The Quaternary is a period of time that has already been divided into two epochs: The Pleistocene, which refers to the period of time 2.588 million to 11.7 thousand years ago. And the Holocene: 11.7 thousand years ago right up to today. The term ‘Late Quaternary’ applies to the past 0.5-1.0 million years, and in this essay I will be addressing the decline in biodiversity within this time. Generally, the term ‘biodiversity’ refers to the variety of life at all levels of biological organisation. It can be split into three categories: species, genetic and ecological. The rate of extinction of species is thought to be between x100 and x1000 faster because of human activity, and 90% of all species that have ever existed are now extinct, and I will be addressing both the direct and indirect causes of this decline throughout this essay.
Previous extinctions due to major climatic and geological changes are very different to that of the recent sudden global changes caused by human activity that has contributed to biodiversity decline. This includes factors such as pollution and population increase, which is ever-growing as humans try to sustain our current living environment. There is a perfect example of this when researching into biodiversity loss in Mauritius. Relevant supporting research has revealed that many extinction events (including the Raven parrot, Dodo, giant tortoise, and fruit bat) over the last 500 years on Mauritius occurred during times of heightened levels of human activity. All of these species had suffered significant environmental pressures in the past, such as major drought events, and survived (de Boer et al. 2015). Yet within approximately 50 years of human occupation and devastation caused by fire, the extinctions began.
The difference between use values and non-use values needs to be distinguished to be able to organise the types of human impact on the decline of biodiversity. Use values can be further divided into two: direct and indirect. Direct causes refer to marketable commodities such as food and medicine which have a direct role in consumption or production. Indirect refers to functions or services of natural systems or processes that are used indirectly, such as photosynthesis and pollination. Non-use values are the values that give people services beyond the physical ones they require. This does also come with an influx of money to charities for example that promise to save species e.g. whales or habitats like the rainforest, so that this nature is still a reality for future generations. Non-use value includes 4 components: Option value: retaining biodiversity for future use/non use, bequest value: passing on biodiversity to future generations, existence value: the value placed simply on the existence of biodiversity irrespective of its uses, and intrinsic value: the inherent worth of biodiversity.
The biologist Jared Diamond coined the phrase ‘evil quartet’ to refer to the detrimental human induced pressure that was being placed on biodiversity. These were: Over-exploitation, habitat-loss and degradation, introduced species and extinction cascades.
One significant example of over-exploitation by humans is the effect that our behaviour has had on the marine environment, leading to the extinction of almost half of the species of existing marine organisms (Powell 1998). Research has shown that cod stocks in the Northwest Atlantic has declined over time. (Kelly et al. 2009) This proceeds ‘The Cod Wars’ from 1958 to 1975 where there was political concern surrounding the future of Icelands traditional fishing grounds, which prompted Iceland to expand its Exclusive Economic Zone (EEZ) from 3 to 200 nautical miles. This was successful as around 1 million tonnes of Cod are still being harvested annually in the Northeast Atlantic, whereas in the Northwest, Cod has been overexploited and therefore its stocks have collapsed after years of over-fishing by humans. The ever decreasing population of Atlantic cod has led to an increase in inbreeding, leading to further disease, habitat alteration and environmental stress on top of the over-fishing, which has caused a steeper decline in the species.
Secondly, the loss of habitat for species particularly due to agricultural activities involving mining, logging, trawling and urbanisation amongst other things. This arguably is the most important cause of species extinction worldwide. Land use change has significantly contributed to the decline of aquatic biodiversity at a global scale. This includes the conversion of wetlands. Recent research has resulted in the estimate that over 60% of wetland area has been converted worldwide since 1900. Wetlands are, as (Mitsch 1993, Mitsch and Gosselink 2000) have named them, the “biological kidneys” of the landscape. With increasing pollutants entering our waterways through burning fossil fuels from transport use and using fertiliser and pesticides on agricultural land, the natural balance of nutrients in such systems is destabilised (Ribaudo et al. 2001). The detrimental effect of this imbalance is hypoxia, due to large amounts of limiting nutrients leeching out of soils and into water systems encourages the growth of primary producers such as phytoplankton and algae. When these producers fall to the benthic layer, a huge amount of dead organic matter accumulates and causes an explosion in the population of decomposer bacteria. These bacteria use a huge amount of oxygen for this process, depleting oxygen levels in the water to a fatal level for most living organisms in the environment, dramatically reducing the biodiversity in the area. The loss of wetlands may end with a loss of plants (the basis of any ecosystem) and animal life, which not only support human interests, but also contribute to the health of other ecosystems, such as streams and rivers (Mitsch and Gosselin). This domino effect will further decrease the biodiversity on an even larger scale. Anthropogenic global climate change through the burning of fossil fuels has also contributed to the degradation of habitat. According to an article written by Thomas Dirnböck Franz Essl Wolfgang Rabitsch, five taxonomic groups (vascular plants, snails, spiders, butterflies, and beetles) in the Austrian Alps will experience a 77% habitat loss (on average) even under the weakest climate change scenario (+1.8°C by 2100). The International Union for Conservation of Nature and Natural Resources has obtained a Red List of species officially classified as ”Threatened” or ”Endangered”. Habitat loss has been identified as being the main threat to 85% of these.
Humans are also guilty of deliberately and accidentally introducing species and causing invasions into biological niches to the detriment of other species already living there. According to the Wildlife Service within The US Department of Agriculture’s Animal and Plant Health Inspection Service, the brown tree snake (Boiga irregularis) was accidentally introduced to Guam in the late 1940s or early 1950s, probably from the Solomon Islands. Native to northeastern Australia, eastern Indonesia, and Melanesia, the brown tree snake has significantly damaged the economy and ecology of Guam. WS’ cooperative program seeks to control snake populations on Guam and prevent its spread throughout the Pacific Rim. The snake has been responsible for numerous power outages across the island each year. It is a practical feeder and will consume whatever is available to it. This species has therefore caused the extinction of most of Guam’s native forest birds and lizards, significantly decreasing its biodiversity. In order to control the decline of biodiversity, lizards, birds, rodents and bird eggs have had to be introduced to account for the decline of native bird populations.
According to Science Daily, ‘extinction cascades’ refers to “where an initial species loss leads to a domino effect of further extinctions”, and biodiversity loss significantly increases the risk of such. According to Dr Dirk Sanders of the Centre for Ecology and Conservation at the University of Exeter, “Interactions between species are important for ecosystem stability…And because species are interconnected through multiple interactions, an impact on one species can affect others as well”. An example of a previous extinction cascade that has occurred in the Late Quaternary period is the New Zealand Moa. This flightless bird became extinct due to hunting and other pressures caused my humans. They were hunted to extinction by Māori. These people relied on these birds as a source of food, materials for clothing (their feathers and skin), and their bones were used as fish hooks and pendants. Due to the domino effect, the extinction of the Moa in turn caused the extinction of the Giant Eagle, as these predators relied on the New Zealand Moa as their food source.
To conclude, these effects from human activity are largely a result of direct consequences, but have also resulted in natural processes causing further extinction due to domino effect and strains on environment that are placed by human activity. The main cause of this biodiversity loss is due to the depredation of the habitats of species. While natural processes may be to blame for a proportion of decline in biodiversity, the detrimental effect and larger scale damage that humans have placed on ecosystems and biodiversity suggests that human activity does seem to have a more significant impact on the decline of species than in the past due to natural causes, as visited earlier in this essay, suggests that human activity is indeed to blame for the steep decline in biodiversity.