Asking the pikas politely…
-Field tests quantifying the behavioral responses of ants to the seeds of twenty Rocky Mountain species were conducted in Gunnison County, Colorado. The results indicate that Claytonia lanceolata Pursh, Corydalis aurea Willd., C. caseana A. Gray., Delphinium nelsoni Greene, and Viola nuttallii Pursh are myrmecochores. The seeds of these species all bear a conspicuous elaiosome and are selectively removed by three species of ants, Formica podzolica Francoeur, Formica canadensis Francoeur, and Myrmica discontinua Weber. These are the first records of ant dispersal from the Rocky Mountains. Comparatively little is known about the ant dispersed (myrmecochorous) plant species of the western United States. Scattered reports suggest that they may be common in some areas, particularly the arid south-west (Berg, 1966; Bullock, 1974; O'Dowd and Hay, 1980; Nesom, 1981) and the moist north-west (Nordhagen, 1959; Berg, 1972). Almost nothing is known about ant dispersal in the Rocky Mountains. Sernander (1906) reported that between 6% and 13% of herbaceous species at high altitudes in Sweden, the French Alps and the north Tyrol were ant dispersed, and speculated that a similar proportion of species might be ant-dispersed in other mountainous regions of the world. Preliminary field experiments with the seeds of Viola nuttallii Pursh strongly suggested that this species is myrmecochorous. This paper reports new information on seed disperal by ants of this and other species. MATERIALS AND METHODS.-The two study sites were located in Gunnison County, in west-central Colorado. One was at an altitude of approximately 3,024m, near the Rocky Mountain Biological Laboratory at Gothic. This is a dry, rocky, subalpine meadow. Areas of little ground cover were mixed with areas of dense vegetation dominated by grasses and false hellebore (Veratrum californicum Durand). There were also small stands of willow (Salix, sp.) and aspen (Populus tremuloides Michx.). The other site was on a steep roadcut near Crested Butte, at an altitude of 2,719m. Vegetation on this site was very sparse and dominated by Corydalis aurea, weeds, and a few grasses. The method for evaluating myrmecochory in a species is detailed in Beattie and Culver (1981) and utilizes both morphological and behavioral criteria. Since ants carry many kinds of objects back to their nests, we looked for morphological adaptations of the seeds which indicate myrmecochory, and specific behavioral responses on the part of the ants. Behavioral responses of undisturbed ant foragers were quantified by the use of bioassays of fresh seeds, in the habitat where the plants were growing. Clumps of five seeds were placed at random in the habitat and observed for periods of up to one hour. Each bioassay was replicated as many times as the supply of fresh material would allow. The responses of ants were classified as follows: ignore-the ant passed close enough to the seed to detect it but exhibited no response at all; antennate-the ant examined the seed with its antennae; pick-up-the ant iesponded by rolling the seed and attempting to pick it up, but the response was not sufficiently intense for the ant to carry it away; remove-the ant removed the seed at least 10 cm. In most cases, an ant which removed a seed 10 cm actually continued to carry it back to the nest. RESULTS.-We bioassayed the seeds of twenty species belonging to fifteen families (Table 1). There was no interaction between ants and the seeds of This content downloaded from 207.46.13.180 on Thu, 08 Sep 2016 06:26:21 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist TABLE 1.-Species bioassayed (species marked by an asterisk were ignored in all bioassays). Boraginaceae Mertensia fusiformis Greene Compositae Agoseris aurantiaca (Hook). Greene* Senecio interregemus Nutt.* Taraxacum officinale Wiggars* Cyperaceae Carex egglestonii Mack.* Fumariaceae Corydalis aurea Willd. C. caseana A. Gray Graminae Melica spectabilis Scribn.* Poa interior Rydb.* Hydrophyllaceae Hydrophyllum capitatum Dougl. ex Benth.* Liliaceae Erythronium grandiflorum Pursh Onagraceae Epilobium minutum Lindl. ex Hook.* Polemoniaceae Collomia linearis Nutt.*
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