COS 315-4 - Examining ecological interactions of urban tree and vertebrate species: a comparative analysis of New Delhi and Bengaluru, India

Abstract: Urban treescapes endow a socio-cultural reflection of a community. Often formed of a homogenized mix of native and non-native trees, these landscapes harbor a significantly rich diversity of vertebrate and invertebrate species. However, little is known about the interactions of these species with their surrounding trees. In this study, we examine the ecological interactions of some important native and non-native tree species with diurnal vertebrates (birds, arboreal mammals) in two megacities in India.

We examine: a) which urban vertebrate species depend on which tree species for food (fruit, nectar); b) whether non-native tree species support more/fewer vertebrates than native trees; and c) if any tree species plays a "keystone" role in providing food resources for urban vertebrates. We identified around 20 focal tree species in New Delhi and Bengaluru (N = 10 individuals/species) for systematic monitoring (1-3 hours/tree, within 4 hours of sunrise) in their flowering/fruiting period, noting abundance and diversity of feeding vertebrates on each tree.

We have monitored approximately 200 trees (250 hours) in Delhi and 160 trees (200 hours) in Bengaluru. In both cities, we found high levels of vertebrate association with several native Ficus spp (9-17 vertebrate spp/Ficus spp). Additionally, in New Delhi, vertebrate feeding activity was high for native Bombax ceiba (24 spp), Ehretia laevis (17), and Erythrina variegata (13), and non-native Morus alba (16) while in Bengaluru, non-native Spathodea campanulata (11) and Muntingia calabura (9) supported large number of vertebrates.

Our data suggest that the native Ficus species serve as a crucial food resource in both cities, cementing their role in food provision in urban ecosystems as similar to that in natural ecosystems. Other native and non-native tree species were also frequently visited by vertebrates. We will present a detailed food-web network analysis to represent our findings, with additional focus on determining whether particular tree species are disproportionately favored by vertebrates suggesting potential “keystone” roles in the urban ecosystem. Rapid urbanization in both these cities in the last two decades has led to the removal of many large Ficus trees to accommodate new urban infrastructure. Our findings will have significant management and conservation implications for urban trees and their associated biodiversity in both cities.