Heterogeneity in Primary Productivity Influences Competitive Interactions between Red Deer and Alpine Chamois

Abstract

Habitat heterogeneity can promote coexistence between herbivores of different body size limited to different extents by resource quantity and quality. Red deer (Cervus elaphus) are known as superior competitors to smaller species with similar diets. We compared competitive interactions and habitat use between red deer and Alpine chamois (Rupicapra rupicapra) in two adjacent valleys in a strictly protected area in the Central Alps. Red deer density was higher in the valley with higher primary productivity. Only here was horn growth in kid and yearling chamois (as a measure for body condition) negatively correlated with red deer population size, suggesting interspecific competition, and chamois selected meadows with steeper slopes and lower productivity than available on average. Conversely, red deer selected meadows of high productivity, particularly in the poorer area. As these were located mainly at lower elevations, this led to strong altitudinal segregation between the two species here. Local differences in interspecific competition thus coincided with differences in habitat preference and-segregation between areas. This suggests that spatial habitat and resource heterogeneity at the scale of adjacent valleys can provide competition refuges for competitively inferior mountain ungulates which differ from their superior competitor in their metabolic requirements.

Fig 1. Location of the two ungulate study areas Val Trupchun and Il Fuorn in the Swiss National Park.

a) SNP = Swiss National Park, T = Val Trupchun (enlarged in b)), F = Il Fuorn (enlarged in c)). The thick black line represents the National Park boundary, the thin gray line national boundaries between Switzerland, Italy and Austria. b, c) 95% Kernel densities (resolution = 30m; search radius = 250m) of chamois (green) and red deer (red; with areas of overlap between the two species indicated in brown), based on visual surveys during August 1997 to 2013. Dark grey shading in the background indicates conifer forest, light grey shading meadows, and white background bare soil (rock, scree or snow). The thin solid black line represents the 2000m, the dashed line the 2400m, and the dotted line the 2800m contours.

Fig 2. Annual counts of chamois and red deer in Val Trupchun and Il Fuorn 1990–2013.

Green lines represent chamois, red lines red deer; solid lines represent Il Fuorn, broken lines Val Trupchun.

Fig 3. Group sizes of chamois (a) and red deer (b) on meadows in Il Fuorn and Val Trupchun.

Fig 4. Horn growth.

Chamois horn growth during the kid and yearling years combined vs. explanatory variables in regional (Val Trupchun and Il Fuorn combined; a1-3) and local (Il Fuorn only; b1-3) linear models. Open symbols in scatterplots represent females, closed symbols males. Plots are shown for all parameters with predictor weights > 50%, but regression lines are only included for continuous variables retained in the most parsimonious model within ∆AICc ≤ 2.

Fig 5. Habitat use.

Effects of parameters (with standard errors in gray) included in most parsimonious GLMM’s within ∆AICc ≤ 2 for use of meadows by adult chamois (coded as 1) vs. red deer (coded as 0) in a) Val Trupchun and b) Il Fuorn. The y-axes are on a logarithmic scale.