Animals and plants affected by global climate change are migrating to new areas where they can thrive. How does this move affect them and the environment?
By Racheli Vox, Angle - a news agency for science and the environment
There is no doubt that immigration is one of the hot topics of recent years. Immigrants from third world countries, or those in a state of war, cross the border in different ways to richer and safer countries in the hope of a new life. In recent years, the climate crisis has also joined the list of factors that influence the migration phenomenon. The extreme changes in the various living environments have led to a worldwide trend of groups and individuals moving from one place to another.
New findings shed light on the dimensions of the migration phenomenon also among two prominent groups of animals: fish and butterflies.
Climate migrants
The effects of the climate crisis on human migration were emphasized in the New York Declaration of the United Nations Conference from September 2016. An example of this phenomenon is the Mekong River Delta in Vietnam, which has been left by about a million people in the last decade, partly due to the collapse of houses due to flooding and erosion of the coastline, frequent drought events and rising in the salinity level of the water intended for the agricultural crops. Environmental changes also led to the migration of millions of Syrian farmers to the cities following a severe drought in the region between 2010-2006, a fact that contributed to the internal pressure that eventually led to the outbreak of a civil protest that later turned into a civil war.
Many agricultural crops will also be forced to "migrate" as a result of the climate crisis, mainly because of the increase in temperature it is causing. Such a risk threatens the cultivation of cherries in Israel today: these trees need hundreds of hours of cold in the winter in order to be able to produce many, high-quality fruits, and a lack of cold may damage the scope of the agricultural produce, the economics of cultivation, and finally even the survival of the trees. Cherries are already grown in Israel today in areas above 600 meters (mainly in the Golan Heights), where the temperatures are relatively low in the winter, and in the not too distant future there may no longer be a place in Israel that is cold enough to grow them. The migration of agricultural crops to new areas will require making many changes in the target areas, which may cause a lot of environmental damage, for example due to the clearing of forests for this purpose.
The migration does not miss the animal world either, with fish being a prominent example of this. Today the rate of ocean warming is about 0.12 degrees Celsius on average per decade. In our region, the southeast of the Mediterranean, the rate is almost ten times higher, and in the last 30 years the water surface temperature has increased by about three degrees - from an average of 24 degrees in the summer to 27 degrees.
The warming of the water hurts the fish because they are cold-blooded animals, so their bodies are more affected by changes in temperature. For this reason, when the temperatures are high, the metabolic rate of the fish increases - which causes them to need more oxygen, in addition, warmer water contains less dissolved gases in general and oxygen in particular, which may make it difficult for some fish species to receive all the oxygen supply they need, and expand the The area of the dead zones that already exist today on the seabed.
There are rare cases where certain fish species manage to adapt to some degree to the warming of the water, but in the vast majority of cases this is not the case. Therefore, many fish migrate north or south and away from the equator towards the poles or move more locally from living in the upper layer of the sea surface to deeper layers of the water, where the temperatures are more similar to those they have become accustomed to throughout evolution. And colder water allows those species to have a slower metabolism and not suffer from a lack of oxygen. The migration occurs mainly when the fish are bigger and therefore need more oxygen. The dimensions of the phenomenon in the various species at the equator may even reach a migration of about 50 kilometers per decade.
In other cases the fish simply stop growing early and remain relatively small throughout their lives, so they need less oxygen. This phenomenon has negative consequences for the survival of the fish (a smaller female fish lays fewer eggs, for example).
The migration of fish is well felt in the waters of Iceland, for example. In the last 20 years, ocean temperatures in the region have risen by 2-1 degrees Celsius. As a result, the troton fish and the Atlantic cod, which are common in the region and beloved by fishermen, are currently migrating north in large numbers and disappearing from the country.
The increase in water temperature also greatly affects the fish that live on Israel's shores. "We definitely see that fish that are used to the cold are disappearing from our area," says Prof. Yonatan Belmakar from the School of Zoology and the Steinhardt Museum of Nature at Tel Aviv University. "Mediterranean cod, for example, is a species that characterizes colder regions. It was much more common here twenty years ago and slowly it is disappearing." According to him, the phenomenon of fish that remain small throughout their lives can also be seen in our region.
The fish that do thrive in Israel are those that love heat, such as the Mediterranean Towson. These native species are joined by many invasive species that arrived in our region as part of the Lespastic migration phenomenon - the passage of fish and other marine creatures from the Red Sea and the Indian Ocean through the Suez Canal to the Mediterranean Sea, which began due to the digging of the canal and its opening in 1869 and continues even more strongly to this day, so that today the Eastern Mediterranean Sea varies greatly.
"There is no doubt that climate change affects the fish in different ways," says Balmker. "It certainly damages the food web and also damages large fish more - and when there are fewer of them it means that people have less to take out of the sea, which will also affect future fishing. There is no doubt that these trends will continue with the worsening of climate change."
Tropical butterflies in the Negev
Other animals that are greatly affected by the climate crisis are the butterflies, which also migrate from the equator towards the poles in search of a cooler climate. "Following the climate crisis, African species are seen in Israel with increasing frequency," says Dobi Binyamini, chairman of the Butterfly Lovers Association in Israel. "In November 2019, it appeared in Jerusalem as the Pelargon flute, a species from South Africa that we had never seen in Israel before. Last January, a barometric socket arrived in Eilat from Central Africa, and the next day we saw butterflies of the Hagga nymph species, which had not been observed in Israel for 20 years. In Kibbutz Naut Smadar in the south of the Negev, tropical butterflies of the blue nymph species have been flying for three years, which arrived there on migration and settled."
At the same time, cold-loving butterfly species may disappear from Israel. "In Hermon, butterflies move to higher altitudes because of the warming," says Binyamini. "The butterflies that are at the peak of Hermon have nowhere else to climb, so they return their equipment and disappear."
Not all species of butterflies manage to move to more suitable areas. According to a study conducted on the subject, in which the distribution of 16 species of British butterflies was examined over the past 40 years, the butterflies' ability to migrate is affected in part by the loss of their natural habitats as a result of human activity, combined with the effects of the climate crisis. According to the study, when the butterflies are surrounded only by environments where they cannot survive, they are unable to leave their habitat and look for a better place to live. This phenomenon affects, for example, a butterfly of the Silver-studded blue species (Plebejus argus), which is now disappearing from Britain due to the reduction of natural areas in the country.
Another variable that affects the migratory ability of the butterflies is the number of their breeding cycles. There are butterfly species in which every year there is one generation, which is born, reaches maturity, sets offspring and dies - while in others the process repeats itself several times during the year. According to a study that examined 130 species of British butterflies and moths, and included data from the years 2014-1995, the difference in the number of reproductive cycles is significant because, due to the climate crisis, winter is warmer and spring starts earlier than before, which causes butterflies of many species to emerge from the cocoon earlier.
In species that are characterized by several reproductive cycles (such as the spotted murre, which was also present in Hermon in the past and a small population of which remains in the northern streams), the early spring gives the butterflies additional time to reproduce, the population increases, and it includes enough individuals to send a "vanguard force" to migrate to colder places. In species that are characterized by only one reproductive cycle per year, such as the High brown fritillary (Argynnis adippe), the early exit from the cocoon may put the butterflies out of sync with the life cycles of the plants on which they depend, which hurts their numbers - and when the population is small, fewer butterflies migrate from it.
And what's next? If current trends continue, the migration of animals, plants and humans across the planet is only expected to increase. Thus, this phenomenon also joins the multitude of ways in which the climate crisis makes our world completely different from what we knew.
More of the topic in Hayadan:
