Abundance and distribution of organic mound-building ants of the Formica rufa group in Yellowstone National Park

摘要

Red wood ants (Formica rufa group) are ubiquitous in many conifer and mixed-conifer forests of northern Europe and Asia. In contrast, relatively little is known about the abundance and distribution of the 24 North American F. rufa group species. As ants are important components of most soil invertebrate communities and are considered ecosystem engineers that alter the flow of energy and nutrients through terrestrial systems, it is important to gain information on their distribution and abundance. We conducted a survey for red wood ant mounds in Yellowstone National Park (YNP), Wyoming/Montana, USA, where human disturbance has been kept to a minimum for over 130 years. We found a total of 85 red wood ant mounds (0.11 to 0.17 mounds/ha) on 327 km of roads and 180 km of the hiking trails we surveyed. The occurrence of ant mounds was higher then expected by random distribution at elevations between 1600 and 2400 m, annual precipitation of 250 to 760 mm, middle and late successional lodgepole pine, late successional Douglas fir forest and non-forested grassland/sagebrush prairie vegetation. Additionally, mounds were clustered in gently sloped not north-exposed locations and in areas that had not recently burned. Most of the mounds detected were inhabited by Formica obscuripes Forel, which occupied 94% of the mounds sampled. Based on a multi-criteria binary Geographic Information System model that we developed, we found that ant mounds were to be expected with a high probability in less then 1% of the YNP area. These results together with the detected low density and small size of the red wood ant mounds within the study area suggest that these insects have a much lower impact on invertebrate biodiversity and ecosystem processes, such as forest productivity and carbon and nutrient cycling on the ecosystem scale compared with their counterparts in European or Asian systems.