Body Size Variations in Caribou Ecotypes and Relationships With Demography

Abstract

In many vertebrates size is one of the most influential and variable individual characteristics and a strong determinant of reproductive success. Body size is generally density dependent and decreases when intraspecific competition increases. Frequent and long‐distance movements increase energy expenditures and, therefore, may also influence body size, particularly in highly mobile species. Caribou (Rangifer tarandus, also known as reindeer) exhibit tremendous variation in size and movements and thus represent an excellent candidate species to test the relationships between body size, population size, and movements. We analyzed body measurements of adult female caribou from 7 herds of the Québec‐Labrador Peninsula, Canada, and we related their morphology to population size, movements, and annual ranges. The herds represented 3 ecotypes (migratory, montane, and sedentary). Ecotypes and herds differed in size (length), shape (roundness), and movements. The sedentary ecotype was larger and moved 4 to 7 times less than the migratory ecotype in the 1990s. At the start of a demographic growth period in the early 1960s, migratory caribou from the Rivière‐George (hereafter George) herd had longer mandibles than caribou of the sedentary ecotype. Mandible length in the George herd declined in the 1980s after rapid population growth, while individuals performed extensive movements and the herd's annual range increased. Migratory caribou then became shorter than sedentary caribou. After the George herd decline in the 1990s, mandible length increased again near levels of the 1980s. Caribou from the migratory Rivière‐aux‐Feuilles herd later showed a similar decline in mandible length during a period of population growth, associated with longer movements and increasing annual range. We hypothesize that the density‐dependent effect observed on body size might have been exerted through summer habitat degradation and movement variations during herd growth. Our study has 2 important implications for caribou management: the distinctiveness of different populations and ecotypes, and the correlations between population trajectories and changes in body condition and habitat.

Have geographical influences and changing abundance led to sub-population structure in the Ahiak caribou herd, Nunavut, Canada?

“…We suggest that the shorter pre-calving migration distance for caribou that calved on Adelaide Peninsula may be from an energetic trade-off between the costs of foraging on the tundra, travel, and predation risk (Couturier et al, 2010). Currently, the high proportion of cows shifting calving locations along the length of the calving ground among years and the switching of cows wintering on the tundra or taiga/foresttundra biome suggests a high degree of plasticity -the ability to change biology or behavior to respond to changes in the environment -in individual behaviour within a population (for example, Couturier et al, 2010). However, variance in inter-annual selection of calving and wintering areas by individual adult females may be reduced if changing environmental conditions increase energetic costs and reduce fitness of cows and calves.…”

An enigmatic group of arctic island caribou and the potential implications for conservation of biodiversity

“…Other demographic and environmental factors may have contributed to the large body size of this unique group of Peary caribou. For example, Courturier et al (2010) have shown that migratory behaviour, population density, and intraspeci c competition may in uence body size of caribou. Regardless, the ultra pearyi remain an enigma because no other noticeably large-bodied caribou have ever been reported on any other island at similar latitude.…”

“…In turn, recent studies have shown that demographic factors can directly impact body condition. For example, among migratory caribou, major in uences on body size include reproductive rates (Taillon et al, 2012), as well as population density, intraspeci c competition, and migration duration (Courturier et al, 2010).…”

Standardized monitoring of Rangifer health during International Polar Year

“…Samples submitted included the lower jaw and metatarsal bone ( Fig. 3b) with skin on, and core data collected included age (using tooth cementum annuli) (Miller, 1974;Matson, 1981), pregnancy, body condition (back fat, marrow fat, and a subjective hunter assessment; Lyver & Gunn, 2004), body size (jaw and metatarsal length; Parker, 1981;Couturier et al, 2010), and presence and intensity of the parasite Besnoitia tarandi in metatarsal skin . Besnoitia cysts were quanti ed in the lab on gross observation using categories of number of cysts per square centimeter [0 = no cysts; 1 = very occasional (< 4 cysts/cm²); 2 = easily observed (4-10 cysts/ cm²); 3 = high density (> 10 cysts/cm²)].…”

“…A technical approach to monitoring body condition began in the mid-1900s, with emphasis on describing and validating condition indices which had allometric relations to the status of muscle, bone and fat, and their chemical constituents: water, protein, lipid, and ash (Dauphiné, 1976;Langvatn, 1977;Ringberg et al, 1981a;Reimers & Ringberg, 1983;Huot & Goudreault, 1985;Adamczewski et al, 1987a;Huot & Picard, 1988;Allaye Chan-McLeod et al, 1995;Gerhart et al, 1996). Monitoring body size (e.g., lower jaw and metatarsal bones) and shape (e.g., heart girth) also provides insight into population trends (Parker, 1981;Crête & Huot, 1993;Mahoney & Schaefer, 2002;Couturier et al, 2010). For the most part, this type of monitoring has been scientist-driven, typically initiated and conducted by wildlife managers or researchers, and often focused on a particular herd intermittently or for a nite length of time.…”