High predation risk decimates survival during the reproduction season

Predators attack conspicuous prey phenotypes that are present in the environment. Male display behaviour of conspicuous nuptial colouration becomes risky in the presence of a predator, and adult males face higher predation risk. High predation risk in one sex will lead to low survival and sex ratio bias in adult cohorts, unless the increased predation risk is compensated by higher escape rate. 

Here, we tested the hypothesis that sand lizards (Lacerta agilis) have sex-specific predation risk and escape rate. We expected the differences to manifest in changes in sex ratio with age, differences in frequency of tail autotomy, and in sex-specific survival rate.

We developed a statistical model to estimate predation risk and escape rate, combining the observed sex ratio and frequency of tail autotomy with likelihood-based survival rate. Using a Bayesian framework, we estimated the model parameters. We projected the date of the tail autotomy events from growth rates derived from capture-recapture data measurements.

We found statistically stable sex ratio in age groups, equal frequency of tail regenerates between sexes, and similar survival rate. Predation risk is similar between sexes, and escape rate increases survival by about 5%. We found low survival rate and a low number of tail autotomy events in females during months when sand lizards mate and lay eggs, indicating high predator pressure throughout reproduction. Our data show that gravid females fail to escape predation. 

The risks of reproduction season in an ectotherm are a convolution of morphological changes (conspicuous colouration in males, body allometry changes in gravid females), behaviour (nuptial displays), and environmental conditions which challenge lizard thermal performance. Performance of endotherm predators in cold spring months endangers gravid females more than displaying males in bright nuptial colouration. 

Methods
Capture-recapture data of sand lizards (Lacerta agilis, Lacertidae, Reptilia) from Hustopeče, Czechia (48.93 N, 16.72 E).

animal - identification of the animal; prefix indicates the latest possible year of hatching
day - day of capture
month - month of capture
year - year of capture
season - phase I started from the arousal from hibernation, and lasted until the first adult male started to lose nuptial colouration; phase II constituted the season after males started to lose nuptial colouration, and lasted until the beginning of hibernation
sex - sex of the animal
ventralia - number of scales in the second rows from the ventral medial line
age - young animals were juveniles and subadults, the remaining animals were considered adult
aged.month - approximate age of the animal in months
regenerate - presence of tail regenerate
predation.attempt - first record of tail regenerate or reduced tail length at recapture
Lreg - tail regenerate length in mm; 0 - animal with intact tail, 0.01 - recent tail autotomy, no tail regenerate growth measurable
tailL - tail length from cloaca to tail tip corrected for body length from rostrum to cloaca48.93 N, 16.72 E48.93 N, 16.72 E)