Seasonal timing of first rain storms affects rare plant population dynamics

Abstract

A major challenge in forecasting the ecological consequences of climate change is understanding the relative importance of changes to mean conditions vs. changes to discrete climatic events, such as storms, frosts, or droughts. Here we show that the first major storm of the growing season strongly influences the population dynamics of three rare and endangered annual plant species in a coastal California (USA) ecosystem. In a field experiment we used moisture barriers and water addition to manipulate the timing and temperature associated with first major rains of the season. The three focal species showed two- to fivefold variation in per capita population growth rates between the different storm treatments, comparable to variation found in a prior experiment imposing eightfold differences in season-long precipitation. Variation in germination was a major demographic driver of how two of three species responded to the first rains. For one of these species, the timing of the storm was the most critical determinant of its germination, while the other showed enhanced germination with colder storm temperatures. The role of temperature was further supported by laboratory trials showing enhanced germination in cooler treatments. Our work suggests that, because of species-specific cues for demographic transitions such as germination, changes to discrete climate events may be as, if not more, important than changes to season-long variables.

Beyond annual and seasonal averages: using temporal patterns of precipitation to predict butterfly richness across an elevational gradient

“…Indirectly, increasing the number of water events throughout the water year may alleviate water stress on host plants, resulting in increased success of developing caterpillars, higher densities of adults and, consequently, greater observed species richness. The first event date is likely to indirectly impact butterfly richness through earlier blooming and increased productivity of host plants (Pitt & Heady, 1978;Levine et al, 2008Levine et al, , 2011. And while the commonly used variable minimum temperature was supported at Suisun, growing degree days was also an important predictor.…”

“…The timing of weather patterns can affect vegetation phenology, as individual plants often use temperature and precipitation patterns as cues for when to initiate germination and flowering (e. g. Levine et al, 2008Levine et al, , 2011Gordo & Sanz, 2010). Additionally, plants might respond to precipitation patterns rather than accumulation over an entire growing season (Knapp et al, 2002;Peñuelas et al, 2004;Sher et al, 2004;Pérez-Camacho et al, 2012), and many small pulses of rain may have a different effect on soil moisture and element cycling than does a single large storm event (e.g.…”

Climate Change Increases Reproductive Failure in Magellanic Penguins

“…Storm timing affects population dynamics in species ranging from plants [70] to mammals [71]. Chick age during the storm, determined by storm timing, was the most important variable in our models.…”

An experimental extreme drought reduces the likelihood of species to coexist despite increasing intransitivity in competitive networks

“…Annual species germination occurs after major autumn rains (Levine et al., ) and, in Mediterranean ecosystems, extreme droughts are often associated with a delay in the start of the rainy season. Therefore, to assess the effect of extreme climatic events on species’ fitness and competitive interactions, we simulated an extremely dry autumn season by replicating the complete experimental design sowing seeds on 10 December 2014.…”