Relative probability of elk occurrence in predator scats
To predict the relative probability of elk occurrence in a
predator-specific scat (Pij ), we contrasted
locations of scats containing elk (n = 157: 24 bear, 75 wolf, 42
coyote, and 16 cougar) to locations of a larger set of scats (n =
870: 257 bear, 363 wolf, 223 coyote, and 27 cougar) from the same
predator species collected but not analysed for prey contents (Spilker,
2019), similar to a use/available design (Manly et al., 2002). By using
scat locations as our available locations (rather than random
locations), we controlled for the influence of landscape features on
where predator scats were located. We avoided a presence-absence of elk
in the scat design because the methods we used to detect elk in scats
could not reliably confirm absence of elk. We used a model selection
approach based on a ΔAICc > 4 to determine
the model with the most support. We determined model covariates as the
density or proportion within a buffer around a scat whose radius was
derived from the mean gut passage time and movement per day (i.e., 3-km
for wolf, 1.5-km for bear, and 2-km for cougar and coyote, Appendix S1,
Supporting Information).
Covariates included green herbaceous biomass (g m-2)
at the peak of the growing season (1 August), derived from a general
linear model based on field sampling of 983 sites across the summer
extent of the Ya Ha Tinda elk herd (Hebblewhite et al., 2008), and
updated for changes in forage availability caused by climate, timber
harvest, and fires (Smolko, 2014; MacAulay, 2019). Because elk must use
the area to be found in the scat and encounters with elk are likely
related to their intensity of use of an area, we also quantified
relative intensity of elk use using a population-level resource
utilization function (RUF; Marzluff et al., 2004) based on utilization
distributions from 6-hour GPS relocations of 66 adult female elk during
2013 – 2016. Variables in the RUF included herbaceous forage biomass,
herbaceous land cover (Hebblewhite et al., 2008), distance to nearest
forest edge, burned vegetation (< 15 years), and wolf
(Hebblewhite & Merrill, 2007) and grizzly bear predation risk (Nielsen
et al., 2002). For more detail, see MacAulay (2019).