Major decline in marine and terrestrial animal consumption by brown bears (Ursus arctos)

Abstract

Human activities have had the strongest impacts on natural ecosystems since the last glacial period, including the alteration of interspecific relationships such as food webs. In this paper, we present a historical record of major alterations of trophic structure by revealing millennium-scale dietary shifts of brown bears (Ursus arctos) on the Hokkaido islands, Japan, using carbon, nitrogen, and sulfur stable isotope analysis. Dietary analysis of brown bears revealed that salmon consumption by bears in the eastern region of Hokkaido significantly decreased from 19% to 8%. In addition, consumption of terrestrial animals decreased from 56% to 5% in western region, and 64% to 8% in eastern region. These dietary shifts are likely to have occurred in the last approximately 100–200 years, which coincides with the beginning of modernisation in this region. Our results suggest that human activities have caused an alteration in the trophic structure of brown bears in the Hokkaido islands. This alteration includes a major decline in the marine-terrestrial linkage in eastern region, and a loss of indirect-interactions between bears and wolves, because the interactions potentially enhanced deer predation by brown bears.

Testing for a predicted decrease in body size in brown bears (Ursus arctos) based on a historical shift in diet

“…Nevertheless, the historical decrease in body size has likely influenced population dynamics because body size is correlated with many population parameters, including population density, productivity, and persistence (Atkinson and Ramsay 1995;Andersson and Iwasa 1996;Post et al 1997;Laundré et al 2007;Wauters et al 2007). The major historical dietary shift in Hokkaido brown bears is likely the result of human activities, such as salmon fishing and dam construction (Matsubayashi et al 2015). If this is the case, then our results suggest that human activities not only caused the historical shift in diet, but also contributed to the downsizing of Hokkaido brown bears (Robbins et al 2004).…”

“…Stable isotope data for the brown bears that lived in the Hokkaido Islands before human colonization (from 4000 BC to the late 19th century) were obtained from Matsubayashi et al (2015) (Supplementary Table S1). 1 Growth stage and sex data were also available for most of the historical brown bears of the eastern region (subpopulation Nos.…”

“…7, 8, 9, 10; Fig. 1; Matsubayashi et al 2015), so we used the stable isotope data of these bears to predict their body size. The ␦ 13 C and ␦ 15 N values of the historical brown bears were, respectively, -18.4‰ ± 1.4‰ (mean ± SD) and 9.4‰ ± 2.7‰ for eastern males (n = 14) and -20.0‰ ± 1.1‰ and 6.7‰ ± 2.5‰ for eastern females (n = 13).…”

“…In the Hokkaido Islands of Japan, a major shift has occurred in the diet of omnivorous brown bears (Ursus arctos L., 1758) over the last 200 years (Matsubayashi et al 2015), which has been characterized by a major decline in the consumption of meat, such as Pacific salmon (species of the genus Oncorhynchus Suckley, 1861) and Sika deer (Cervus nippon Temminck, 1838), due to human activities. To our understanding, such a dietary shift from a carnivorous to a largely herbivorous diet in omnivorous wild animals has not been reported previously elsewhere in the world.…”

“…These analyses were performed separately for each sex, because several previous studies have suggested that male and female growth patterns are different in brown bears (Bershinikov et al 2004;Mowat and Heard 2006). Finally, we predicted the differences in body sizes between modern and historical bears using the isotopic values for each as reported in Matsubayashi et al (2015).…”