Summary: Real vs. artefactual absences in species
distributions: tests for Oryzomys albigularis
(Rodentia: Muridae) in Venezuela
Robert P. Anderson* Division of Vertebrate Zoology (Mammalogy), American Museum
of Natural History, Central Park West at 79th
Street, New York, NY, USA
Aim Numerous geographical information system (GIS)-based techniques for estimating
a species' potential geographical distribution now exist. While a species' potential dis-
tribution is more extensive than its documented range, the lack of records from some
suitable regions may simply derive from inadequate sampling there. Using occurrence
records of both the study species and the more inclusive overall target group, I propose a
progression of statistical models to evaluate apparent absences in species distributions.
Location Northern Venezuela.
Methods Employing data from the Smithsonian Venezuelan Project (a large set of
standardized mammalian inventories undertaken across Venezuela), I tested distribu-
tional hypotheses for the sigmodontine rodent Oryzomys albigularis (Tomes, 1860).
Those inventories collected O. albigularis in two of the five major montane regions of
northern Venezuela (the Cordillera de Me´rida/Macizo de El Tama´ and Cordillera de la
Costa Central). I used the Genetic Algorithm for Rule-Set Prediction (GARP) to estimate