Estimating lizard home range: The Rose model revisited

In 1982, B. Rose pointed out that home-range area could easily be underestimated unless sufficient numbers of sightings were obtained for each individual, and recommended a population-specific test to determine the minimum sample size at which home-range area can be accurately measured. This recommendation has been generally ignored. We explore how sample size affects interpretation of space use data in male lava lizards, Microlophus albemarlensis, and male eastern collared lizards Crotaphytus collaris. Using the criteria established by Rose, the minimum sample sizes for collared lizards and lava lizards were 45 and 84 sightings, respectively. These are much larger samples than we anticipated and reinforce the need for empirical determination of minimum sample size. Our data suggest that lizard movement rate is a better predictor of minimum sample size than home-range area. Collared lizard home ranges were over 10 times larger than lava lizard home ranges, yet the higher movement rates of collared lizards resulted in a minimum sample size that was about one-half that of lava lizards. Restricting data collection to any one-quarter of the total study period would have markedly underestimated home-range area and home-range overlap in both species. Every lizard of both species had a core area within their home range, suggesting the absence of major temporal shifts during the study. On average, lava lizard core areas occupied 21.7 +/- 2.8% of total home-range area, yet core areas included 78.8 +/- 3.1% of all lizard sightings. Collared lizard core areas averaged 25.4 +/- 2.4%, with a lower percentage of collared lizard sightings occurring within core areas (66.3 +/- 3.0%). There was only one incidence of core overlap in either species. Lava lizards may be defending core areas but in an unusual manner, what amounts to 'sit-and-wait territoriality." This unusual mode of space use would not be detectable from a smaller number of sightings per individual.