When I started monitoring the generic distribution of ants I had two goals: 1) obtain an idea of the generic richness and assemblage by regions, and 2) obtain a distribution map as accurate as possible for each extant genus. Well, very quickly I have been confronted to a major problem in those two goals with the presence of exotic genera around the globe. Humans have been extremely successful (not necessarily a good thing) in dispersing exotic species all around the planet; and this is a now a problem when we try to understand patterns of diversity if we don’t discriminate between native and exotic taxa.
So beside the generic database, I have created a second one for the exotic species. Some good reviews have been made in the past on the frequency of ant introductions (McGlynn 1999, Suarez et al. 2005, Ward et al. 2006), on exotic species of specific locations (take a list of ants in Hawaii that are all introduced, list for Florida, Netherland,…), or on specific species (Wetterer 2007, 2008, Wetterer et al. 2009, …). However, there is still a few cases where boundaries, native regions are not clearly identified (e.g. Tapinoma melanocephalum, see Wetterer 2009). To add to the confusion, some exotic species or some tramp species have been described from their introduced range prior to be identified in their native range.
My goal, as I said was to identify the native range of genera and not to make a catalog of all the introduced regions for a given taxa (even if I expect to reach such result in the future). So the generic map have to be handle with precaution concerning the exotic genera. Here is in a few point what information is irrelevant and which one is not.
– If you look for all the locations where a genus has been introduced, those maps will provide part of information but the referencing in this case was not exhaustive.
– The maps are at the generic level, so the presence of native species in a region (in green) will eclipse the potential presence of an exotic genus (in orange). For example, you can notice that no regions of the South East USA are in orange, where Solenopsis invicta has been introduced because native species such as Solenopsis molesta are found in the same regions.
– At the opposite, in a few case, the genus might be present, but not found yet (or I should say that I did not find a record for it), but an exotic species have been found. So the region is in orange, but could also be in blue.
I hope that this post will clarify the extant to which the exotic genera can be perceived in the distribution maps, and as I update the maps regularly, the gaps for exotic presence should be filled progressively.
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