2,4‐D Herbicide, Vegetation, and Pocket Gopher Relationships Black Mesa, Colorado

Abstract

In a 7—year study on Black Mesa, Colorado, elevation 10,000 ft 2,4—D herbicide treatment initially reduced forb abundance and northern pocket gopher (Thomomys talpoides) populations 80% to 90%. Both forbs and pocket gophers remained at low levels on one area but returned to pretreatment levels on the other area. The decline in pocket gopher numbers was caused by an inability to survive where their preferred food (forbs) was eliminated by herbicide treatment. The decline was not caused by movements of the animals from sprayed areas, or by direct or indirect toxicity of 2,4—D. The common grasses offer, at best, only a marginal diet for northern pocket gophers; only succulent grasses or those bearing corms or rhizomes yield a subsistence diet. Limited sampling did not indicate that the spray treatment affected the numbers of other small mammals.

Recent Changes in the Farmland Fauna with Special Reference to the Decline of the Grey Partridge

“…Application of 2,4-D to grassland in the U.S.A. removed various herbs and changed the diet of the small mammals Thomomys talpoides and Peromyscus spp.-but this only affected the survival of the former (Johnson 1964;Tietjen, Halvorsen, Hegdal and Johnson 1967). The composition of the weed-seed fraction of the diet of the adult partridges (Perdix and Alectoris) has changed continually throughout this century, partly as a result of the use of herbicides, but there is considerable evidence that the adult survival rate is unchanged (Potts 1970).…”

Diet selection and plant nutritional quality in Attwater's pocket gopher (Geomys attwateri)

“…Annual dicots were not sprayed with herbicide during autumn 1993 because regrowth was low and these plants were a smaller component of the diet (Williams and Cameron 1986). 2,4-D had little or no toxicity to pocket gophers at these concentrations (Tietjen et al 1967;Hull 1971).…”

“…Because of the high cost of burrowing and the patchy distributions of plants, fossorial rodents often use area-restricted search to forage within patches of food plants once they are located (Jarvis and Sale 1971;Benedix 1993;Rosi et al 2000;Seabloom and Reichman 2001). As for aboveground herbivorous rodents, fossorial rodents such as pocket gophers also ingest a mixture of monocots and dicots, ostensibly to benefit from variation in nutrient content among species of plants (Ward and Keith 1962;Wilks 1963;Myers and Vaughan 1964;Tietjen et al 1967;Williams and Cameron 1986). In addition, some fossorial rodents exhibit dietary specialization (sensu Shipley et al 2009).…”

“…Additionally, Tietjen et al (1967) found that individual Thomomys talpoides fed monocot diets died or lost body mass while those fed dicot diets gained body mass. Rezsutek and Cameron (in press) found that low protein and high fiber content in the diet of Geomys attwateri likely resulted in a diet of such poor quality during summer that breeding was reduced.…”

Subterranean Rodents as Pests: The Case of the Pocket Gopher

“…Pocket gophers generally prefer to feed on forbs (dicots) over grasses (monocots) (Keith et al 1959). Consequently, the selective removal of forbs with the herbicide 2,4-D has reduced Thomomys gopher densities (Keith et al 1959;Tietjen et al 1967).…”