Bale monkeys is unusual among primates and other mammals for its intense specialization a single species of bamboo which accounts for 77% of his diet in continuous forest of Ethiopia. Human degradation and life in fragments has hugely impacted on their feeding strategies. This research is significant because Bale monkeys are at high risk of extinction due to small geographic distribution and ongoing deforestation in their habitat , and in order to design an effective conservation management plans we have to understand if they exhibit enough dietary flexibility to cope with human degradation . The author has justified the research by comparing activity, and dietary patterns of Bale monkeys between continuous and fragmented forest. Based on research ,it is hypothesized that their feeding strategies would be highly influenced due to lower habitat quality and less food availability in fragmented forests. The one prediction made is that Bale monkeys are able to adapt to a greater diversity of the food items ,and plant species due to low abundance of bamboo in fragments. It is also predicted that the Bale monkeys in continuous forest would be bamboo specialist, however the one in fragmented area would have diet more similar to generalized species. The hypothesis is tested by the study which was conducted over a 12 month period to understand the effects of habitat modification on Bale monkeys, by comparing vegetation composition and structure, climatic data and feeding strategies in fragmented habitats(patchy and hilltop) and in continuous forest(group A and B).
Material and methods
Study site and habitat characteristics: The author has carried out study in the continuous Odobullu forest and two fragments Kokosa forest (hereafter Patchy fragment) and Afursa forest (hereafter Hilltop fragment) which are 9km away from each other and 16 kms from continuous forest. The Odobullu are bamboo dominant , patchy fragment consists of degraded bamboo and ,in Hilltop the bamboo has nearly extirpated. Both patchy and Hilltop fragments were dominated by bamboo forest only three decades ago. It is important to understand current habitat characteristics in order to do the further research .
Study Groups: The author selected four groups of Bale monkey :two groups in the continuous forest (Continuous A and Continuous B), one group in the Patchy fragment and one group in the Hilltop fragment. These groups were studied for four months from dawn to dusk on a near daily basis. The selection of these four groups by the author seems pretty adequate to comprehend the impact of human degradation on their dietary flexibility .
Climate: Climatic data such as annual rainfall and minimum and maximum temperature has been recorded for a period of 12 months and based on the graph it is observed that the annual rainfall is slightly more in fragmented forest than continuous forest , and the mean annual temperature is significantly higher in forest fragments. I do believe that climate plays an important role in the plant growth but this material doesn’t serve a major purpose in this particular research.
Vegetation and temporal patterns of food availability: The author sampled the vegetation in the range of study groups using two complementary techniques. In first technique ,author calculated all large trees with diameter at breast height (DBH);10cm in 50m x 10m vegetation quadrat along with species name and growth form. In second technique , all plants ;=2m tall are identified and counted within randomly selected 50% of vegetation quadrat. With this Technique ,they sample all bamboo ,shrubs and forbs that monkey depends on are less than 10cm DBH. Following the above two techniques ,author classified plant growth in five different categories:bamboo, tree, shrubs, lianas and forbs. To estimate the biomass of each large tree species and bamboo, the author calculated the basal area (BA) of each tree species from the DBH recorded using the formula (BA = 0.5 × DBH2 × ?).
To examine the temporal pattern of food availability , the author analyzed data from eight different species five trees, two shrubs and a bamboo. These monitored plants were given relative abundance score for each of its potential food item such as young and mature leaves ,flowers, ripe fruit and shoots from 0-8. The author calculated the monthly mean phenological scores for young leaves, fruits, and shoots for each individual plant species, and the monthly food availability index (FAI) for each plant part by multiplying the mean phenology scores of species i with the mean basal area of species i and density of the corresponding species i per ha. Based on these calculations , it is concluded that these plants species are available in abundance in continuous forest and relatively less in patchy and Hilltop fragments
It is relevant for the author to explain the vegetation and temporal pattern of food availability and the methods used are really detailed and provide accurate data as seen in the graph stated(Fig2 of research) Based on these methods we can prove our prediction that bamboo is much widely grown in continuous forest as compared to fragments.
Feeding ecology: Author assessed dietary composition for each month by determining the proportion of food items, growth forms and species consumed in each study group. The author recorded food items such as bamboo young leaves, bamboo mature leaves, non-bamboo young leaves ,non bamboo mature leaves, bamboo shoots, bamboo branchlets, roots, fruits, seeds, stems, petioles, insects or mushrooms and, plant growth form as tree, bamboo, shrub, lianas or, forbs. Based on data accumulated, the author calculated the annual consumption of food items, growth forms and species as the means of the 12 monthly values for each category.and he also calculated the relative food selection ratios by dividing the proportion of annual percentage of feeding records on a particular species i by the percentage stem density of species i in the study group’s home range.
To estimate the species richness, the author calculated annual dietary diversity indices for each group using the Shannon–Wiener index, dominance index and evenness index , and to assess differences in inter-month dietary similarity among groups in continuous forest and forest fragments, author calculated the inter-month Morisita– Horn’s similarity indices of each group using Estimates. To assess the annual diet overlap among groups in continuous forest and forest fragments, we also calculated between group Morisita–Horn similarity indices.
With the above method,The author has explained the proportion of feeding records devoted to different food items by the four different groups of Bale monkeys. The author has used a much more complex approach to explain the species richness as compared to the similar research (https://onlinelibrary.wiley.com/doi/pdf/10.1002/ajp.22760) where species diversity was calculated with scan sampling.
In this specific research, The author has mainly talked about four sub groups feeding strategies but hasn’t explained much about the Bale monkeys behaviour such as locomotion mode while travelling , postural behaviour or any other activities such as resting, socializing or vocalizing. I believe overall knowledge of these sub groups behaviour is required to understand their dietary flexibility .
Author initially calculated and compared variables for each Bale monkey study group individually and examined the differences using the one-way analysis of variance (ANOVA) model followed by the Turkey honest significant difference (HSD) post hoc test. And he constructed a sample-based rarefaction curve plotting species richness with sampling effort (number of observation days) using PAleontological STatistics (PAST) software to perform a valid comparison of dietary species richness among groups. To examine differences in monthly dietary dominance and evenness indices between continuous forest and fragment groups, he used a generalized linear model (GLM) as recommended for proportional data .One-way ANOVA to test for differences in the percentage consumption of each food item and growth form between continuous forest and fragment groups, AND also used Linear regressions between food availability index and percentage consumption of plant food items among the four Bale monkey groups
Vegetation description and temporal variation in resource availability: The vegetation in the two continuous forests is abundant and is more similar in its composition than in the fragments , Monthly food availability indices of bamboo leaves, non bamboo leaves and fruits are much higher in continuous forests(Fig 2). However , vegetation in forest fragments are much more diverse.
Dietary species richness, diversity and similarity: Dietary species richness was much higher in a group inhabiting forest fragments.As explained in (figure 3a )the mean monthly Shannon–Wiener diversity index of food species was significantly higher in fragments than in continuous forest. However, mean monthly dietary species evenness was not much different between groups living in fragments and those in continuous forest as stated in fig 3b. Lastly, according to (fig 3c )mean monthly food plant species dominance was significantly higher for groups in continuous forest than for those in fragments . Between-month dietary species similarity was significantly greater for groups in continuous forest than for groups in forest fragments Fig. 3d). Annual dietary species overlap was much lower between the two fragment groups than for the groups in continuous forest
Food item consumption :Groups in continuous forest mostly feeds on young bamboo leaves and less on non-bamboo young leaves, fruits, stems, petioles, seeds, and insects than groups in forest fragments (Fig. 4).There was no difference in the consumption of bamboo shoots and flowers between continuous forest and fragment groups.
Consumption of different growth forms :Because of higher diversity of trees, shrub, forb and graminoid species in forest fragments in comparison to continuous forest , groups in fragmented area spend most time feeding on the diversity available than on bamboo.
Top five species consumption:The cumulative percentage of the annual diet accounted for by the top five plant species was much higher in groups inhabiting continuous forest than in groups in fragments .Bamboo was the top food species consumed in both continuous forest groups (Mean = 81.2%) and in Patchy fragment group (30.2%) but was only the 10th most eaten food species in Hilltop fragment group (1.6%). Instead, in Hilltop fragment where bamboo was especially rare, a grass, was the top plant species (15.3%) in the annual diet (Table 1).
Dietary preference:From table 2 , it is stated that, bamboo had selection ratios of just below 1.00 in continuous forest(ContinuousA=0.94 and Continuous B = 0.95) with extremely high stem density in this forest type. The fragment groups also exhibited comparable selection ratios to those of the continuous groups(Patchy = 0.76; Hilltop: 1.00). For the fragment groups, the most selected food species were the trees Erythrina brucei (27.83) in Patchy fragment and Hagenia abyssinica (10.42) in Hilltop fragment.
Author has compared the dietary flexibility of Bale monkeys to other primates how habitat degradation has shifted their diet more to secondary successional species, such as shrubs, forbs, or graminoids. ,and to other exotic species or human crops which results in human-monkey conflict in fragmented area. According to author, Primates and Bale monkeys have more species richness in their diet in fragmented area than in continuous forest. Bale monkeys in continuous forest are bamboo specialists whereas due to bamboo eradication ,Bale monkeys in fragmented forest diversified their diet in order to survive.
Author has also made an comparison of dietary flexibility in Bale monkeys relative to other Chlorocebus species,. Chlorocebus species eats a varied diet with top food such as fruit in Nigerian and Senegalese populations to gum or flowers in Kenyan populations (C. pygerythrus(Table 4) , and young leaves and shoots of bamboo in Bale monkeys (C. djamdjamensis) in continuous forest. The author has revealed in his study that bale monkeys and other Chlorocebus species in fragments consumes less specialized diet than the one living in continuous forest such as percentages of fruit and graminoid consumption by C. djamdjamensis in fragments were similar to those in East African C. pygerythrus populations (Table 4) or invertebrate consumption by the Hilltop group of C. djamdjamensis same as invertebrate consumption by C. sabaeus in West Africa (Table 4). The author has reasoned Bale monkey’s ability to alter their diet with two explanation First, they may retain some of the ancestral ecological flexibility characteristic of other members of the genus Chlorocebus, and second possibility is that hybridization between C. djamdjamensis and parapatric C. aethiops and C. pygerythrus in fragmented forest areas.
The author has also talked about bamboo consumption across bamboo eating mammals in his discussion that other than Bale monkeys of Ethiopia , there are five other mammals which are highly dependent on bamboo :giant pandas in China 34, 94, red pandas in India, Nepal, Bhutan, Myanmar, and China 96, bamboo lemurs in Madagascar 26, 95, Assamese macaques in China 68, 96,and golden monkeys in Uganda and Rwanda 67, 97 ,and how these primates have dietary flexibility in fragmented area where bamboo is scarce , and can cope with a certain threshold of habitat destruction. Finally ,author has discussed about implications for conservation and management. It is shown in this study that Bale monkeys have flexibility to cope with lower habitat quality and food availability, However it is still close to become an endangered species because of crop raiding which has put them at higher risk of hunting by humans and deforestation..Many useful conservation measures should be enforced to ensure the long term persistence of bale monkeys such restoration programs undertaken at fragments should focus on increasing fragment sizes, reducing edge effects, and mitigating human monkey conflict, and continuous bamboo forest habitat in the southern Ethiopian Highlands should be protected from further deforestation.
With this discussion ,author has thoroughly supported his hypothesis that habitat degradation has affected the feeding strategies of Bale monkeys in fragmented forest. By extending the study with comparison of Bale monkeys to other primates, bamboo consuming mammals, and Chlorocebus species , author has validate his predictions of Bale monkeys in continuous forest being bamboo specialist ,however the ones in the fragmented forest have a ability to adapt to a greater diversity of food items. The study suggests that Bale monkeys may retain some of the ancestral ecological flexibility assumed to be characteristic of the genus Chlorocebus, within which all extant species except Bale monkeys are regarded as ecological generalists, and like other bamboo eating primates. Bale monkeys can cope with a certain threshold of habitat destruction. The author has enhanced the research by adding the reasons that why Bale monkeys are threatened species despite having the dietary flexibility and the conservative measures that should be taken to ensure their long term persistence
The author in this research has mainly discussed that how human degradation has affected habitat quality and feeding strategies of Bale monkey. We can extend this work by examining the additional effects of bamboo habitat loss and fragmentation on Bale monkeys such as activity budget, home range use and movement rate . The hypothesis will be that feeding strategies, movement rate and activity budget would highly influence due to less habitat quality and food availability in fragmented forest. Based on this hypothesis The one prediction made is that Bale monkeys are able to change their ecology ,behaviour and adapt to other greater diversity of the food items ,and plant species due to low abundance of bamboo apia in )fragments. Second ,they uses an energy minimizing strategy to cope with a lower availability of primary food species i.e.bamboo and lastly that Bale monkeys in continuous forest are bamboo specialist ,however the one in fragmented forest have more diversified diet. We can conduct this study by comparing activity budget between two species from fragmented forests (Patchy and Hilltop fragments ) and other two from continuous forest(Continuous A and Continuous B).
During scans, individuals are recorded from four different forests as performing one of the following behaviours: feeding , moving (any locomotor behaviour), resting (inactive), socializing (playing, grooming, engaging in agonistic or sexual activity) or vocalizing. A total of 28,583 individual behavioural scan records during 2085 h of observation (Continuous A = 441 B = 432; Patchy fragment = 601; Hilltop fragment = 611) over 234 group follow days Continuous A = 52; Continuous B = 54; Patchy fragment = 61; Hilltop fragment = 67)The author calculated the proportions of time spent on different activities by dividing the number of behavioural records for each activity category with the total number of activity records. He used the behavioural records of the group to calculate the activity budgets per day and averaged within each month to construct monthly activity budgets for each study group (mean ± SD records; Continuous A = 453.5 ± 81.7; Continuous B = 458.3 ± 139.0; Patchy fragment = 854.5 ± 135.2; Hilltop fragment = 615.7 ± 113.6). The grand mean proportions of the monthly budgets provided the annual activity budgets for the entire study period. The author combined social behaviours (agonism, grooming, playing, and sexual activity) in our data analyses because some of these behaviours accounted for