Bryophytes typically have a small body size and are widely distributed around the world. Research suggests bryophytes have various kinds of secondary metabolites and natural compounds which have many biological activities. High acid-detergent fiber (ADF) concentrations found in the mosses make them indigestible. For these reasons, bryophytes are not thought to be grazed by herbivorous mammals. However, studies found mosses were eaten by a variety of vertebrates and birds in cold environments. Reindeer feed mainly on mosses in winter. Mosses account for about 10% of their winter diet. The reason reindeer feed on mosses is that they contain a special chemical compound, arachidonic acid, not synthesized by reindeer themselves. Mosses contain a high concentration of arachidonic acid. Ingestion of arachidonic acid could benefit animals in several ways: (1) arachidonic acid is one of the precursors of some prostaglandin hormones, (2) because it has a low melting point (-49.5℃) arachidonic acid might contribute to lowering the melting point of fats in the animal's extremities, (3) most importantly, arachidonic acid affords protection to cell membranes against the effects of cold. Consuming this fatty acid may afford the reindeer better protection against cold weather.
We analyzed reindeer feces in Aoluguya, a minority community in the Great Khingan mountain range of Inner Mongolia, to study the bryophyte species consumed by reindeer. The feces samples were collected in April, June, and September in 1999 and analyzed microhistologically. The results show residual leaf fragments of bryophytes account for a large proportion of the feces; only leaf fragments of bryophyte, and not other plant parts, keep distinctively recognizable forms. The morphologic features of cells were seen clearly and distinctly. We found 5.63%, 2.2%, and 12.92% of the sample content collected in April, June and September was from bryophytes, respectively. Four genera comprise most of the bryophyte material found in the reindeer feces: Pleurozium Mitt., Dicranum Hedw., Aulacomnium Schwaegr., and Ptilidium Nees., with Pleurozium schreberi making over 70% of the total. Polytrichum juniperinum was found in relatively large amounts only in sample content collected in September. Didymodon Hedw. and Racomitrium Brid. were found occasionally in the sample content. A small amount of bryophyte leaf fragments which could not determined to species comprised less than 0.01% of the sample content. Reindeer appear to feed on bryophytes seasonally but the species and relative proportion of the main species of bryophytes consumed do not change significantly. Obviously the eating habits of reindeer are selective.
We also measured the coverage and phytomass of bryophytes of four forest types used by reindeer: Pinus pumila-Larix gmelinii forests, Ledum palustre var. angustum-Larix gmelinii forests, Rhododendron dahuricum-Larix gmelinii forests and Helodia. The result shows the coverage and phytomass of one or two species of bryophytes are higher than other species in every forest and Hylocomium splendens, Sphagnum spp. and Pleurozium schreberi are dominant bryophytes in the four types of forests we investigated. The genera found in the reindeer feces account for 45.5% of the genera by the total number of genera found in the four forest types. If grazing reindeer prefer to graze the most abundant bryophytes in their habitat, these species would have more grazing pressure than less frequent species. The selection of bryophytes by reindeer is determined by the abundance of the bryophyte species itself.