Abstract
AimTaxon co‐occurrence analysis is commonly used in ecology, but it has not been applied to range‐wide distribution data of partly allopatric taxa because existing methods cannot differentiate between distribution‐related effects and taxon interactions. Our first aim was to develop a taxon co‐occurrence analysis method that is also capable of taking into account the effect of species ranges and can handle faunistic records from museum databases or biodiversity inventories. Our second aim was to test the independence of taxon co‐occurrences of rock‐dwelling gastropods at different taxonomic levels, with a special focus on the Clausiliidae subfamily Alopiinae, and in particular the genus Montenegrina.LocationBalkan Peninsula in south‐eastern Europe (46N–36N, 13.5E–28E).MethodsWe introduced a taxon‐specific metric that characterizes the occurrence probability at a given location. This probability was calculated as a distance‐weighted mean of the taxon's presence and absence records at all sites. We applied corrections to account for the biases introduced by varying sampling intensity in our dataset. Then we used probabilistic null‐models to simulate taxon distributions under the null hypothesis of no taxon interactions and calculated pairwise and cumulated co‐occurrences. Independence of taxon occurrences was tested by comparing observed co‐occurrences to simulated values.ResultsWe observed significantly fewer co‐occurrences among species and intra‐generic lineages of Montenegrina than expected under the assumption of no taxon interaction.Main conclusionsFewer than expected co‐occurrences among species and intra‐generic clades indicate that species divergence preceded niche partitioning. This suggests a primary role of non‐adaptive processes in the speciation of rock‐dwelling gastropods. The method can account for the effects of distributional constraints in range‐wide datasets, making it suitable for testing ecological, biogeographical, or evolutionary hypotheses where interactions of partly allopatric taxa are in question.
Highlights
Speciation is often classified as adaptive or non-adaptive
The majority of speciation events is allopatric (Coyne & Orr, 2004; Turelli, Barton, & Coyne, 2001), but an increasing number of studies suggests that sympatric speciation, when ranges of sister taxa overlap, is probably less exceptional than previously thought (Bolnick & Fitzpatrick, 2007; Li et al, 2016)
Some authors claim that allopatric speciation is driven mostly or entirely by nonadaptive factors (Gittenberger, 1991, 2004; Wilke, Benke, Br€andle, Albrecht, & Bichain, 2010), but most speciation events can be best explained by a combination of adaptive and non-adaptive forces (Dieckmann, Metz, Doebeli, & Tautz, 2004; Olson & Arroyo-Santos, 2009)
Summary
It is strictly adaptive when the evolution of a new species is triggered by adaptation to a new niche This predominantly in situ process is characterized by descendant sister species remaining in sympatry and showing apparent differences in their habitat preferences. Divergence is initiated by non-adaptive processes (e.g. drift) and, even if descendants adapt to distinct habitats, that is a consequence, rather than cause of the speciation (Rundell & Price, 2009). We compared pairs of species and those of higher taxa at different stages of taxonomic/phylogenetic relatedness (Godoy et al, 2014) Our goal with this was to identify which was the likely phylogenetic level in their divergence at which niche segregation happened and, to provide indirect information on the significance of adaptation in the process of speciation. We present a methodological framework that is capable of simulating range-wide occurrence patterns of multiple species with partially overlapping ranges and data obtained by spatially varying survey effort
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