Biodiversity Loss in the 21st Century: The Sixth Mass Extinction
Many people don't think about the world in terms of it being shared with potentially another 10 million species, many of which are supporting each other in complex and intricate ways. We feel safe and secure in our constructed environments, in a world where resources seem abundant and limitless, but the planet is a shared one, housing a variety of fascinating creatures and organisms, from the smallest bacteria to the tallest trees. It is because of these organisms that we are able to sustain ourselves, and the resources they provide are in no way limitless.
Below is a look at our planets, 'Biodiversity', Earths species richness, and the current issues that are faced today.
- What is Biodiversity?
Biological Diversity (better known as biodiversity) is the buzz word which describes the variety of living organisms on Earth and the variety of ecosystems they form. There are millions of different plants, animals and micro-organisms which make up the Earths biodiversity and many species survive in only one specific ecosystem. About 1.7 million species of living organisms have been identified to date and about 15,000 new species are discovered each year, even new birds and mammals. On average about 3 new species of birds are found each year. Although many assume that nearly all mammal species are known to scientists, between 1993 and 2011, 408 new mammalian species had been discovered, around 10% of the previously known fauna. The total number of living species is estimated to be between 2 million and 100 million, with the most common estimates being around 10 million. Biologists estimate that to date we have identified less than 10% of bacteria, about 5% of fungi, only about 2% of nematodes (roundworm) species and less than 20% of insect species. Insects account for a high proportion of all known species despite having little known about them. The best-studied and most completely known groups are birds and mammals (roughly 9000 and 4000 respectively), although together they account for less than 1% of all known species.
Biodiversity is not just a measure of species richness but also includes the variety found within species such as races and breeds as well as differences which may exist between individuals of the same groups.
Noss and Allen Cooperrider, leading conservation biologists, offered following working definition of biodiversity: “Biodiversity is the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever changing and adapting”. Loss of biodiversity is more than loss of a species but can also mean loss of genetic and ecosystem diversity through alteration of structure and disruption of ecological and evolutionary processes.
- The “Biodiversity Crisis”: Species Extinction
Extinction occurs when the last individual of a species dies. Extinction is a natural process, no species will exist forever as species will evolve or disappear altogether. However, current extinction rates are being driven beyond normal rates of extinction, this rapid and accelerated extinction of species and their habitats is known as the biodiversity crises. Alarmingly, biological diversity is currently decreasing at an unprecidented rate. Based on fossil records ‘background’ extinction rates (that which ‘normally’ occurs) is about 1-10 species per 1 million species per year or 10-100 species per year. Conservation biologists estimate that known species are presently becoming extinct at a rate of 50-500 times the natural rate of background extinctions. Some suggest that deforestation in rain forest habitats has increased extinction rates to between 1000 and 10,000 times the background level. Extinction estimates vary widely as it is difficult to know if a species is gone as around 85-95% of Earths species have not yet been discovered. Ecologists and conservation biologists warn that we are in the early phase of the 6th major extinction episode in Earths history and that this current extinction episode might eventually surpass some of the great mass extinctions of the past, including that which wiped out the dinosaurs 65-70 million years ago. It is feared that by the year 2100 a third of all plant and animal species could be headed for extinction.
Periods of mass extinctions have taken place due to sudden changes in sea levels, climate change (including the impact of a colliding comet), and volcanic activity. During these periods of sudden changes, those species which were better adapted to new circumstances than others left descendants. Species that evolve fast enough to colanise new habitats in time and geographic space survived and flourished.
The present extinction episode differs from past ones in that the extinctions are occurring in a tremendously compressed period of time (just a few decades as opposed to hundreds of thousands of years), much faster than rates of speciation (or replacement), preventing species the opportunity to adapt and evolve to new niches. Another difference from previous mass extinctions is that current extinctions are predominantly human driven. Humans have spread to almost all areas of Earth. Whenever we invade an area the habitats of many plants and animals are disrupted or destroyed, which contribute to their extinction. Animal extinctions are not the only concern, larger numbers of plant species are becoming extinct today than in previous mass extinctions. Because plants are the base of the terrestrial food web, the extinction of animals that depend on plants isn’t far behind.
The number of species lost during the past 500 years, as documented by The International Union for the Conservation of Nature and Natural Resources (IUCN) is around 785 extinctions worldwide including 78 mammals, 138 fish, 28 reptiles, 39 amphibians and 103 boney fishes as of 2008. These numbers are woefully incomplete, especially for invertebrates. Many other extinctions are not included in the number which are likely to have occurred, but not yet been documented adequately to be formally listed as extinct. The list is therefore likely a severe underestimate.
The IUCN Red List of threatened species is a catalog of taxa that face a high risk of global extinction. For many groups, only certain species have been evaluated. The list also includes species that have been evaluated over only a fraction of their ranges. In 2008 the Red List consisted of 16,928 species of animals and plants facing extinction but this number is very conservative. Many more species are suggested to face extinction, especially among plants and invertebrates. According to the UN Global Biodiversity Assessment, more than 31,000 plant and animal species are currently threatened with extinction, other surveys indicate that this number is also seriously underestimated. The “Hundred Heartbeat Club” is a list of species with only a hundred or less animals of that species left in existence, such species include the Javan Rhino, Hawaiian Crow, Philippine Eagle, and formerly the Chinese River Dolphin before it’s extinction in 2008, to name only a few.
- Causes of Biodiversity Loss: Humans as a Driving Force for Species Extinction
Species are becoming extinct more rapidly then researchers can study them. Alarmed by these extinctions, biologists are mobilising to more rapidly identify new species and to conserve biodiversity. Many biologists agree that describing and classifying all the surviving species of the world should be one of the great scientific goals of the 21st century. Clearly humans directly or indirectly cause many or most species declines and extinctions through our demands and consumption, and depleting the Earths living natural resources at an alarming rate. Wherever humans have gone we have altered the environment and shaped it to meet our needs. Not only do we destroy every type of habitat we also fragment and modify habitats through logging, burning, overgrazing, and other activities, thereby diminishing its quality for many organisms. In only a few generations we have transformed the face of the Earth, placed a great strain on the Earths resources and resilience and profoundly affected other species. As a result of those changes many people are concerned with environmental sustainability and the ability to meet humanity’s current needs without compromising the ability of future generations to meet their needs. Many environmental concerns exist today, rapidly expanding human populations underlies and exacerbates all environmental problems. Increasing populations are placing an unsustainable stress on the environment, as humans consume ever increasing quantities of food and water and more energy and raw materials and produce enormous amounts of waste and pollution. Rapidly increasing populations (as in developing countries) tend to overwhelm and deplete a countries soils, forests and other natural resources. Additionally, widespread poverty and insecurity drive people to adapt ways of life that degrade the environment upon which they depend, so that sustainable livelihoods cannot be maintained. In highly developed nations an individuals resource demands are large, far above requirements for survival. To satisfy their desires rather than their basic needs, people in more affluent nations exhaust resources and degrade the global environment through excessive consumption and “throw away” lifestyles. Wealth often fuels consumption patterns that undervalue and drive the over-exploitation and depletion of natural resources. It took thousands of years for human populations to reach 1 billion, a milestone that took place around the year 1800. It took 130 years to reach 2 billion (in 1930), 30 years to reach 3 billion (in 1960), 15 years to reach 4 billion (in 1975), 12 years to reach 5 billion (in 1987), 12 years to reach 6 billion (in 1999), and 12 years to reach 7 billion (2011). Only 211 years to increase the population from 1 billion to 7 billion, an unprecedented increase in human population. The population increase is not because of increased rates of birth but rather due to the dramatic decrease in death rates. The more people there are the more demands we put on the environment and the more we threaten other species. The result is the extinction of the least resistant and least adaptable species.
Below is a list of how humans contribute to biodiversity loss, along with other factors which need to be considered…
- Land Use Change:
Habitat Destruction/Fragmentation/ Modification (linked to
human expansion: roads, agriculture, logging (resources), housing)
Land alteration represents the single largest human caused threat to biodiversity, as these changes modify habitats to such a degree that they are no longer suitable environments for animals to live within in terms of moisture and temperature alterations, reduced food availability, destruction of refuges, and degradation or elimination of other critical physical, chemical or biotic characteristics of the land. Changes in land can also kill animals directly, as the disturbances take place.
Habitats are commonly fragmented by large amounts of land being converted for agricultural use, this is practiced throughout the world. Isolated fragments suffer a reduction in species richness, prevention of access of animals to breeding sites, reduced recruitment and reduced genetic diversity within populations. Small fragments often have fewer species recorded than larger fragments resulting in a reduction of population sizes, reduction of immigration rates, forest edge effects and changes in community structure.
Forest edge effects concerns distribution of forest edge species and inner forest species. Some species are better evolved to exploit the edges of the forest and some more suited to live further within the forest, as habitats are fragmented and modified the distributions of inner forest and edge species alters accordingly, this can result in increased conflicts and reduced species populations.
- Environmental Contaminants: Insecticides, Mutagens, Consumer Waste
A second threat to biodiversity is the contamination of air, water, and land with organic chemicals and other toxins. Various pollutants from mercury to fertilizers and pesticides harm wild populations of animals. Amphibians are particularly susceptible to contaminants, with some pollutants expressing sub-lethal effects such as stunted growth and development, deformities and behavioural abnormalities, or effect reproduction by disrupting hormone systems or causing gonadal abnormalities.
Toxins can also be passed on to a secondary species such as the case with a particular pesticide, DDT, and it’s devastating effect on several bird populations including robins, peregrine falcons and ospreys. Although DDT was non-lethal to those creatures that were initially exposed to the compound, the birds which preyed upon the contaminated creatures would, over time, accumulate a lethal amount of DDT in their system and succumb to DDT poisoning. A variety of bird species were dramatically affected by this pesticide despite the fact that they were not directly exposed to it.
- Climate Change:
Global Warming/ Cooling and Increased UV Radiation
Global climate change is a threat of great long-term importance. Climate change can effect animal populations both directly and indirectly. Direct effects include temperatures which exceeds the animals’ level of tolerance, or drought that the animals cannot endure physiologically so it dies outright. Furthermore, levels of UV-B radiation might be lethal to some animals such as amphibians. Indirect effects could include reduced prey abundance and increased density of predators. Climate change can also alter seasonal breeding patterns of animals resulting in heightened competition for calling and egg-laying sites, and ultimately in diminished recruitment. Competition among juveniles (especially within the self-sufficient herptiles) can also lead to decreased recruitment. Climate change can also disrupt periods of hibernation and aestivation, effecting the animals ability to find food.
Changes in temperature could further encourage the emergence of new or old infectious diseases by creating conditions more hospitable to the disease and/or inducing physiological stress from sub-optimal temperatures, suppressing the animals immune system and making them more susceptible to pathogens.
- Emerging Infectious Diseases
Emerging infectious diseases (EID’s) can be described as diseases which have recently appeared in populations, and diseases that are rapidly increasing in incidence, virulence, or geographic range. Examples of EID’s include foot and mouth disease (as seen in domestic production animals), Ebola (as seen in mountain Gorilla’s and recent outbreaks among human populations in Central Africa), the iridovirus (as seen in ectotherms and invertebrates) , and the chytrid fungus in amphibians. EID’s are not only a threat to the conservation of global biodiversity but pose a substantial threat to domestic animals and human health.
Furthermore, EID’s can be particularly devastating, not only to those species with small populations but also to species which express a lack of genetic variability, such as the cheetah. Lack of genetic variation can be a serious contributing factor to a lack of disease resistance, thereby presenting a vulnerability to EID’s. EID’s can be spread by human activities such as the case of the chytrid fungus which has since spread to every continent on earth facilitated by the global trade in amphibians.
Uncontrolled Commercial Harvesting for Pet Trade, Medicine, Meat, Fur,
Hunting, Persecution, Over Control of Pests and Predators, Trophies etc
A fifth threat leading to species declines and extinctions is over-exploitation by humans for food, medicines, pets or products such as skin or fur. Humans exploit species for economic benefit leaving the wildlife trade related to some of the most important underlying causes of biodiversity loss.
Overkill results from hunting at a rate above the maximum sustainable yield. The most susceptible species are those with low birth rates (i.e. large mammals such as whales, rhinos and elephants). These animals are even more vulnerable if they are valued as food or an easily marketable commodity. Over-collection can result in the same trends of decline in wild populations when a species is not able recover quickly enough before the numbers become unsustainable. The population biology of many species is not fully understood so it is often impossible to determine sustainable harvest levels, often resulting in collection and kill rates that exceed the populations’ level of tolerance. Even if enough individuals remain in a population to successfully find each other and breed, the depleted population will almost certainly experience decreased genetic diversity.
- Introduction of Invasive Species
Another one of the leading causes of species declines and extinctions is the introduction of species, either deliberately or accidentally, to areas where they do not normally occur where they become invasive.
Animals may be introduced intentionally for biological control of pest species or the intentional release of exotic pets. Accidental introductions can occur when exotic pets escape or stowaway animals are transported to other locations unwittingly, such as the case of the Brown Tree Snake, which has devastated the majority of the native bird population in Guam. Introduced species can eliminate native species through predation, competition, hybridization, disease or habitat destruction.
A review by Atkinson (1989) demonstrated that 22 species and subspecies of reptiles and amphibians have disappeared worldwide as a direct result of alien animals. In New Zealand alone, 9 species of reptiles and amphibians and 23 bird species have become extinct since 1000 AD through introductions. Invasive species have the biggest impact on islands, where indigenous species have often evolved in the absence of strong competition, parasitism, or predation. As a result, introduced species thrive in those optimal ecosystems resulting in the decline of native populations, which have no effective defense against, or ability to adapt to the presence of an invasive species. Islands are characterized by high rates of endemism, which means they hold unique species in small numbers. Commonly found invasive mammals including rats, cats, goats, rabbits, pigs and few others that are responsible for most damage to island ecosystems and island species declines.
- Chain of Extinctions
It is important to be aware that the extinction of one species may bring about the demise of another, this is known as secondary extinction. For example, the extinction of a plant (genus Hibiscadelphus) resulted in the disappearance of the Hawaiian honeycreepers, its pollinators. There have also been several instances of predators and scavengers dying out following the disappearance of a species which represented its food source, these species which are essential to a functional ecosystem are known as keystone species.
There is no doubt that human activities are the leading cause of the current biodiversity crisis and therefore can only be halted by a change in the way we behave towards our environment. Failing to conserve what we currently have would only pave the way for easier and faster depletions in years to come.
The problems faced by biodiversity are many, from habitat loss, to species and genetic diversity loss. An integrated approach is required to even begin to tackle the issues. There is undoubtedly a need for sustainable development and adequate use of resources.
Conserving biodiversity is a complex matter and is our shared responsibility that relies on the involvement of many different partners including both governmental and non-governmental organization’s, communities and volunteers, businesses and private companies to all contribute to sustaining the Earths rich biodiversity. No one group or organization can tackle the challenges of biodiversity loss alone.
To approach the issue of Biodiversity loss we do not necessarily need new strategies, but simply improve and better enforce the systems already in place. The key stakeholders of the world need to ensure that they are aware of the obligations they have towards Biological Diversity and that a united approach would allow for various strategies to build on each other’s efforts and successes for a common goal.
The loss of our planets species would be a loss for everyone. Biodiversity is the basis for our existence, providing humanity with irreplaceable resources (food, clothing, medicine etc), clean water, fresh air and nutrient rich soils, and beauty and is our heritage and our legacy. The planet has barely been explored, we do not know how many species are on Earth, nor do we now how intricate or delicate the ecological mechanisms that keep natural communities running smoothly are, but we do know once a species is gone, it is gone forever.
Image sourced from igreenhero.com
© 2014 Cat Read
© 2014 Cat Read