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Chapter 12 - Herbivore Abundance: Bottom-up and Top-down Influences
from Part III - The Big Mammal Menagerie: Herbivores, Carnivores and Their Ecosystem Impacts
Norman Owen-Smith, University of the Witwatersrand, Johannesburg
Book:

Only in Africa

Published online:

09 September 2021

Print publication:

07 October 2021, pp 181-198
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Summary

This chapter compares the potential impacts of seasonal food abundance and predation risks on herbivore populations. It describes how herbivore species differ in their response to seasonal rainfall variation. Major droughts can induce severe population crashes. Abundant water accentuates local food depletion. Food shortages may cause animals to incur greater exposure to predation so that bottom-up and top-down influences are entangled. Demographic shifts may lower prey vulnerability to population growth rates, dependent on body size, and sustainable recruitment thresholds. Savanna ungulates differ in the breadth and seasonal timing of birth seasons. Medium–large grazing ruminants produce the most biomass annually. Browsers and equids are consistently less abundant than grazers, while smaller herbivores are more narrowly distributed regionally. Populations also expand and contract in their distribution.