PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 44 - Grassland ecology II
Heritage Ballroom IV, Marriott
Presiders: J Ely
Prairie dogs and harvester ants as disturbance agents on the shortgrass steppe: implications for habitat heterogeneity.
Alba Lynn, Christina*,1, Detling, James1, 1 Colorado State University, Fort Collins, CO
ABSTRACT- The distribution and density of harvester ant (Pogonomyrmex occidentalis) nests and prairie dog (Cynomys ludovicianus) mounds on the shortgrass steppe in eastern Colorado, USA, have implications for habitat differences on prairie dog colonies (both species present) versus off colonies (only ants present). Prairie dog burrows and ants nests similarly denude vegetation and alter soil characteristics. We described how nest and mound density, distribution, size, and their effect on vegetation contribute to habitat heterogeneity on and off prairie dog colonies. Ant nest density did not differ on and off colonies (25.2 nests/ha on colonies; 25.4 nests/ha off colonies; P= 0.97), nor did the average distance from a focal nest to its nearest-neighbor nest (14.3 m on colonies; 13.2 m off; P = 0.53). However, nest area on colonies (1.47 m2) was significantly larger than off (1.05 m2; P = 0.035), translating into a 41% increase in ant-cleared vegetation (m2/ha) on colonies. Nests were overdispersed in relation to other nests (R = 1.3, where R is a ratio representing the degree of departure from a random distribution designated by 1), but aggregated in relation to mounds (R = 0.78). More than 43% of nests occurred within <3 m of mounds, while 27 out of 124 nests (22%) occurred directly on, or adjacent to, mounds (with “adjacent” meaning the denuded soils of nests and mounds graded together and could not be distinguished). Mounds had significantly more cover (14% ± 4.92) than nests on colonies (3.8% ± 1.85; P = 0.007) and marginally significantly more cover than nests off colonies (8.1% ± 3.95; P = 0.08).
Key words: shortgrass steppe, disturbance, prairie dogs and harvester ants