Strength of a Trophic Cascade Between an Apex Predator, Mammalian Herbivore and Grasses in a Desert Ecosystem Does Not Vary with Temporal Fluctuations in Primary Productivity
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There has long been debate regarding the primacy of bottom-up and top-down effects as factors shaping ecosystems. The exploitation ecosystems hypothesis (EEH) predicts that predators indirectly benefit plants because their top-down effects limit herbivores’ consumption of plants, and that the strength of trophic cascade increases with increasing primary productivity. However, in arid environments, pulses of primary productivity produced by irregular rainfall events could decouple herbivore–plant and predator–prey dynamics if high conversion efficiency from seed biomass to consumers allows the rapid build-up of consumer populations. Here, we test predictions of the EEH in an arid environment. We measured activity/abundances of dingoes, red kangaroos and grasses, and diet of dingoes, in landscapes where dingoes were culled or not culled over 3 years. Dingo activity was correlated with rainfall, and their tracks were less frequent at culled sites. Kangaroo abundance was greater at sites where dingoes were culled and increased with rainfall in the previous 6 months. Grass cover was greater at sites where dingoes were not culled and increased with rainfall in the previous 3 months. During a period of average rainfall, dingoes primarily consumed rodents and increased their consumption of kangaroos during a period of drier conditions. Our results are consistent with the hypothesis that suppression of an apex predator triggers a trophic cascade, but are at odds with the EEH’s prediction that the magnitude of trophic cascades should increase with primary productivity. Our study demonstrates that temporal fluctuations in primary productivity can have effects on biomasses of plants and consumers which are in many ways analogous to those observed along spatial gradients of primary productivity.
Keywordstrophic cascade arid apex predator herbivore vegetation top down bottom up
The Australian Research Council funded this research. We thank Brenton von Takach Dukai, James Rees, Georgeanna Story, Bush Heritage Australia, North Australian Pastoral Company, Chris Dickman and Bobby Tamayo for their assistance. Comments by B. Bestelmeyer and two anonymous reviewers greatly improved this paper.
- Burnham KP, Anderson DR. 2002. Model selection and multimodel inference: a practical information-theoretic approach. New York: Springer.Google Scholar
- Caughley G, Shepherd N. 1987. Kangaroos: their ecology and management in the sheep rangelands of Australia. Cambridge: Cambridge University Press.Google Scholar
- Clarke K, Gorley R. 2006. PRIMER v6: user manual/tutorial (Plymouth routines in multivariate ecological research). Plymouth: Primer-E Ltd.Google Scholar
- Melis C, Jędrzejewska B, Apollonio M, Bartoń KA, Jędrzejewski W, Linnell JDC, Kojola I, Kusak J, Adamic M, Ciuti S, Delehan I, Dykyy I, Krapinec K, Mattioli L, Sagaydak A, Samchuk N, Schmidt K, Shkvyrya M, Sidorovich VE, Zawadzka B, Zhyla S. 2009. Predation has a greater impact in less productive environments: variation in roe deer, Capreolus capreolus, population density across Europe. Glob Ecol Biogeogr 18:724–34.CrossRefGoogle Scholar
- Zuur A, Ieno E, Walker N, Saveliev A, Smith G. 2009. Mixed effects models and extensions in ecology with R. Gail M, Krickeberg K, Samet JM, Tsiatis A, Wong W, editors. New York (NY): Spring Science and Business Media.Google Scholar