As you drive your new car out of the showroom, its value drops dramatically, and then keeps on dropping. It’s not quite as bad with the Virtual Museum. But, from the time it is uploaded, the “value” of every record does slowly decrease. A record in the Virtual Museum has three components: species, place and date. The record is evidence that a particular species was recorded at the place on the date. But, as that date recedes into the past, the record becomes less and less valuable as evidence that the species STILL occurs at the site. The record needs to be “refreshed”.
This blog aims to answer two questions. (1) How do I find when a species was last recorded at a place? (2) What is the rate at which a record loses value through time, and how often does it need to be “refreshed”?
We first need to define what we mean by a “place”. For Virtual Museum purposes this is a “quarter degree grid cell” (QDGC). These are almost exactly square on the equator, about 27 km north to south and 27 km east to west. At the northern and southern limits of Africa, about 35°N and 35°S, a QDGC is still 27 km north-south, but has shrunk to 23 km east-west. Not quite square, which is why we talk about “cells”. There is nothing magic about the choice of the QDGC as “place”. But this unit of area has long been used in biodiversity mapping in Africa, especially southern Africa. There are about 2,000 QDGCs in South Africa, and about 50,000 in Africa as a whole. If you define the “place” as some smaller unit, then you have to worry about refreshing records in an even bigger number of places. The QDGC represents a convenient trade-off between a fine grid and a manageable number of grid cells.
So the first question boils down to: “How do I find when a species was last recorded in a quarter degree grid cell?” The blog Quarter-degree-grid cells made simple will help you find the six-character code for grid cells south of the equator in Africa. The trick described there is to google the name of the place and ask for the coordinates (eg search for “Kuruman coordinates”, to try to find coordinates in the format of decimal degrees (Kuruman is 27.450°S 23.433°E) and then follow the instructions in the blog to find the code for the QDGC (2723AD)).
To get a list of the scorpions of Kuruman, the incantation is
http://vmus.adu.org.za/vm_locus_map.php?vm=scorpionmap&locus=2723AD
and you will find that (at the time of writing this blog) one species is listed, Pseudolychas ochraceus, photographed on 8 November 2018 (see http://vmus.adu.org.za/?vm=ScorpionMAP-3505).
But the focus of this blog will be on QDGC 2528CA, which covers central Pretoria, and the area northwards just west of the N1 (“Pretoria North”). It is an area characterized by rapid and relatively recent urban sprawl:
This map is available at
http://vmus.adu.org.za/vm_locus_map.php?vm=reptilemap&locus=2528CA
The map is the same no matter what you put for “vm=” in the incantation. This section of this blog is going to focus on the reptiles for this grid cell, so I chose vm=reptilemap.
Below the map is a list of the 78 species of reptile recorded here. The top 14 lines look like this:
The columns are self-explanatory. For the purpose of this blog, only one is important: “Last recorded”. This gives the date of the newest record of the species in the grid cell. The dates, quite frankly, are alarming! In row 8, the last record of Boomslang was in 1990. That is three decades ago. Does this snake still occur here? It almost certainly does, in spite of the pressures of development. But it still needs to be formally “refreshed” and confirmed by the submission of a new photographic record.
In this list of 14 species, the oldest date in the “last recorded” column is for the Dusky Worm Lizard. There are two records of this reptile, the most “recent” from 1911. This highlights the fact that the ReptileMAP database includes all the museum specimen data, going back to the year dot, assembled for the SARCA project. These old museum records are really valuable in pointing out what species we should be on the lookout for now.
The “youngest” record is for the Southern Tree Agama, last “refreshed” on 10 February 2016 (curated at http://vmus.adu.org.za/?vm=ReptileMAP-156645). There are 18 records of this species in this QDGC; you can see them by clicking on “Records” at the end of the line when you have this “live” on your screen (it won’t work on this screenshot).
Here are the last eight species on the list of 78 for QDGC 2528CA, Pretoria North:
It tells us that Puff Adder was last refreshed on 10 September 2018, less than a year ago. This is the most recent of 59 records, and can be found at http://vmus.adu.org.za/?vm=ReptileMAP-167360.
The bottom row is key. It tells us that there are a total of 1,271 reptile records for this QDGC. That is a lot of records. Then come two dates. The top date, with the single asterisk, is the median of the 78 “Last recorded” dates. So half the species were last seen before 14 December 1988, and half the species after that date. 1988 is a long time ago. There is a massive need to refresh the reptiles in this QDGC.
How do some of the other sections of the Virtual Museum compare on this criterion? To get the dragonflies and damselflies from OdonataMAP, the incantation used above changes to
http://vmus.adu.org.za/vm_locus_map.php?vm=odonatamap&locus=2528CA
The map is the same as the map above, but the species list looks like this:
There are only 10 species. The median date of the most recent records is 4 February 2017, which is excellent. The Little Wisp has a “Last recorded” date in 1999. This is a specimen record: http://vmus.adu.org.za/?vm=OdonataMAP-205285 – it has no photograph. It is a candidate to be “refreshed”. (The lower date, with two asterisks, 22 November 2016, is the median date for all 16 records.)
Here is the LepiMAP incantation:
http://vmus.adu.org.za/vm_locus_map.php?vm=lepimap&locus=2528CA
It shows that there are 2,390 records of butterflies and moths for the QDGC 2528CA, and that 178 species have been recorded here. That is awesome. But the median date for the “Last recorded” column is 8 January 2009. That is a whole decade ago. To keep this information up-to-date, there are lots of opportunities here for species to be refreshed!
For BirdPix, the incantation
http://vmus.adu.org.za/vm_locus_map.php?vm=birdpix&locus=2528CA
shows that there are 118 records of 58 species, and that the median date of “Last recorded” is 4 September 2013. That is six years ago. There is a general need even here for refreshment. Please explore these ideas for the QDGCs and species groups that interest you. The pattern of the incantation to the website always has this format:
http://vmus.adu.org.za/vm_locus_map.php?vm=lepimap&locus=2528CA
You need to change lepimap to the section that interests you, the 2528CA to the quarter degree grid cell which you want to explore.
The recommended fieldwork strategy in the QDGC is to have a target list of “long-in-the-tooth” species that you want to refresh, but to grab every opportunity that comes your way. You can pre-empt the need to refresh species by keeping the entire data base “young”.
It would be fantastic to be able to produce “up-to-date” distribution maps for species using data from, say, the most recent three years. Here is an amazingly encouraging pair of maps:
The top map shows the distribution of the Common Dotted Border, using 2,483 records since 1 January 1980. It includes historical data from museums and private collections assembled during the SABCA project. In QDGCs with only historical data, the shading is grey. If there is photographic Virtual Museum data, the shading is green. The bottom map is based on 555 Virtual Museum records submitted in three-and-bit years since 1 January 2016. The lower map is inevitably sparser, but it is identical in overall pattern. This is a remarkable achievement by the citizen scientists of Team LepiMAP!
These two maps illustrate the value of keeping the database refreshed!
(The inset illustration of this butterfly is one of the most recent submissions of a Common Dotted Border. The photograph was taken on 29 June 2019 by Neil Thomson in the Waterberg, Namibia – see http://vmus.adu.org.za/?vm=LepiMAP-688689. It is one of three records of the species from QDGC 2017AD, and is a bit to the north of the two Namibian records shown on the maps.)
Now we need to tackle the second question. How quickly does a record lose value? It would need a workshop of biodiversity experts to provide a good answer, but here is a first stab at this. Suppose a record has value 100% at the time when it is made. The “value” is the strength of the evidence that the species occurs at this date and place. After three years the value might be 80%. After five years, the value might drop to 50%, after 10 years to 10% and after 20 years, the record might have no value at all. In other words, the fact that a species was recorded in this grid cell 20 years ago is useless as evidence that I can still expect it to persist there. These suggestions can be turned into a graph, with the gaps between the values above joined by straight lines:
Not everyone would agree with this precise curve, but the general shape is likely to be right. In an era with unprecedented rates of development and climate change, records of biodiversity need to be “refreshed” at regular intervals to provide ongoing evidence of the persistence of a species at a locality. For the Virtual Museum, we would love records to be refreshed before three years have elapsed. This would enable us to generate up-to-date distribution maps, such as the one above for Common Dotted Border.
The Virtual Museum is open for refreshments.
