Table 3.
Description of most supported models (models with the lowest AIC scores with cumulative weights up to 1.0) developed to estimate grizzly bear population density using spatial capture-recapture data from the Northern Continental Divide Ecosystem in northwestern Montana, USA.
| Modela | D | p0 | σ | ΔAIC | Weight | CumWt |
|---|---|---|---|---|---|---|
| Females | ||||||
| 1 | ~linear | ~year + dur + jul + jul2 + beh + spatial covs | ~year | 0.00 | 0.61 | 0.61 |
| 2 | ~linear | ~year + dur + jul + beh + spatial covs | ~year | 1.26 | 0.32 | 0.93 |
| 3 | ~year | ~year + dur + jul + jul2 + beh + spatial covs | ~year | 5.24 | 0.04 | 0.98 |
| 4 | ~year | ~year + dur + jul + beh + spatial covs | ~year | 6.51 | 0.02 | 1.00 |
| Males | ||||||
| 1 | ~linear | ~year + dur + jul + jul2 + beh + spatial covs | ~year | 0.00 | 0.95 | 0.95 |
| 3 | ~year | ~year + dur + jul + jul2 + beh + spatial covs | ~year | 5.80 | 0.05 | 1.00 |
Spatial detection histories were derived from genetic identification of individual bears from hair collected at natural bear rub sites. For females, a single outlier point in 2010 was removed from the dataset. See Table S1 online for descriptions of the complete set of candidate models.
aModel notation: D: density (bears/1,000 km2). p0: baseline detection probability. σ: sigma; spatial scale parameter related to the amount of space used by each individual. ΔAIC: cumulative change in Akaike Information Criterion. Weight: measure of support for each model. CumWt: cumulative measure of support for the models. ~: “a function of”. linear: density is a linear function of time. year: parameter is year specific. dur: duration of sampling interval; number of days since previous sampling visit. jul: Julian date; linear effect of season on detection probability. jul2: Julian date squared; quadratic effect of season on detection probability. beh: behavioral response; a visit of some bear at some bear rub changes its subsequent probability of detection at that rub. spatial covs: spatial covariates: cover: percent of mean canopy cover within 250 m of the trap. cover2: percent of mean canopy cover squared. curv: standard deviation of terrain curvature within 250 m of the trap. sec: security level as determined by land ownership policies at the trap: 10 = U.S. National Park Service, 7 = U.S. Forest Service, 3 = state/other public, 1 = private).