Ipomopsis aggregata exhibits substantial powers of regrowth following removal of its primary shoot by herbivores, but Bergelson and Crawley found no evidence of overcompensation in several studies: 1) in a comparison between individuals on grazed and ungrazed sides of exclosure fences, 2) in a comparison between artificially clipped and control plants in one population in the Okanagan National Forest, Washington, or 3) in comparisons between grazed and ungrazed plants in 14 natural populations. The authors tested whether ungulate grazing affects the population size of Ipomopsis aggregata by comparing populations inside and outside deer exclosures at 7 sites in the western United States. Results showed that the presence of grazers can lead to substantially reduced plant population density. This decrease in population density is not correlated with a decrease in the reproductive output of individuals, and instead must be due to other direct or indirect effects of ungulate grazers.
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