The Effects of Climate Change on Birds, Insects, and Plants

Bill Young

How will climate change affect the environment? How will birds be affected? How will insects be affected? How will plants be affected? Scientists are trying to find the answers to these questions, and current research suggests that climate change needs to be addressed with great urgency to avoid possibly catastrophic effects. Within the scientific community, there is no dispute about whether climate change is real and is happening now. The major remaining questions involve its speed and likely severity.

In 2014, the National Audubon Society issued a report saying that by the year 2080, climate change will imperil the populations of nearly half of the bird species in the United States (314 to be precise). Most of the declines will be due to shifting and declining habitat ranges. Birds who have evolved to live in a particular climatic zone might suddenly experience warmer temperatures. These temperatures are likely to change too quickly for birds to adjust.

But why can't birds adjust by flying to higher elevations where temperatures are closer to what they are accustomed? One answer is that habitats at higher elevations are not currently vacant and waiting for "climate refugee" birds to arrive. The newcomers would have to compete with birds already occupying these niches. More importantly, while a habitat at higher altitude might better suit a species with respect to temperature, it might lack many other characteristics necessary for survival. Most bird species have evolved to consume certain food sources. The food might include particular types of insects, who in turn might rely on particular plants. If the plants are not in the new habitat, the insects might not be there either. The birds would need to find a new food source, or they would not survive. Also, plants cannot fly, and they might need more time to colonize a new area, assuming they could do it all.

Research by a British plant scientist named Caroline Dean suggests possible problems plants might experience when trying to colonize new areas. She has extensively studied a small plant called Thale Cress (Arabidopsis thaliana), which was one of the first organisms to have its genome sequenced. This fast-growing plant is found from the Equator to the Arctic Circle, and it has a very small amount of DNA in each cell. These attributes make it an excellent plant for research studies.

Dean has researched three main issues. First, she knew that some plants need to overwinter before they bloom, while others do not, and she wanted to explore the molecular differences between these two types of plants. Secondly, for the plants that overwinter, she wanted to discover how they know they have experienced winter, and how they know the right time to flower in the spring and not get fooled by a stretch of unusual weather in the fall or the winter. And third, she wanted to find out the molecular differences between plants that flower near the Equator and those that flower in far northern latitudes. All three subject areas have important implications for plants experiencing climate change.

Thale Cress uses many different cues to know when to flower, including day length, temperature, and the condition of internal sugars. Dean's experiments discovered that a particular gene in the plant makes a protein that serves as a brake to keep the plant from flowering. With an automobile, you need to release the brake and step on the accelerator for the car to go. If the brake is on, the car will not go, no matter how much you press on the accelerator. The corresponding brake for Thale Cress is the "do not flower" gene, and the accelerator is warm temperatures and the longer days of spring. Epigenetics is a process which involves the transmission of genetic information without altering DNA sequences. Epigenetic regulation allows Thale Cress to switch off the gene (release the brake), enabling the plant to flower.

When the gene in Thale Cress is switched to the "do not flower" position by cold weather, it is in that position in every cell of the plant. Each cell has a mechanism that can be either on or off. Dean uses the analogy of how hair slowly turns gray on older people. If you examine the head of someone who is going gray, you will not find any hairs that are gray. You will find some that are dark and some that are white, and people who look at the overall head perceive it as gray. Eventually, all of the hairs might become white.

With the genes in Thale Cress, the cool temperatures in the autumn and winter keep the "do not flower" gene in the "on" position, preventing the plant from flowering. Gradually, as winter is coming to an end and temperatures begin to warm, the "do not flower" gene, cell-by-cell, switches to the "off" position. Once the gene is off, it stays off. When the "do not flower" gene in enough cells is switched off, the brake is released, and the plant can flower.

Because Thale Cress occurs in such a wide range of habitats, Dean was able to compare how its genes behave in plants from northern Sweden, where the winters are very cold, to those in the south of France, where temperatures are much warmer. She discovered that in Sweden, the genes in plants needed 10 weeks to reach a level of "switched-offness", while in France, they needed only 4 weeks. She also discovered that if you take a plant from Sweden and transplant it in France, it will still require 10 weeks to flower. Thale Cress in Sweden appears to have undergone mutations in the coding of its "do not flower" gene which affect the timing of when it flowers, making it different from Thale Cress in warmer climates.

Dean discovered that plants were not monitoring average temperature, as was believed for a long time. They monitor the peak afternoon temperature and the lowest temperature at night. The plants reacted more to the absence of warmth than the presence of cold. This discovery has significant implications for agriculture and when farmers should begin to plant. The implications also are important for non-agricultural plants. Temperatures are likely to fluctuate more as climate becomes more unstable, which could affect the timing of a plant's flowering.

The issue of timing has serious implications for life forms that have evolved over thousands of years in a relatively stable climate. Their activities might be linked to the activities of other life forms. For instance, birds might time their spring migration to coincide with when insects are likely to be most abundant along their migratory route. The key factor for when insects emerge might be temperature, while the key factor for when birds begin to migrate might be day length. Plants might respond to stimuli that are different from those affecting birds and insects. Over long periods of the Earth's history, temperature, day length, and many other stimuli have mostly been in sync. But if the climate warms, the insects might come out earlier, and fewer might be around when the birds arrive. And the insects might not be able to survive if their host plants are not available.

To look at a specific timing problem in the bird world, European cuckoos are migrant species who winter in Africa. They are parasitic nesters — they lay their eggs in the nests of other bird species, and those host species raise the young cuckoos. Parasitic nesting requires precise timing to be successful, and when the host species alter their nesting schedules because of climate change, the cuckoos are less successful in parasitizing nests. This is already happening, and cuckoo numbers in Europe have declined substantially.

The scientific community still has scant knowledge about how genetic processes work at the molecular level. The study of DNA is still relatively new — many people currently living were around before the announcement of the structure of DNA was made in the early 1950s. While the level of scientific understanding of cells has increased dramatically since then, there still are many things scientists have not yet figured out about how DNA works. The study of epigenetics is even more recent. Learning more about how epigenetic switching mechanisms work could have important implications, including for the treatment of human diseases.

Unfortunately, treating the effects of climate change on the natural environment will be much more difficult than treating human diseases. The important discoveries of Caroline Dean help to explain how a plant is likely to respond as the climate changes, but her discoveries do not provide guidance to prevent climate change from happening. Taking action to mitigate climate change is the biggest challenge facing people in the first quarter of the 21st century, especially for residents of the developed world. How people respond will determine how many birds, insects, and plants will still be around for people to enjoy 50 years from now.