Irrespective of the vegetation type, D. melanogaster was the most dominant. D. melanogaster is known to be primarily found in environments disturbed by man, in open areas, or in degraded and urbanized environments, which are characterized by a pronounced degree of environmental stress (Acurio, Rafael, & Dangles, 2010; Da Mata, McGeoch, & Tidon, 2008; Penariol & Madi-Ravazzi, 2013). This could be the reason why this species was observed to be the most dominant of the species collected. This finding is similar to that of (Guruprasad & Padmaja, 2016) who also reported the predominance of the Sophophora subgenus from different altitudes of Chamundi Hill, India and the report of (Mahato & Gupta, 2018) who recorded a high percentage of Drosophila melanogaster of the subgenus Sophophora and Zaprionus indianus of the subgenus Zaprionus at Hazaribag, India. The unknown species in this study could be a native species, which was not captured in the taxonomic keys that were used.
It was also observed that the total number of individuals collected decreased with across the vegetation type Northwards. The decrease in number collected could be as a result of the decrease in vegetation cover, which is a reflection of rain fall, temperature and anthropogenic activities. The decrease could also be as a result of recorded increase in temperature and decrease in relative humidity as one moves up North despite same time and hours of sampling. This finding further proves that temperature and amount of rainfall affects the survival and population growth of Drosophila species (Torres & Madi-Ravazzi, 2006) and vegetation cover also plays an important role in density of Drosophila (Raj & Krishna, 2015).
The value of Simpson diversity index (D), which measures the probability of two randomly selected individuals from a sample might belong to the same species; Shannon-Wiener index (H), which measures the value of species as a function of their frequency in the community; species Evenness (j), which mathematically quantifies how equal the community is; Berger-Parker index (1/d), which shows the relative abundance were calculated. Lower values of the Simpson index indicate higher diversity, and value of 1 indicates no diversity while for Shannon Wiener index, Evenness and Berger Parker index, higher values indicate higher frequency, evenness and relative abundance respectively. The lower value of Simpson index observed in Southern Guinea savanna indicates that this vegetation zone is more diverse in Drosophila species composition, which could be due to the higher the diversity of flowering plant composition in this zone. This finding is similar to the report of Raj and Krishna (2015), who reported a higher diversity of Drosophila species along the lake region of the Karapuzha dam, India. The authors attributed it to the rich vegetation diversity near the lake.
The populations of humans inhabiting the zones had relationships with the number of caught flies, species diversity and annual temperature. The significant positive correlation between the human population and species diversity indicated that higher the higher the number of humans inhabiting an area, the higher will be the diversity of human commensal fruit flies in that area. Annual temperature however, had a negative relationship with all other parameter. This suggests that the higher the temperature, the lower the number of humans capable of inhabiting that area, the lower the number of fruit flies and the lower the species diversity. This goes further to prove the significant effect of temperature in the biology of the commensal fruit flies.