Variation in Primate Abundance Along an Elevational Gradient in the Udzungwa Mountains of Tanzania

Barelli, Claudia; Palacios, Juan Francisco Gallardo; Rovero, Francesco

doi:10.1007/978-1-4614-8175-1_12

Cited by 7 publications

(4 citation statements)

References 47 publications

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“…Meanwhile, all three target species are found in greater abundance in these forest habitat types (i.e. from lowland deciduous to sub-montane evergreen) than at higher elevation, evergreen montane forest [ 19 , 46 ]. For these reasons, we are confident that the temporal trends we obtained provide adequate indications about the conservation status of these threatened primate populations.…”

Section: Discussionmentioning

confidence: 99%

Primates Decline Rapidly in Unprotected Forests: Evidence from a Monitoring Program with Data Constraints

et al. 2015

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Growing threats to primates in tropical forests make robust and long-term population abundance assessments increasingly important for conservation. Concomitantly, monitoring becomes particularly relevant in countries with primate habitat. Yet monitoring schemes in these countries often suffer from logistic constraints and/or poor rigor in data collection, and a lack of consideration of sources of bias in analysis. To address the need for feasible monitoring schemes and flexible analytical tools for robust trend estimates, we analyzed data collected by local technicians on abundance of three species of arboreal monkey in the Udzungwa Mountains of Tanzania (two Colobus species and one Cercopithecus), an area of international importance for primate endemism and conservation. We counted primate social groups along eight line transects in two forest blocks in the area, one protected and one unprotected, over a span of 11 years. We applied a recently proposed open metapopulation model to estimate abundance trends while controlling for confounding effects of observer, site, and season. Primate populations were stable in the protected forest, while the colobines, including the endemic Udzungwa red colobus, declined severely in the unprotected forest. Targeted hunting pressure at this second site is the most plausible explanation for the trend observed. The unexplained variability in detection probability among transects was greater than the variability due to observers, indicating consistency in data collection among observers. There were no significant differences in both primate abundance and detectability between wet and dry seasons, supporting the choice of sampling during the dry season only based on minimizing practical constraints. Results show that simple monitoring routines implemented by trained local technicians can effectively detect changes in primate populations in tropical countries. The hierarchical Bayesian model formulation adopted provides a flexible tool to determine temporal trends with full account for any imbalance in the data set and for imperfect detection.

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Section: Discussionmentioning

confidence: 99%

Primates Decline Rapidly in Unprotected Forests: Evidence from a Monitoring Program with Data Constraints

et al. 2015

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“…Due to intense logging over the past 50 years, most of MT and MG forests, as well as the lower zones of MW and US, present mainly secondary, regenerating cover, which is intermingled with closed canopy areas of deciduous and semi-deciduous forest. Interestingly, Udzungwa red colobus seem to prefer this regenerating and variably disturbed forest habitat, where they are more abundant and live at higher densities (Araldi et al 2014;Barelli et al 2014). Presence of higher group densities at lower elevations, and in semi-deciduous forest zones, can probably be explained by their higher rate of new leaf production (Lovett et al 1988;Lovett 1993).…”

Section: Discussionmentioning

confidence: 95%

Physiological stress levels in the endemic and endangered Udzungwa red colobus vary with elevation

et al. 2015

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Habitat loss and fragmentation inevitably cause biodiversity decline, a major concern for the conservation of endangered species. Primates are of particular interest, because they are highly vulnerable to forest fragmentation. In this study, we investigated faecal glucocorticoid measurements (FGCM), an indicator of physiological stress, in an endemic and IUCN-endangered monkey species inhabiting forest blocks in the Udzungwa Mountains in south-central Tanzania. The Udzungwa red colobus (Procolobus gordonorum) is threatened by hunting, and habitat degradation and loss due to agricultural expansion. They are highly folivorous, more abundant at lower elevations, but able to persist in extremely small forest blocks. We collected faecal samples in four forest blocks that differed in size, level of human impact (hunting and past logging activities) and ecological factors to examine the potential influence on stress hormone output. Across all four forests, we did not find any clear effect on FGCM levels of the variables considered, apart from elevation. Red colobus had higher FGCM levels at lower elevations, where their seemingly optimal habitat occurs, but concomitantly where greater human disturbance is found. Although our results should be interpreted with caution and confirmed with further study, we suggest that this species is not negatively influenced by a moderate level of human activity, consistent with ecological modelling data.

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“…The higher encounter rates we observed in the closed canopy forest are consistent with habitat association preference of African nocturnal primates. This preference may be attributed to availability of abundant food and shelter resources in the lowland moist rainforest for the African primates [56]. The diverse and rich vegetation cover types within and around Oban Hills Region provides suitable habitats for the species, supporting the species with specific habitat needs.…”

Section: Discussionmentioning

confidence: 99%

Population Abundance and Density Estimates of Poorly Documented Near-Threatened Calabar Angwantibo (Arctocebus calabarensis) in Oban Hills Region

Omifolaji,

Adedoyin,

Ikyaagba

et al. 2024

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Population abundance and density estimates play important roles in biodiversity conservation assessment and can lead to prioritization of conservation efforts, strategies, and management. The Calabar angwantibo (Arctocebus calabarensis) is a poorly studied, Near-Threatened nocturnal, arboreal mammal species occurring only in the lowland moist tropical rainforest blocks of southeastern Nigeria and southwestern Cameroon. Like other arboreal nocturnal mammals, there are gaps in knowledge of the distribution and abundance of this species, which may be facing population declines due to habitat loss and hunting. In this study, we investigated the abundance and density of A. calabarensis in the Oban Hills Region of Nigeria. We conducted systematic distance sampling survey along 32 transects in different habitats in a 1227 km of survey efforts. A total of 41 sightings of A. calabarensis were detected, resulting in an abundance of 7345 individuals (95% CI = 1.51–4.37) with an estimated density of 2.57 animals/km2. The estimated population abundance is 6515 individuals in closed-canopy forests and 830 individuals in secondary forests, with encounter rates of 0.52 individual/km2 and 0.60 individuals/km2 in the closed canopy and secondary forest habitats. The global estimates encounter rate of A. calabarensis across the habitat types is 0.33 individuals/km2 and population abundance of 4456 individuals. Our findings indicate that the A. calabarensis populations can adapt to low changes in forest habitat modifications resulting from increasing and widespread forest disturbance by human-dominated activity, which is giving way to forest clearance for agriculture cultivation and infrastructural development. Our findings help to fill a knowledge gap regarding this species and may help establish a baseline for future management, population monitoring, and conservation of the cryptic population of A. calabarensis in Cross-Sanaga Forests.

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Variation in Primate Abundance Along an Elevational Gradient in the Udzungwa Mountains of Tanzania

Cited by 7 publications

References 47 publications

Primates Decline Rapidly in Unprotected Forests: Evidence from a Monitoring Program with Data Constraints

Primates Decline Rapidly in Unprotected Forests: Evidence from a Monitoring Program with Data Constraints

Physiological stress levels in the endemic and endangered Udzungwa red colobus vary with elevation

Population Abundance and Density Estimates of Poorly Documented Near-Threatened Calabar Angwantibo (Arctocebus calabarensis) in Oban Hills Region

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