J. Range Manage. 52:370–377 Botanical composition of cattle and vizcacha diets in cen- tral Argentina ELIANA E. BONTTI, ROBERTO M. BOO, LILIA I. LINDSTRÖM, AND OMAR R. ELIA Authors are assistant and fellow, Departamento de Biología and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); professor and researcher, Departamento de Agronomía (UNS) and Comisión de Investigaciones Científicas (CIC); assistant, Departamento de Agronomía (UNS); research technician, CONICET. Centro de Recursos Naturales Renovables de la Zona Semiárida (CERZOS). Avenida San Andres 800 (8000) Bahía Blanca, Argentina. Abstract Resumen Cattle (Bos taurus) and vizcacha (Lagostomus maximus) Las dietas de vacunos (Bos taurus) y vizcachas (Lagostomus diets were examined monthly in the semiarid Caldenal in cen- maximus) fueron examinadas mensualmente en el Caldenal tral Argentina. Cow-calf operations are the most important semiárido del centro de Argentina. La ganadería es la princi- economic activities within the region. In spite of a widespread pal actividad en la región. A pesar que la vizcacha se encuen- distribution of the vizcacha in Argentina, comparative studies tra ampliamente distribuida en la Argentina, existen pocos of the diet of cattle and vizcacha are scarce. The objective of estudios comparativos de la dieta de vacunos y vizcachas. El this work was to analyze the botanical composition, seasonal objetivo de este trabajo fue analizar la composición botánica, trends, and possible dietary overlap between cattle and viz- tendencias estacionales y posible superposición dietaria entre cacha. Diets were determined by microscopic analysis of cattle vacunos y vizcachas. Las dietas se determinaron por análisis and vizcacha feces collected from November 1994 through microhistológico de heces de vacunos y vizcachas recogidas December 1995 in a shrubland community of the southern desde noviembre de 1994 hasta diciembre de 1995 en una Caldenal. Grasses were the bulk of the diet for both herbi- comunidad arbustiva del sur del Caldenal. Las gramíneas vores. Piptochaetium napostaense (Speg.) Hack. was the most fueron el principal componente de la dieta de ambos her- abundant grass in vizcacha (53%) and cattle (40%) diets. bívoros. Piptochaetium napostaense (Speg.) Hack fue la Prosopis Caldenia Burk. pods partially (34%) replaced this gramínea más abundante en las dietas de vizcachas (53 %) y grass in cattle diets during late summer and fall. Consumption vacunos (40 %). Los frutos de Prosopis caldenia Burk. reem- of P. napostaense was generally higher (13%) in vizcachas plazaron parcialmente (34%) a esta gramínea en la dieta de than in cattle, especially during the dry period of the study vacunos durante el verano tardío y otoño. Las vizcachas gen- (21%). During the drier months, cattle consumed more of the eralmente consumieron más Piptochaetium napostaense (13 less preferred grasses (48%). Forbs were poorly represented %) que los vacunos, especialmente durante el período seco del in the diets perhaps because of scarce rains and low availabili- estudio (21%). Durante los meses más secos los vacunos con- ty. Classification and ordination techniques revealed seasonal sumieron gramíneas menos preferidas (48 %). Las trends and overlapping diets. A greater overlap (75%) was dicotiledóneas herbáceas fueron escasas en la dieta de ambos found during the wet period due to simultaneous consumption herbívoros, quizás por la baja disponibilidad debida a las of P. napostaense by both herbivores. Trends in diet diversity escasas lluvias. Las técnicas de clasificación y ordenamiento were similar with indices generally higher for cattle than for revelaron las tendencias estacionales y la superposición de vizcachas, especially during the dry period. dietas. Una gran superposición de dietas (75%) se encontró durante el período húmedo del estudio debido a que ambos herbívoros consumieron principalmente Piptochaetium napos- Key Words: free ranging cattle, diet composition, semiarid taense. Las tendencias en la diversidad dietaria fueron simi- area, microhistology. lares con índices generalmente más altos para el ganado que para las vizcachas, especialmente durante el período seco. Wild and domestic herbivores directly influence plant com- munities with their selective grazing. Floristic changes are highly variable and depend on many factors such as prefer- ences of herbivores, the relative abundance and availability of forages, season of the year, and temporal and spatial overlap We would like to thank H. Canessa, F. Zanetti, S. Aman and M. U. García when more than one species grazes the same area. Lorenzana for invaluable assistance. Two anonymous reviewers and the associate The Southern Espinal (Fernández et al. 1989) or District of editor made helpful suggestions which improved a previous version of the manu- script. Research was funded by Consejo Nacional de Investigaciones Científicas y the Caldén (Cabrera 1976), commonly referred to as the Técnicas (CONICET), Universidad Nacional del Sur (UNS), and Comision de Caldenal, is a temperate semiarid region in central Argentina Investigaciones Científicas (CIC). characterized by the presence of Prosopis caldenia Burk. The Manuscript accepted 3 Oct. 1998. landscape in the southern Caldenal is dominated by shrub- 370 Journal of Range Management 52(4), July 1999 lands with a very rich grass layer. Poor site is a Calciustoll with a petrocalcic were analyzed using Student’s t test range management is common through- horizon at an average depth of 0.60 m (Ho: the relative composition of dietary out the region, and soil erosion and plant (Fernández et al. 1989). components were equal in vizcacha and community deterioration are incipient The research area supports a plant cattle feces; n = 10 for vizcacha and n = but generalized (Fernández et al. 1989, community defined as "Unidad C" by 15 for cattle). Bóo and Peláez 1991). Bóo and Peláez (1991). This community Vegetation cover was visually esti- The plains vizcacha (Lagostomus is characterized by a woody species mated with the Braun-Blanquet (1979) maximus, Chinchillidae) is a native cover of 50–70 % with Prosopis calde- abundance-cover scale in March 1995 rodent of Paraguay, Bolivia, and nia Burk., P. flexuosa D. C. and (late summer), August 1995 (winter), Argentina that inhabits grasslands and Condalia microphylla Cav. as the most and December 1995 (late spring), and scrub (Branch and Sosa 1994). It is abundant. The herbaceous cover is about we compared diet composition and for- abundant in the Southern Caldenal and 40–50% with Piptochaetium napos- age abundance for those months. Cover has been considered a plague in taense (Speg.) Hack. and Stipa tenuis estimation permits a rapid and non- Argentina since 1907 because of its bur- Phil. as the major grasses. Stipa spe- destructive measure of food abundance, rowing and foraging habits. Adult ciosa Trin. et Rupr. and S. gynerioides and estimates were made in and out of females (2.9–3.3 kg), adult males Phil. are frequent, and S. clarazii Phil., vizcacha colonies to detect possible dif- (4.5–5.6 kg) and young individuals live Poa ligularis Nees and Pappophorum ferences in community composition. in groups of 9 to 14 individuals per mucronulatum Nees are scarce. P. Plant taxa were grouped in 4 classes: colony (Branch et al. 1993). Daily napostaense and S. tenuis are good for- woody species, forbs, preferred grasses intake by adults is 1.7–4.7% of body age species that replace Stipa clarazii and non-preferred grasses. This group- weight (Jackson 1985), and areas around Phil and Poa ligularis Nees under mod- ing was made because of the difficulty the vizcacha colonies are characterized erate continuous grazing (Distel and of identifying some taxa to species level by bare soil with scarce, low-growing Bóo 1995). Bare ground (30–40 %) is especially during the winter when vege- forbs and grasses. colonized during wet years by annual tative forms of grasses are similar. Studies of the diet of cattle and viz- forbs, mostly Medicago minima (L.) However, it was important to differenti- cacha in semiarid Argentina are very Grufberg and Erodium cicutarium ate preferred and non-preferred grasses scarce. Giulietti and Jackson (1986) L’Herit. Annual above ground net pri- because diets may be correlated with studied food habits of vizcacha and cat- mary production in this plant communi- forage availability. The woody species tle and found little similarity in their ty for S. tenuis was 862 kg ha-1, and 684 group included Prosopis caldenia, diets. They concluded that potential kg ha-1 for P. napostaense in a year with Prosopis flexuosa, Condalia microphyl- competition was low between both her- 532 mm of rainfall (Distel and la and Ephedra spp. The forb group bivores, but knowledge of the botanical Fernández 1986, Distel 1987). included Erodium cicutarium and composition of vizcacha and cattle diets Fifteen independent fecal samples Medicago minima. The preferred grass- where both herbivores graze a common from different mature cows were col- es included Piptochaetium napostaense, area is much needed. The objective of lected monthly from November 1994 to Stipa tenuis, Pappophorum mucronula- this work was to analyze the botanical December 1995. These samples were tum, Poa ligularis and Stipa clarazii. composition, seasonal variation, and analyzed following Bóo et al. (1991) to The non-preferred grasses included dietary overlap of cattle and vizcacha obtain 20% (P<0.05) precision in the Stipa speciosa, Stipa gynerioides, Stipa diets in