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Madagascar as a model region of species diversification

2009; Elsevier BV; Volume: 24; Issue: 8 Linguagem: Inglês

10.1016/j.tree.2009.03.011

1872-8383

Miguel Vences, Katharina C. Wollenberg Valero, David R. Vieites, David C. Lees,

Animal Ecology and Behavior Studies

Tropical biotas provide excellent settings in which to explore mechanisms of evolutionary diversification, yet these processes remain poorly understood. Pioneering work on biodiversity patterns and diversification processes in other tropical regions has recently been complemented by studies in Madagascar. Here we review diversity models and diversification mechanisms proposed for the fauna of this island and the perspectives for testing them. Madagascar has a diverse biota that has evolved in isolation, and is characterised by regionally pronounced and locally steep environmental gradients, common patterns of microendemism across taxa and numerous evolutionary radiations. These characteristics establish Madagascar as a promising system for the study of pattern and process in species diversification. Tropical biotas provide excellent settings in which to explore mechanisms of evolutionary diversification, yet these processes remain poorly understood. Pioneering work on biodiversity patterns and diversification processes in other tropical regions has recently been complemented by studies in Madagascar. Here we review diversity models and diversification mechanisms proposed for the fauna of this island and the perspectives for testing them. Madagascar has a diverse biota that has evolved in isolation, and is characterised by regionally pronounced and locally steep environmental gradients, common patterns of microendemism across taxa and numerous evolutionary radiations. These characteristics establish Madagascar as a promising system for the study of pattern and process in species diversification. formation of species by the separation of populations into two or more different geographical areas in which they undergo phenotypic or genetic divergence (equivalent to vicariant speciation, but with no need for a physical barrier, i.e. can be due to dispersal or ecology). the tendency of phylogenetic lineages to remain with their original biomes rather than colonising new ones. areas within a biome with an increased number of species occurring nowhere else in the domain; in the watershed mechanism, centres of endemism are those areas where rivers have headwaters at low elevation. a statistical technique for analysing and predicting spatial patterns of turnover in community composition (beta diversity) across large regions. formation of species by adaptation of populations to different conditions along an environmental (e.g. elevational) gradient, rather than by vicariance; usually, the process is assumed to occur under parapatric conditions. the generally observed increase of number of species per unit area toward low latitudes or the equator. a high proportion of species with narrow range sizes. the increasing overlap of species ranges toward the centre of a shared geographical domain owing to geometric boundary constraints in relation to the distribution of species’ ranges and midpoints. This leads to a peak of species richness in the centre of the domain. the tendency of species to retain ancestral ecological characteristics, such as aspects of their fundamental niche. the effect of montane topography on weather (e.g. an aspect-specific precipitation pattern). the formation of species in adjacent areas (usually with a hybrid or contact zone). a method for exploring cross-taxon relationships between traits by correcting for autocorrelation with phylogeny. a concept of species delimitation in which individuals belonging to a species are defined by the presence of one or more fixed, apomorphic characters. the spatial (geographical, discussed here) or temporal (stratigraphic or phenological) change in species composition (beta diversity). A high spatial species turnover is often caused by a high proportion of microendemic species. the rapid accumulation of scientific names owing to processes other than new discoveries of taxa (i.e. ‘splitting,’ the unwarranted elevation of taxa to a higher level such as species, or other taxonomic errors, such as overreliance on a particular species concept). the formation of different populations and eventually different species by the formation of a physical divide between them (equivalent to allopatric speciation, but with a physical barrier needed); assumed to be nonadaptive (i.e. it does not require either of the new species to adapt to different environmental conditions).