Humans Strengthen Bottom-Up Effects and Weaken Trophic Cascades in a Terrestrial Food Web
Open Access
- 8 May 2013
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLOS ONE
- Vol. 8 (5), e64311
- https://doi.org/10.1371/journal.pone.0064311
Abstract
Ongoing debate about whether food webs are primarily regulated by predators or by primary plant productivity, cast as top-down and bottom-up effects, respectively, may becoming superfluous. Given that most of the world's ecosystems are human dominated we broadened this dichotomy by considering human effects in a terrestrial food-web. We studied a multiple human-use landscape in southwest Alberta, Canada, as opposed to protected areas where previous terrestrial food-web studies have been conducted. We used structural equation models (SEMs) to assess the strength and direction of relationships between the density and distribution of: (1) humans, measured using a density index; (2) wolves (Canis lupus), elk (Cervus elpahus) and domestic cattle (Bos taurus), measured using resource selection functions, and; (3) forage quality, quantity and utilization (measured at vegetation sampling plots). Relationships were evaluated by taking advantage of temporal and spatial variation in human density, including day versus night, and two landscapes with the highest and lowest human density in the study area. Here we show that forage-mediated effects of humans had primacy over predator-mediated effects in the food web. In our parsimonious SEM, occurrence of humans was most correlated with occurrence of forage (β = 0.637, pppppp ppp<0.0001). Our results contrast with research conducted in protected areas that suggested human effects in the food web are primarily predator-mediated. Instead, human influence on vegetation may strengthen bottom-up predominance and weaken top-down trophic cascades in ecosystems. We suggest that human influences on ecosystems may usurp top-down and bottom-up effects.Keywords
This publication has 28 references indexed in Scilit:
- Correlation and studies of habitat selection: problem, red herring or opportunity?Philosophical Transactions Of The Royal Society B-Biological Sciences, 2010
- Differential risk effects of wolves on wild versus domestic prey have consequences for conservationOikos, 2010
- Remote sensing and forest inventory for wildlife habitat assessmentForest Ecology and Management, 2009
- Human predators outpace other agents of trait change in the wildProceedings of the National Academy of Sciences of the United States of America, 2009
- Resource Selection Functions Based on Use–Availability Data: Theoretical Motivation and Evaluation MethodsThe Journal of Wildlife Management, 2006
- Global Consequences of Land UseScience, 2005
- Impact of Food and Predation on the Snowshoe Hare CycleScience, 1995
- Grass Utilization and Grazing Distribution within Intensively Managed Fields in Central AlbertaJournal of Range Management, 1995
- Food Webs: Linkage, Interaction Strength and Community InfrastructureJournal of Animal Ecology, 1980
- Responses of National Park Elk to Human ActivityThe Journal of Wildlife Management, 1978