How useful are transect surveys for studying carnivores in the tropical rainforests of Borneo?

Transect surveys are a widely used tool in the study of wildlife populations. Here, we review different forms and objectives of transect surveys, discuss the need for and briefl y describe principles of good study design, and discuss various biological measurements employed in the study of carnivores in the rainforests of Borneo. We discuss the conservation value of these measurements, underlying assumptions in using different approaches, and why these assumptions cannot often be met in the study of Bornean carnivores. We argue that transect surveys are of little use as a stand-alone technique for carnivore studies in Borneo; numbers of encounters from genuinely random transects are too low to be amenable to quantitative analysis, whereas observations from non-random transects are biased and cannot be used for drawing any sort of wider inference. We consider approaches in which transect surveys could be implemented in conjunction with other techniques. In general, limited conservation resources could be better spent on other techniques and other measures that can usefully inform conservation

Patterns and consequences of invasion of tropical montane forests by Cestrum aurantiacum Lindl. in the Western Ghats

In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics

On a Dhole trail: examining ecological and anthropogenic correlates of Dhole habitat occupancy in the Western Ghats of India

Although they play a critical role in shaping ecological communities, many threatened predator species are data-deficient. The Dhole Cuon alpinus is one such rare canid with a global population thought to be < 2500 wild individuals. We assessed habitat occupancy patterns of dholes in the Western Ghats of Karnataka, India, to understand ecological and anthropogenic determinants of their distribution and habitat-use. We conducted spatially replicated detection/non-detection surveys of dhole signs along forest trails at two appropriate scales: the entire landscape and a single wildlife reserve. Landscape-scale habitat occupancy was assessed across 38,728 km2 surveying 206 grid cells of 188-km2 each. Finer scale habitat-use within 935 km2 Bandipur Reserve was studied surveying 92 grid cells of 13-km2 km each. We analyzed the resulting data of dhole signs using likelihood-based habitat occupancy models. The models explicitly addressed the problematic issue of imperfect detection of dhole signs during field surveys as well as potential spatial auto-correlation between sign detections made on adjacent trail segments. We show that traditional ‘presence versus absence’ analyses underestimated dhole habitat occupancy by 60% or 8682 km2 [naïve  =  0.27; ≏ ψL (SE) =  0.68 (0.08)] in the landscape. Addressing imperfect sign detections by estimating detection probabilities [ˆpt(L) (SE)  =  0.12 (0.11)] was critical for reliable estimation. Similar underestimation occurred while estimating habitat-use probability at reserve-scale [naïve  =  0.39; ˆψs (SE) =  0.71 (0.06)]. At landscape scale, relative abundance of principal ungulate prey primarily influenced dhole habitat occupancy. Habitat-use within a reserve, however, was predominantly and negatively influenced by anthropogenic disturbance. Our results are the first rigorous assessment of dhole occupancy at multiple spatial scales with potential conservation value. The approach used in this study has potential utility for cost-effectively assessing spatial distribution and habitat-use in other species, landscapes and reserves

The Role of Perches in Accelerating Seed Arrival in Human abandoned Clearings Within Bhadra Tiger Reserve, India

Volume: 105Start Page: 317End Page: 32

The Role of Perches in Accelerating Seed Arrival in Human abandoned Clearings Within Bhadra Tiger Reserve, India

Seed arrival is often the primary limitation to forest regeneration in denuded landscapes, with the number of seeds arriving diminishing rapidly with increase in distance from remnant seed sources. We compared seed rain collected at different distances from the forest edge in seed rain traps with and without introduced bamboo perches in human abandoned agricultural clearings in Bhadra Tiger Reserve. The number of seeds collected per trap below perches was 38 times greater than the number of seeds collected in traps without perches. The species richness of seeds collected per trap below perches was ten-fold greater than in traps without perches. Our study showed that introducing artificial perches is an effective method to improve seed arrival into tree-less habitats, as has been found in studies elsewhere

Patterns of seed rain and seedling regeneration in abandoned agricultural clearings in a seasonally dry tropical forest in India

Forest recovery in abandoned pastures and agricultural fields is often impeded, therefore it is important to understand the factors limiting regeneration. Patterns of seed arrival and regeneration in five abandoned agricultural clearings nested within a seasonally dry tropical forest in India were examined along five transects radiating from the forest edge into the clearings. Wind-dispersed seeds dominated the seed arrival in clearings compared with vertebrate dispersed seeds: 5563 wind-dispersed seeds and 1094 vertebrate-dispersed seeds of 14 and 13 tree species, respectively, were recorded. Numbers of the former declined steeply with increasing distance from the forest, whereas the latter showed no evident pattern with distance. Seeds of the invasive herb, Chromolaena odorata, were abundant in clearings. Although wind-dispersed seeds greatly outnumbered vertebrate-dispersed seeds, seedlings and saplings of vertebrate dispersed species were three times more abundant than those of wind-dispersed species, indicating distinct differences in patterns of actual and effective seed dispersal. This points to recruitment limitation, and suggests that seed arrival may not be the principal barrier to regeneration in these clearings. Nonetheless, the clearings are likely to revert to forest over time

Measuring Indian giant squirrel (Ratufa indica) abundance in southern India using distance sampling

A large body of work on the ecology of sciurids is based on comparing patterns of abundance across either space or time. However, in most cases investigators choose to use surrogate measures of abundance, such as indices based on species or sign encounter rates, or trapping rates. This requires the assumption that detection probabilities are equal at all sites (or time periods) sampled, an assumption that is difficult to meet under field conditions. We demonstrate the application of line transect-based distance sampling, a technique that explicitly models and accounts for detection probability, to estimate ecological densities of Indian giant squirrels in forested habitats. Line transect surveys were carried out at several sites and the number of detections included: 86 (Bandipur), 152 (Nalkeri), 110 (Sunkadakatte), 304 (Muthodi) and 236 (Lakkavalli). The encounter rates ranged from 0.179/km in Bandipur through 0.296/km (Nalkeri), 0.368/km (Sunkadakatte), and 0.625/km (Lakkavalli), to 0.779/km in Muthodi, while the estimated probabilities of detection were 0.517 (Bandipur), 0.532 (Nalkeri), 0.531 (Sunkadakatte) 0.548 (Lakkavalli) and 0.604 (Muthodi). The estimated mean squirrel densities (± standard error of the density) ranged from 2.37 (0.33) squirrels/km2 in Bandipur through 4.55 (0.44) squirrels/km2 in Nalkeri, 4.86 (0.62) squirrels/km2 in Sunkadakatte, to 10.20 (0.82) squirrels/km2 and 12.26 (1.10) squirrels/km2 in Muthodi and Lakkavalli respectively. We discuss design, field survey and data analytic considerations for rigorously estimating squirrel density and abundance

Mammals make use of cashew plantations in a mixed forest-cashew landscape

Heterogeneous landscapes harboring mosaics of natural habitat and agriculture are increasingly gaining conservation focus in the tropics. While research on cash crops such as coffee, rubber, and oil palm has led to an understanding of their role as supplementary habitats, such has remained limited in cashew plantations despite it being a cash crop of global significance. We conducted a study to understand the occurrence of terrestrial mammal species in a mixed forest–cashew landscape in the northern Western Ghats, India. During January to April 2016, we used trail cameras to sample a total area of 25 km2 divided into 100 grid cells of 0.25 km2 each. We deployed six trail cameras for a 24 h period in each grid cell and obtained photo-captures of 11 species in forests, of which nine were detected in cashew plantations, but most species showed low capture rates. For three of these species—Indian crested porcupine, sambar, and wild pig—we modeled habitat use as a function of site-specific attributes. Wild pig showed a higher probability of use of cashew than forest, while porcupine and sambar did not show any pronounced differences between the two land uses. The probability of habitat use by sambar and porcupine was positively influenced by undergrowth but not for the wild pig. Wild pig habitat use was positively related to increased proximity of human settlements and increasing distance to forests, but the pattern was unreliable for sambar and porcupine. Our preliminary study demonstrates that a subset of terrestrial mammals in the forest makes use of cashew plantations and highlights the need for further research in forest–cashew landscapes to assess conservation opportunities.Ministry of Education (MOE)Published versionFunding for this work was provided by core grants to NCBS-TIFR by the Department of Atomic Energy (India) and a program grant from the Tata Trusts. AR received support from the Tier 1 project grant: Singaporean Ministry of Education Tier 1 RG145/19. This work comprises EOS contribution number 339