Coexistence of three sympatric cormorants (Phalacrocorax spp.); partitioning of time as an ecological resource.

Mylswamy Mahendiran

doi:10.1098/rsos.160175

Abstract

Resource partitioning is well known along food and habitat for reducing competition among sympatric species, yet a study on temporal partitioning as a viable basis for reducing resource competition is not empirically investigated. Here, I attempt to identify the mechanism of temporal partitioning by intra- and interspecific diving analyses of three sympatric cormorant species at different freshwater wetlands around the Delhi region. Diving results indicated that cormorants opted for a shallow diving; consequently, they did not face any physiological stress. Moreover, diving durations were linked with seasons, foraging time and foraging habitats. Intraspecific comparison suggested that cormorants spent a longer time underwater in early hours of the day. Therefore, time spent for dive was higher in the forenoon than late afternoon, and the interspecific analysis also yielded a similar result. When Phalacrocorax niger and Phalacrocorax fuscicollis shared the same foraging habitat, they tended to differ in their foraging time (forenoon/afternoon). However, when P. niger and Phalacrocorax carbo shared the same foraging time, they tended to use different foraging habitats (lentic/lotic) leading to a mechanism of resource partitioning. Thus, sympatric cormorants effectively use time as a resource to exploit the food resources and successful coexistence.

Highlights

In heterogeneous environments, niche differentiation functions as a mechanism of coexistence among competitors [1], usually along habitats, food resources, time axis or a combination of them
Temporal partitioning is a viable mechanism for reducing resource competition and sometimes trade-offs in foraging ecology as well [6,7,8]
Time appeared to be a farless common mode of resource partition among sympatric species when compared with habitat [9] and food type [3,9]

Summary

Introduction

Niche differentiation functions as a mechanism of coexistence among competitors [1], usually along habitats, food resources, time axis or a combination of them. Sympatric species evolve different activity patterns to reduce interspecific 2 resource and interference competition [1,3,4,5]. Temporal partitioning is a viable mechanism for reducing resource competition and sometimes trade-offs in foraging ecology as well [6,7,8]. Time appeared to be a farless common mode of resource partition among sympatric species when compared with habitat [9] and food type [3,9]. Ecological interactions over time have been observed in a number of communities viz., reptiles [10,11], birds [12] and mammals [6], the mechanism of time as an ecological resource is still poorly understood [3,12,13]

Methods

Results

Conclusion