Impact of Habitat Fragmentation on Plant -Frugivore Interactions in Lowland Tropical Forests of Upper-Assam North East

Abstract

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.