Abstract
Animal home ranges derive from the distribution of resources across the
landscape. For example, home ranges of tortoise species in the U.S.
revolve around networks of burrows. However, human disturbances that
damage shelter sites can decrease habitat suitability, individual
survival, and population persistence. We investigated effects of burrow
distribution and availability on space use of the Sonoran Desert
Tortoise Gopherus morafkai at two populations with different habitat
structures to determine the extent to which habitat capacity is defined
by factors subject to management, such as vegetation, relative to more
permanent features such as rock shelters. We also demonstrated the
superiority of autocorrelated kernel density estimation, illustrating
flawed conclusions that could arise from the use of traditional
home-range estimators. Home-range size increased with the number of
available burrows at both sites. At the Florence Military Reservation
(FMR), with numerous caliche caves and few rock burrows, larger home
ranges effectively compensated for 1/3 the burrow density as that of
Sugarloaf Mountain, which predominantly featured rock burrows. Female
tortoises had smaller home ranges than males despite having similar
burrow densities. Females revisited individual burrows more often than
males at Sugarloaf, which may relate to female use of preferred nesting
sites; however, lower availability led males to revisit burrows at
similar rates as females at FMR. Pairs of tortoises at FMR shared 72%
more burrows than pairs at Sugarloaf, and pairs of females shared 33%
fewer burrows than female-male pairs across both sites. Space and burrow
use at FMR and Sugarloaf are consistent with predictions of how animals
choose patches for their home ranges in ways that are optimal with
respect to spatially distributed resources. Populations largely reliant
on pallets or soil burrows may be more subject to declines due to
anthropogenic impacts from grazing or off-highway vehicle use or due to
increasing temperatures.