A discrete stage-structured model of California newt population dynamics during a period of drought

Predicting the effects of manual crayfish removal on California newt persistence in Santa Monica Mountain streams

“…The adult newt equilibrium population of 648 adult newts is greater than current estimates of the Cold Creek population of 572 adult newts (Bucciarelli et al, unpublished), which is expected since our model does not incorporate newt population declines due to drought. Equation 15is consistent with the equilibrium solution of the newt population model by Jones et al (2017), which predicts 651 adult newts in the absence of drought. When crayfish are present but no trapping regime is implemented, we assume C is constant and 14reduces to…”

“…We model newt egg production using a Michaelis-Menten enzyme kinetics metaphor where stream habitat space acts as a catalyst and crayfish competitively inhibit newt egg-laying. This builds upon the crayfishfree discrete model of newt populations in Jones et al (2017). During the breeding season, newts maintain a roughly 1:1 sex ratio given a sufficiently large population (Marshall et al, 1990), so we assume the fertile female egg population is A L = A t /2 newts, where A t is the number of adult newts at time t. A female newt can reproduce once per year and lays 2-3 egg masses with 15-30 embryos each (Brame, 1968;Kats et al, 2013).…”

“…Considering that global anthropogenic warming is increasing the probability of droughts like the exceptionally dry and warm period from 2012 to 2015 (Diffenbaugh et al, 2015), newt population declines may be exacerbated by increasingly extreme seasonality in precipitation (Sodhi et al, 2008). Newts are sensitive to drought conditions in their native regions despite living in terrestrial burrows after metamorphosis because adult newts return to SMM streams each year to lay eggs, which hatch to become aquatic larvae (Jones et al, 2017).…”

“…However, none have modeled newt and crayfish interactions in the wild. We have developed in parallel a separate newt population stage-structured model to examine the impact of drought on newt persistence (Jones et al, 2017) in the absence of crayfish. We now explore the impact of restorative measures, such as crayfish trapping, on newt persistence or time to extinction in streams with crayfish present.…”

Longevity and population age structure of the arroyo southwestern toad (Anaxyrus californicus) with drought implications

“…Many aquatic and semi-aquatic species adapted to southwestern and Mediterranean ecosystems are similarly at risk from reduced surface water availability, leading to reduced aquatic connectivity, recruitment, and survivorship (Jaeger et al, 2014;Jones et al, 2017;Leidy, Bogan, Neuhaus, Rosetti, & Carlson, 2016;Lovich et al, 2017;Montgomery et al, 2015). For species that burrow and forage in adjacent terrestrial systems, increased drought stress can further affect overwinter survival and prey availability due to reduced soil moisture and associated plant and animal mortality (Lovich et al, 2017;Venturas et al, 2016).…”