Browsing by Author "Page, Navendu"

Now showing 1 - 2 of 2

Impact of Habitat Fragmentation on Plant -Frugivore Interactions in Lowland Tropical Forests of Upper-Assam North East
(Wildlife Institute of India, Dehradun, 2019) Jain, Abir; Page, Navendu; Rawat, G.S.
Tropical forests are considered the storehouse of biodiversity. One of the key ecosystem processes that governs the diversity of tropical trees is seed dispersal. Tropical forests globally face deleterious effects of habitat fragmentation such as loss of habitat area, reduced species richness and altered community composition. Forest fragmentation can also alter mutualistic interactions between plants and seed dispersers, disrupting key ecosystem processes like seed recruitment and regeneration. In the past century, logging, habitat conversion to tea plantations and agricultural fields have resulted in the fragmentation of the last remaining lowland tropical forests of Upper Assam in north-east India. However, these isolated forest fragments might also hold a great potential to preserve native biodiversity distributed across patches. There is paucity of information on impacts of habitat fragmentation on plant–seed disperser interactions from Asia. 2. In this study, I investigate the impacts of habitat fragmentation on plant-disperser communities. The impacts were assessed at the level of the community and at the level of species guilds (body size, habits, and families). 3. The plant-frugivore interactions were recorded by systematically walking 27 trails across two habitat categories: contiguous forest sites (n=2) and fragmented sites (n=4) over the duration of four months. Spot census was carried out to record interactions between a fruiting plant and frugivores. Fruit handling behaviour of birds and fruit crop size of plants were also recorded. Plants and seed dispersers that interact with one another, forms a network. 4. I constructed presence-absence networks for each habitat type, which represents all plant-seed disperser interactions recorded in the contiguous forests and the forest fragments. ‘Network-level’ properties were obtained to understand the influence of fragmentation on plant-seed disperser communities and ‘Species-level’ properties were obtained to assess the roles of species guilds in each of these communities. 5. Although, the networks for contiguous and fragmented forests were similar in terms of total number of mutualist species participating in its organisation, their composition was different. On an average, frugivores had one plant partner more in the contiguous forest, while plants had three frugivore partners more in the forest fragments.
The effect of disturbance-induced changes in vegetation structure and arthropod abundance on mixed-species bird flocks in the oak forests of the Western Himalaya
(Wildlife Institute of India, Dehradun, 2024) Satish, Aditya; Page, Navendu; Bangal, Priti; Shahabuddin, Ghazala
Mixed-species flocks are an interactive group of insectivorous birds that forage together and move in the same direction. Flocks provide foraging and anti-predatory benefits to participants. Habitat disturbance may affect flocks by – a) altering presence or abundance of participating birds in the community or b) altering flocking propensities of species. 2. I investigated the effects of habitat disturbance on flocks in the Western Himalaya of Uttarakhand, India. Disturbance was mediated through two mechanisms – changes in vegetation structure and arthropod abundance (food availability). I examined how these environmental variations impacted flocks at a community level through changes in flock richness, flock size, number of flocks encountered and flock composition. I also explored how flocking propensity (a species-specific tendency to join flocks) is impacted by these variables. 3. Flocks are a subset of the insectivorous bird community. I found that insectivore richness and abundance decreased with reduced structural complexity of vegetation caused by disturbance. Reduced structural complexity also led to a corresponding decline in flock richness, size and number of flocks encountered in disturbed sites. With regards to variation of flock composition with disturbance, I found no clear species-composition-based clustering in transects with similar disturbance levels. 4. There seems to be an interactive link between arthropods, insectivorous birds and disturbance. Disturbance was correlated with strong declines in foliage arthropod abundance, which in turn contributes to lower insectivore richness and abundance. Flying arthropod abundance largely remained constant with disturbance, so I would like to draw 2 attention to the effect of foliage arthropod abundance on flock variables in the following sections. 5. The number of flocks encountered increased with foliage arthropod abundance. Since insectivores in undisturbed sites are supported by a larger prey base, the higher frequency of flocking may be correlated to the larger pool of insectivores that are available to flock at a given time. I did not find significant effects of foliage arthropod abundance on flock richness and flock size. 6. I found that flocking propensity of the three most common species (Gray-hooded Warbler, Black-throated Tit and Green-backed Tit) in flocks showed a declining trend with higher disturbance. I also observed that the propensity of these species showed an increasing trend with higher foliage arthropod abundance. However, none of these relationships were statistically significant. More detailed research is recommended to investigate these preliminary patterns further, to better understand the complex interactions between propensity, disturbance and food availability. 7. To conclude, disturbance was found to have a negative impact on mixed-species flocks, primarily by altering the presence and abundance of insectivorous birds. From a habitat perspective, insectivores suffered declines due to the simplification of vegetation structure. Insectivores also face food scarcity as foliage arthropod abundance decreases. The combined effect of habitat loss and reduced food availability in disturbed sites leads to lower insectivore richness and abundance, which is in turn reflected in fewer, smaller and more species-poor flocks.