Ecological Archives E093-057-A4

Benedikt R. Schmidt, Walter Hödl, and Michael Schaub. 2012. From metamorphosis to maturity in complex life cycles: equal performance of different juvenile life history pathways. Ecology 93:657–667.

Appendix D. Description of the projection matrix model.

To estimate the asymptotic population growth rate we formulated a female based matrix projection model with 5 age classes (toadlet, 1 year old, 2, years old, 3 years old, more than 3 years old) using a post-breeding census and a projection interval of one year (Caswell 2001). The dominant eigenvalue of the projection matrix is an estimate of the asymptotic population growth rate, and thus of fitness. The projection matrix for the spadefoot toads is:

A  
 
 
φ1yA1F1φtadpole0.5   φadA2F2φtadpole0.5   φadA3F3φtadpole0.5   φadA4F4φtadpole0.5   φadA5F5φtadpole0.5
φ1y 0 0 0 0
0 φad 0 0 0
0 0 φad 0 0
0 0 0 φad φad
 

where:

A1 = α1
A2 = α1 + (1 - α12
A3 = α1 + (1 - α12 + (1 - α1)(1 - α23
A4 = α1 + (1 - α12 + (1 - α1)(1 - α23 + (1 - α1)(1 - α2)(1 - α3)

The parameters in the model are:

φtadpole: tadpole survival using the relationship logit(φtadpole) = -5.24 + 8.09 × 10-5 x - 8.49 × 10-10 x², where x is the number of eggs in the pond (we used x = 90’000; regression model from Hels and Nachman 2002).
φ1y: first year survival (own model averaged estimates)
φad: adult year survival (based on our own data, we used an estimate of 0.43)
α1: probability to start to reproduce when 1 year old (own model averaged estimates)
α2: probability to start to reproduce when 2 year old (own model averaged estimates)
α3: probability to start to reproduce when 3 year old (own model averaged estimates)
F1: number of eggs a female of age 1 is producing, using the relationship F1 = 80.4BM1 (Hels 2002), where BM1 is body mass of 1 year old toads (12.8g)
F2: number of eggs a female of age 1 is producing, using the relationship F2 = 80.4BM2 (Hels 2002), where BM2 is body mass of 1 year old toads (15.6g)
F3: number of eggs a female of age 1 is producing, using the relationship F3 = 80.4BM3 (Hels 2002), where BM3 is body mass of 1 year old toads (21.2g)
F4: number of eggs a female of age 1 is producing, using the relationship F4 = 80.4BM4 (Hels 2002), where BM4 is body mass of 1 year old toads (25.1g)
F5: number of eggs a female of age 1 is producing, using the relationship F5 = 80.4BM5 (Hels 2002), where BM5 is body mass of 1 year old toads (30.2g)

First year survival and the age-specific probabilities to reproduce depended on body condition (PC1) and timing of metamorphosis, and we therefore calculated the population growth rate for different conditions. This population model assumes that females which have reproduced once, reproduce every year and that the males are an unlimited resource. To account for uncertainty in parameter estimates, we estimated confidence intervals for the population growth rate using simulation (see Schaub et al. 2009 for details). In each of the 1000 iterations we sampled φ1y, φad, α1, α2, and α3 from beta distributions that were given by the estimated means and sampling variances of the corresponding parameters. For the other parameters of the matrix model no measures of uncertainty were available.


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