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Research article - Peer-reviewed, 2022

Predation strongly limits demography of a keystone migratory herbivore in a recovering transfrontier ecosystem

Watson, Fred; Becker, Matthew S.; Smit, Daan; Droge, Egil; Mukula, Teddy; Martens, Sandra; Mwaba, Shadrach; Christianson, David; Creel, Scott; Brennan, Angela; M'soka, Jassiel; Gaylard, Angela; Simukonda, Chuma; Nyirenda, Moses; Mayani, Bridget;

Abstract

Large herbivore migrations are imperiled globally; however the factors limiting a population across its migratory range are typically poorly understood. Zambia's Greater Liuwa Ecosystem (GLE) contains one of the largest remaining blue wildebeest (Connochaetes taurinus taurinus) migrations, yet the population structure, vital rates, and limiting factors are virtually unknown. We conducted a long-term demographic study of GLE wildebeest from 2012 to 2019 of 107 collared adult females and their calves, 7352 herd observations, 12 aerial population surveys, and concurrent carnivore studies. We applied methods of vital rate estimation and survival analysis within a Bayesian estimation framework. From herd composition observations, we estimated rates of fecundity, first-year survival, and recruitment as 68%, 56%, and 38% respectively, with pronounced interannual variation. Similar rates were estimated from calf-detections with collared cows. Adult survival rates declined steadily from 91% at age 2 years to 61% at age 10 years thereafter dropping more sharply to 2% at age 16 years. Predation, particularly by spotted hyena, was the predominant cause of death for all wildebeest ages and focused on older animals. Starvation only accounted for 0.8% of all unbiased known natural causes of death. Mortality risk differed substantially between wet and dry season ranges, reflecting strong spatio-temporal differences in habitat and predator densities. There was substantial evidence that mortality risk to adults was 27% higher in the wet season, and strong evidence that it was 45% higher in the migratory range where predator density was highest. The estimated vital rates were internally consistent, predicting a stable population trajectory consistent with aerial estimates. From essentially zero knowledge of GLE wildebeest dynamics, this work provides vital rates, age structure, limiting factors, and a plausible mechanism for the migratory tendency, and a robust model-based foundation to evaluate the effects of potential restrictions in migratory range, climate change, predator-prey dynamics, and poaching.

Keywords

demography; migration; population; predator-prey; survival; wildebeest; Zambia

Published in

Ecology and Evolution

2022, volume: 12, number: 10, article number: e9414
Publisher: WILEY

Authors' information

Watson, Fred
California State University Monterey Bay
Becker, Matthew S.
Montana State University Bozeman
Smit, Daan
Zambian Carnivore Programme
Droge, Egil
University of Oxford
Mukula, Teddy
Zambian Carnivore Programme
Martens, Sandra
Zambian Carnivore Programme
Mwaba, Shadrach
Zambian Carnivore Programme
Christianson, David
University of Wyoming
Zambian Carnivore Programme
Montana State University Bozeman
Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies
Brennan, Angela
World Wildlife Fund
M'soka, Jassiel
United States Agency for International Development (USAID)
Gaylard, Angela
African Parks Zambia
Simukonda, Chuma
Department of National Parks and Wildlife
Nyirenda, Moses
Worldwide Fund for Nature
Mayani, Bridget
Zambian Carnivore Programme

UKÄ Subject classification

Ecology
Evolutionary Biology

Publication Identifiers

DOI: https://doi.org/10.1002/ece3.9414

URI (permanent link to this page)

https://res.slu.se/id/publ/119447