Realized Niches of East African Hornbills Across Species Ranges and Resource Gradients

Gwen Antell
Walter Jetz
Start Date: 
April, 2015

Working with Ph.D. candidate Katherine Mertes of the Jetz Lab, I am investigating the differences in realized niches of two Tockus hornbills across their species ranges with respect to variation in competitor density and biologically relevant environmental factors like vegetation density. Using remotely-sensed data and observations from Katherine and my fieldwork at Mpala Research Centre, Kenya, I have quantified differences in behavioral time budgets and diet composition across an environmental and latitudinal gradient for each hornbill species, sex, and breeding status.  I am currently constructing species distribution models for Von der Decken’s hornbills based on behavioral observations and will incorporate interspecific competition factors into the models. We also plan to use behavioral observations and dietary preferences in niche models to determine the effects of competition and habitat quality on ecological niche overlap at sites throughout the range overlap of the two study species.

Species distribution models rely on the assumption that climatic and topographic variables affect where organisms live, but many studies show that resource partitioning and competitive interactions also affect species distributions. Although both biotic and environmental factors can constrain species distributions, these influences interact in many and complicated ways. Knowledge of the degree of competition across a species range, coupled with an understanding of the resource requirements of a species, may allow models to predict species distributions more accurately and yield insights on fundamental principles of biogeography. Knowledge of how resource quality influences species distributions through interspecific competition and food preferences applies to conservation strategy formulation as well. Although the IUCN currently lists neither study species status as a concern, their population sizes have not been quantified and Von der Decken’s Hornbill populations appear to be decreasing. Feeding ecology observations in conjunction with vegetation assessments have been used to propose habitat management strategies that protect areas with important foods for endangered hornbill species.