Sierra Nevada Subalpine Zone - Species Interactions

Species Interactions

The harsh conditions present in the subalpine zone are sufficient to keep competitive interactions at a minimal level. Species interactions theory predicts that competition should be low in stressful environments and that positive, mutualistic interactions should be favored (e.g.) In fact, lichens, which are mutualisms between fungi and algae or cyanobacteria, are common in subalpine and alpine ecosystems. The clumpy nature of subalpine vegetation is also in part a manifestation of a positive interaction, whereby individuals increase their fitness by having neighbors that reduce the effects of high wind and cold temperatures.

There is a mutualistic interaction between Clark's nutcracker and two pines of the subalpine zone. Most pine species are wind-dispersed and their seeds are flat and winged. However, whitebark pine and limber pine both have non-winged, succulent seeds that have probably co-evolved with Clark’s nutcrackers. These birds, which use the seeds as a staple food source, cache seeds in the soil and in cracks of rocks. Like most caching species, the nutcrackers store more than they can ever find and eat, so many of the seeds can germinate when conditions are favorable. In the subalpine, this type of seed dispersal may be particularly advantageous because seeds find themselves immediately protected from high winds and low temperatures, and are therefore more likely to succeed during germination.