Abstracts: Body Size Variation in Caribou Ecotypes and Relationships with Demography

One of the bigger arguments amongst Caribou biologists is what is the relationship between the different forms we see, and how important they are. For example, on one hand you have the big migratory herds like Western Arctic, but then you have more woodland herds like the Mentasta. Finally, there are sedentary montane herds. All three look like they have different things going on morphologically too, according to these authors. I'm fairly willing to believe that, and I'm willing to believe their mechanism - that it's habitat induced variation, and not anything genetic. That is to say, they're like that because they live there, and if they didn't live there, they wouldn't be like that.


Here's the abstract

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 Que ́ bec-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 Rivie` re-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 Rivie` re-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.

Couturier, Otto, Côté, Luther and Mahoney. 2010. Body Size Variations in Caribou Ecotypes and Relationships With Demography. J. Wildlife Management, 74, pp. 395-404. DOI: 10.2193/2008-384

Totally unrelated, but I met Shane Mahoney last year - I think it as at the Wildlife Soc. 2009 meeting, but I'm fuzzy on that point. He's an entertaining guy, and as smart as it gets. Côté is also very clever, though I been able to meet him directly yet.