2. Change in Biodiversity
2-1 Drastically changed biodiversity during the Anthropocene period
Today, only a single species, humans, has greatly multiplied and caused changes in the present global environment, geology and ecosystem. The changes could not have been happened without human interferences. Such a period of time is called the Anthropocene. In addition, unprecedented and significant impacts, such as invasive species associated with the movement of people and goods, has occurred. By reviewing natural history material accumulated up to now, many examples of such changes in biodiversity due to human activities can be found.
What is Anthropocene?
The term was proposed by Paul J. Crutzen (2002), referring to the period when agriculture led to the mass proliferation of humans on the earth, and their activities led to changes in the environment on an unparalleled scale. Characteristics of this period include global warming, extinction of organisms at an unprecedented rate, global migrations.
2-2 A wild primrose species extinct in Tokyo Metropolitan
During the Edo period, colonies of wild primrose, Primula sieboldii (Primulaceae) established and bloomed in various locations throughout the downstream from the Arakawa River in the Kanto Plain, especially in Ogunohara (Arakawa Ward, Tokyo), Ukimagahara (Kita Ward, Tokyo; Kawaguchi City, Saitama Prefecture) and Todagahara (Toda City, Saitama Prefecture). The area was popular during the spring flowering season and many people would come to enjoy the fields. When the water level rose, silt would be carried downriver, and the fields would be set on fire in the spring. These conditions are considered to have created suitable habitats for primroses. After the Meiji period however, man-made river improvements changed the environment and the native habitat declined. Today, natural habitat only remains in Tajimagahara (Saitama City, Saitama Prefecture) and is carefully protected as a national special natural monument.
▲A herbarium specimen of Primula sieboldii collected at Todagahara, downstream Arakawa river in 1891. A valuable record of an extinct native habitat
▲A scene of Todagahara when colonies of wild primrose flourished.
▲Natural habitat of primrose which still remains today in Tajimagahara, Saitama City, Saitama Prefecture.
2-3 Effects from an overabundant deer population
Distribution map of Sika deer
The population of deer in Japan (Cervus nippon, sika deer) has increased rapidly over the past 30 years. In recent years, this has affected human life, including collision with cars and trains, and the spread of blood-sucking land-dwelling leeches (yamabiru).
In areas with a dense deer population, plants and shrubs are decimated, creating bare land and causing landslides. In addition, as various plants disappear, insect larvae which rely on those plants for food disappear as well, creating a negative chain reaction. Various theories regarding the cause for the increase in the deer population have been proposed, but regardless of the reason, if immediate action is not taken to address this serious condition, many plants and animals, including endemic species, may become extinct.
▲ Areas significantly damaged by deer foraging
Plants grow on the forest floor in front of the fence to keep deer out. However, nothing grows behind (outside of the fence).
▲Carterocephalus palaemon, a butterfly species on the brink of extinction due to the increased deer population
2-4 Once “extinct” Oriental stork in Japan
Ciconia boyciana (Oriental storks) mainly feeds on loaches, pond snails, and other small animals living in rice paddies and wetlands. Due to pesticide poisoning and the sharp decline in aquatic animals, oriental storks were pushed to the brink of extinction in Japan. In 1971, the last wild stork was rescued in Toyooka City, Hyogo Prefecture, and subsequently storks became extinct in the wild. However, a pair from China was donated to Tama Zoological Park in 1985, and the institution succeed in artificial breeding of the species in Japan for the first time in 1988. In 2007, the first field breeding of a released pair was observed, and the field population recovered to approximately 300 individuals by 2022. The stork has come to symbolize the restoration of wetland ecosystems through organic farming in rice paddies and agricultural land improvement.
▲Oriental storks was familiar to humans, and was depicted in various natural history diagrams before their extinction.
2-5 “Kunimasu” (a land-locked Pacific trout), affected by human activities
“Kunimasu” (Oncorhynchus kawamurae), described as a new species in 1925, was endemic to Tazawako Lake, Akita Prefecture and inhabited the lake to the bottom with a depth of 300m. Highly acidic hot spring water began to be released into the lake in 1940 due to power generation and other reasons, leading to the extinction of the trout sometime after in the 1940s. However, it was rediscovered in Saiko Lake, Yamanashi Prefecture, in 2010. In 1935, eggs of the trout from Tazawako Lake were introduced to Saiko Lake and the species miraculously survived after repeated generations. The trout is conserved in balance with human living today, but it is a fish with a history of being adversely affected by human activities.
▲Tazawako lake, Akita Prefecture-Introduced→Saiko Lake, Yamanashi Prefecture
2-6 Change of rural environments (satoyama) and the decline of organisms inhabiting such areas
Satoyama is a mixed environment, including agricultural fields, houses, and forest areas. Created by people living a life centered on agriculture, it is maintained by regular management, such as cutting trees for various useful materials and burning grassland areas to maintain hayfields.
The environment of satoyama has been greatly affected by recent large-scale developments, agricultural land improvement, changing human lifestyles. Accordingly, organisms whose life is dependent on the satoyama are threatened.
Many species of aquatic insects in the satoyama that live in rice paddies and irrigation channels have been already registered in the red list of the Ministry of the Environment. In addition to environmental changes, habitat loss due to the use of powerful pesticides and increase of invasive alien species can be seen in the background.
▲ Typical satoyama landscape of the old days. Various elements are mixed together.
Representative aquatic insects of the satoyama are declining
▲Cybister chinensis (diving beetle) ▲Kirkaldyia deyrolli (giant water bug)
2-7 Increase in butterflies caused by naturalized plants
Eurema laeta (spotless grass yellow butterfly) is distributed throughout Japan from Honshu to Yakushima Island. Larvae feed on Chamaecrista nomame , a leguminous plant.
This plant has decreased due to man-made river improvements, etc., and the butterfly species has also suffered decline. In the 2000’s, a closely related plant Chamaecrista nictitans, which is native to North America, naturalized in the Tokai region and began to spread with strong fecundity. As the butterfly’s catepillars began to feed on the C. nictitans, these butterflies also began to increase again.
However, since this increase is not due to restoration of its original environment, it is a bittersweet situation.
Habitat in the Oi River basin, Shimada, Shizuoka Prefecture
▲Larva on Chamaecrista nictitans plant
▲Nectar glands of Chamaecrista nictitans differ from C. nomame and are petiolate.
▲Adult Eurema laeta flying among Chamaecrista nictitans growing in the Oi River basin, Shimada City, Shizuoka Prefecture, Japan.
2-8 Categories of threatened species (classification by the Ministry of the Environment).
Classification in the red data book (book of collected information on threatened organisms) and the red list (list of names of threatened species) is as follows, based on data such as number of individuals existing in Japan and rate of decline of the population.
Categories (ranks) of threatened species by Ministry of the Environment
Extinct: Considered extinct in Japan
Extinct in the wild: Species only existing in captivity or human cultivation, or clearly outside their natural distribution range in the wild.
Critically Endangered Class IA: Extremely high risk of extinction in the wild in the very near future
Endangered Class IB: High risk of extinction in the wild in the very near future, but not to the same degree as Class IA
Vulnerable Class II: Species at an increased risk of becoming endangered
Near Threatened: Species currently not at immediate risk of becoming threatened, but may be given an “threatened” classification depending on changes in habitat conditions.
Data deficient: Species for which information for evaluation is lacking
・Quantitative assessments based on the number of remaining individuals, rate of decline, or the probability of extinction calculated from these figures have gradually been introduced. (Detailed criteria regarding quantitative assessments are set for each category)
・Categories by the Ministry of Environment are used as indicators of “the risk of extinction in Japan” and do not consider information regarding non-Japanese populations of the same species.
・The International Red List assesses the threat of extinction for all wild species. Cases which do not fall under any of the above categories are listed as “LC (Least concern).” In Japan however, ‘LC’ has not been established.
Categories of endangered species shown in this exhibition comply with the Red List 2020 of the Ministry of the Environment, except where otherwise noted.