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|Data by Research Category|
Dataset: Density and cover of winter annual plants
The purpose of this investigation was to answer three general questions: 1. How does the modification of soil properties and the ratios of resources (e.g., water-N) by ants alter species assemblages of winter annual plants at the edge of the ant nests? 2. How does the "spring cleaning", clipping, predation or herbivory by ants affect success of the winter annual plants at the edge of ant nests? 3. Are there significant differences in the floristic assemblage and belowground standing crop (root biomass) between the edge of ant nest and the surrounding unaffected soils? Data set contains density and cover of all winter annual plants measured at regular intervals. Density is expressed as the number of individuals of a species per square meter. The cover of each species was calculated as the area covered by a perpendicular (not vertical) projection of its aerial parts onto the ground surface and expressed in covered area (cm squared) per square meter.
This study was conducted at three sties on the Jornada LTER during winter-spring 1987. A burrograss-tobosa swale grassland was site 1, an area dominated by the perennial grasses Scleropogon brevifolia (burrograss) and Hilaria mutica (tobosa). This area is located 3,000 ft. (1,000 m) SE of the playa bottom or playa basin (College Playa) and subject to rare sheet flooding. A playa fringe (College Playa) was site 2, an area characterized by scattered Prosopis glandulosa (mesquite) mixed with Yucca elata and Larrea tridentata (creosotebush). The upper basin slope was site 3, an area characterized by a fairly uniform cover of Xanthocephalum sarothrae (snakeweed) and a high diversity of annual forbs and grasses. The soil series described on the watershed by Wierenga et al. (1987) from site 1 to site 3 are Dalby (Typic Torrerts, fine), Headquarter (Ustollic Haplargid, fine loamy), Bucklebar (Typic Haplargid, fine-loamy), and Dona Ana (Typic Haplargid, coarse-loamy), respectively.
field data sheetsMethods:
During winter 1987, eight Pogonomyrmex rugosus nests at site 1, five Pogonomyrmex rugosus nests at site 2 and seven Pogonomyrmex rugosus nests at site 3 were randomly selected and systematically sampled. At each nest, a 0.16 square meter quadrat frame was randomly placed at the ant nest edge, a second 0.16 square meter quadrat was also placed on the ant nest edge opposite to the first quadrat. Two additional quadrat frames were placed 5 meters distance from the two at the edge of the ant nests. These quadrats represent the soil unmodified by the activity of the ants and served as a reference.
The density and the cover of all winter annual plants were measured at regular intervals (approximately 30 days). Density was expressed as the number of individuals of a species per square meter. The cover of each species was calculated as the area covered by a perpendicular (not vertical) projection of its aerial parts onto the ground surface and expressed in covered area (cm2) per m2 and in percentage. Overlap was always counted, resulting in the potential for total cover to exceed 100%. Density and cover is measured four times, at the end of January, February and March and in mid-May. Each measurement required three to four days to complete. Affinity for ant nest edge for each species was calculated as mean cover of a species on the edge of an ant nest divided by the sum of mean cover of that species n the edge of an ant nest and mean cover on the reference sites. This was expressed as percentage. Mean cover of all species was determined as an arithmetic mean throughout the experiment.
4 times (January, February, March, mid-May)