Experimental evidence of trophic cascades initiated by large vertebrate predators is rare in terrestrial ecosystems. A serendipitous natural experiment provided an opportunity to test the trophic cascade hypothesis for wolves (Canis lupus) in Banff National Park, Canada. The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley (low‐wolf area), whereas wolves made full use of an adjacent area (high‐wolf area). We investigated the effects of differential wolf predation between these two areas on elk (Cervus elaphus) population density, adult female survival, and calf recruitment; aspen (Populus tremuloides) recruitment and browse intensity; willow (Salix spp.) production, browsing intensity, and net growth; beaver (Castor canadensis) density; and riparian songbird diversity, evenness, and abundance. We compared effects of recolonizing wolves on these response variables using the log response ratio between the low‐wolf and high‐wolf treatments. Elk population density diverged over time in the two treatments, such that elk were an order of magnitude more numerous in the low‐wolf area compared to the high‐wolf area at the end of the study. Annual survival of adult female elk was 62% in the high‐wolf area vs. 89% in the low‐wolf area. Annual recruitment of calves was 15% in the high‐wolf area vs. 27% without wolves. Wolf exclusion decreased aspen recruitment, willow production, and increased willow and aspen browsing intensity. Beaver lodge density was negatively correlated to elk density, and elk herbivory had an indirect negative effect on riparian songbird diversity and abundance. These alternating patterns across trophic levels support the wolf‐caused trophic cascade hypothesis. Human activity strongly mediated these cascade effects, through a depressing effect on habitat use by wolves. Thus, conservation strategies based on the trophic importance of large carnivores have increased support in terrestrial ecosystems.

There is growing concern that populations of migratory ungulates are declining globally. Causes of declines in migratory behavior can be direct (i.e., differential harvest of migrants) or indirect (i.e., habitat fragmentation or land-use changes). Elk (Cervus elaphus) are an important big game species in North America whose migratory behavior is changing in some montane ecosystems. We evaluated evidence and hypotheses for changes in migratory behavior and population decline in one of Canada's largest elk populations, the Ya Ha Tinda. We compared the ratio of migrant to resident elk (M:R) in the population and seasonal spatial distributions obtained from 22 winter and 13 summer helicopter surveys between 1972 and 2005. Timing of migration and the summer distribution for a sample of radiocollared elk also was compared for 1977-1980 (early period) and 2001-2004 (recent). The population M:R ratio decreased from 12.4 (SD ¼ 3.22) in the early period to 3.0 (SD ¼ 1.63). The decrease was greater than expected based on population change. Declines in M:R also mirrored behavior of radiocollared elk. More than 49% of radiocollared elk we monitored resided near the winter range year-round by [2001][2002][2003][2004], and migrants were spending less time on summer ranges. We found winter range enhancements, access to hay fed to wintering horses, recolonization by gray wolves (Canis lupus), and management relocations of elk were most consistent with observed elk population growth (adjusted for harvest and removals) and the change in migratory behavior. However, we could not isolate the effects of specific factors in time-series population modeling. We believe directly relating migrant and resident demography to habitat and mortality factors will be required to understand the mechanisms affecting migratory behavior in this and other montane elk herds. (WILDLIFE SOCIETY BULLETIN 34(5):1280-1294

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