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The species level and the nonphylogenetic concepts

Speciation event and speciation process. As seen above, biologists can strongly disagree about the species definition.104 However, to the exception of possible disagreement about the speciation event itself (survival, or not, of the stem species), there is generally much less discrepancy about the likely grand mechanisms of speciation140: allopatry, mutation, genetic drift, disruptive selection,22 ecological adaptation, hybridization, , etc. Interestingly, most of these mechanisms,

when considered for sexually reproducing insects, are processes tending to increase the reproductive isolation between “future” species, which is an indirect recognition to the importance of the biological concept of species.

The biological and evolutionary concepts. Both the biological and evolutionary definitions of species are not very useful to understand the successive steps from the past to the present state of biodiversity. However, both of them, especially the evolutionary concept, compel us to gather biological information specific to the populations under study. Their openness to various analytical approaches leads us to define species in a more informative way, in accordance with species definitions and known speciation mechanisms.

Taking into account known speciation processes to understand the species status of a population is where the evolutionary concept could be the most useful. Its receptiveness to discussion provides richer biological information on populations and their possible species status. Importantly, the evolutionary concept is also the only modern concept allowing discussion about infraspecific populations and decisions about the utility of giving them subspecific names. For instance, the partial reproductive isolation of T. platensis with T. delpontei would make them subspecies according to the biological or Hennigian concepts. Whereas the ecological adaptation of T. delpontei to particular bird’s nests makes it a true evolutionary species.

It might be useful to mention here the existence of an Ecological Concept of Species,141 which was progressively abandoned because of two reasons: (1) many subspecies or even simple local populations of the same species may show different ecological adaptations and (2) the rate of speciation largely exceeds the rate of ecological changes.142

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