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Comment arising from a paper by Wittmer et al.: hypothesis testing for top-down and bottom-up effects in woodland caribou population dynamics

  • Population Ecology
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An Erratum to this article was published on 24 October 2007

Abstract

Conservation strategies for populations of woodland caribou Rangifer tarandus caribou frequently emphasize the importance of predator–prey relationships and the availability of lichen-rich late seral forests, yet the importance of summer diet and forage availability to woodland caribou survival is poorly understood. In a recent article, Wittmer et al. (Can J Zool 83:407–418, 2005b) concluded that woodland caribou in British Columbia were declining as a consequence of increased predation that was facilitated by habitat alteration. Their conclusion is consistent with the findings of other authors who have suggested that predation is the most important proximal factor limiting woodland caribou populations (Bergerud and Elliot in Can J Zool 64:1515–1529, 1986; Edmonds in Can J Zool 66:817–826, 1988; Rettie and Messier in Can J Zool 76:251–259, 1998; Hayes et al. in Wildl Monogr 152:1–35, 2003). Wittmer et al. (Can J Zool 83:407–418, 2005b) presented three alternative, contrasting hypotheses for caribou decline that differed in terms of predicted differences in instantaneous rates of increase, pregnancy rates, causes of mortality, and seasonal vulnerability to mortality (Table 1, p 258). These authors rejected the hypotheses that food or an interaction between food and predation was responsible for observed declines in caribou populations; however, the use of pregnancy rate, mortality season and cause of mortality to contrast the alternative hypotheses is problematic. We argue here that the data employed in their study were insufficient to properly evaluate a predation-sensitive foraging hypothesis for caribou decline. Empirical data on seasonal forage availability and quality and plane of nutrition of caribou would be required to test the competing hypotheses. We suggest that methodological limitations in studies of woodland caribou population dynamics prohibit proper evaluation of the mechanism of caribou population declines and fail to elucidate potential interactions between top-down and bottom-up effects on populations.

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Authors and Affiliations

  1. Ontario Terrestrial Assessment Program, Ontario Ministry of Natural Resources, 1235 Queen Street East, Sault Ste. Marie, ON, Canada, P6A 2E5

    Glen S. Brown

  2. Wildlife Consultant, P.O. Box 521, Dowling, ON, Canada, P0M 1R0

    Lynn Landriault

  3. National Council for Air and Stream Improvement, P.O. Box 1490, Station B, Montreal, PQ, Canada, H3B 3K5

    Darren J. H. Sleep

  4. Department of Biology, Laurentian University, Sudbury, ON, Canada, P3E 2C6

    Frank F. Mallory

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  1. Glen S. Brown
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  2. Lynn Landriault
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  4. Frank F. Mallory
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Correspondence to Glen S. Brown.

Additional information

Communicated by John Fryxell.

An erratum to this article can be found at http://dx.doi.org/10.1007/s00442-007-0881-1

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Brown, G.S., Landriault, L., Sleep, D.J.H. et al. Comment arising from a paper by Wittmer et al.: hypothesis testing for top-down and bottom-up effects in woodland caribou population dynamics. Oecologia 154, 485–492 (2007). https://doi.org/10.1007/s00442-007-0855-3

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