There is not a straightforward answer to this. I think the major criteria should be the distance of the "new" record to the known distribution area, as is related with the regular home ranges and dispersal abilities of the species, and the presence or not of barriers or corridors connecting sites. Second, the presence of habitats known or supposed to be adequate to the species; this has to be also with the adaptability of it. Third,  the degree of knowledge (research history) of the area; ¿it is an unexpected record or was just a matter of time before somebody registered it? This last one has not to be directly with your question, but I think it is important in the mind of the coleagues to recognize and accept such distributional expansions.

Saludos

Dear Cristian,

I agree - sufficient evidence should be provided to the scientific community about how identification was carried out (biometric measures, diagnostic criteria adopted, possibly a picture of the specimen, etc.). Ideally new records leading to significant changes in a species' range should be published in scientific journals after a peer review process. 

Please find here an example from our bat work: 

https://www.researchgate.net/publication/263089380_Reassessing_the_breeding_range_limits_for_two_long-distance_migratory_vespertilionid_bats_Pipistrellus_nathusii_and_Nyctalus_leisleri_in_the_Italian_Peninsula

I hope this helps, all best

Danilo

Article Reassessing the breeding range limits for two long-distance ...

Hi Cristian,

Further to the helpful comments above of Danilo and Luis above, to provide a quantified context to the range expansion you might also look at  using a standard distribution metric (such as the IUCN's Extent of Occurrence polygon, or Area of Occupancy grid) to develop a mathematic metric for the current distribution, and the changed distribution with the new locality record(s) included - that will give you an idea of how important the spatial increase is.

Also, if it is a new habitat type that could be particularly important, even if there is only a minor spatial increase, since that may change the knowledge base on the amount of 'suitable' or 'potential' habitat within its overall range.

What kind of species are you looking at, and what scale of distribution?

Jason

Hello,

Not sure this will answer your question fully, however its relevant to it: in the paper attached I did a ecological niche model with all the previously known species occurrences before conducting field work. Then I searched for the species in the range margins both outside and inside the area given as adequate for the species. I found 19 knew occurrences, although a few were inside the previous range.

This is the paper:  https://www.researchgate.net/publication/268443984_Combining_distribution_modelling_and_non-invasive_genetics_to_improve_range_shift_forecasting

Cheers,

Article Combining distribution modelling and non-invasive genetics t...