Chapter 5 - Biodiversity knowledge as of 2009
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The Ants of Africa Chapter 5 - Biodiversity knowledge as of 2009 |
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Summary Following on from my earlier thoughts on biodiversity based on information on West African ants, this page pulls together much wider findings on the ants of the whole of sub-Saharan Africa. It also incorporates records from the small series of recent revisions of genera, most having only a few member species, and sources such as www.Antweb.com. |
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Introduction Endangered species The IUCN Red List of Endangered Species includes a few ants from sub-Saharan Africa [http://www.iucnredlist.org/static/introduction - accessed 25 August 2009]. These, Anoplolepis nuptialis (Santschi, 1917), Cardiocondyla zoserka Bolton, 1982, and Pheidole neokohli (Wasmann, 1915), are listed as vulnerable. Whilst it is true there are few records of these is that any reason for them to be regarded as "vulnerable". The queen of An. nuptialis was first described by Prins (1982) and he gave details of seven separate findings. The other two, both inquilines or social parasites, each have been recorded only once. C. zoserka was suggested as perhaps dependent on Cardiocondyla shuckardi but that, however, was described as the commonest and most widespread endemic species (of Cardiocondyla) in the Afrotropical Region (Bolton, 1982). Ph. neokohli was found as a parasite of Pheidole melancholica but again the host is quite widely recorded and apparently abundant. Species Richness Robertson (2002) put forward estimates of the number of ant species likely to be found in Africa. His summary had: "Forty-three of the 82 Afrotropical ant genera (52%) have been revised to modern standards resulting in a 50% increase in number of species. There are currently 1705 species of ants known from the Afrotropical region, a figure that could increase to over 2136 species if all ant genera receive a modern revision. To incorporate all undescribed species, total Afrotropical ant species richness was calculated by extrapolating from data on the proportion of undescribed species collected at Mkomazi Game Reserve in Tanzania and the Cape of Good Hope section of the Cape Peninsula National Park in South Africa. On this basis there are an estimated 3105 species of ants in the Afrotropical region, with 45% undescribed or currently occupying an infraspecific taxonomic rank. This extrapolation assumes that the average range sizes of described and undescribed species are similar, which in reality is unlikely because widely distributed species are more likely to have been collected and described. I present a method that distinguishes between widespread and localised species to correct for this problem, which extrapolates 4093 Afrotropical ants species, with 58% of species estimated to be undescribed or currently recognised only at infraspecific rank. It would take a highly productive systematist at least 21 years to complete revisions of the unrevised ant genera. A strategy is presented for improving specimen collection and taxonomy of Afrotropical ants". Naming of ants The pentanomial system, of genus, subgenus, species, subspecies (or stirps) and variety, was described by Ward (2007) as "a peculiar and unwieldy" nomenclature. If peculiar in this context means unique, Ward was wrong. The mosquito systematists also used such a system although in, for instance, the bench mark work of J.N. Belkin, Mosquitoes of the South Pacific (Belkin, 1962), it was reduced to a trinomial, retaining the subgenus level. I find the subgenus is a useful separation when dealing with genera containing many member species. Similarly, Longino (2003a) appears to regard the subgenus as a reasonable nomenclatorial level. Robertson (2000) wrote of "poorly applied quadrinomials ... that do not correspond with evolutionary relationships". How one could deduce much, if anything, about evolutionary relationships from simple descriptive taxonomy is not clear. On a historical note, in 1853, Mayr, in a pioneering paper on "Einige neue Ameisen", provided some of the first taxonomic descriptions that were accurate and sufficient enough for the reader to feel assured he could identify the ant in question (Mayr, 1853). Two years later, the now Med. Dr. Gustav L. Mayr wrote the "Formicina austriaca" (Mayr, 1855). This set the benchmark for all ant taxonomy, including full taxonomic definitions and, for the first time, dichotomous keys. The only thing missing, apart from five examples of wing structure, were drawings. In the "Die Ameisen des baltischen Bernsteins", there are over 100 accurate, high quality drawings (Mayr, 1868). Mayr's last ant taxonomy paper was published in 1907. All this from a man who was a schoolmaster or principal and was never employed in the Vienna: Museum. In the same era, Frederick Smith at the British Museum:was writing minimalist descriptions in the style unchanged since Fabricius in 1787. Now we come to Auguste Forel, who as he recorded in 1922, began publishing in 1869. In 1920, he wrote in his 231st paper how the glaucoma prevented him from continuing to describe ants. His first major ant work was his 1874, "Les Fourmis de la Suisse", in which he expressed his admiration for the works of Mayr and related how he adopted Mayr's methods for the analytical tables. In a curious move, Forel noted how it was contrary to reproach Mayr for "la trop grande multiplication des genres". In his short biography of Forel's hyperproductive protégé, Felix Santschi, Wehner noted how all eminent myrmecologists before Forel (1874) had strictly used binomials (Wehner, 1990). Forel introduced the deliberate splitting of species into subspecies and variations, although he used the term "race" and Santschi used "stirps" for these lower levels. Forel himself said that he used "races" for species that were badly determined or showed transitions between them, one could also call them "sub-species". Seemingly he felt this would be helpful for dealing with intermediate or aberrant forms. The difficulties this system imposed were summed up by André (1881): "with the ants the separation of species presents great difficulties, and nothing is harder than to decide where the species ends and the variety commences". This muddled and muddling thinking prevailed for the next 80 years. Its legacy still makes it difficult for any one trying to sort out field collections and to evaluate variations in behaviour, etc. Many of Forel's taxonomic descriptions were quite brief, often based on comparisons with other species (thus assuming the reader had access to the earlier publications) and very rarely had illustrations. He did not produce any comparative works or keys or, at least , not for African ants. It seems ironic that the adherents of the strict binomial have resorted to use of the term "species-group". Ward (2007) cited Wilson (1955) as a leader in the modern taxonomy but the latter retained the subgenus. Wilson himself criticised separation of specimens into species on the basis of "a single character of pilosity" and referred to the statement in the joint paper of Wilson & Brown (1953), "that the species is only completely objective in terms of local faunas, i.e. where discrete populations co-exist at the same place at the same time". Brown (1958g) used subgenera as did Wilson & Taylor (1967). Suddenly, it appears, Brown (1973a) chose to abandon subgenera but create species-groups. At one point he wrote "the genus [Crematogaster] has been split into subgenera, but these are apparently only species groups, and some of them weak at that". Although widely cited, especially the appendix, as an authority for synonymization of genera and subgenera, Brown's paper is totally lacking in true taxonomy, presenting his opinion at that time. Brown wrote of "a good many more 'projected synonymies' that have never been proposed anywhere formally in print". A little later, he argued against the recognition of Stenomyrmex as a formal subgenus of Anochetus, referring to it as "(no) more than an arbitrarily-defined species group" (Brown, 1978). Neither Brown or Wilson contributed further to the matter but a consequence seems to be the use of notes such as a very variable species to encompass what had been viewed as subspecies. For example some Cataulacus species by Bolton (1974a), who later had to disentangle some of his synonymy (Bolton, 1982). Bolton commented often on the proliferation of names in his seminal revisionary works, and, in his identification guide to ant genera, wrote of "a welter of unnecessary names based on uncritical splitting, unrecognized identity, and mis-interpretation of generic limits" (Bolton, 1994). He regarded the amassing of names in the nineteenth and early twentieth centuries, seemingly as "an end in itself, with authors apparently racing each other to produce as many self-attributed names as possible". Roberston (2000) referred to the problem of revisions based on collections with limited geographic coverage that omit species and population variation. |
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Sources of data The distribution records collated here have been gleaned from 461 papers of an essentially taxonomic nature, the earliest being published in 1767 and the most recent in 2008. Additional distribution data came from 189 papers dealing with either the biology/ecology of species or providing the results of surveys. Unfortunately since about 1950, e.g. Weber (1943c and 1952a), very few perpetrators of surveys have followed up the reports with any novel taxonomic work. Moreover, in the 30 or so taxonomic revision papers published since 1970, even where the morphospecies collected in surveys have been among the specimens later recognised, in some cases as new species, it is rare to find any reference to the survey publications. For instance, Watt, Stork & Bolton (2002) on the diversity and abundance of ants in relation to forest disturbance and plantation establishment in southern Cameroon. Also, Fisher (2004) on diversity patterns of ants along an elevational gradient on Monts Doudou in southwestern Gabon. He reported a total of 310 species in 56 genera, noting that 195 species were unnamed). To some extent, however, there was a failure to identify species even though modern keys were available, e.g. 37 Tetramorium species. Over the past six years a number of people have sought my help in identifying ants, mostly from sub-Saharan Africa. I have endeavoured to identify all the specimens. This has been facilitated by the work of Donat Agosti and Norman F Johnson in creating the www.antbase.org on-line access to almost all ant papers ever published. With that access, somewhat surprisingly, separation of taxa has proved possible to a remarkable extent. As a first step it was necessary to construct dichotomous keys for the many genera with no keys or only limited keys from the first half of the twentieth century. Ward (2007) described the need to create "species pages" for all of the world's ants. Here on this website there are species pages for every one of the known taxa from sub-Saharan Africa. Without undertaking the herculean task of sighting all the type specimens, some of which may no longer exist, I cannot claim certainty of identification in every instance. The advent of inexpensive and simple to use digital cameras, however, has enabled me to produce diagnostic photomontages of each of the taxa I have examined, thus providing an on-line voucher collection. In that I continue my effort of 1976 in separating 201 species from Nigeria, almost all shown in accurate drawings (Taylor, 1976-80). Of those, 121 were first records for Nigeria. The specimens were deposited as a voucher collection with the British Museum of Natural History, with many duplicates left with the insect collection at the Cocoa Research Institute of Nigeria. Almost 100 of the taxa were designated by genus and code names. Some have since been identified in revisionary papers and I have endeavoured to recognise the remainder. Thus, I have compiled a webpage update to Taylor (1976-80). |
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Identification of ants collected in modern surveys and other findings Most of these findings are otherwise unpublished.
The Ghana specimens are held by Sky Stephens. The specimens from almost 1300 samples currently remain in my care but will be deposited in the Oxford University Museum of Natural History. |
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Analysis of findings As at August 2009, I recognise 1946 species (a small number
being as yet unnamed). A frequency score was derived for each species
by allocating values as follows: The scores were then entered in a standard Excel 2003 spreadsheet. The arrangement of countries is approximately in line with the ecological zones but, as will be seen in the analyses graphs, some parts, e.g. northern Angola and southern Sudan, have species in common with the Congo Basin forest. |
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General biodiversity Figure 1
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Arbitrary categorisation of species Score 40+ = 30 species; 30-39 = 40 species; 20-29 = 84 species; 10-19 = 236 species (ca. five countries); 7-9 = 206 species (ca. four countries); 5-6 = 234 species (ca. three countries); 3-4 = 420 species (ca. two countries); 1-2 = 687 (single records); 6 species are dubious for Africa. This shows ubiquity and revels nothing about numerical abundance in terms of individuals. An indication of the systematic range of occurrences can be gauged from Figure 2. |
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Figure 2: Graph of distribution scores for all sub-Saharan ant species(as at August 2009); horizontal axis arranged in alphabetical order of subfamilies and member species
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Most ubiquitous species The top 31 species and their recorded distribution are shown in Figure 3. Because of the Forelian scepticism of an apparently ever increasing numbers of species, for about 90 years from 1874 there was a confusing practice of denoting subspecies (or stirps) and even quadrinomial varieties (Forel, 1874; Arnold, 1962). This has made it impossible to be definite about the distribution of several of the commonest "species", among them "Camponotus maculatus", "Crematogaster castanea", "Crematogaster impressa", "Dorylus nigricans/burmeisteri", "Lepisiota capensis", "Oecophylla longinoda" and "Pheidole megacephala". Some spurious results arise from the use of apparently similar coding for denotation of unidentified species, e.g Genus species A. |
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Figure 3: Spreadsheet extract showing the recorded distribution of the top 31 species
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The analysis is distorted, however, by the simple fact that national boundaries bear no relation to ecological zones. The map below (Figure 13) illustrates the true situation [Source - http://www.lib.berkeley.edu/EART/maps/africa-veg.gif]. |
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Comparisons
As the graphs show the same data sorted according to different criteria, thus there are some species appearing in two graphs. There are no species in common between the two main Tanzania lists - the Mkomazi specimens all being arboreal (possibly a small number of those ascending from the ground) and in Graph 5, whereas all the Usambara species were collected by a terrestrial ecologist, Valery Grebennikov, with a main interest in Scarabaeidae, and in Graphs 1-4. |
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Figure 13: Africa vegetation
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Abundance versus ubiquity The vast majority of ant species have small to minute colonies. For such species almost nothing is known of the distribution of colonies. Driver ants Anomma have vast colonies but perhaps one colony per hectare (or even greater area) as the food needs for the wholly carnivorous colony must be vast. Acacia dominants of the eastern African tree savannah occupy almost everyone of the millions of trees. For instance, Crematogaster mimosae is known from only four countries and Cr. nigriventris from five, but the sheer numerical abundance of both has to be vast. On the wholly man made cocoa monoculture of the Cameroun west through to Sierra Leone perhaps as many as 35% of the trees are occupied by Oecophylla longinoda as a dominant. In the vast rain forests of the Congo Basin the canopy dominants may well be one of the Crematogaster (Atopogyne) species, which is also found on cocoa where there are large trees remaining within the cocoa farms. |
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Discussion To return to Robertson (2002) on the number of ant species likely to be found in Africa. He noted there are currently 1705 species of ants known from the Afrotropical region, a figure that could increase to over 2136 species if all ant genera receive a modern revision. To incorporate all undescribed species, total Afrotropical ant species richness was calculated by extrapolating from data on the proportion of undescribed species collected at Mkomazi Game Reserve in Tanzania and the Cape of Good Hope section of the Cape Peninsula National Park in South Africa. On this basis there are an estimated 3105 species of ants in the Afrotropical region, with 45% undescribed or currently occupying an infraspecific taxonomic rank. This extrapolation assumes that the average range sizes of described and undescribed species are similar, which in reality is unlikely because widely distributed species are more likely to have been collected and described. Robertson gave a method that distinguishes between widespread and localised species to correct for this problem, which extrapolates 4093 Afrotropical ant species, with 58% of species estimated to be undescribed or currently recognised only at infraspecific rank. My view is far more restrictive. I have 1300 samples in my collection comprising 565 species (all with photos original to this site). The collection contains what appear to be 35 new species (one new genus, one possible new genus); 125 species otherwise known solely from the original description; 54 species previously reported only twice; 45 species reported only two-three times previously; and, 339 common species. Most of the samples came from the quite intensive surveys reported above. The surveys, which between them utilised all the standard methods of sampling invertebrate fauna, produced 35 taxa that I feel may be new species and I consider another 33 taxa merit resurrection or elevation from synonymy or other lower status. I separated 70 species from the Ghana survey by Sky Stephens. The survey results suggest about 12.5% new species (about half previously categorised as of subordinate status). Earlier, I separated 201 species from Nigeria, 14 were named subsequent to my original publication and only 10 remain as possible new species. The Nigeria work of Bolton and myself yielded 11.9% new species. In total on this website I have a total of 100 species with new or revived status, those not from the survey coming from my perusal of all the original descriptions. That gives 5.1% of the grand total 1942 species. A large proportion of the species I have separated come from disentanglement of the subspecies and varieties of Dorylus species. Other revisions come in some quantity from battling with the Pheidole and Crematogaster, two major genera in all senses but apparently avoided by most modern taxonomists. Digital photography has made it much easier to compare specimens so, hopefully, this battle will progress further. The variance, I suggest, stems from Robertson having examined two rather isolated areas with a consequent higher level of endemicity than, possibly, anywhere else on the continent. The two Tanzania surveys I report, from the Mkomazi and Eastern Arc Mountains, yielded 14.3% and 12.1% new species respectively. Perhaps Robertson under appreciated the quantity and depth of the many collections made elsewhere by explorers and missionaries between about 1880 and 1940. For instance, the 565 species in samples sent to me contain 224 that have been reported no more than three times, i.e. almost 40%. Nearly one-quarter of the species were known only from the holotype collections. The vast majority of the species I identified as found for only the second time have come from the original type location country or from a neighbouring country, e.g from Tanzania known before from Kenya, from Gabon known before from Angola. Robertson cites the estimate by Watt et al. (1997) that 40% of the ants they captured in Mbalmayo Forest Reserve in southern Cameroun were undescribed. Considering that some named 300 species are known from Cameroon, to have such a large precentage as undescribed seems highly unlikely. Perusal of the component studies in the Mbalmayo Forest (Watt, Stork & Bolton, 2002) reveals many species listed by genus and code designation but, to me, that may reflect a lack of determination to match species to original descriptions. One genus since revised is Technomyrmex, by Bolton (2007). Five species were listed by code names from Mblamayo leaf litter. Of those four were recognised as alreday known and one was described as a new species. Even the last, Technomyrmex parviflavus, was already known, having been illustrated by me as Technomyrmex species T4 (Taylor, 1978: 57, also listed in Taylor, 1981; among publications never cited by Bolton). There is a factor not mentioned by Robertson that may underly his higher estimations of total species. Table 1 listed the Afrotropical ant genera that have modern revisions. He compared "Initial species", i.e. before the revision, and "Final species" to gain an "Increment coefficient". Apart from the Ocymyrmex ants, which almost all inhabit the historically almost uncollected southern African dry savannah and deserts, the significant increments in species numbers have been in genera of small to minute ants. Other than Leptogenys, the genera of larger ants gave few new species and their definition was counterbalanced by synonymization. Leptogenys generally appear to have a cryptic lifestyle and this may explain the relatively sudden recognition of several new species (Bolton, 1975a). In his Table 3, Robertson has a column headed Afrotropical species and listing the following: Total recorded species 1705. From revised genera, No. widespread species (distributed over three or more countries) 249 and No. localized species (recorded from only one or two countries) 594. Total species 843, with 70.5% being localized species In my breakdown of 1939 species, the division is localized 1107; in three or four countries 440 species; widespread 390 species; 57.2% being localized. The demarcation even then is somewhat misleading as, other than the top 31 species (Figure 3), there is no almost pan-African ubiquity. The next level is of regionally distributed species, but the total score per species is affected by the number of countries. For instance, the Sahel zone covers some five vast countries and the species score poorly compared with those from areas with several small to minute nations. Although many of the ecozones of the continent now have been subject to the activities of exhibitions historically, together with ecological or crop protection entomologists in modern times, there are lacunae. Most notable is the swathe of savannah running south through a vast area of central Tanzania and south through Zambia. |
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References specific to this page Fisher, B. L. 2004. Diversity patterns of ants (Hymenoptera: Formicidae) along an elevational gradient on Monts Doudou in southwestern Gabon. California Academy of Sciences Memoir, 28, 269-286. Robertson, H.G. 1999. Ants (Hymenoptera: Formicidae) of Mkomazi. Pp. 321-336 in M. Coe, N. McWilliam, G. Stone & M. J. Packer (eds) Mkomazi: the Ecology, Biodiversity and Conservation of a Tanzania Savanna. London: Royal Geographical Society. Robertson, H.G. 2002. Afrotropical Ants (Hymenoptera: Formicidae): Taxonomic Progress and Estimation of Species Richness. Journal of Hymenoptera Research, 9, 71-84 Ward, P.S. 2007. Edward O. Wilson and his contribution to ant systematics, pp 3-7. In Snelling, R.R., Fisher, B.L. & Ward, P.S. (eds). Advances in ant systematics (Hymenoptera: Formicidae): homage to E.O. Wilson - 50 years of contributions. Memoirs of the American Entomological Institute, 80. Watt, A.D., Stork, N.E. and Bolton, B. 2002. The diversity and abundance of ants in relation to forest disturbance and plantation establishment in southern Cameroon. Journal of Applied Ecology, 18, 39: 18-30. Wilson, E. O. and W. L. Brown. 1953. The subspecies concept and its taxonomic application. Systematic Zoology, 2, 97-111. |
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©2009, 2012 - Brian Taylor CBiol FSB FRES 11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K. |
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