Document: LUC-3-56-8

Predation risk and food quantity in the selection of habitat by black tailed jack rabbit (Lepus californicus): An optimal foraging approach.

MARIN, A.* ¹, L.HERNÁNDEZ ¹ and J.W.LAUNDRÉ ^1,2

Instituto de Ecología, A.C.-CEISS, Aldama, Mexico ¹
Idaho State University, Pocatello, ID, USA 83209 ²

Abstract:
Foraging theory predicts there is a balance between the cost and benefit that each individual takes in selecting a food patch. Two main factors taken in account should be: (1) the quantity (benefit) of the food obtained, and (2) the risk (cost) of being killed while eating. In the Chihuahuan Desert (Mapim Biosphere Reserve) we previously determined that densities of black tailed jackrabbits (Lepus californicus) are higher in tobosa grasslands (Hilaria mutica) than mesquite-creosotebush-prickly pear shrublands (Prosopis glandulosa-Larrea tridentata-Opuntia rastrera) (25.2 ind/km² vs 16.8 ind/km², P = 0.043, t=2.14, d.f. = 22). Additionally we observed zones of high and low use inside each habitat area. We tested the prediction that jackrabbits incorporate food quantity and predation risk in their selection of foraging habitat. To test this prediction, we established an experimental design with two blocks (shrubland and grassland), two factors (high and low densities) and seven repetitions (bimonthly samples).We measured three variables at 20 points along eight, 200 m transects: (1) The number of scats collected in 10 m² plots for an estimate of use by jackrabbits, (2) Vegetation structure (density, coverage, and height) at each point for an estimate of predation risk and (3) Number of shrubs, grasses, and forbs found in line transects at each point for an estimate of food quantity. We found jackrabbits used grasslands more than shrublands (P= 0.03). However forage production in shrublands was significantly higher than grasslands. Within each habitat type, we found no difference in structure between high and low use areas but did find significantly higher forage production in high use areas. We interpreted these results as supporting the predictions of optimal foraging theory. Given equal predation risk levels within a given habitat jackrabbits were selecting areas based only on level of food resources. However, when faced with different risk levels, jackrabbits showed a preference for lower quality grasslands where they could more easily detect and thus escape predation than in the dense shrublands. In conclusion, optimal foraging theory seems to adequately explain habitat use patterns of jackrabbits in the desert environment.

Keywords: Optimal foraging, Jack rabbit, Chihuahuan desert

This abstract is being presented at: 2:30 PM in session:
Oral Session #17: Mammalian Herbivory.