In a new blog, Graeme Buchanan describes some details of a new study from University of East Anglia and BirdLife International on the conservation impacts of revised species taxonomy
Species are generally used as the basic unit of conservation. Conservationists monitor species’ populations and ranges to assess the status of species. These statuses are often used to set conservation priorities, whether at the local, national, regional, or global level. However, the identification of species is not always straightforward. Think about the chiffchaff and willow warbler in the UK; they look similar but have different songs but were thought to be the same species. The great naturalist Gilbert White was correct when he suggested that they were in fact different species.
Biologists need to be able to identify species in a consistent and accurate way, yet taxonomy is complex. There is considerable discussion over what a species is, and in turn how many species there are. There is no simple hard and fast rule. BirdLife International recently undertook a comprehensive review of avian taxonomy and bird species across the globe. This was based on the application of objective scoring criteria often based on plumage characteristics and size measurements, as described by Tobias et al in 2010, and published genetic data where it existed to produce a global taxonomic checklist. Consequently, rather than being based on hours in the field in exotic location, this major review involved many hours by dedicated researchers in museums and the reading of many scientific papers in journals.
It resulted in the number of recognised species increasing by over 1000, or around 10%. Some previously recognised species were combined together (lumped) as they were insufficiently distinct to be considered a species, while others were split because they were sufficiently distinct based on the assessment criteria. In these cases, the previously recognised species can be considered the ‘parent’ species. A particularly good example of the review is illustrated by the species formerly recognised as the Red-bellied Pitta (Pitta erythrogaster) from South-East Asia. This species was split into twelve species, as shown below:
Figure from Handbook of Birds of the World, Lynx Edicions.
But what effect does such a major review have on conservation priorities? Are the newly recognised species at greater risk of extinction, do they inflate the average extinction risk, and is there a spatial shift in conservation priorities? These were the questions that formed the basis of a recently published study. Ashley Simkins led the study as part of his Masters’ degree at University of East Anglia, supervised by Richard Davies with additional supervision and support from Paul Donald at BirdLife International and RSPB. After Ash had done all the number-crunching he found that the species which were split were generally less threatened with extinction (based on the IUCN Red List category - the international standard in assessing extinction risk) than species with unchanged taxonomy. An obvious explanation for this is that the extinction risk of taxonomic splits could be underestimated due to knowledge about threats and population trends of the newly recognised species being poorer than was the case for their ‘parent’ species.
However, this seems unlikely to us as the information used in assigning species Red List category (e.g. range size, forest loss, and other threats) are known equally well the newly recognised and the unchanged species. Instead it is possible that the split species really were less threatened. Interestingly, species that were new to science (described for the first time in recent years) were more likely to be threatened that the other species examined. Indeed, the new to science species were so threatened that their inclusion was responsible for a slight increase in the overall level of threat categories for birds.
The next question to answer was whether there are hotspots where there were high numbers of newly recognised species, or if they were distributed evenly across the planet. Overlaying the range maps of species indicated that the split species were not in fact evenly distributed across the planet. Instead there were hotspots in the northern Andes, Himalaya and islands of south east Asia. All of these areas are already recognised for high levels of species richness. Consequently, even though the absolute number of newly recognised species was high, the relative number was lower in most cases.
This was not the case in the islands of south east Asia though which, while already being species rich, had a very high number of new species such that it had a high relative and absolute number of newly recognised species. Additionally, while there were not many newly recognised species in north Africa, the low species richness here meant that this area stood out in terms of relative increase. This is useful information as the adequacy of coverage of species ranges by protected areas has received a lot of conservation attention. Most of the previous studies onto this topic have found that most species ranges are inadequately covered by protected areas, leaving the species at potentially greater risk. Consequently, the final step in the analysis was to assess whether the newly recognised species were covered by protected areas.
The result was that the average percentage coverage of species’ ranges did not differ from the value of coverage before the revision. While there was no decrease, the level of coverage was still low, indicating that protected area coverage of species’ ranges was still inadequate. This is despite reported increases in the global coverage of protected areas. The areas with the highest number of newly recognised species, especially Eastern Amazonia (emerging hotspot of threatened richness), the Philippines, and Java, were also the areas with the lowest protected area coverage. On the map below the orange areas have high numbers of newly recognized globally threatened species but low protected area coverage while blue areas have high protected area coverage and low number of newly recognized globally threatened species. The white areas are where both are low and black areas where the number of newly recognised globally threatened speci8es and protected area coverage are both high.
Map from https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/acv.12545
There will always be changes in taxonomy: scientific knowledge will increase, and there will be future splits and lumps, and new species will be identified. However, understanding the importance of this major taxonomic review on conservation priorities was a necessary step in the conservation of new and existing species. Ash describes some more aspects of this study here.
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