Tettigoniidae, Krauss, 1902

Massa, Bruno, 2021, Orthoptera Tettigoniidae as indicators of biodiversity hotspots in the Guinean Forests of Central and West Tropical Africa, Zootaxa 4974 (3), pp. 401-458 : 445-455

Tettigoniidae as indicators of biodiversity hotspots

Probably, while in the northern emisphere, the biodiversity crisis and the decline of insects appear to be due to climate change and to use of pesticides in agriculture, in the tropical forests of Africa, the decline of insects may depend mainly on the forest destruction. Sánchez-Bayo & Wyckhuys (2019), consulting 73 papers that deal with the decline of insects, have observed a sharp decline that can lead to the extinction of 40% of insects in the world in the next few decades. Most of studies used by them are located in the North Europe and North America, only single papers concern tropical areas. In particular, in terrestrial ecosystems butterflies (Lepidoptera), bees and bumblebees ( Hymenoptera ) and coprophagous beetles ( Coleoptera Scarabaeidae ) were the most vulnerable species, while the major groups of aquatic insects (Odonata, Trichoptera and Ephemeroptera) have already lost a considerable amount of species. Only a small number of species are increasing; they are arthropods with a wide ecological niche and very adaptable, generalists that live in many ecosystems, adapting to different ecological niches.

Guinean forest of West Africa represent one of the world areas containing the highest number of endemic species. Table 1 lists all the species of Tettigoniidae of the subfamilies Pseudophyllinae , Conocephalinae , Hexacentrinae , Phaneropterinae , Mecopodinae and Hetrodinae that have been recorded in the concerned African areas. The total number of Tettigoniidae of the subfamilies here considered amounts to 332 in the area of Guinean forests plus Central African Republic and Gabon; 242 of them live in the Cameroon-Nigeria subregion plus Central African Republic and Gabon, 216 in the subregion of Upper Guinea. In the Upper Guinean subregion 87 (40.3%) species resulted to be endemic, while in the Cameroon-Nigeria plus Central African Republic and Gabon 87 (35.9%) species are endemic ( Table 1 ); in both cases the occurrence of endemic taxa resulted higher than in plants and vertebrata (only except for amphibians), which, following Mittermeier et al. (2011) are: plants 20%, mammals 14.9%, birds 9.4%, reptiles 25.2%, amphibians 38.4%, freshwater fishes 27.9%. Out of 332 species, 122 (36.7%) have a wide distribution, covering West and Central Africa, and 32 (9.6%) species living in the Cameroon-Nigeria subregion, but not in the Upper Guinean subregion, are also distributed in other areas of central or east Africa, mainly in the Democratic Republic of Congo.

However, Tettigoniidae living in Tropical Africa have the highest richness in the central-eastern and southern countries; for example some tribes are absent in the Guinean forests [the tribe Agraeciini Redtenbacher, 1891 of the subfamily Conocephalinae is present with only one species, Anthracopsis gigliotosi Karny, 1907 ; the tribe Eugastrini Karsch, 1887 of the subfamily Hetrodinae has only one representative, Spalacomimus liberianus (La Baume, 1911) ] and some genera of Phaneropterinae , represented by many species, are only restricted to the eastern and southern Africa. The only exception seems to be that of the subfamily Pseudophyllinae , which, following Orthoptera Species File online ( Cigliano et al. 2021), in tropical Africa consists of 118 species (subspecies are here excluded), 71 (60.2%) of them only present in Central-West tropical Africa. However, from the biogeographical point of view, in tropical Africa an east-west species impoverishment occurs, with the lowest values of species richness just in the isolated West Guinean forests, but also a high percentage of endemism occurrence in West forests.

The number of Tettigoniidae species in single hotspots resulted very high, also compared with similar studies (cf. Table 1 ): Mt. Tonkoui ( Côte d’Ivoire): 81 (present study); Taï National Park ( Côte d’Ivoire): 88 (present study); Dzanga-Ndoki National Park ( Central African Republic): 134 (Massa et al. 2020, present study); Miombo Woodlands ( Tanzania): 56 ( Hemp & Heller 2019); Gorongosa Park ( Mozambique): 55 ( Naskrecki & Guta 2019). This is the probable result of intense researches carried out with the aid of the light trap.

Interestingly, putting the known species in four chronological categories of description date (before 1900, between 1901 and 1950, between 1951 and 2000, 2001-today) we may have an objective information on the fact that a high percentage of species (19.9%) has been discovered only in the present millennium ( Fig. 45 ). Thus, very likely the number of species will grow in the next years if further entomological surveys are carried out. Naskrecki (2008) pointed out that some tropical African Orthoptera are known only from the type material and some of them probably became extinct; further, the speed with which forest habitats change suggests that many species will become extinct before they are even discovered. Extinction is the gravest consequence of the biodiversity crisis, since it is irreversible, and generally it is preceded by the rarity. We may presume that the extinction rate among the still unknown species is higher than that of the known species, since they are mostly rare species, and generally rarity is synonymous with vulnerability. Very likely species recently described on single specimens are already threatened or in verge of extinction.

Following Reid & Miller (1989), biodiversity conservation is the management of human interactions with the variety of living forms and ecosystems, maximizing the benefits and maintaining their potential, in order to meet the needs and aspirations of future generations. However, this is possible when human populations live normally without risking their lives every day for war and disease. According to Turner et al. (2010) desperate human populations are driven toward further environmental degradation, and the forest decline is likely to be accelerated during the ongoing SARS-CoV pandemic in 2020-2021; further the Guinean area of Africa is known as one of the areas with the highest infant mortality due to malaria. The Gross Domestic Product is the single indicator considered by developed societies, the index of the “well-being” of a country. The path of continuous population growth has led us to the current frightening environmental and social situation which has caused an incredible devastation of terrestrial and marine ecosystems, the alteration of fundamental biogeochemical cycles, the dramatic loss of biodiversity, climate change and a profound social inequality, to name just some of the most evident and widely documented phenomena.

Human activities have elevated the rate of species extinctions to a thousand or more times the natural rate ( Pimm et al. 1995). The forest degradation makes fauna extremely vulnerable. In tropical Africa deforestation is the major threat to animal and plant species; plantation agriculture has been very significant in replacing forest in Côte d’Ivoire, parts of Ghana, southern Nigeria, western Cameroon and Bioko (Mittelmeier et al. 2011) and of course it is very difficult to establish how many species this deforestation has negatively involved. The breadth of the concept of biodiversity reflects the interrelationships between genes, species and ecosystems. Since genes are components of species and species of ecosystems, the alteration of the structure at each level of this hierarchy can modify the others.

Figures

FIG. 45. Number of species of Tettigoniidae of the subfamilies Pseudophyllinae, Conocephalinae, Hexacentrinae, Phaneropterinae, Mecopodinae and Hetrodinae of central-west tropical Africa, described before 1900, between 1901 and 1950, between 1951 and 2000, and between 2001 and today.