23 August 2019

Climate Relations Out-of-Sync

Phenology is a branch of science dealing with the relations between climate and periodic biological phenomena, such as bird migration or plant flowering (Merriam-Webster).

Welcome back. I first heard the term phenology in the early 1970s. University colleagues in atmospheric sciences were analyzing images acquired by NASA’s newly launched Earth Resource Technology Satellite (later renamed Landsat) to monitor the seasonal changes in vegetation in the eastern U.S.

Today, as you might imagine, climate change is playing havoc with phenological relationships. When there’s a phenological mismatch--when the timing of the life cycles of interacting species changes at different rates--the impact can be serious if adjustments cannot be made. Given the rate at which climate is changing, some species may not be able to adapt fast enough.

A phenological mismatch: The color of the snowshoe hare’s fur, white in winter and reddish brown in summer, aids concealment from predators. But the transition is in response to seasonal daylight, which may be out of sync with its background when climate change causes snow to come late or melt early (photo from commons.wikimedia.org/wiki/File:Snowshoe_hare_transitional_coloring.jpg).
Various studies have observed, analyzed and documented examples of phenological mismatch. I’ll review two of those studies--one old, one new--and provide links to a few others in the P.S.

Migrating Birds’ Late Arrival
A 2001 study by researchers from Groningen University, Netherlands, and the Netherlands Institute of Ecology reported how the increase in spring temperatures affected the European pied flycatcher (Ficedula hypoleuca). 

The late-arriving European pied flycatcher (from
This long-distance migrant winters in Africa, then flies to Europe to lay eggs just in time for the chicks to hatch and feed on recently emerged winter moth caterpillars. The phenological mismatch arises because climate change has caused trees to leaf out earlier, which in turn causes the caterpillar population to peak earlier.

To compensate, the flycatcher has advanced the date of its egg-laying over the last decades but not enough to make up for its late arrival. The timing of its spring migration appears to be determined internally by day length, which is unaffected by climate.

The researchers found that flycatchers have declined sharply where the date of peak caterpillars advanced the fastest.

Plant and Pollinator Timing
Different researchers have examined the phenological mismatch between flowering plants and ground-nesting bee pollinators. The most recently published investigation of the topic is by researchers affiliated with Japan’s Hokkaido University and the Arctic University of Norway. (The Hokkaido researcher published earlier results in 2013 with a collaborator affiliated with Canada’s University of Calgary.)

The flowering ephemeral,
Corydalis ambigua
The researchers examined a spring flowering ephemeral, Corydalis ambigua, and its pollinator, overwintered bumblebees. The work involved 19 years of monitoring and a snow removal experiment in a cool-temperate forest in northern Japan.

They determined that, following snowmelt, the length of the plant’s pre-flowering period depended strongly on the ambient surface temperature, ranging from 4 days (at greater than 7°C) to 26 days (at 2.5°C).

The pollinator bumblebees emerged when the soil temperature reached 6°C, which was predictable by an accumulated soil degree-day model. Bee foraging after emergence might vary with air temperature.

Together, these results suggest that a phenological mismatch would tend to occur when snow melts early but soil warming progresses slowly. Early snowmelt caused by climate warming would thus result in the plant’s flowering ahead of the emergence of its pollinator, compromising seed production.

Wrap Up
So, along with the weather events we’ve been experiencing with global warming, we should expect changes we may not recognize as being associated with climate, such as the increase in shark attacks--rising ocean temperatures drive sharks northward, while warmer air and water temperatures drive more people to the beach. And there will be many phenological mismatches we never recognize. Thanks for stopping by.

Phenology background:
Study of flycatcher migration in Nature journal: www.nature.com/articles/35077063
Studies of plant and bee pollinators mismatch in Japan:
2013: www.ncbi.nlm.nih.gov/pubmed/24358716
2019: royalsocietypublishing.org/doi/full/10.1098/rspb.2019.0573
Article on 2019 plant and bee pollinators study on ScienceDaily website: www.sciencedaily.com/releases/2019/07/190712120230.htm
Examples of other phenological mismatch studies:
Climate change surprises: nautil.us/blog/7-surprises-that-climate-change-will-throw-us

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