INVESTIGADORES
BORGHI Carlos Eduardo
congresos y reuniones científicas
Título:
South American Drylands, Heterogeneity, Adaptation and Converge of Small Mammals
Autor/es:
R. A. OJEDA; G. DIAZ; S. M. GIANNONI; C. E. BORGHI; CAMPOS, CLAUDIA; V. CORBALÁN; S. TABENI; DACAR, MARIANA
Lugar:
Louvain-la-Neuve
Reunión:
Congreso; Rodents et Spatium; 2002
Resumen:
Aridlands
were an important scenario in the evolution of the Southamerican mammalian
biota. A large proportion of the dryland species (ie. several marsupials,
edentates, caviomorph and murid rodents) are not found elsewhere in the New World. In part, this degree of endemism and
adaptation to xeric existence is a consequence of evolution in highly
heterogeneous and isolated mosaic of drylands in the southern part of the
continent since the Oligocene. However, in comparisons with other deserts of
the world (i.e.the North American
deserts), some of the Southamerican
drylands, such as the temperate Monte Desert of Argentina, were regarded, for more than two decades, as impoverished in terms of their small
mammal species richness and in the repertoire of xeric adaptations when
compared with ecomorphological traits such as bipedal locomotion, granivory,
water balance and so on, regarded as paradigmatic features to desert existence.
As a result, the desert biota that
lacked the kangaroo rat syndrome were regarded as non-adapted to xeric
existence. The "lack of adaptations" of the South American lineage of
murid rodents (sigmodontine rodents) has been atributed, by some authors, to
their relatively recent entrance to South America
after the completion of the Panamian bridge, 3.5 million years ago, and to
their short time of expossure to arid habitats. Recent studies, however,
discard some of these previous notions pointing out the need to be careful when
accepting paradigms constructed largely from one continent. South
America possesses a high diversity of tropical, highland, coastal
and continental dryland biomes. In a finer scale, the small mammal (less than 500 g) assemblage varies
widely (species richness and composition) between these major arid biomes (Caatinga, Brazil; Atacama desert
, Peru, Chile; Altiplano,
Peru, Chile, Bolivia
and Argentina; Monte and Patagonia, Argentina).
The Andean Altiplano desert or Puna, and
the lowland Monte
Desert possesses the
highest species richness and endemisms. The Andean drylands (above 3,500 m) were a major
scenario in the cladogenetic process of murid rodents. This is reflected in the
number of endemics, which account for more than 50 % of the Altiplano rodents.
Richness of small mammals decreases towards lowland aridlands in both sides of
the Andes. This may be explained by low
rainfall, little (scarce?) vegetation as well as climatic unpredictability. At
a lower level (ie. the Monte
Desert) the importance of aridlands have been noted
when addresing Argentina´s diversity of mammals. At a regional and local
scales, the temperate Monte Desert is a
highly heterogeneous landscape, from
very simple, live-sand dunes patches, to more complex habitats such as those
composed of creossote bush, grasses, and mesquite (Fabacea: Prosopis) habitats.
The small mammal assemblage of the Monte desert shows a marked spatial and
temporal heterogeneity, a highly diversified trophic ecology and differential
responses to habitat perturbations.Here we review evidence on biogeographical,
ecological, physiological, morphological and behavioral studies of small
mammals of the South American drylands, and the temperate Monte Desert in
particular, that portrays the heterogeneity of these biomes at different scales
as well as the rich array of adaptations and convergence with counterparts from
other deserts of the world