Elk

Native hunters of the Northwest Coast valued the local wapiti subspecies (Cervus elaphus roosevelti) greater than any other land animals as a source of both food and raw materials for tools. Wapiti population size depends on the quantity and quality of their preferred foods: easily digestible, high protein plants that occur most abundantly in meadows and thickets, particularly after spring and summer rains. Changing climate regimes affected the productivity of these foods but there is disagreement about whether climate periods with long dry summers helped or hindered wapiti populations on the Northwest Coast. Lepofsky et al. (2005) suggests wapiti abundance increased in periods with persistent summer drought due to increased fire frequency destroying forests and expanding meadows, and increasing the productivity of their preferred foods. While Broughton et al. (2008) suggests wapiti abundance decreased in periods with low spring-summer precipitation due to reductions in the duration and forage quality of the growing season.
The goal of this thesis is to eliminate one of these hypotheses with a systematic analysis of wapiti remains from six sites in western Whatcom County representing 300 to 5300 cal yr BP. Stable isotope analysis of nitrogen and carbon in wapiti bone collagen from contexts closely associated with radiocarbon dates. Mammal remains from levels closely associated to these radiocarbon dates were separated and counted to determine mammal NISP, and wapiti remains were identified to determine wapiti NISP. The relative abundance of wapiti was determined by dividing wapiti NISP by mammal NISP and converting to a percentage for each radiocarbon date, and for each climate period. Relative wapiti abundance was found to be dependent on climate period, with significantly lower wapiti abundance relative to other mammals during hot, dry climate periods. The δ13C values are low compared to other regions worldwide and remain stable through time suggesting that closed canopied temperate rainforests were the dominant terrestrial environment over the last 5300 calendar years. During the Medieval Warm period δ15N values are significantly higher suggesting that the hottest driest conditions of the late Holocene occurred at that time. During the warm dry climate periods such as the Medieval Warm Period, increased seasonality would lead to reduced hunting return and plant forage rates for people.

In this article the accumulative aspect of rock art is discussed.
In light of the simple fact that we are seeing rock art panels in their final form, questions concerning the interrelation between figures deriving from different time periods are addressed. The author’s aim is to draw attention to the long continuity of rock art sites and show how greater awareness of this aspect will affect
the way we comprehend this material in general. The continuity of rock art sites is exemplified by means of a case study of Nämforsen, located in the province of Ångermanland, northern Sweden.

Eph family receptor tyrosine kinases (including EphA3, EphB4) direct pathfinding of neurons within migratory fields of cells expressing gradients of their membrane-bound ligands. Others (EphB1 and EphA2) direct vascular network assembly, affecting endothelial migration, capillary morphogenesis, and angiogenesis. To explore how ephrins could provide positional labels for cell targeting, we tested whether endogenous endothelial and P19 cell EphB1 (ELK) and EphB2 (Nuk) receptors discriminate between different oligomeric forms of an ephrin-B1/Fc fusion ligand. Receptor tyrosine phosphorylation was stimulated by both dimeric and clustered multimeric ephrin-B1, yet only ephrin-B1 multimers (tetramers) promoted endothelial capillary-like assembly, cell attachment, and the recruitment of low-molecular-weight phosphotyrosine phosphatase (LMW-PTP) to receptor complexes. Cell-cell contact among cells expressing both EphB1 and ephrin-B1 was required for EphB1 activation and recruitment of LMW-PTP to EphB1 complexes. The EphB1-binding site for LMW-PTP was mapped and shown to be required for tetrameric ephrin-B1 to recruit LMW-PTP and to promote attachment. Thus, distinct EphB1-signaling complexes are assembled and different cellular attachment responses are determined by a receptor switch mechanism responsive to distinct ephrin-B1 oligomers.

The forage intake rate of grazing ungulates is limited either by the rate at which they encounter food items, or the rate at which food items are handled. Whether an ungulate is encounter- or handling-limited influences spatial and temporal depletion of forage, daily time budgets, and ultimately animal condition. Previously, vegetation abundance has been used as a surrogate for an ungulate's encounter rate with food items and related to observed bite rate to determine whether intake rate is encounter- or handling-limited. In temperate climates snow accumulation during winter limits access to vegetation by forcing animals to wade and paw through snow to consume underlying vegetation, increasing the amount of time required to encounter a food item. As a result, an ungulate may be handling-limited when foraging in a high biomass system under snow-free conditions, but becomes encounter-limited when snow accumulates. We derived a model that provides a frame work for estimating the rate at which a grazing ungulate encounters vegetation by considering foraging velocity, vegetation biomass and the time required to paw away snow when present. We then used data from focal observations of 36 wild elk Cervus canadensis wintering on a montane grassland in the Canadian Rockies of Alberta, Canada, to apply our model and estimate encounter rate over a range of vegetation abundance and snow conditions. Using AICc in a model selection approach we found that an asymptotic regression model of observed bite rate as a function of estimated encounter rate provided a better fit than similar models using only vegetation abundance as the explanatory variable. An asymptotic model suggests elk were handling-limited in the absence of snow, but became encounter-limited when snow accumulated. Our results demonstrate the importance of considering the influence of factors other than vegetation abundance on the intake rate of grazing ungulates.