Data evaluation

Though data on primates, hornbills, food and non food trees were collected with precision and accuracy the following major constraints were noted during the surveys:

¾ Poor estimation of perpendicular distance.

¾ Hunting and trapping activities noted along the transect lines and gun shots during the survey period.

¾ Insufficient data for endangered primate species such as the preuss red colobus, the drill and the chimpanzee.

¾ Some surveys were not conducted due to the involvement of team members in various village events (wedding, death, traditional festivities, political meetings).

2.4.7 Data analysis 2.4.7.1 Data processing

Field data on primates, hornbills and vegetation (food and non food resources) were recorded on field forms designed for that purpose. Recorded data were cross-checked by the field supervisor and the project leader and entered into the computer on Excel Software, where they were again cross-checked. From Excel data bank, they were imported to other Software (Distance Sampling, EstimateS version 5.0.1, Statistica) for analysis. Field forms were kept for eventual verifications.

2.4.7.2 Vegetation

Differences in tree abundance and species richness between study sites were analysed using One-Way ANOVA and Tukey’s HSD test (Fowler & Cohen 1996). In all statistical tests, STATISTICA for windows was used (StatSoft, 2001). Species richness was observed using EstimateS 5 version 5.0.1 (Colwell, 1997) from the number of species observed in the pooled number of samples (Sobs). These methods of tree abundance and species richness analysis fit into this study, in the sense that density of small trees in logged forests is usually much higher

than unlogged forest predominated by large trees with fewer undergrowth. With reference to Kessler (2005), we compared the taxonomic and structural composition of tree families (family diversity) between logged and unlogged study sites. For each tree family, we calculated the number of individuals (NI) per hectare, the number of species(NS) per hectare, the basal area (BA) per hectare, the family relative density (FRd= % of NI of a family of the total NI), the family relative diversity (FRdi= % of the number of species of a family relative to the total species number), the family relative dominance (FRdo= % of the BA of a family of the total BA) and the family importance value (FIV= FRd+FRdi+FRdo). The structural composition was determined by comparing the distribution of tree diameter classes between sites. A two dimensional ordination of the species composition of the different transects was based on tree abundance data and was being carried out using correspondence analysis (StatSoft, 2001).

2.4.7.3 Primate and hornbill population densities

Primate and hornbill population densities were estimated using the programme Distance Sampling Programme (Buckland et al., 2001). Prior to data analysis, the following assumptions were considered:

¾ Primates and hornbills on the transects line are detected with certainty

¾ Primates and hornbills are detected at their initial location prior to their movements

¾ Measurements of detected primates and hornbills on line transect are exact.

Perpendicular distances were measured to the nearest meter from the line to the position of each detected selected animals (primates and hornbills). The survey effort was calculated for each transect as the sum of all distances that were walked without disturbance by rain or other unforeseen events. Density (D) of selected animals was calculated as the number of groups (clusters) observed (n) divided by the transect width (w), the transect length (L) and the probability that randomly chosen group within the survey area a = 2wL is detected (Pa). An estimate of Pa was obtained using the Distance Sampling software 4.0 (Thomas et al., 2002).

D = n/(2wLPa)

Models describing a different way in which the probability of sighting an object decreases with distance from the line transect centre (half-normal, hazard rate and uniform models) were fitted to the data and the Akaike Information Criterion (AIC) was used to select models with the least number of parameters and the best fit (Buckland et al., 2001). Observations were pooled by transects. As for the detection function, all observations beyond 100m for

primates and 50 m for hornbills were discarded (right truncation). For the truncation of the cluster size estimation , all observations beyond 30m (for primates) and 20m (hornbills) were discarded. Densities were estimated at global and stratum levels while encounter rates and cluster sizes were estimated only at stratum level. We used Half-normal cosine key function for all analysis and the mean of observed cluster for the cluster size estimation. The truncated data enable an increase in precision of the estimates. The relationship between primates and food resources was checked with the Spearman Rank Correlation Coefficient (Fowler and Cohen, 1996). The value of the correlation coefficient (r) could be either positive or negative.

The correlation was considered very week (0.00 ≥ r ≤ 0.19), weak (0.20 ≥ r ≤ 0.39), modest (0.40 ≥ r ≤ 0.69), strong (0.70 ≥ r ≤ 0.89) and very strong (0.90 ≥ r ≤ 1.00). These parameters determine the degree of relationship between the two measured variables (animals and food resource). The value of the coefficient correlation was tested (Tukey’s honest significance test P) to determine whether the correlation was statistically significant or not.

2.4.7. 4 Survey effort

From 1999 until 2002, the four ecological teams from Bajo (unlogged I), Mgbegati (unlogged II), Bayip Arsibong (logged I) and Etinkem (logged II) covered a total of 962 km as indicated in Table 2.5

Apart from logged II, in which no transect was established in 1999, primate and hornbill surveys started in the other three study sites in which only two permanent transect lines were by then established and a total of 326 km were walked (survey effort) from unlogged I (118 km), unlogged II (106 km) and logged I (102 km) respectively. In order to have a representative sample for the strata, a new study area (logged II) was selected based on logging activities, but also from the ecological parameters such as climate, topography and vegetation and additional permanent transect lines were established.

In 2001 each study site was made up of six permanent transect lines and a total of 356 km were walked from unlogged I (90 km), unlogged II (82 km), logged I (98 km) and logged II (86 km). In 2002, due to the phasing out of the Korup project, the survey effort dropped to 266 km with an average of 66.5 km per study site.

This study takes into account only surveys that were effectively covered (2 km effectively walked from peg 0 m until peg 2000 m) without disturbances from rain, village events (wedding, funeral, and other traditional ceremonies) and absence of at least two of the survey team members.

Transects were walked by the three team members according to a designed schedule and with an average speed of 1h30 mn per kilometre.

48

urvey effort in unlogged and logged study sites from 1999 – 2002. 1999-2000 2000-2001 2001-2002 Transect Length km walkedTransect Lengthkm walkedTransect Lengthkm walkedTotal km walked in logged area d I 1 2 62 1 2 22 1 2 10 2 2 60 2 2 24 2 2 10 3 2 3 2 20 3 2 14 4 2 4 2 22 4 2 8 5 2 5 2 4 5 2 14 6 2 6 2 4 6 2 14 288 d II 1 2 54 1 2 22 1 2 12 2 2 52 2 2 22 2 2 10 i 3 2 3 2 14 3 2 8 4 2 4 2 14 4 2 10 5 2 5 2 2 5 2 10 6 2 6 2 4 6 2 10 244 d I 1 2 58 1 2 44 1 2 10 2 2 60 2 2 42 2 2 10 h 3 2 3 2 2 3 2 12 4 2 4 2 2 4 2 12 5 2 5 2 0 5 2 12 6 2 6 2 0 6 2 12 276 d II 1 2 0 1 2 26 1 2 10 2 2 0 2 2 22 2 2 10 3 2 0 3 2 16 3 2 12 4 2 0 4 2 14 4 2 10 5 2 0 5 2 4 5 2 14 6 2 0 6 2 4 6 2 12 154

3 RESULTS