Reference: Prugh, L.R. et al. (2018) Ecological winners and losers of extreme drought in California. Nature Climate Change, v.8 819-824. doi.org/10.1038/s41558-018-0255-1.
Feature Image: “No smoking” and fire risk sign at one of the trailheads within Griffith Park, Los Angeles, CA. Source: personal archive (Sept, 2018).
All the leaves are brown…and the sky is grey
I am a Brazilian researcher living in the United States for less than 5 years, and I have been hearing about the notorious (and scary) California drought crisis, even before I moved here. Not only is the temperature higher and the air drier for longer periods of time there, but the frequency and size of major vegetation wildfires has substantially increased in the past decade, a threat compounded by increasingly depleted water reservoirs (also known as aquifers). Sorry, but I have bad news for you Californians and Cali-lovers: studies indicate that these major fires will surge to over 50% by 2050 and that the water crisis will continue due to intensification of climate change conditions. In 2017-2018, major news highlights were made about entire neighborhoods being destroyed by these massive wildfires (Figure 1) and major CA cities running out of water. But what about the defenseless wildlife and vegetation? How are these communities being shaped under such extreme conditions, while not being able to immediately evacuate like us humans?
A recent study by Dr. Laura Prugh and collaborators aimed to answer exactly that: how did plant and animal communities of California respond to drought effects of 2012–2015? This period has been identified as the driest period in the past 1,200 years for this global biodiversity hotspot located near Bakersfield, CA. The authors wanted to know: what happens when certain living-organism groups survive and grow, while others die? Why does this happen during droughts?
To answer these questions, the authors monitored the amount of plants, insects, reptiles, birds and mammals from before and after the major drought period (2007-2015). With that, they determined which groups were the “winners” and “losers”, and which characteristics made them thrive or perish. These features include body mass, population growth rate, diet or growth form, and position on the local food chain.
Let the drought games begin!
In total, the scientists monitored 423 species within a semi-arid grassland community located close to Bakersfield, CA (i.e., Carrizo Plain). Within these species, 25% were classified as losers, 4% as winners, and 71% that were not significantly affected by the drought. The “4%-ers” included six beetle species, one ant species, one plant, one reptile, two birds and one rodent. Thus, even though there was a strong decline in the total number of individuals within species, the extreme drought did not result in overwhelming number of locally extinct species. This seemingly successful survival was attributed to the groups’ pre-drought abundance numbers and their diet (animal) or growth form (plants); and for longer drought periods (2-3 years), maximum population growth rate was the main predictor.
Based on these metrics, rare species across all groups were more likely to win and, consequently, resulted in a jump in the population number by the end of the drought period. The authors attribute this surprising feat to the drought disturbance factor stressing more abundant and dominant species, and making way for more shy and less competitive species. Additionally, species with smaller bodies and higher growth rates were also more likely to be winners, such as birds and insects. When considering the groups’ position in the overall food chain, the drought affected the plant populations more rapidly (less than a year into the drought) due to water shortages, followed by herbivores, omnivores and insectivores, and finally by carnivores responding more strongly after three growing seasons. These trends can be explained by certain animal species, such as rodents for example (Figure 3), having food stored and not necessarily depending on the plants that succumbed earlier to the drought. Meanwhile carnivores can still prey on species that increase with the drought (for example, the Golden-eagle of Figure 2). Hence, the drought resistance of certain key species may be critical in determining the community-wide response to drought events.
… California dreamin’ on such a “dry and warm” day
Overall, this study highlights that what affects living communities is not always the direct effect of major climatic events, such as physical damages caused by fire or dehydration by reduced water supply. The authors share an interesting perspective on how the dynamics of species within a community can unbalance a certain group of organisms that can potentially shape an entire ecosystem if longer droughts are to occur. Although few species were considered to be losers, and rare species were the most favored by the drought due to a less competitive ecosystem, it is very early to claim victory and to say confidently that more conservation efforts are not required for such grassland ecosystems.
There is much more to learn about the recovery processes for environments following major climatic events. Until then, studies like this excites us ecosystem researchers that not all is lost, and that more research will possibly lead to many more wins in the fight against the loss of species habitats in the US and across the globe.