Short, medium and long‐term effects of density on the demographic traits of a threatened newt

Abstract

Mediterranean streams undergo seasonal reductions in water availability that may affect amphibian demography due to habitat loss and the concentration of individuals in the shrinking aquatic habitats. However, there are few empirical examples of how increased population density experienced by larval stages produces long‐term effects on growth and fitness at postmetamorphic stages. We tested the effect of four different larval densities on the demography and growth of the endangered stream‐dwelling newt Euproctus platycephalus. By manipulating larval populations in experimental aquaria, we analyzed the short‐term effects of density in terms of growth and mortality rates as well as of social behavior. To assess medium‐ and long‐term effects we tested the metamorph individuals after 1 and 3 years, respectively, and adults for maternal effect by assessing the relationship between mean larval size and fecundity. Larval body size and growth rate appeared inversely proportional to larval density. Density affected the incidence of aggressive behavior by increasing the rate of mutilation to arms and tail. One‐year‐old salamanders raised at the highest larval density grew significantly less. All 3‐year‐old individuals reached comparable body size and body condition irrespective of initial larval density. Salamanders presented a positive relationship between maternal size and (1) fecundity and (2) larval size. In natural conditions, increased density may cause slower growth and a reduction in the percentage of individuals reaching metamorphosis. Prolonged dry periods and increased water withdrawals for agricultural and industrial practices have almost certainly affected the population dynamics of Sardinian newt populations in the long term.

Can a cow save a newt? The role of cattle drinking troughs in amphibian conservation

“…Indeed, newts use aquatic habitats during the breeding period and adopt a terrestrial lifestyle during the rest of the year, consuming invertebrates that comprise a large part of their diet (Joly & Giacoma, ; Schabetsberger & Jersabek, ; Vignoli, Luiselli, & Bologna, ). Adult body size should be attained mainly during the juvenile phase of life even if the aquatic larval phase is thought also to be responsible for adult growth (Halliday & Verrell, ; Vignoli et al, ). It would be expected, therefore, that different habitat conditions and feeding strategies in aquatic habitats would affect adult body sizes, with body size in artificial water bodies smaller than in natural ones (Nobili & Accordi, ).…”

Pipefish embryo oxygenation, survival, and development: egg size, male size, and temperature effects

“…Together, our results support a growing number of studies, on a variety of taxa, that have been unable to show that large eggs, with a supposedly unfavorable surface-area-to-volume ratio for gas diffusion, are more susceptible to oxygen limitations during development (Einum et al 2002; Braga Goncalves et al 2015b; Polymeropoulos et al 2016; Rollinson and Rowe 2018). However, the smaller embryo sizes observed in the more densely packed broods of small males may result from constraints in other types of paternal investment, such as nutrient provisioning, as found in burying beetles (Monteith et al 2012), or due to sibling competition, as found in newts (Vignoli et al 2018).…”

Designing an optimal large‐scale reintroduction plan for a critically endangered species

“…We represented each population using a simple logistic growth modelreflecting density dependence as hypothesized for this species (Colomer et al, 2014) and observed in other stream‐dwelling newts (Gill, 1979; Petranka & Sih, 1986; Vignoli et al, 2018). We parameterized the model using available evidence for C. arnoldi or for its sister species C. asper (ecologically broadly similar), and formally elicited expert judgement (Table 1).…”