Seed predation and selection exerted by a seed predator influence subalpine tree densities

Area of Science:

• Ecology
• Forest Ecology
• Wildlife Ecology

Background:

• Strongly interacting species can have significant direct and indirect effects on ecosystems.
• Pine squirrels (Tamiasciurus spp.) are dominant pre-dispersal seed predators of limber pines (Pinus flexilis) and whitebark pines (P. albicaulis).
• These squirrels significantly reduce seed abundance by harvesting most cones and decreasing seed accessibility, impacting seed dispersal by Clark's Nutcrackers (Nucifraga columbiana).

Purpose of the Study:

• To investigate the impact of pine squirrel seed predation on the recruitment and stand densities of limber and whitebark pines.
• To determine if reduced seed availability due to pine squirrels limits pine regeneration.

Main Methods:

• Comparative analysis of stand densities in areas with and without pine squirrels.
• Evaluation of seed availability and accessibility influenced by squirrel predation.
• Consideration of alternative ecological factors, such as precipitation, influencing stand densities.

Main Results:

• Stand densities were approximately two times greater in areas lacking pine squirrels compared to areas where they were present.
• Evidence suggests pine squirrels suppress seed availability, leading to reduced pine recruitment.
• Precipitation was considered as a potential limiting factor but did not fully explain the observed differences in stand densities.

Conclusions:

• Pine squirrels significantly depress stand densities of limber and whitebark pines through seed predation.
• The reduction in pine recruitment by pine squirrels has potential cascading impacts on Western subalpine ecosystems.
• These foundation tree species are vulnerable to the ecological effects of dominant seed predators.