Assessment of capybara (Hydrochoerus hydrochaeris) populations in the wetlands of Corrientes,Argentina

Ten sampling sites were selected to represent six distinct habitat types used by capybaras (clean lagoons, dirty lagoons, cutwaters, fens and marshes, gallery forests, and erosion ditches). The sites were sampled during winter (July and August); densities were expressed as number of capybaras per linear km of shoreline (C/LKS). The sites were classified as protected from poachers (P), under light hunting pressure (LHP), and under heavy hunting pressure (HHP). Clean protected (P) lagoons had three times as many capybaras as LHP ones (30.7 and 10.9 C/LKS, respectively), and thirty times those under HHP (1.0 C/LKS). Protected marshes and dirty lagoons had even higher capybara densities (52.5 and 50.0 C/LKS, respectively). Gallery forests under LHP had low densities (6.3 C/LKS), and protected cutwaters intermediate densities (27.5 C/LKS). Erosion ditches had exceptionally high densities (900 C/LKS), probably because cattle were fenced out, reducing forage competition. These densities, when converted to the standard unit area measurement (individuals/ha), were similar to those obtained by other researchers in the Brazilian Pantanal, and somewhat smaller than those in the Venezuelan Llanos. Mean number of capybaras per group remained relatively constant in all habitats (averages ranged between 9.2 and 11.8 individuals/group) but its coefficient of variation was much higher in LHP sites, probably because social structure was altered severely by hunting. The overall ratio of young to adults and juveniles was 1:7.4. In one of the sites, 13 of 34 groups (38.2%) were with young (average of 17 capybaras per group, 4.7 of which were young), confirming that this species can reproduce all year long.Requests for reprints should be sent to: Dr. J. Rabinovich.     

Intraspecific variability of beaver teeth (Castoridae: Rodentia)

The metric variability of the teeth of Castor fiber Linné, 1758 and Castor canadensis Kuhl, 1820 with age are assessed. The ages of the studied specimens of C. fiber range from about 2 months to 16–17 years. Measurements of all teeth are given, and show a large range of size variation over all ages. The greatest size ranges can be observed for incisors, premolars, and third molars. Size variations of the fossil beavers Steneofiber eseri v. Meyer, 1846, Steneofiber castorinus Pomel, 1847, Anchitheriomys suevicus Schlosser, 1884, and Trogontherium cuvieri Fischer de Waldheim, 1809 are compared with those of C. fiber, and are of the same range and magnitude. It seems that it is nearly impossible to age beavers exactly with non‐invasive methods on the basis of tooth morphology, namely by the form and pattern of enamel islands on the chewing surface of the cheek teeth. Therefore, in conclusion, it is suggested that the observed variability in the size of fossil beaver teeth should be interpreted as changes with age in accordance with the overall size range in C. fiber. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 926–936.     

The Geographic Spread of “El mal de las caderas” in Capybaras (Hydrochaeris hydrochaeris)

The aim of this work is to describe an epidemiological model for a capybara (Hydrochaeris hydrochaeris) population. The model considers a tabanid (“mutuca”) population (Diptera: tabanidae), as a vector for the disease called “mal de las caderas” in Estero del Ibera, Corrientes, Argentina. The study of this problem has ecological and economical importance since the meat and the hide of the capybara can be an exploitation resource. At first, a threshold value is determined as a function of the model parameters, obtaining a critical carrying capacity which determines the disease propagation or eradication. Then as the carrying capacity condition for the disease existence is satisfied, the existence of traveling wave solution is studied. Independent speeds are considered for the susceptible capybaras, the noninfected insect, and the disease. The speed of propagation for this model is obtained as function of model parameters followed by a discussion of strategies for controlling the spread of the disease. N.A. Maidana is a fellowship Fapesp and partially supported by Grant Fapesp (temático).     

Capybara (Hydrochoerus hydrochaeris) distribution in agroecosystems: a cross-scale habitat analysis

Aim The aim of this study was to understand the spatial distribution of capybara (Hydrochoerus hydrochaeris) according to habitat attributes, using a multiscale approach based on fine‐ and broad‐scale variables in agroecosystems. Location Piracicaba river basin, south‐eastern Brazil (22°00′–23°30′ S; 45°45′–48°30′ W). Methods Potential habitats for capybara were selected in order to evaluate species presence/absence from October 2001 to December 2002. In each site, habitat attributes were sampled in the field (fine scale) and from GIS maps (broad scale) in terms of their presence or absence close to water. The variability of land cover between study sites was described by principal components analysis. Chi‐square tests were calculated for capybara presence/absence and the presence of each habitat attribute. A linear discriminant function analysis was used to describe to what extent the species’ presence could be explained by habitat attributes. Results The species presence was predominantly related to flat open areas (slope ranging from 0% to 6%) (χ² = 37.054, d.f. = 4, P < 0.001), covered by sugar cane or cultivated pasture (χ² = 84.814, d.f. = 9, P < 0.001). Terrain curvature, water meadows, aquatic vegetation, forest cover and open areas resulted in the best combination of variables, explaining 69.7% of capybara occurrence in the study sites in this river basin. Main conclusions Capybaras are widespread in the Piracicaba river basin, except in elevated areas. The spatial distribution of capybara was associated with the main types of land cover in the river basin – sugar cane plantations or pasture – both key food sources for capybara. This probably explains the species’ recent abundance in the region, since an intensive process of landscape alteration has taken place in this region owing to the expansion of agriculture in recent decades. These results may be useful in understanding the relationship between recent landscape modifications and the species’ population expansion in agroecosystems.