Efectos potenciales sobre el medio socioeconómico

ity of an observation by evaluating the match between the location of an observation and its species identification. They use two aspects of an observation. The first is the location, which determines the context of species observed around it, or of tags mapped around it. The second is the species identifi- cation, which determines which context species or context tags are expected, according to the species’ observed community or OSM environment. In a case with a high level of similarity, the location of the candidate observation matches the species given by the observer. Its location is similar to places where the target species is usually observed, when the candidate observation’s species or tag context is con- sidered. This makes the location of the candidate observation appear plausible in light of the given species. In a case with a low level of similarity, the location does not match the species identification. Its location is not similar to places where the target species is usually observed. This makes the loca- tion of the candidate observation appear implausible in light of its species identification.

Discussion of evaluation results revealed that there are species whose observed communities or OSM environments are similar, because these species are observed in the same locations. Therefore, ob- served communities or OSM environments of target species observed in the same places tend to be similar. This finding is very important for how the observed communities approach and the OSM envi- ronments approach can be used to estimate the plausibility of the location of an observation in light of its species. A high similarity value shows that the candidate observation’s location matches places where the target species is usually observed, but the candidate species might be any other species usu- ally observed in the same places, or in places with similar species or tag context, and consequently having a similar observed community or OSM environment. An observation of one of these other spe- cies in the same location as the candidate observation would be just as plausible. Obviously, certainty of species identification is of no small importance here.

In a citizen science environment, certainty of species identification is determined by a number of fac- tors. Of particular interest are species which can easily be mixed up with one another due to similar physical appearance, similar sound utterance, or otherwise similar features. Experience and training on the side of observers mitigates this problem, but casual citizen science observations of organisms are also provided by untrained and at least in part inexperienced observers. This fact was already used in

this work to synthesize implausible observations by swapping species identifications of real observa- tions of species which are often mixed up due to physical similarity, but live in different habitats which should provide different species or tag contexts. For the current discussion, species are also important which are easily mixed up, but are observed in the same places for whatever reasons, and therefore have similar observed communities or OSM environments. In candidate cases which are plausible, these are the species which are the most likely species alternatives at a given location. A high similarity value makes the candidate location appear plausible, but does not allow for ruling out that the species could be mixed up with a different species usually observed in similar places, especial- ly a physically similar species. However, it is also implausible in this case that the species actually observed was a physically similar species usually observed in locations which have a different context. In implausible cases, either the location might be incorrect, or the species might be erroneous, and then all other species with an observed community which is similar to the candidate species’ are also unlikely. It is, however, possible in these cases that the observation is in truth of a species which is physically similar to the species given in the candidate observation, but which is usually observed in different places. A test for this case could consist of calculating similarities between the candidate context at hand and the observed communities or OSM environment of the proper species. If a high similarity value would be found, it would point to a possible mix-up of these species.

All of these considerations, of course, do not apply for species which are easily and clearly identifia- ble, with no species physically similar enough for even an unexperienced observer to mix them up. Such species exist (examples will be discussed below) and produce cases where the species identifica- tion of a candidate is certain to a high degree. Another factor making a species identification certain (also for more difficult species) is a very experienced observer. If the observed community approach or the OSM environments approach find a high level of similarity of candidate context and observed community or OSM environment with such a candidate case, both species and location are plausible. For low similarities, the location is implausible, while the species is plausible, and if there is an error, it is more likely on the side of the location. A gross mix-up of species cannot, of course, be ruled out either, but is unlikely. An experienced observer will also lead to a high degree of certainty in species identification in an observation, at least for the species or species groups in which the observer spe- cializes. This includes observations of species which are hard to identify or easily mixed up with phys- ically similar species. In all cases where a low similarity value makes the candidate location appear implausible, it is always possible that the candidate observation comes from a location with a context which was so far not represented in the data, and therefore appears unusual when compared to the existing observations available for the candidate species.

Analog considerations apply for the reported location of an observation. The approaches to plausibility estimation discussed here can make a reported location appear plausible or implausible, but any simi- lar location would result in a similar plausibility for an observation of the same species. This applies to observations with certain and uncertain species identification in the same way. Even if species identi- fication is certain and context at the reported location matches the observed species’ observed com- munity or OSM environment, all locations with a similar species or tag context are just as plausible. With implausible observations, there are of course a very large number of alternative locations, be- cause many different context situations may result in equally low similarity index results. This leads to the question of certainty of location in an observation. ArtenFinder and iNaturalist, like many other web-portals for reporting observations of organisms, provide map viewers to locate an observation by clicking on the map. Various types of base maps and other geographic information are usually availa- ble in these viewers. iNaturalist provides Google map and satellite images, while ArtenFinder has OpenStreetMap, aerial photographs, and also official topographic maps and relief. Uncertainty is therefore introduced by the variable ability of volunteers to correctly read such forms of geographic

information, and to correctly place their observations on them. This factor of uncertainty is similar in nature to volunteer uncertainty in species identification, depending very much on the individual abili- ties of the volunteer. Also, when placing an observation on the map, observers can choose a scale by zooming in or out, thereby inherently selecting a level of precision in placing their observation. On a small scale, an observation will probably be placed accurately, but with relatively low precision in the correct area (e.g., in a certain part of a town, on a lake, or in a stretch of forest). On a larger scale, an observation may be placed much more precisely, e.g., in an isolated tree in which a bird was actually seen. In both ArtenFinder and iNaturalist, observers are free to choose the scale at which they place their observation in the map. This choice may or may not reflect the actual certainty of the observed position on the side of the observer. An observer may have a very precise recollection of the actual position of an observation, but may still use a small scale when actually submitting the observation, resulting in low precision. iNaturalist automatically generates an accuracy value depending on the chosen map scale, which can also be manually changed by the observer before submitting the observa- tion. In iNaturalist also, an address search allows for placing an observation in a certain street address, introducing uncertainty of geocoding to accuracy, and uncertainty of the actual position used for an address in the geocoding process to precision. Both ArtenFinder and iNaturalist do not use user- defined observation areas, an option which is available in some other platforms (e.g., naturgucker.de), and a factor reducing precision, but usually not accuracy. Errors or inaccuracies in the maps and other sources of geographic reference used in a map viewer will, of course, also directly result in errors of observation location. With apps for reporting observations by using mobile devices (also provided by ArtenFinder and iNaturalist), uncertainty of geographic location is mostly determined by the technical properties of the Global Positioning System (GPS) sensor in the device used, as well as by the usual factors for GPS accuracy, such as satellite constellation and shadowing effects through infrastructure and vegetation (e.g., Zandbergen & Barbeau 2011).

Table 5.4.1: Considerations on plausibility of location and species identification for candidate cases. High similarity of candidate context and ob-

served community or OSM environment

Low similarity of candidate context and ob- served community or OSM environment Reported location matches species identification.

 Reported location plausible for reported species.

 Reported location equally plausible for any species with a similar observed community or OSM environment (espe- cially relevant: physically similar spe- cies).

 Reported location implausible for any species with a different observed com- munity or OSM environment (including physically similar species).

 Any other location with matching species or tag context equally plausible.

Location does not match species identification.  Reported location implausible for report-

ed species.

 Reported location also implausible for any species with a similar observed community or OSM environment (in- cluding physically similar species).  Large number of alternative locations

equally implausible.

Table 5.4.1 summarizes the considerations described here, for the two main cases of a plausible or an implausible candidate observation. The information provided by the observed communities approach or by the OSM environments approach to plausibility estimation of casual citizen science observations of organisms is limited. Especially with plausible observations, it is important to keep in mind that there are often alternative species and locations which would render similar plausibility estimations. An implausible case may basically represent either an error in species identification or in position. The

latter is more likely with species which are usually identified with high certainty, or it may represent a correct but unusual observation. These considerations are overlaid by the influences of observation density on the similarity measures used here, which were discussed in detail earlier. They introduce another set of factors to this discussion, which are rooted in the VGI nature of the data. All of these considerations are best examined and illustrated by using examples from the data use cases at hand, first on the level of species and their observed communities, and then also on the level of individual candidate observations.

5.4.2 Observed Communities Examples: Illustrating Target Species and Candi-