species extinctions
Our world includes a huge number of different species all interlinked in a network of life. How many has never been counted, but the literature suggests approximately 9 to 10 million. We all enjoy the benefits of this rich diversity of which we are part, but our huge and growing population plus our industrial scale use of modern technologies have placed numerous species under such great stress that many species are now threatened by extinction.
It should be appreciated that often the problem is caused by good intentions spoiled by lack of foresight. To give some examples from my local neighbourhood, I can think of 4 areas of rare wild plants. The first has become a housing development, the second (even though within a wilderness park) was cleared for a walking path, the third was paved for public parking and the fourth in a graveyard was cleared and replaced by well manicured lawn. And these are just small scale examples. How often has our society encouraged clearing great swaths of virgin land to feed the hungry, to provide employment, or to generate wealth.
Human interference is impacting many of the world's species of flora & fauna, whether through deforestation, destruction of habitat, over fishing, water diversion, ocean acidification or climate change. Therefore it seems sensible that species extinctions are real and are occurring at a faster and faster rate. Also the consequences of extensive species extinctions are so severe it is essential that we ascertain the actual situation.
Certainly this problem has drawn the attention of the scientific community, and the International Union for Conservation of Nature (IUCN) has begun to inventory living species along with an evaluation for each species as to vulnerability of extinction. The IUCN's inventory, called the Red List is dynamically growing and regularly updated. This is a large on-going job. IUCN has expanded their list of species examined greatly over the past 2 decades, but still have examined only a small proportion of all living species. Also re-evaluation for all living species is too large a job for annual re-evaluation.
On examining IUCN's Red List summary data chronologically there is an obvious upward trend in numbers of species at risk of extinction, which is compatible with my previous model-based charts. Unfortunately we can not take this as proof of increased extinction because you are looking at an increasing trend within a fast increasing number of species examined -- the statistical requirement of independence is not met.
Further thoughts:
1. It seems to me that extremely rare unknown species are far less likely to be found before becoming extinct, than less rare unknown species. Thus the growing inventory likely greatly under estimates the actual situation.
2. Internet search reveals several scientists have published trend charts showing many thousands of species recently have gone extinct, many more each year. How are these charts ground truthed ?
It should be appreciated that often the problem is caused by good intentions spoiled by lack of foresight. To give some examples from my local neighbourhood, I can think of 4 areas of rare wild plants. The first has become a housing development, the second (even though within a wilderness park) was cleared for a walking path, the third was paved for public parking and the fourth in a graveyard was cleared and replaced by well manicured lawn. And these are just small scale examples. How often has our society encouraged clearing great swaths of virgin land to feed the hungry, to provide employment, or to generate wealth.
Human interference is impacting many of the world's species of flora & fauna, whether through deforestation, destruction of habitat, over fishing, water diversion, ocean acidification or climate change. Therefore it seems sensible that species extinctions are real and are occurring at a faster and faster rate. Also the consequences of extensive species extinctions are so severe it is essential that we ascertain the actual situation.
Certainly this problem has drawn the attention of the scientific community, and the International Union for Conservation of Nature (IUCN) has begun to inventory living species along with an evaluation for each species as to vulnerability of extinction. The IUCN's inventory, called the Red List is dynamically growing and regularly updated. This is a large on-going job. IUCN has expanded their list of species examined greatly over the past 2 decades, but still have examined only a small proportion of all living species. Also re-evaluation for all living species is too large a job for annual re-evaluation.
On examining IUCN's Red List summary data chronologically there is an obvious upward trend in numbers of species at risk of extinction, which is compatible with my previous model-based charts. Unfortunately we can not take this as proof of increased extinction because you are looking at an increasing trend within a fast increasing number of species examined -- the statistical requirement of independence is not met.
Further thoughts:
1. It seems to me that extremely rare unknown species are far less likely to be found before becoming extinct, than less rare unknown species. Thus the growing inventory likely greatly under estimates the actual situation.
2. Internet search reveals several scientists have published trend charts showing many thousands of species recently have gone extinct, many more each year. How are these charts ground truthed ?
Although the IUCN all species inventory is inappropriate for statistical analysis I thought that the best subsets might be sufficiently complete to allow statistical analysis. I arbitrarily set criteria that reliable data sets should exceed 500 known species, should have better than 95% equivalence in size between different years of inventory, plus close to 100% re-evaluation each year. The above table shows number of species for Mammals, for Birds, for Amphibians, and for Gymnosperm Plants, -- these 4 groups appear to have the most complete evaluations within the Red List. These 4 groups came closest to meeting these criteria.
My table tabulates first the counts of described species as summarized in the annual Red List reports, second the ratio of these values to the most recent (2019) expressed as % (to keep the table readable I just do every 4th year), and third is the % of group re-evaluated in the most recent report. These statistics show even these most complete groups still are being inventoried, the total count for each increasing year to year and therefore trend analysis is somewhat dubious.
The table additionally shows both the number of species in each group known to be extinct, plus IUCN's best estimate as to proportion of each group's species thought to be under threat of becoming extinct.
2020 update: It appears I was overly optimistic over last several years that these data sets were nearing completion. All 4 groups continue to show increasing numbers of described species. The anomalous 2018 count for amphibians now seems resolved, touch wood. All four groups are estimated to have significant % of species at risk of extinction. Only Birds were 100% re-evaluated last year. I deleted all my extinction related trend & forecast charts as not meeting statistical requirement of independence.