As some of you know, I do love a good herbarium and as I was reading more about them, I went down a bit of a rabbit-hole. So this month I thought I would write about how herbaria can contribute to phenology -seasonal life events – but also include how climate variation can affect phenological changes in other organisms.
By documenting structures in a herbarium that contain diagnostic features such as leaves, flowers, fruits etc, stages of phenology become apparent. As well as using specimens to identify the plant, they can also be used to work out the timing of its annual growth and reproductive cycle. Because the plant is labelled with the date and where it was collected, we can compare phenological changes over time and space; studies comparing past and present flowering times correlated with meteorological data, show a trend linking spring temperatures to earlier flowering (Primack, 2004). By telling us about past environments and flowering dates, herbarium specimens can help make predictions about the future.
Shifts in phenology, one of the most commonly predicted effects of global change, are a cause for concern because such shifts could lead to a mismatch between plants and other organisms such as their pollinators. Studies using large sets of digitalised herbarium specimens have confirmed that this indeed happening. An example is a study by Hutchings et al. (2018) of pollination in the early spider orchid. When it flowers, this orchid emits a fragrance that smells like a female mining bee, Andrena nigroaenea. The male bee typically emerges in the spring before the female, at the same time that the orchid is flowering. The male bee is attracted to the flower and attempts to copulate with it, picking up pollen in the process, which it deposits on the next early spider orchid flower that attracts it. A comparative study of herbarium specimens of this orchid over the last 150 years from the Kew and Sloane herbaria, specimens of the mining bee from Oxford’s Museum of Natural History, and climate data indicates that warming temperatures are causing the orchids to flower earlier and the female bees to appear earlier. This means that the orchid is now competing with the female bee for the male’s attention, and that fewer flowers are pollinated. Less pollination means fewer offspring for the orchid, less genetic diversity and so less adaptability to environmental change.
Research published in the Royal Society of Open Science this month (J.C Laloë & G.C Hays) indicates that climate warming may cause the feminisation of marine turtle populations as well as a reduced hatchling survival. Their research reported that even with the most extreme phenological shift to date (an 18-day advance in nesting per °C increase in sea surface temperature), temperatures will continue to increase at nesting sites with climate warming. Marine turtles exhibit temperature-dependent sex determination and these temperature rises could lead to increased female biased sex ratios as well as a decrease in hatchling production, resulting in long-term survival concerns. This suggests that a phenological shift in nesting will often not be enough by itself.
Organisms that are unable to shift their phenology to match the climate change may decline as their demands for a certain resource aren’t met. Phenology is argued to be the most sensitive biological indicator of climate change and recording phenological events will capture ecosystem changes before they happen.