Measuring the benefit of habitat selection

We used a behavioral bioassay to estimate the advantages that two species of gerbils (Gerbillus allenbyi and G. pyramidum) experienced by preferring a semistabilized dune habitat over a stabilized sand habitat. We used the magnitude of foraging effort by the gerbils to signal the difference between the two habitats. When they were foraging as much in stabilized sand as in semistabilized dune, we inferred that these habitats were providing equivalent rewards. We performed a series of experiments in two 1-ha field enclosures, each containing similar proportions of stabilized sand and semistabilized dune. Each enclosure contained a population of only one of the species. By varying the amount of seeds added (either 0.5, 1, 2, or 3 g of seeds in 18 seed trays) to each habitat and monitoring the behavior of the gerbils, we were able to fit a curve that reflected the change in habitat preference as a function of seed addition rate. We were also able to show how much seed addition had to be added to bring the two habitats into equal use. Each species required only 13 g/ha/night to entirely offset the advantage of the semistabilized dune. Copyright 2002.