Perplexing Fiddler Crab, Uca perplexa (Fiddler Crab of the Week)

The Perplexing Fiddler Crab, Uca perplexa, is found throughout most of the islands of the western Pacific, from Japan down to Malaysia across Indonesia, the Philippines and Papua New Guinea, the eastern coast of Australia and out toward remote islands such as Fiji, Samoa, and French Polynesia. It’s name comes from the confusion that arose in trying to separate this species from closely related forms, particularly Uca annulipes and Uca lactea with which its range overlaps in many areas. In the field these species can be told apart somewhat by color: the major claw in Uca perplexa tends to be more yellow while that of Uca annulipes is more red, although there are other similar species which may also have red and/or yellow claws so its not an absolute indicator.

Because of its spread over so many remote Pacific Islands, in terms of raw area (as well as longitudinal range), it is one of the most widespread fiddler crab species, likely second only to Uca tetragonon (which resides in much of the same area, but is also common throughout the Indian Ocean as well). Given that most of its range area is open ocean, it’s an open question as to whether it actually occupies more shoreline than a widespread continental species such as Uca tangeri.

New Features on the Site

This month’s site update contains a number of new features beyond the standard citation and reference updates. In particular, three new elements are now on the site. Two of these were discussed as upcoming in previous posts, but are now live. The third has its own description posted earlier today:

  1. Charts showing the chronology of name usages
  2. Word clouds of name usages
  3. Point location pages

Hopefully these all add a little more information that may prove useful.

Point Location Data

My previous discussions of range maps (see part 1 here) focused on areal (or linear) representations of where different species might be found. Another type of location data has been part of the site for awhile but was never explicitly compiled into a useful form…until now.

Individual records of species usages (such as those found on the citation pages) often list the particular location to which the name applies. This location can be fairly specific (e.g., a particular river mouth) or extremely broad (e.g., a country or ocean basin). These location names are stored as part of the database; a number of years ago I decided to standardize the names to allow for better analysis and consistency. As much as possible, the names found on the website reflect the current name of the location, rather than the historical name that might have appeared in the original publication, although the historical names are kept as synonyms (invisible until now).

Beyond just standardizing the names, every location was given a latitudinal and longitudinal representation. These coordinates lack precision, but represent a quick-and-dirty estimate of what the location name might represent. For a broad area, the coordinates usually match a major coastal city or the rough center of the coastal area; for smaller islands, the center of the island might have been used.

I’ve been using the coordinates for a few years to help identify misidentified records and/or errors in the database. By plotting the locations associated with different names, it is fairly easy to find major outliers; these can then be examined to determine if the error was a recording error on my part or a (potential) error made by the original authors.

In this new release, the point location data is now public and is used in a variety of different ways and places on the site.

Species Pages

The species pages (as well as the general geography page) now show a point location map in addition to the traditional range map. These point location maps represent all of the places where the database believes a particular species is actually found (as opposed to where an author said it was found). These should generally match the range maps, although there are certainly cases where they diverge; at some point these differences will be used to update/fix the range maps and/or the underlying point-species references. Additionally, the point maps are only up-to-date based on citation records added to the database. Aberrant locations where no fiddler crabs are found are indicated by a different color symbol.

Every recorded point location of a fiddler crab in the database. Blue points represent clearly erroneous entries where no fiddler crabs are actually found. The point in central northern Africa (border of Libya and Niger) was a lat/lon error in the database which has already been corrected.

Name Pages

The name pages (both compound and specific name) now show a point map indicating all of the places where a particular name was used, if any (some names are not associated with any specific location so maps are left off of those pages). This is different than the species pages, because this indicates author usage rather than the algorithmicaly and/or expertly adjusted species meanings found on the species pages.

Location Pages

Every location has its own page as well. Each location page includes the latitude and longitude used to indicate its position (as well as a map of the point), cross-references to locations that contain or are contained within the location based on the hierarchy mentioned below, lists of currently recognized species found within the location, and lists of names (both compound and specific) which have been used for species at the location.

The species and name lists automatically fill in missing names by including all names found at any sublocation of the hierarchy (names inferred as such are indicated by a symbol). This should allow one to more readily access complete lists of names or species for an area without having to worry about the vagaries of historical records.

Location pages can be accessed in two ways. First, from the general geography page, there are now a pair of indices of all locations. The first index represents a rough hierarchical sorting of locations, lumping sub-locations into larger locations (e.g., a city within a state within a country). The second index is a pure alphabetical listing of all locations, including the historical names, not just the modern names. Second, all location pages can also be accessed from any page/record which mentions that location; the locations in the tabular records automatically link to the associated location page.

Problems and Limitations

These location data are not perfect. Some known problems include:

  • Species may be missing from locations just due to holes in observations. For example, Uca pugilator is not recorded for Deleware, even though it falls right in the middle of the known range of the species and is found in neighboring states.
  • Less precise records may have a point location which seems to indicate the presence of a species well outside its actual range. Thus a species recorded from “Central America” might use a point location to indicate this area well outside the actual range of the species in question if it is limited to only one end of the region.
  • The hierarchy is imperfect in a number of ways. This limits how readily it can combine and infer records from subregions into large regions. Some of this can be fixed and updated over time, but other parts may be very difficult to fix, or impossible to put into a strict hierarchy. For example, take the country of Panama. We can combine all of the subrecords of Panama under the country entry to indicate all of the species found in Panama. However, once we do that, we cannot readily also combine the coasts of Panama into the individual Atlantic or Pacific regions which have separate species assemblages. Under the hierarchical structure, we either have to keep the two coasts of Panama separate or we have to abandon the Atlantic and Pacific basins as part of the natural hierarchy (for now I’ve done the latter).
  • Most of the Google maps of individual point locations default to a higher zoom than one would prefer (essentially, the begin maximally zoomed). There’s an easier, imperfect solution to this and a tedious, better solution. I’m working on the latter, but it’ll be awhile before the default zoom will be fixed for all locations.

All of the point location data in the database are directly based on what has been reported in publications. There are other potential sources of location records that might be integrated at some point, including more formal museum specimen records such as those found in GBIF or more informal, citizen-science records such as those from iNaturalist (although I note that at least some of the latter records are included in the former). For now I’d prefer not to mix and match these with the data on this site, but in the long run it will be worthwhile to explore how to combine them.

I’ve been playing with these location data for a few years and the new pages offline for a few months. It seems time to make them generally available; if you find obvious problems or flaws, please let me know so we can endeavor to make them better.