Fig 1.
Home range polygons estimated using three different methods.
The polygons represent the 90% probability isopleth of sea otter number 1392, a female in Monterey Bay, CA. Note the overlap between home range polygons and land for LoCoH (middle; 17% of the home range overlapped with land) and KDE (left; 10%), but not for PHRE (right; 0%).
Fig 2.
Frequency distribution of the percent of home range area that overlapped with land for each method.
We calculated the percent of the 90% probability isopleth that overlapped with land (N = 126 sea otter home ranges for each method). Three methods are compared: KDE (top), LoCoH (center), and PHRE (bottom).
Fig 3.
Average (± SD) home range area and the coefficient of variation across sample sizes of sighting locations.
Home range estimates were iterated 10 times across each sample size for 26 different animals (data for only one animal shown, ID = N-1225-03-S). Closed circles show home range area and open circles show the coefficient of variation. The solid lines denote the asymptotic curves for the data and the dashed lines denote the asymptotic curves for the coefficients of variation. Three methods are compared: KDE (top), LoCoH (center), and PHRE (bottom).
Fig 4.
Receiver operating characteristic curves comparing predictive accuracy of KDE, LoCoH, and PHRE.
Sighting data from 26 animals were used to generate home range estimates (200 random points were selected for ten iterations). For each iteration 100 presence and 1,000 pseudo-absence data were generated to calculate the area under the curve (AUC). Plotted curves show composite estimates for all iterations. Calculated curves can be compared to the grey dotted line, which denotes an AUC of 0.5 where presence and absence predictions are no better than chance.
Fig 5.
Map of available habitat at the Monterey Bay (north of Garrapata State Park) and Big Sur (south of Garrapata State Park) study sites.
Because habitat available to foraging sea otters (between 0 and −39 meters depth) extends farther offshore in Monterey Bay, there is greater opportunity for sea otters to increase home range area and access to resources by extending home ranges offshore. In contrast, sea otters in Big Sur are forced to extend their home ranges along the coastline to access more resources. Characteristic home ranges for females at each study area are shown in red (Monterey Bay) and yellow (Big Sur).
Fig 6.
Home range length (km) plotted as a function of area (km2) for otters at two sites in central California.
Data represent values obtained from home range estimates created using KDE (top), LoCoH (middle), and PHRE (bottom). Solid, black points represent Monterey Bay (N = 92) and open, blue points represent Big Sur (N = 34). Fitted power functions are shown by solid lines, with standard error shown by lighter dashed lines. Length increased more rapidly with home range area for sea otters at Big Sur compared to Monterey Bay (i.e. Big Sur home ranges were more elliptical).