Submitted to: Society for Range Management Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/6/2005
Publication Date: 2/1/2005
Citation: Clements, C.D., Young, J.A., Harmon, D.N. 2005. Rodent consumption of fourwing saltbush seeds and seedlings [abstract]. Proceedings of the Society for Range Management, February 5-11, 2005, Fort Worth, Texas. 58:62. Interpretive Summary:
Technical Abstract: Fourwing saltbush (Atriplex canescens) is one of the most valuable shrubs in arid and semi arid rangelands. Due to its' value it is a widely used native shrub in the rehabilitation of western rangelands. Granivorous rodents play an important role in the seed harvesting and dispersal of many browse species, such as antelope bitterbrush (Purshia tridentata), yet little is known on just how granivorous rodents interact with fourwing saltbush. We monitored the interaction of granivorous rodents on fourwing saltbush seeds in northwestern Nevada in the fall of 2003 and seedlings in the spring of 2004. The site is located at Eagle Valley, 80 km east of Reno, Nevada. The site is dominated by an overstory of fourwing saltbush, spiny hopsage (Grayia spinosa), and greesewood (Sarcobatus vermiculatus) with an understory of Indian ricegrass (Achnatherum hymeniodes). The site is at an elevation 1,265 m of and receives an average of 2.1 cm of annual precipitation. We hypothesized that rodents would harvest fourwing saltbush into their cheek pouches, in an attempt to cache them, and consume a significant number of seeds in the process. We also hypothesized that the rodent would also consume a significant number of fourwing saltbush seedlings as we have experienced with another important browse species, antelope bitterbrush. Seed and seedling predation by various rodents was investigated by using portable livetrap enclosures, 60 cm by 30 cm by 35 cm with 0.7 cm mesh hardware cloth. Rodent populations were censused using mark-and-release trapping during the duration of the study. The most common rodent species captured were the desert kangaroo rat (Dipodomys deserti) and the Merriam's kangaroo rat (Dipodomys merriami). One hundred uncleaned fourwing saltbush seeds, previously collected from the site, were placed (uncleaned) within each portable enclosure (n=10) and placed out within a grid nightly and recorded each morning for 4 consecutive days of 4 separate weeks over a 2 month period in the fall of 2003 to monitor rodent harvest and consumption. Two other portable enclosures were also placed out without trap mechanisms for controls. We recorded 95 observations in which rodents entered these portable cages with seeds. Rodents did not harvest and collect fourwing saltbush into their cheek pouches as we had hypothesized. The behavior that they exhibited was cleaning off all or part of the wings and removing the embryo. Rodents consumed 39% of the fourwing saltbush embryos they came in contact with. The Merriam's kangaroo rat consumed approximately 45% and the desert kangaroo rat 29%. Twenty-five fourwing saltbush seedlings were grown in the greenhouse and then placed out in these portable enclosures in te spring of 2004 as was done the previous fall. During the seedling monitoring stage of this experiment 61 observations were recorded in which 93% of the fourwing seedlings were consumed by these rodents. The Merriam's kangaroo rat consumed 96% of the seedlings, the desert kangaroo rat 100% and the chisel-toothed kangaroo rat (Dipodomys microps) 82%, respectively. Fourwing saltbush seedling predation is much higher that we have previously reported on with antelope bitterbrush seedlings, another important western browse species, yet the absence of seed harvest, cleaning, and assumed subsequent caching that would follow is somewhat mysterious to us.