When no color pattern is available: Application of double observer methods to estimate population size of the Alpine salamander

Figures & data

Figure 1. The alpine salamander, Salamandra atra, a fully terrestrial and completely black amphibian, endemic of the Central and Eastern Alps and Dinaric Alps.

Table 1. List of candidate models, ranked by AICc

Model	Parameters	AICc	ΔAICc
p(Observer+Width) λ(Canopy+Ruggedness)	7	314.41	—
p(Observer+Width) λ(Canopy+Ruggedness+TPI)	8	314.67	0.26
p(Observer+Width) λ(Canopy+Ruggedness+TPI+Shelter)	9	316.90	2.49
p(Observer+Width) λ(Canopy+Ruggedness+TPI+Width)	10	319.40	4.99

Table 2. Parameter estimates and 95 percent confidence intervals from the best model. Detection parameters are on the logit scale. Abundance parameters are on the log scale

Parameter		Estimate	95% Confidence interval
Detection (p)	Intercept (observer 1)	2.13	1.16–3.1
	β Observer 2	−0.38	−2.63 to 1.86
	β Width	−1.00	−1.91 to −0.09
Abundance (λ)	Intercept (canopy: high)	0.04	−0.24 to 0.33
	β Canopy: low	−0.61	−1.35 to 0.12
	β Canopy: medium	0.40	0.02–0.80
	β Ruggedness	0.52	0.36–0.67

Figure 2. Plots representing the relationship between expected values of abundance and detection and covariates included in the best model. Transect width is expressed in meters. Three plots for abundance represent different levels of canopy. Blue and red lines represent the mean for abundance and detection, respectively. Grey lines represent 95 percent confidence intervals.