I had a similar problem last year. Here is a report that I sent to Tony Iwane @tiwane, who kindly consulted an engineer to look into the problem. I really appreciate their efforts with this mystery. During our correspondence I learned that iNat uses an algorithm to estimate species totals, rather than using exact counts, presumably to reduce computing time. After an initial email exchange, I started tracking my species totals over time. Eventually, the issue stopped happening, and I haven’t noticed it happening since. I’m not sure whether iNat staff fixed the problem, or if for some reason it just stopped. Here is my report to them from last year, in case this helps.
The “Elastic” Algorithm Subtracts Species on the Explore Page Instead of Adding Them
@JohnDReynolds. 18 Sept 2024
Since 10 July 2024 I have added 17,120 observations but “lost” 351 species from the estimation.
The Explore URL I have been using is https://www.inaturalist.org/observations?view=observers.
With the following URL suggested by Tony Iwane… https://www.inaturalist.org/observations?hrank=species&lrank=subspecies&place_id=any&subview=map&user_id=johndreynolds&verifiable=any&view=species
…the number of species is going up while the total from the Explore page is declining.
Clearly, the “Elastic” estimator has been subtracting species instead of adding them.
The slope of the relationship is not quite 1:1. I have been losing about 0.8 species for every new species I add.
Does this happen to other people?
Yes. Since 5 July 2024 I have been occasionally tracking species totals from the Explore page of observers with a lot of observations. I noticed that @damontighe dropped steadily from 12,059 species on 5 July to 11,919 on 29 August despite adding 725 observations. Today (18 Sept 2024), the first time I looked since then, he has gone up for the first time since 5 July, to 12,108 after adding 254 observations.
Not due to taxonomic changes or IDs
Clearly, taxonomic changes (and IDs) cannot explain these declines, since the URL suggested by Tony shows my totals are indeed increasing. Note too that the problem only started on 10 July 2024, and community IDs usually add more species to my total than they remove.
This has happened previously, and been solved!
There is a Forum thread in which people noticed the species total on iNaturalist was decreasing steadily. A fix was reported.
https://forum.inaturalist.org/t/total-number-of-inat-species-is-decreasing/31811
It also happened to @cypselurus for his species totals. He told me it eventually stopped happening:
https://forum.inaturalist.org/t/observed-species-total-going-down-over-past-few-days/51143
The negative trend over 9 weeks lasts year suggests there is an issue with the way the cardinality aggregation is working. Maybe it was over-estimating, and started correcting itself, triggered by my addition of new species, leading to subtraction of species? I don’t know; I’m grasping.
Postscript: As noted at the start of this post, the above is what I wrote to Tony a year ago. I am no longer losing species from the reported total on the Explore / Observers page when I add species. But I noticed @dbeadle has lost about 150 species over the past 2 months. Again, kudos to the iNat team for looking into it, even though the cause remains a mystery, to me at least. I know how busy the iNat team are, and it’s amazing to me that they are able to keep up with so much growth on the site, while maintaining its speed. This may not be a very important bug, but the Explore / Observers page is kind of fun, so I’ll be curious to see if this leads anywhere.
John Reynolds