2.4 | Habitat Classification
Habitat classifications were developed using Light Detection And Ranging
(LiDAR) surveys and high-resolution aerial photo in 2009 by the Applied
Geomatics Research Group (Nova Scotia Community College, Middleton, Nova
Scotia; van Beest et al. 2014). Non-vegetated habitat classes included
bare sand, ocean, human structures (buildings with fenced perimeters),
and freshwater ponds. Vegetated habitat classes were characterized by
their dominant plant species: grassland (marram grass), heath (mixed
juniper, crowberry, and blueberry), sandwort, and beach pea. Vegetated
classes subcategorized into ‘sparse’ or ‘dense’ (e.g. sparse grassland
and dense grassland) in original classification efforts were combined in
our analyses.
To quantify individual variation in local environment, we calculated the
area of habitat classes overlapping a 150-m radius circular buffer
centred on the location of sample collection in R (v3.5.1). A 150-m
radius buffer corresponds approximately to the observed median daily
movement of horses in 2014 (positive skewed distribution, median: 108
m/day; median 317 m/day), and so is expected to coarsely reflect the
types of environment, and therefore forage, encountered during the 24
hours preceding defecation. Habitat class variables were calculated as
the area of a given habitat class relative to the total occupiable
terrestrial area included within an individual’s buffer
(AreaBuffer – AreaBuilding–
AreaOcean). Sandwort abundance was zero-inflated and
non-normally distributed. Further, resource selection analysis of Sable
Island horse foraging behaviour suggests horses actively select for
sandwort when it is present, while other vegetated habitat classes are
used in proportion to their abundance on the local landscape (personal
communication K. Johnsen). For these statistical and biological reasons,
sandwort was parameterized as ‘present’ or ‘absent’ in our analyses.
Only vegetated habitat classes were parameterized in analyses to limit
model inflation and avoid collinearity between terms.