areas of high bly Humphries & Parenti (1986, 1999). endemicity separated from other such areas by a In cladistic biogeogra^hy, a phylogeny is first decided gap. The gap may be defined as an area of determined, after which, known distributions of the low endemicity between the two areas of high taxa in the phylogeny are superimposed upon the endemicity e.g. the Sinaloan gap between the terminal nodes of the cladogram. It is the ances- Cortez and the Mexican marine Provinces. Alterna- tor-descendent branching of a clade which indi- tively it may be defined as the région of co-occur- cates the séquence (although not the timing) of rence of endpoints in species distributions vicariant events and hence the relationship (and (Hastings 2000). relative âge) of each area. Areas of endemism are The first biogeographer to employ endemism as not a primary component of any data set analysed an analytical, rather than a descriptive tool, was in cladistic biogeography and the number of probably Wallace (1876) who used the numbers of endémies in a given area (cf. Wallace above) is ir- endémies as a measure of island âge. He hypothes- relevant to any hypothèses of area relationships. In ised that the more endémie species that occurred on contrast, endémies have been used as the primary an island, the more archaic that island was likely to biogeographic data set in parsimony analysis of be, the assumption being that older islands had ex- endemicity (PAE) devised by Rosen & Smith perienced a longer period of time for the occur- (1988). PAE uses a cladistic method, but bypasses rence of phylogenesis. the requirement for a prior phylogenetic analysis. Croizat (1958), developed a biogeographic Taxa are treated as équivalent to characters and methodology (panbiogeography) for transforming their distributions are the équivalent of character the recorded distributions of individual taxa into states. In cladistic terminology, taxa which occur simplified pathways (tracks) and then combining in one place only are équivalent to autapomorphies, several of thèse individual pathways into a sum- those occurring in ail of the studied sites are équiv- mary (generalised track) which could be used to alent to plesiomorphies and as in phylogenetic hypothesise the historical évolution of the biota cladistics, neither have information content and are concerned. This method has