Sunday, 23 February 2020

Populations of small Carnivores are becoming homoginised in the Niger Delta.

Carnivores are indicative of ecosystem health and integrity, and can potentially affect food web and community structure of lower trophic levels. Several studies of sympatric African Carnivore species have demonstrated that ecological separation is primarily related to dietary differences. As specialisation and resource selectivity is generally stronger in small carnivores than large ones, they may serve as useful indicator species of the state of an ecosystem. Thus, understanding the changes taking place in the assemblage and abundance of carnivores may allow the determination of the state of conservation of a particular habitat.

In a paper published in the African Journal of Ecology on November 2019, Glorious Onuegbu and Godfrey Akani of the Department of Animal & Environmental Biology at Rivers State University of Science and Technology, Luca Luiselli, also of the Department of Animal & Environmental Biology at Rivers State University of Science and Technology, and of the Institute for Development, Ecology, Conservation and Cooperation, and the Department of Zoology at the University of Lomé, Fabio Petrozzi of Ecologia Applicata Italia, Daniele Dendi also of the Department of Animal & Environmental Biology at Rivers State University of Science and Technology, the Institute for Development, Ecology, Conservation and Cooperation, and the Department of Zoology at the University of Lomé, John Fa of the Division of Biology and Conservation Ecology at Manchester Metropolitan University, and the Center for International Forestry Research, and Adaobi Ugbomeh and Ibiso Georgewill, again of the Department of Animal & Environmental Biology at Rivers State University of Science and Technology, describe the results of a study of small Carnivore diversity in the Niger Delta based upon animals being sold in bushmeat markets.

In the Niger Delta, members of four small carnivore families: Mustelidae (Weasels, Badgers, Otters, etc.) of which ther are two species, Viverridae (Civets and Genets), also two species, Nandiniidae (African Palm Civits), one species, and Herpestidae (Mongooses), three species. All are found in forest and forest‐derived habitats in the region. However, knowledge of their biology is still poorly understood primarily because of their secretive and nocturnal habits.

Small Carnivores are regularly consumed as bushmeat and sold in markets in West and Central Africa. Using records of species and individuals of small Carnivores sold in bushmeat markets, it is possible not just to uncover noteworthy aspects of their biology, but also determine whether hunting may be causing biotic homogenisation within the catchment supplying the markets. Onuegbu et al. use data from three markets in the surroundings of the city of Port Harcourt in Rivers State (Niger Delta, Nigeria) to evaluate whether a biotic homogenisation process on taxonomic, species richness diversity characteristics and perhaps substitution of species has occurred. They also compare their results with data from other markets in the same area and from other sites in southern Nigeria and neighbouring Benin Republic.

The study was carried out in the Rivers State, Nigeria. Rivers State has over 5 million inhabitants and a density of more than 630 persons/km². During the last 30 years, agricultural and industrial expansion throughout the region has caused severe fragmentation of the existing forests. The study area's climate is characterised by a long rainy season from April through to the end of September.

Map of Rivers State in southern Nigeria, showing the three sample stations. Onuegbu et al. (2019).

Onuegbu et al. monitored three bushmeat markets: Omagwa, Oyigbo and Mbiama. These study stations were chosen because they represent localities in which hunting, alongside traditional agriculture, provide important economic revenues for the resident rural population. These localities differ in terms of vegetation cover and human population density; the latter being significantly higher in Mbiama than in the other localities. Hunters living in bushland and forest patches, often more than 7 km away from the market, regularly supply a variety of animal carcasses for their sale.

In this study, Onuegbu et al. made the implicit assumption that small Carnivore abundance in bushmeat markets can be used as a proxy of small Carnivore abundance in the field. They surveyed bushmeat markets during the dry season (December 2017–March 2018) and in the wet season (May 2018–August 2018). Sampling effort was identical in the three market sites; they visited each market three times per week during 8 months (48 daily visits in each season). During each sampling day, Onuegbu et al. counted all animal carcasses on sale, including small Carnivores. All markets were visited between 7.00 am and 11.00 am, in order to be able to count and inspect carcasses as hunters dropped them with the bushmeat traders, and before traders dressed these (burning off the hairs/fur and butchering) making it more difficult to identify the species.

A total of 1206 carcasses of small Carnivores were recorded in the three study markets. The largest number (699) was observed at the Omagwa market, followed by Oyigbo (416) and Mbiama (91).

Onuegbu et al. recorded four different taxa, all Least Concern in the International Union for the Conservation of Nature's Red List of Threatened Species: the Flat‐headed Kusimanse, Cṛossarchus platycephalus, a member of the Herpestidae (1176), African Civet, Civettictis civetta (21), African Palm Civet, Nandinia binotata (6) and Genets, Genetta spp., possibly Genetta maculata (3). In all three markets, Cṛossarchus platycephalus accounted for over 97% of the total number of observed individuals, and the relative frequency of occurrence of the various species did not vary significantly among study areas.

The four observed small Carnivores: (a) Civettictis civetta (from Omagwa), (b) Genetta sp. (from Oyigbo), (c) Crossarchus platycephalus (from Omagwa) and (d) Nandinia binotata (from Omagwa). Onuegbo et al. (2019).

The number of carcasses was higher in the wet season than in the dry season, independently of the market and species. The increase in the number of traded carcasses from the dry months to the wet months was smooth and regular in the Oyigbo market, whereas numbers varied significantly in the other two markets. The number of carcasses was significantly positively correlated with monthly rainfall in all study markets.

Sex ratios were significantly skewed towards females in both Cṛossarchus platycephalus and Civettictis civetta, but sample sizes in Nandinia binotata and Genetta spp. were to small to assess. For Cṛossarchus platycephalus, the same female biased sex ratio was observed during both the dry and the wet seasons.

The basic premise of Onuegbu et al.'s study is that because hunters do not specifically target small Carnivores, the numbers appearing in the markets reflect their relative abundance in the market catchment areas. Using this data, they conclude that there is evidence that biotic homogenisation and species substitution is occurring in the eastern Niger Delta region.

Ongoing homogenisation process has already been shown for Snakes and Chelonians. Similarly, Onuegbu et al. demonstrate that there is evidence of impoverishment of the small Carnivore community in the Rivers State agro‐forestry systems from comparisons between their study area and more heavily forested areas in the central Niger Delta and in Benin. They show that in their study area, only four species were found compared with 5–7 taxa in the central Niger Delta and Benin. Notably, in the three studied markets, the smallest species (i.e., Cṛossarchus platycephalus) accounted for more than 95% of all individuals observed. This species is also the best adapted to forest‐derived grasslands as it feeds essentially on Rodents, which become an abundant food resource in such altered habitats. Thus, Onuegbu et al.'s data suggest a process of functional similarity of biotas over time, associated with the establishment of species that have similar 'roles' in the ecosystem and with the loss of those possessing unique functional 'roles'.

Comparison of our results with data obtained for the same area about a decade ago shows that although only three species were recorded then, their relative abundances were more equilibrated than in the present study. There were also significant differences in the frequency of occurrence of the various species, particularly the dramatic increase in the relative abundance of Cṛossarchus platycephalus; in 2009, the species was not observed. This is a clear signal of an ongoing species substitution process, which mirrors data on Cobras from the same area, where Naja nigricollis (a mainly savannah species) was clearly substituting Naja melanoleuca (a mainly forest species) in almost every suitable habitat in the region. Analogous to the patterns observed for Cobras, Cṛossarchus platycephalus, a small group‐living species typical in deforested and heavily altered landscapes, is taking over This species is nowadays very common in the deforested grasslands and plantations of the Port Harcourt region, possibly due to the greater abundance of rodents (their main food type) in these habitats.

Onuegbu et al.'s study also confirmed the occurrence of Nandinia binotata in the surroundings of Port Harcourt, though this species was not considered present in the Niger Delta in 2007. This species is also one of the most intensively traded Carnivore species in African forests.

In Onuegbu et al.'s study, they show there is clear seasonal pattern in the number of carcasses of Cṛossarchus platycephalus that peaked during the rainy months. Although for the other three species the sample was too small for any statistical analysis, in the Niger Delta, Nandinia binotata was previously recorded slightly more often during the wet season with no significant inter‐seasonal difference. In Gabon, Nandinia binotata females gave birth to young from June to January each year (that is in both dry and wet seasons), which is apparently linked to fruiting seasonality as this species is mainly frugivorous.

Finally, in two of the species recorded (Cṛossarchus platycephalus and Civettictis civetta) the sex ratio of the traded individuals was significantly female‐skewed. Data on sex ratios of African small carnivores are very scanty, and thus, comparisons are problematic. Female‐skewed sex ratio was also observed in Nandinia binotata in Gabon. but sex ratio was even in Nigerian Nandinia binotata and Civettictis civetta, or males were significantly more numerous than females in other small Carnivore species of bushmeat markets in Nigeria, including Genetta sp..

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1 comment:

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