Precipitation quantity and timing affect native plant production and growth of a key herbivore, the desert tortoise, in the Mojave Desert

Abstract

Background: Deserts may be disproportionately vulnerable to changes in precipitation that accompany global climate change due to complex evolutionary relationships of species to historical conditions. Based on current and projected climate scenarios for the southwestern United States, we manipulated rainfall timing and quantity and measured the response by plants and the growth and behavior of the desert tortoise (Gopherus agassizii) to precipitation in the eastern Mojave Desert. Results: We found that winter-dominant rain -the current prevailing pattern in the eastern Mojave Desert -and greater total rainfall correlated with greater cover and species richness of plants. Winter-dominant rain also correlated with a higher proportion of native plants flowering relative to invasive plants. Juvenile tortoises grew more rapidly when they were subjected to rainfall treatments that associated with increased plant abundance and species richness, while their behavior appeared more driven by water availability. Conclusions: Our results suggest that precipitation timing may be as important as rainfall quantity when considering total effects of climate change on arid-adapted systems. Further research should explore how the timing of rainfall may interact with aridity or temperature to influence total effects due to climate change on arid communities.

Head-started Agassiz’s desert tortoises Gopherus agassizii achieved high survival, growth, and body condition in natural field enclosures

“…Although these responses are complicated or obscured by the large variation in growth rates (Table S1), the large individual variation is consistent with results from numerous studies of desert tortoise growth (e.g. Nagy & Medica 1986, Turner et al 1987b, Medica et al 2012, physiology (Nagy & Medica 1986, Peterson 1996, Henen 1997, Henen et al 1998, Drake et al 2012, Nafus et al 2017, and behavior (Woodbury & Hardy 1948, Medica et al 1980, Nagy & Medica 1986, Nafus et al 2017. Such large variation may appear extreme, but it is likely exaptive for desert reptiles (Bradshaw 1988(Bradshaw , 1997 and other ectotherms (Pough 1980), and central to their species' success in arid environments.…”

“…Despite irrigating to counter drought conditions (i.e. to hydrate tortoises and promote food plant growth), our juveniles' overall growth was not higher than average rates in wild juvenile tortoises but was comparable to rates in other irrigated headstart facilities (4.2−11.9 mm yr −1 ; Nagy et al 2015a, Nafus et al 2017, Mack et al 2018, Tuberville et al 2019).…”

Effects of roads and roadside fencing on movements, space use, and carapace temperatures of a threatened tortoise

“…The second peak in road crossing activity corresponded with monsoon events near our study site (Supplementary Fig. 2) and in the eastern Mojave (Beatley, 1974;Kurc and Benton, 2010;Nafus et al, 2017). At this time, between day of year 175-215, rainfall accumulates on roads and nearby from runoff.…”

Phylogeny, host use, and diversification in the moth family Momphidae (Lepidoptera: Gelechioidea)

“…As in other phytophagous insect systems [90,97–99], plant phenology may be a driver of momphid specialization. Because many Mompha are strictly dependent on reproductive structures of Oenothera for larval survival, adult eclosion must be synchronized with reproductive periods of their hostplants, which may be especially important in arid areas where precipitation and temperature–essential for modulating the timing of flowering [100,101] are commonly unpredictable. Hostplant allelochemicals can also influence phytophagous insect specialization [102,103].…”