In African savannas, are donor and trophic control of ungulate prey coupled by apparent competition?

Aug 23, 2026

Understanding how donor (bottom-up) and trophic (top-down) modes of population control shape food web structure and dynamics remains a central ecology goal, yet mechanistic consensus is lacking. Two recurring patterns suggest generality: predators trigger trophic cascades and power-law predator-prey relationships often linked to donor control. Using ungulate assemblage data from three African savannas, the study shows coupled donor and trophic control via non-reciprocal apparent competition (NRAC). Rankings and dynamics across additional savannas support NRAC as a candidate mechanism.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages52

Reading Time2 h 11 min

AccessFree to download

Abstract

Introduction

1 In African savannas, are donor and trophic control of ungulate prey coupled by apparent 2 competition? 3 4 5 Authors: 6 Nicholas J. Georgiadis 1, Justine A. Becker2, Adam T. Ford3, Douglas N. Kamaru4, Jacob R. 7 Goheen4 8 9 10 1. 4718 SW Pendleton St., Portland OR 97221 (independent researcher) 11 2. Department of Ecology, Montana State University, Bozeman, MT, USA 12 3. Department of Biology, University of British Columbia, 1177 Research Road, Kelowna, 13 British Columbia, V1V 1V7, Canada 14 4. Department of Natural Resource Ecology and Management, Iowa State University, 15 Ames, Iowa, USA 16 17 Contact and Corresponding Author: Nicholas J. Georgiadis ([nicogeo@uw.edu](nicogeo@uw.edu)) 18 19 20 Open Research Statement 21 Data used to derive Figure 2 were originally published in graphic form in Georgiadis et al. 22 (2007b), and are provided as numerical values in the Supplementary Information for this 23 manuscript as Table SI 1. A subset of data from the database published by Daskin and 24 Pringle (2018), which were used to perform the analysis described in Table 2, is provided in 25 Dryad: [http://datadryad.org/share/vTtYm0p8erwl8RozWe4I7L04lGfTZ0SyALojeQhI660](http://datadryad.org/share/vTtYm0p8erwl8RozWe4I7L04lGfTZ0SyALojeQhI660) 26 27 Artificial Intelligence (AI) Policy Statement 28 During preparation, and at multiple points in developing the manuscript, AI tools Undermind 29 and ChatGPT were used to 1) Reference discovery: targeted questions (over 70 in total) were 30 submitted to Undermind to identify relevant literature concerning specified ecological 31 concepts, models, and case studies. 2) Summarize: ChatGPT was used to generate summaries 32 of selected published papers, which were then checked against original sources. These tools 33 were used iteratively across the manuscript, particularly in sections synthesizing theory and 34 empirical case studies, to help ensure coverage and correct interpretation of relevant 35 literature. All interpretations, arguments, and conclusions are our own. 36 37 Key words and phrases: 38 apex predator, bottom-up control, community structure, endangered species, food webs, 39 power law, predation, predator-prey dynamics, top-down control, trophic cascade 40 41 Abstract 42 Understanding how donor (bottom-up) and trophic (top-down) modes of population control 43 shape food web structure and dynamics has long been a major goal of ecology, yet consensus 44 about mechanisms is lacking. Two prevalent patterns hint at generality in mechanisms that shape 45 predator-prey communities. First, within communities, herbivore biomass declines and plant 46 biomass increases in the presence of predators, regardless of ecosystem productivity, evoking a 47 trophic cascade. Second, across communities, predator biomass density increases sublinearly 48 with prey biomass density, a ‘power law’ which often is assumed to arise from donor control. 49 We show how both patterns can emerge simultaneously, using data from ungulate assemblages 50 in African savannas. Within three savannas where mechanisms underlying trophic dynamics are 51 understood (the Greater Serengeti ecosystem, Kruger National Park, and the Laikipia highlands), 52 prey biomass is dominated by one or a few ungulate species that are donor controlled, yet they 53 support most of the predators. The same predators also consume less abundant prey species that 54 are trophic controlled. In effect, donor and trophic control of prey are coupled by generalist 55 predators via ‘non-reciprocal apparent competition’(NRAC) . Within 56 African savannas where 56 ungulate biomass densities but not dynamics are known, mean ungulate biomass rankings 57 resemble those of Serengeti, Kruger, and Laikipia, and are therefore consistent with the 58 hypothesis of NRAC. Under NRAC, total prey biomass declines within systems because trophic- 59 controlled prey a

FAQs

What ecological question does the paper address?

Whether donor (bottom-up) and trophic (top-down) control of ungulate prey are coupled through apparent competition, and how this shapes food-web structure and dynamics.

Which two macroecological patterns are used as clues?

Predators are associated with herbivore biomass declines and plant biomass increases (trophic cascade), and predator biomass increases sublinearly with prey biomass density, often described by power laws.

How do the authors explain why both patterns can arise together?

They show both patterns emerge simultaneously through non-reciprocal apparent competition (NRAC) mediated by generalist predators, where donor-controlled dominant prey support most predators while trophic-controlled prey are suppressed.

Aug 23, 2026

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