P

atterns in the availabilityand utilization
of resources are important constraints on the social
organization of mammals, as established by early
studies of primates (Crook and Gartlan 1966), antelopes
(Jarman 1974), and carnivores (Macdonald 1983). In par-
ticular, the temporal and spatial dispersion of food and
shelter, along with other factors such as predation pressure,
affect the costs and benefits of forming groups. In turn, the
social behavior and grouping patterns of individuals of any
species have a strong influence on the structure and dy-
namics of their populations. Although studies of rodents
have explored relationships between resource dispersion,
spatial systems, and demography (e.g., Ims 1988; Ostfeld
1990; Wolff 1993b), the cascade of links between resources
and sociality have been a lesser focus in studies of this Or-
der than those mentioned previously.
Here we review data from studies of two species of hys-
tricognath rodents, the mara (Dolichotis patagonum) and
the capybara (Hydrochaerus hydrochaeris). The suborder
Hystricognathi includes rodents from the Old World, such
as porcupines (Old World Hystricidae) and the mole-rats
(family Bathyergidae). Caviomorphs is the term commonly
used for South American Hystricognaths. Having been iso-
lated from other rodents some 50 million years ago, cavio-
morphs evolved separately from those on other continents.
They occupy a diversity of niches and, as a result, many
contemporary species of South American histricognaths are
comparable in ecological and morphological terms to other
terrestrial herbivores such as ungulates, macropods, and
lagomorphs (Moreira and Macdonald 1996). The mara is

a member of the family Caviidae, while capybaras are in a

family of their own: Hydrochoeridae (Mones and Ojasti

1986). We compare the two species in terms of their social

organization, behavior, and resource use in the habitats they

occupy, and highlight ecological factors influencing their

sociality (summarized in table 33.1). We conclude that al-

though maras and capybaras live in conspicuously different

landscapes, their societies can be interpreted as the products

of remarkably similar resource dispersion features. Further-

more, our studies lay a foundation that reveals these species

to be models for future studies of the interaction between

resource availability and social organization.

The Species and Their Habitats

The capybara (fig. 33.1) is a 50 kg semiaquatic grazer whose

range spans much of South America. Capybaras have been

studied particularly in Venezuela (e.g., Ojasti 1973; Mac-

donald 1981a, 1981b), but also Columbia (Jorgenson

1986), Brazilian Pantanal Matogrossense (Schaller and

Crawshaw 1981; Alho et al.1987a, 1987b) and Brazilian

Amazonia (Moreira and Macdonald 1993). Capybaras are

abundant in the low Llanos region of Venezuela, where the

habitat consists of tropical savannas —vast, flat plains dom-

inated by grasses — and where the climate is characterized

by marked wet /dry seasonality, producing a severe water

shortage at the height of the dry season and extensive flood-

ing in the wettest months. The region comprises three phys-

iographic units: (1) esteros(ponds), most of which dry up

Chapter 33Social Organization and Resource

Use in Capybaras and Maras

David W. Macdonald, Emilio A. Herrera, Andrew B. Taber,

and José Roberto Moreira