Pre-European diets II
Regional reconstructions of pre-European habitat & distributions
On the page devoted to Pre-European grizzly bear diets I feature a handful of foods that were almost certainly critical sources of energy and nutrients for grizzlies in parts of the western US where they are currently extirpated: salmon, bison, oak mast, and seeds of whitebark and pinyon pines. I also highlighted a handful of excavated foods. Notably, though, I didn't talk about berries, another critical source of energy. Nor did I attempt to integrate and synthesize the information that I've assembled on pre-European bear foods in map form.
I attempt to remedy this deficit here where I offer reconstructions of habitat for much of former grizzly bear habitat in the western US. I do this primarily in the form of maps that represent gradients of diversity for various categories of bear foods, including berries, tree mast, roots, and grazed foods. Because I did not have access to geospatial maps of species abundance, I reckoned diversity simply as the numbers of species of each plant category present in a given area. You will also find a map for the northern Rockies that delineates speculative foraging economies based on information that includes prevalence of berry-producing shrubs. I end with a highly refined map of grizzly bear distribution derived from merging information about bear foods with fine-scale maps of vegetation types, coupled with a consideration of the likely limits imposed by climate (primarily heat and drought) on where grizzly bears could live. You can find a description of my sources of information on pre-European grizzly bear foods at Pre-European diets.
Northern US Rockies
The maps immediately above are the basis for reconstructing pre-European grizzly bear foraging economies in the northern US Rocky Mountains and adjacent Great Plains and Pacific Northwest. The varying hues of green in the map to the left correlate with the number of important berry-producing shrubs that were present. The darker the green the greater the number, ranging from one to four of the following: huckleberry (Vaccinium membranaceum), serviceberry (Amelanchier alnifolia), chokecherry (Prunus virginiana), and buffaloberry (Sheperdia canadensis). Light tan denotes core bison distribution; darker brown, the distribution of vegetation types dominated by Gambel oak (Quercus gambelli); and the dashed blue line, the eastern limit of spawning anadromous salmonids. The map to the right shows the distribution of whitebark pine, differentiated by current levels of exploitation by extant black and grizzly bears. The darker the green the heavier the documented levels of pine seed consumption. The dashed black line in this map denotes the approximate eastern limit of a pronounced Pacific maritime influence.
So...the take away? Prior to the extirpations and other dramatic reductions of salmon spawning runs in the Pacific Northwest, the Columbia River basin was a salmon-berry system. On the berry side, huckleberry was, as it is now, probably the most heavily consumed fruit. Going east, the berry component of grizzly bear diets probably dropped dramatically as the climate became ever more continental. At higher elevations, grading to the foothills, this was a meat and pine seed system, but with a significant fraction of berries. Farther east yet, at lower elevations, the grizzly bear diet was almost certainly dominated by meat, primarily bison, but still with significant representation of berries and roots (for more on this Great Plains diet see immediately below). The dramatic transition between berries and terrestrial meat in the current grizzly bear diet of the Northern Continental Divide is shown by the inset map at far left (thanks to research by Rick Mace). The dashed lines of varying colors represent isopleths for the percent contribution of meat to the bear diet, which rises dramatically and rapidly from around 12% west of the continental divide to in excess of 88% as one moves east out onto the plains. Which lends weight to the probable importance of meat to plains-dwelling grizzlies (see Terrestrial meat and The bison factor). Finally, moving south along the spine of the Rockies, you enter an economy where acorns were almost certainly of considerable importance to pre-European grizzlies, probably augmented by bison meat and berries (e.g., chokecherries and serivceberries).
Salmon, berries, bison & oak
Whitebark pine
Great Plains
Black Hills
The maps immediately above show the diversity of known or probable grizzly bear plant foods on the Great Plains, differentiating roots (farthest left) from berries (center) from mast-producing tree species (farthest right). The darker the brown, red, or green, the greater the number of species present of each food type.
The most prominant root foods were probably cattail (Typha latifolia), breadroot (Psoralea sp.), Jerusalem artichoke (Helianthis tuberosus), and groundnut (Apios americana). Of these, we have the greatest documentation of grizzlies digging breadroots. Turning to berries, the most heavily used by bears (as in the northern Rockies) were chokecherry, serviceberry, and buffaloberry (Sheperdia sp.), plus American plums (Prunus americana). Finally, in the category of mast, grizzlies probably consumed hazelnuts (Corylus cornuta) and oak acorns in the very few places where they were abundant.
The bar graph to the immediate right attempts to quantify the relative importance of top foods (including meat sources) to not only grizzly bears, but also to their competitors on the Great Plains: black bears and people. This is based on a compendium of direct observations. According to this synthesis, grizzlies on the Great Plains ate a lot of bison meat, chokecherries, plums, serviceberries, buffaloberries, and breadroots. And, of this, the food source that was most available to them--i.e., entailing the least competition--was bison carrion. Given the probable importance of bison to plains grizzlies, it is worth looking at The bison factor for more detail, including a map of bison distribution at different periods.
Putting this all together: The northern Great Plains stands out as the most productive environment for grizzlies, especially reckoned in terms of the energetically most important foods: meat and berries (again, see The bison factor). By contrast, the southern plains appear to be relatively impoverished in all regards: berries, roots, and bison. Interestingly, the eastern margin of the Great Plains is a comparatively rich source of root foods; Jerusalem artichoke and groundnut, in particular. But, then, root foods tend to not be that energetically rewarding for grizzlies (see Nutrition). At a finer scale, most habitat productivity was probably concentrated in the moister and more fertile river bottoms and woody draws of the Great Plains (see the center map above, which includes the major rivers of this region). Certainly this would be the case for all of the berry-producing species. Finally, the Black Hills area stands out as a particular hot spot when it comes to grizzly bear foods, including contrations of berries, mast, root foods, and even bison. All of this aligns with where grizzlies appear to have been most abundant at the time of first extensive contact with Europeans (see The Holocene).
Pacific Coastal Areas
Here, the maps immediately above show diversity of different grizzly bear plant foods in California and Oregon. Parenthetically, I limited my reconstruction to these two coastal states because Washington (unlike California and Oregon) lacked a comprehensive online floral atlas. Most of the observations that informed my identification of grizzly bears foods came for the book (California Grizzly) by Storer and Tevis. But not wholly. My other sources included the journals of European explorers, contemporary black bear studies, and ethnobotanical studies. These latter sources were especially important because the ones focused on grizzlies rarely identified the specific root, oak, or clover species being exploited by the observed bears. By contrast, ethnobotanical studies go to great lengths to identify these species and the reasons why they were used by humans.
Clovers were apparently heavily grazed by grizzlies in coastal meadows of California. The two most likely candidates include variegated clover (Trifolium variegatum) and bull clover (T. fucatum; see the map farthest left). Considering roots, there were probably numerous species exploited by grizzlies, including tule (Typha latifolia), wild carrot (Daucus pusillus), blue dick (Dichelostemma capitatum), Ithurial's spears (Triteleia laxa), tuberous sanicle (Sanicula tuberosa), Brodiaea elegans, and yampa (Perideridia sp.). As with roots, grizzlies ate the berries of numerous species, the most important of which were probably manzanita (Arctostaphylos glauca, glandulosa, viscida, etc.), wild cherries (Prunus ilicifolia), wild grapes (Vitis californica), wild plums (Prunus subcordata), serviceberries, and, along the north coast, salmonberries (Rubus spectabilis), and huckleberries (Vaccinium ovatum). Finally, there was oak mast; probably one of the most important of foods. These included Quercus dumosa, berberidifolia, garryana, wislizeni, agrifolia, kelloggii, and lobtata. The references to grizzlies eating acorns in and around the central valley of California are so numerous as to preclude even a summary. In addition to these vegetal foods, coastal grizzlies ate significant quantities of animal matter, including carrion from whales, ungulates such as elk and deer, pocket gophers, and insects such as ants and hornets. Finally, I refer you to spawning salmonids. You can find a map of the pre-European extent of salmon spawning runs on the page devoted to Pre-European diets I.
Putting this all together? Northern California, the California coastal ranges, and areas surrounding California's Central Valley were proabably overun with grizzlies exploiting the rich vegetal food resources. Salmon were an additional important part of the mix in coastal Oregon and much of northern California. Based on this evidence, there is little reason to doubt previous observations regarding the abundance of grizzly bears in coastal California and adjacent areas surrounding the Central Valley. There was lots of food to support them, including an abundance of acorns, augmented by spawning salmon farther north. No wonder First Peoples of this region were apparently in constant negotation with grizzlies over use of space and foods.
A habitat-based reconstruction of pre-European grizzly bear distribution
I conclude this page with a reconstruction of grizzly bear distributions in the western US based on integrating information about all of the factors that likely determine where grizzlies can live, and in what numbers. Much of this is based on the distributions of key foods in different vegetation types. I relied heaviliy on a comprehensive set of state-level vegetation maps produced by the US Evironmental Protection Agency, specifically their Level 3 Ecoregion maps. I also integrated information about climate, specifically those parameters that defined extreme desert conditions as well as areas of sustained extreme heat. I considered an average July temperature of >80 oF to be a threshold above which grizzly bears would be dealing with significant thermoregulatory stress. Grizzlies evolved in the extreme cold of northern Pleistocene environments (see Evolutionary biogeography), with little resulting tolerance of sustained high heat.
Red areas denote what I speculate was core range and, orange areas, adjacent peripheral range that
was occupied by transient grizzlies or by residents during periods of more clement conditions. You will notice that on the Great Plains in particular core and peripheral distributions are substantially correlated with riverine habitats. Extreme desert (>80oF & <4" annual ppt) is denoted by dark gray and less extreme desert (>75oF and 4-8" of ppt) by light gray. The dashed black line marks the northern boundary of areas south of which ambient temperatures probably limited where grizzlies could live; in the southern Central Valley of California, the Mohave and Sonoran Deserts, parts of the Chihuahuan Desert, and the southern Great Plains of Texas and eastern Oklahoma.
This reconstruction warrants a few comments: The largest areas of contiguous core distribution were almost certainly in the northern US Rockies, followed by Colorado and northern California and southwestern Oregon. It is probably no coincidence that these areas supported, or continue to support, the last grizzly bear populations (see Extirpations). By contrast, there is little reason to believe that grizzlies were present in the Great Basin in any numbers; certainly not in the Mohave and Sonoran Deserts. This map furthermore suggests that grizzly bears living in the Davis Mountains of Texas, the Steens and nearby Owyhee Mountains of Oregon and adjacent Idaho, and in the Chuska Mountains of northeastern Arizona probably existed as island populations. Finally, the reconstructed distribution of grizzlies on the Great Plains suggests, first, that bears here were quite vulnerable to competition with people and black bears, as well as the elevated lethality of westward-moving European explorers and settlers (see The lethality factor) and, second, that the southern plains and adjacent regions of Texas were truly not a very hospitable environment for grizzly bears.
