A conceptual model for migratory tundra caribou to explain and predict why shifts in spatial fidelity of breeding cows to their calving grounds are infrequent

Abstract

Calving grounds of migratory tundra caribou (Rangifer tarandus) have two prominent characteristics. Firstly, the cows are gregarious, and secondly, the annual calving grounds spatially overlap in consecutive years (spatial fidelity). The location of consecutive annual calving grounds can gradually shift (either rotationally or un-directional) or more rarely, abruptly (non-overlapping). We propose a mechanism to interpret and predict changes in spatial fidelity. We propose that fidelity is linked to gregariousness with its advantages for individual fitness (positive density-dependence). Our argument is based on a curvilinear relationship between the density of cows on the calving ground (which we use to index gregariousness) and spatial fidelity. Extremely high or low densities are two different mechanisms which can lead to reduced spatial fidelity to annual calving grounds and reflect the caribou's adaptive use of its calving ranges.

What Happened to the Beverly Caribou Herd after 1994?

“…One explanation is that there was a true numerical decline in Beverly herd size as death rates consistently exceeded birth and recruitment rates. The shift in calving distribution to the Ahiak herd's calving ground between 2006 and 2009 was a consequence of the collapse in calving densities as the remaining Beverly cows switched to maintain the advantages of gregarious calving (Gunn et al, 2012). If this explanation is correct, then the Beverly herd is no longer identifiable as a distinct herd.…”

“…The Beverly herd has three immediate neighbouring herds with traditional calving grounds recorded through Aboriginal knowledge and aerial surveys: the Qamanirjuaq traditional calving grounds about 400 km to the southeast (Heard, 1983;BQCMB, 1999a, b), the Bathurst calving grounds about 450 km to the northwest (Heard, 1983;Gunn et al, 2012), and the Ahiak calving grounds 250 km north along the Queen Maud Gulf coast (Heard et al, 1987;Gunn et al, 2000Gunn et al, , 2013a (Fig. 1).…”

Denning ecology of barren-ground wolves in the central Canadian Arctic.

“…The distribution of barren-ground caribou is density-dependent such that range expansion and contraction are a function of the size of the herd (Simmons et al 1979, Bergerud et al 1984, Heard and Calef 1986, Messier et al 1988, Couturier et al 1990, Gunn et al 2012. Gunn et al (2013) reported that the winter range of the Bathurst herd has contracted since 2002, corresponding to the decline of the herd.…”

“…Heard and Calef (1986) and Heard and Williams (1992) suggested that tundra wolf populations respond numerically to changing caribou densities. Space-use patterns of barrenground caribou are density-dependent where the expansion and contraction of their range is a function o f the population size of the herd (Simmons et al 1979, Bergerud et al 1984, Heard and Calef 1986, Messier et al 1988, Couterier et al 1990, Gunn et al 2012. When caribou are abundant, the herd returns earlier to the southern portions of the summer range and within closer proximity to the denning areas of wolves, thus providing wolves with greater access to prey when the nutritional demands of pups are high.…”

“…Estimates in 2014 indicate the population has decreased below 30,000 animals (Adamczewski et al 2014), representing a > 90% decline in abundance. At large spatiotemporal scales, range use patterns of barren-ground caribou, including the extent of distribution, are density-dependent (Simmons et al 1979, Bergerud et al 1984, Heard and Calef 1986, Messier et al 1988, Couturier et al 1990, Gunn et al 2012). …”