Species native in one Belgian region, but not in another

[timadriaens]

A problem (already raised in #32) arising from including regional distributions in the unified checklist (see #45 and #43) is that eventually, species that have been introduced in one region but are native in another, are included in the checklist of alien species of Belgium. I think it would be best to not include those in the unified? Some examples are

• Podarcis muralis is there because it is non-native to Flanders (introduced with habitat material probably and still spreading along the railway network).
• Natrix helvetica which was introduced in Flanders and Brussels but is native in Wallonia (and of conservation concern everywhere)

@damianooldoni @peterdesmet We should decide what to do with such cases, because it is strange they appear on a Belgian alien species checklist.

[damianooldoni]

I understand your point, @timadriaens. About the examples you mention:

• Podarcis muralis comes from RINSE: https://www.gbif.org/species/145954456 and it has distribution location Belgium only (see distributions:http://api.gbif.org/v1/species/145954456/distributions)
• Natrix helvetica comes from Ad hoc checklist: https://www.gbif.org/species/148437871 and it has distribution location Flemish region only

I think that the unified checklist, which is published as the Global Register of Introduced and Invasive Species - Belgium, should contain only taxa which are alien in all Belgium. As written in checklist's general description on GBIF:

It contains information on 2,500+ validated non-native taxa in Belgium.

As Belgium = Flanders + Brussels + Wallonia, I read the sentence above as follows: non-native in Belgium = non-native in Flanders AND non-native in Brussels AND non-native in Wallonia

Or logically speaking with symbols: the function _nonnativity is a AND function with respect to sum:

non_nativity(a+b) = non_nativity(a) AND non_nativity(b)

The other interpretation, where the function _nonnativity is a OR function with respect to sum:

non_nativity(a+b) = non_nativity(a) OR non_nativity(b)

sounds me quite strange and can arise cases as mentioned by @timadriaens above. The problem is that sometimes the error is at checklist level (see example 1) so we start with wrong information.

[timadriaens]

I agree that for the unified checklist of Belgium we only have to consider species that are non-native in all regions (so the and-function). Some species are non-native to Belgium and have only been recorded in one region, sometimes the only thing we know is that it's non-native to Belgium and we don't have regional information. On the other hand, if it is present in one region, it is also present in Belgium of course.

scientific name	...	location	country code	occurrence status	date first observation	date last observation	degree of establishment
scientific name	...	Flanders	BE	present	2008	2012	reproducing
scientific name	...	Wallonia	BE	present	2012		reproducing
scientific name	...	Wallonia	BE	present	2012		reproducing

In fact the RINSE checklist is correct because the working area of that project was entirely in Flanders in that case. And the add hoc for Natrix is also correct as the species IS non-native but only in Flanders... So in order for the AND function to work properly the regional distribution should be filled for all the species? Which means we have to triplicate every record?

[damianooldoni]

As the problem of these two species comes back while discussing indicators, this problem, already theoretically important, becomes in practice also relevant, and therefore should be solved. The solution, I think, is adding the DwC term establishmentMeans with value native for Wallonia in the checklist distribution. @timadriaens , @peterdesmet , @qgroom , what do you think about it?

[timadriaens]

yes, that should do it I think.