Browsing Rangeland Ecology & Management, Volume 60, Number 4 (July 2007) by Subjects
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GPS Error in Studies Addressing Animal Movements and ActivitiesGlobal Positioning System (GPS) error, associated with free-ranging animal studies, remains a concern in range/animal research. For distance measures, errors may be additive over time and increase as sampling frequency intensifies. The first study assayed effects of coordinate integration time (10 hourly intervals), 10 GPS collars, and range of unit movement (0 to 90 m in 10-m intervals as treatments) on bias of GPS measures of distance. ‘‘Bias’’ was the difference between measured distances and distances derived from GPS coordinates of units moved over a surveyed grid. A second study evaluated four methods (regression modeling, minimum distance threshold, motion sensor threshold, and a combined minimum distance/motion sensor technique) for extracting perceived movements from GPS data acquired from cattle. A classification assessment compared observation data of cattle with their corresponding GPS records after filtering by the four techniques. Except for immobile GPS collars in study 1, bias of distance measures was inconsequential for movements ranging from 10 to 90 m (differentially corrected mean bias = 0.18 m +/- 0.12 m SE). When collars were immobile, GPS error generated about 1.7 m +/- 0.7 m SE of perceived travel per record with postdifferentially corrected coordinates (P < 0.05), and 3.9 m +/- 0.8 m SE with uncorrected data. At specific times, post-differential correction failures can affect (P < 0.05) GPS measures of distance. Using any of four proposed techniques, one may effectively filter data sets to remove perceived travel accrued when cattle were resting with 81% to 92% of resting intervals correctly classified. The most effective regression technique suggested cattle travels were overestimated by about 15.2% or 1.15 km daily without filtering.
Toxic Alkaloid Concentrations in Delphinium nuttallianum, Delphinium andersonii, and Delphinium geyeri in the Intermountain RegionLow larkspurs (Delphinium nuttalliunum Pritz., Delphinium andersonii Gray) and plains larkspur (Delphinium geyeri Greene) often poison cattle grazing on western North American rangelands. The dominant toxic alkaloid in larkspur is methyllycaconitine (MLA); other very toxic alkaloids in low and plains larkspurs are nudicauline and geyerline. Toxic alkaloid concentrations in larkspur near or above 3 mg g-1 present significant risk to grazing cattle. D. nuttallianum from Utah and Colorado, D. andersonii from northern Arizona, and plains larkspur (D. geyeri) from Wyoming were collected for analysis. Concentrations of MLA in D. nuttallianum ranged from 0.8 to 4.5 mg g-1 in Utah and Colorado; total toxic alkaloid concentrations were often above 3 mg g-1. D. nuttallianum differed (P = 0.09) in MLA concentration between locations but not phenological stages (P = 0.41). Concentrations of nudicauline ranged from 0.7 to 4 mg g-1 in D. nuttallianum and were different (P = 0.01) between locations and phenological stages (P = 0.004). D. andersonii was consistently toxic because the total toxic alkaloid concentration fluctuated from 3 to 6 mg g-1 over the growing season. The concentration of geyerline in D. andersonii was equal to or greater than MLA at each phenological stage, thus adding to the toxicity. The concentration of toxic alkaloids in D. geyeri was typically highest (2-4 mg g-1) in immature plants, although toxic alkaloid concentrations in plants during the pod stage of growth sometimes increased. Only trace amounts of nudicauline were found in D. geyeri, as most of the alkaloid fraction was other N-(methylsuccinimido) anthranoyllycoctonine (MSAL) alkaloids. Total alkaloid concentration (MSAL and non-MSAL alkaloids) in D. geyeri sometimes exceeded 15 mg g-1. Concentrations of toxic alkaloids in D. nuttalliunum, D. andersonii, and D. geyeri often did not significantly decline during the growing season as typically found in tall larkspurs. Thus, risk to grazing cattle may remain high until these plants are dormant.