Friday, September 27, 2013

Caribou diet

Woodland caribou (Rangifer tarandus-caribou) are the largest of all caribou subspecies in North America endemic to boreal forests. As I have detailed before in a different case I am not a big fan of subspecies and therefore I consider the woodland caribou as species but that is not the theme of this post. Actually, The numbers in woodland caribou herds have decreased over the years, their habitats have shrunk too, limiting the areas in which they can be found. Therefore, woodland caribou is considered a threatened species under Canada's Species at Risk Act.

Although there are likely multiple cumulative effects on declining caribou populations, the least studied relate to diet and food quality because these factors have been difficult to study under realistic field conditions This poor understanding of diet, has presented a key uncertainty with respect to understanding nutrition and energetics as response variables to the factors influencing population viability. Winter diet in particular may be a critical factor limiting maintenance of body fat and protein and affecting productivity.

In a new publication colleagues tried to tackle this problem with more recent methods. They compared traditional microhistology methods with DNA Barcoding of fecal samples and with the analysis of videos from collared animals in the wild. Microhistological methods in this context encompass the microscopic search for unique and identifiable plant or lichen pieces from undigested tissues found in a fecal sample. Not only is it difficult to find a lot of undigested material but what ever one finds needs to show enough traits to assign it to a particular species.

Based on more traditional methods such as direct observation and microhistology it was assumed that only a few lichen and woody plant species make up the diet of woodland caribou. It looks like the opposite is true. The researchers retrieved DNA Barcodes for 76 species consumed by woodland caribou, comprising 32 lichen species, 19 tree species, 11 moss species, and 11 species of herbs and grasses. They also present high variability of the proportion of lichen species among the sampled individuals. These results were corroborated by video camera estimates of their winter diet composition.

Overall it becomes clear that these two new technologies, video cameras and DNA Barcoding, can be used to determine the diet of woodland caribou. I would dare to add that only those can actually help to understand the caribou diet to an extend that leads to most effective conservation strategies. Especially DNA Barcoding provides an unprecedented species resolution for this type of samples especially when a reference library of sufficient size and quality is in place as it was in this case (500 species of plants and lichens).

Barcoding provides high species resolution at a fraction of the cost of video estimates, but does not provide the secondary information on habitat types, encounter rates with critical food types, and degree of feeding selectivity provided by animal-borne video technology.

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