Ecological winners and losers of extreme drought in California

Abstract

An unprecedented era of climatic volatility is altering ecosystems across our planet 1. The potential scale, pace and consequences of this global change have been modelled extensively 2 , yet little empirical research has quantified the impacts of extreme climate events on the composition of contemporary ecological communities. Here, we quantified the responses of 423 sympatric species of plants, arthropods, birds, reptiles and mammals to California's drought of 2012-2015-the driest period in the past 1,200 years 3 for this global biodiversity hotspot. Plants were most responsive to one-year water deficits, whereas vertebrates responded to longer-term deficits, and extended drought had the greatest impact on carnivorous animals. Locally rare species were more likely to increase in numbers and abundant species were more likely to decline in response to drought, and this negative density dependence was remarkably consistent across taxa and drought durations. Our system-wide analysis reveals that droughts indirectly promote the long-term persistence of rare species by stressing dominant species throughout the food web. These findings highlight processes that shape community structure in highly variable environments and provide insights into whole-community responses to modern climate volatility. The frequency, severity and duration of droughts is increasing due to global warming 4-6. High socioeconomic costs of severe droughts are among the most worrisome of climate change impacts, and effects on natural ecosystems may likewise be substantial 7. Predicting the ecological impacts of drought is complicated by the fact that species can be impacted through multiple pathways. Drought affects communities directly through physiological impacts on species' survival and growth rates, and indirectly by altering species interactions such as competition 8,9. Some theoretical models show that droughts can increase coexistence probabilities through selective mortality on dominant species 8,10 , while others predict that drought can increase dominance through increased competitive intensity 9. Here, we tested these conflicting predictions regarding the pathways through which drought impacts ecosystems, while broadly characterizing the response of a community to a once-in-amillennium climate-induced disturbance. Theoretical predictions of drought effects are rooted in plant ecology 11 , and it is not known whether they apply to animal populations that may primarily be indirectly affected by soil moisture deficits. Drought may affect all trophic levels similarly via generalized processes of disturbance or competition. Alternatively, drought effects may move up the food web with time lags or opposing effects. For example, droughts in sub-Saharan east Africa have led to ungulate die-offs 12 , resulting in a short-term resource pulse for scavengers 13. Thus, the effects of drought on resource availability differ among trophic levels and over time. Emerging studies indicate that droughts can strongly affect the dynamics of animal popula...

Long‐term monitoring of a highly invaded annual grassland community through drought, before and after an unintentional fire

“…Harrison et al () found a decline in mean community specific leaf area with drought. Similar to our data, Prugh et al () identified Calandrinia menziesii as a drought ‘winner’, while Erodium spp., Bromus madritensis and Bromus hordeaceus remained unchanged. Likewise, Lupinus bicolor increased strongly both at our site and those monitored by LaForgia et al () and Prugh et al ().…”

“…Still, our findings are consistent with declines in both above‐ground cover and seed banks of exotic grasses in other California grasslands during the recent drought, paralleled by increases in some native forbs (Harrison, Gornish, & Copeland, ; LaForgia, Spasojevic, Cse, Latimer, & Harrison, ). Similarly, in a predominately native California grassland the recent drought corresponded with disproportionate declines of the most common species and compensatory increases in some rarer competitors (Prugh et al, ). Those findings suggest a hypothesis for the patterns we observed, as declines in the dominant Bromus diandrus at our site correlated with increases in both other exotic grasses and native forbs (Figure ).…”

“…Other recent research similarly suggests that species‐specific responses to abiotic stress and disturbance are more important than broad differences between invasive and native species (Funk & Zachary, ). Encouragingly, species trait‐based approaches show promise for improving predictions (Harrison et al, ; LaForgia et al, ; Prugh et al, ). Harrison et al () found a decline in mean community specific leaf area with drought.…”

Effects of climate warming on Sphagnum photosynthesis in peatlands depend on peat moisture and species‐specific anatomical traits

“…SPEI was then calculated as precipitation minus ETo over the June–September period using spei R function. We used the reverse of SPEI values as a DI (Prugh et al, ), such that DI = −1 × SPEI. Positive DI values indicate an increase of aridity while negative DI values indicate the opposite.…”

“…All models were fitted including plots nested with date as a random effect on the intercept to correct for the inflation of the residual degrees of freedom that would have occurred if we were using repeated measurements as true replicates. The nlme package in R was used to run these models(Pinheiro, Bates, DebRoy, Sarkar, & R Core Team, 2019;R Core Team, 2019). As a proxy for drought, we used the total amount of precipitation at the site 2 weeks before each sampling campaign to estimate the intensity and frequency of drought.…”