The big picture

Ever thought about how you effect habitats and biodiversity? Human presence, development and population growth can adversely affect habitats by:

• Conversion of land to urban use containing high levels of buildings and roads.
• Removal for use for agriculture purposes.
• Fragmentation through transport routes such as roads and railways.
• Degradation through over-exploitation of natural resources such as timber.
• Degradation through pollution which can have effects both locally and further away from the source e.g. gaseous emissions from use of fossil fuels can lead to localized photochemical smog, regional acid rain and at a global level contribute to climate change.

Figure 1. Urban and farming development.

Loss or degradation of habitats can lead to a decline in species numbers and biodiversity. With so many species at potential threat, it can be difficult to decide which species to focus our limited resources and time on. The conservation status of a species is determined in an attempt to decide where to place our conservation efforts.

As discussed in the subtopic 'An introduction to biodiversity', some regions such as tropical biomes have greater biodiversity than other regions due to climatic conditions that allow high levels of productivity. Habitat degradation in these tropic biomes can result in dramatic loss of biodiversity.

Figure 2. Forest in a tropical biome where habitat loss can result in significant loss of biodiversity.

Hence sustainable development is especially important in these regions and conservation challenges include exploitation of resources without damaging the habitat and resources for the future.

How many species are there on Earth?

Have you ever looked around you and wondered how many species exist? No one actually knows the answer. Estimates vary widely from 5 million to more than 50 million, with a few suggestions even as high as 100 million.

Estimating species numbers

Various methods have been used to ascertain the number of species, which include the following:

Host-specific species. A common method is to intensively count the number of species in one area and then extrapolate this to a wider area. An example of this is when Terry Erwin (1982) collected and counted 162 host-specific species of beetles within the canopy of one tropical species of tree (Leuhea seemannii) in the Panamanian rainforest and extrapolated this to the estimated 50,000 species of trees found in tropical forest giving a value of 8.1 million species of beetle. Erwin then suggest that based on the assumption that only 40% of all canopy arthropods are beetles and these canopy species only account for two thirds of all arthropod species, the total number of all tropical forest arthropods is about 30 million.

Figure 1. A high variety of beetle species exist.

Try for yourself!

Using the information in the above account about Erwin's study show how (i) the estimated number of tropical tree beetle species was calculated and (ii) the estimated total number of tropical arthropod was calculated.

Ratio of temperate and tropical species. This method is based on fairly extensive knowledge of the number of temperate species and that of the number of mammals and birds in tropical areas. It has been found that the number of mammals and birds in the tropics is 2-3 times greater than the numbers of these groups in temperate regions and hence an assumption has been made that this ratio can be applied across all other groups of species. Using this method the estimated number of species calculated is between 3 million and 5 million.

Figure 2. Species of mammals from temperate habitats.

Taxonomic classification system. This classification system created by Carl Linnaeus (1758) groups organisms according to observed similarities. Using physical characteristics organisms are first designated a kingdom, followed by a phylum and widening out to groups of classes, order, family and genus. At each stage the number of groups increases. A group of researchers led by Mora, (see below for link to scientific paper published in 2011) examined the number of species within this pyramid hierarchy and identified a numerical pattern which they then applied to animals, plants, fungi, protozoa and chromista (group of algae). Using this approach Mora's team, have estimated the number of eukaryotic (multicellular) organisms to be 8.7 million.

Data from taxonomy group experts. An alternative approach used by the UN Global Biodiversity Assessment in 1995 was to collate data from experts of each group of organisms.

Click here to read the journal article by Mora, Tittensor, Adl, Simpson & Worm, 2011. PLoS Biology. How Many Species Are There on Earth and in the Ocean? 9(8).

The video 'Millions of Undiscovered Species on Earth, Study Finds' considers the findings of the research conducted by Mora et al.

Unknown species

Figure 4. Species yet to be found.

Some groups we know more about than others such as terrestrial mammals and birds which have been extensively studied and documented. Some areas have also been more fully examined such as temperate regions compared to tropical regions.The majority of species have yet to be identified, the 2005 Millennium Ecosystem Assessment estimated less than two million species have been formally described.

There are numerous problems associated with directly counting the number of species globally. These include:

• Some species may be counted more than once. Following identification the same species may have been labeled with different names, possibly due to natural variation within a species, identification in different locations or where checks with historic records have not occurred.
• Groups of species which are very small such as bacteria are difficult to isolate and identify.
• Some species such as deep sea organisms are difficult to access.
• Some species may become extinct before we even know about their existence. The number of species on Earth are constantly changing with some disappearing whilst at the same time through the process of evolution new species are emerging. Scientists estimate the rates of extinction are currently 100 to 10,000 times greater than background rates (natural losses expected without human influence) resulting in a loss of 0.001% to 0.1% of total species each year. As discussed in subtopic 3.2 we maybe currently experiencing the 6th mass extinction, this time caused by us.
• Lack of taxonomy expertise to cover all groups of species.
• Lack of finances to fully fund identification of all species.
• Coordination required across the globe to create one unique species inventory.

Figure 5. Golden Toad in Costa Rica declared extinct in 1989.

Creating species list

Figure 6. Making a species list.

Attempts to create more comprehensive species list include:

• Discover life in America, a project that aims to provide a list of all species within the Great Smoky Mountains National Park. Various government groups, environmental organizations and universities are working together to identify every species and learn more about the estimated 100,000 species in the National Park.
• CatalogueCatalogue of Life is an ongoing project with the aim of producing a single global list of all species together with their associated taxonomic hierarchy. To date it has compiled validated information from over 130 other datasets from across the world. It is used by various conservation organizations including the International Union of Conservation Nature who produce the Red List of threatened species.
• Species 2000, also aims to produce a list of all the species on Earth by collating information from group of species databases.

Using the United Nations Environmental Programme World Conservation Monitoring Centre (UNEP-WCMC) website, find information about the number of species recorded in your country. Compare this to another country of your choice. Can you see any differences? How can the differences or similarities be explained?

How do humans influence biodiversity?

Humans can threaten species directly through hunting or harvesting or indirectly through activities leading to destruction or degradation of habitat or action contributing to climate change. The rate at which biodiversity is being threatened has increased since the industrial revolution and is considered to be linked to human population growth.

Population Growth

The human population has increased exponentially since the industrial revolution when death rates decreased as a consequence of developments in science and technology leading to improvements in sanitation, healthcare, nutrition and agriculture.

Figure 1. World population growth and period of the industrial revolution.

With growth in human population there is increasing demand on natural resources which has led to over-exploitation of species, habitat degradation, human introduction of alien species and pollution of the environment, all contributing to species extinction.

Figure 2. Species extinction and human population.

Graph source: Scott, J.M. 2008. Threats to Biological Diversity: Global, Continental, Local. U.S. Geological Survey, Idaho Cooperative Fish and Wildlife, Research Unit, University Of Idaho.

Over-exploitation of resources

Renewable resources such as animals, fish and plants need to be managed sustainably to secure a continued supply. They need time to re-generate, otherwise, numbers will fall below a threshold level from which they cannot recover. The population will become exhausted and collapse. Hence, hunting or over-harvesting for food, timber, medicines, skins and furs can led to species loss.

There are many historical examples of when humans have colonized an area (e.g. Easter Island), and the growth in population has exceeded the carrying capacity of the area and exhausted the local environment leading to loss and extinction of species.

Overfishing, the exploitation of the seas has been well documented. Newfoundland in Canada historically had an extremely high productive fishery. However, following years of over fishing, stocks become exhausted and the fishery collapsed. In 1992 a moratorium was imposed on the cod fishery in Newfoundland by the Canadian government.

Figure 3. Over exploitation in Newfoundland, Canada leading to crash in fish population.

Source: UNEP/GRID-Arendal. 2007. Millennium Ecosystem Assessment.

Habitat fragmentation, degradation and loss

Forests have often been exploited for construction material, firewood, food and medicines. Land cleared to use for settlements, industrial development, grazing and growing crops.

With technological developments in the 1950s farming intensified in many countries. Areas such as wetlands previously unsuitable for arable farming could now be drained resulting in habitat loss. With mechanization, larger areas of land could be farmed and yields could be further improved with the use of fertilizers and pesticides. Subsequent agriculture run-off rich in nitrates and phosphates from fertilizers, pesticides and organic matter (from slurry and silage) led to pollution and degradation of aquatic habitats.

Figure 4. Large scale farming.

In developing countries subsidence farming is more prevalent. Here an increase demand for food by a growing population has sometimes led to loss of soil fertility where the land becomes exhausted and is no longer able to support the crops. Hence, people have often resorted to clearing forest areas to use for agriculture. Soil erosion rates are frequently high in these cleared areas and soil fertility declines rapidly. In some cases slash and burn techniques are used to clear forest areas, where fire may become out of control and penetrate deep into the forest. Both the reduction in forest habitats and fire threatens many species.

Figure 5. Use of slash and burn to clear forest habitat.

In order to meet the demands of a growing population, activities such as mining, logging and water extraction have all increased. In addition, technological developments and changing lifestyles have increased our demand and use of some materials. For example the demand for rare earth metals used in computers, rechargeable batteries and mobile phones have doubled just in the past 10 years to about 200,000 tons.

Ecological impacts of mining include fragmentation of habitats through development of roads to transport the mined goods and for movement of the workforce and other materials. Mining often involves clearance of forest leading to soil erosion and siltation of rivers. Groundwater and surface waters can become contaminated with pollutants such as metals (acid mine drainage). Dust and particulates released into the air can also contaminate and reduce air quality. The physical disturbance and noise in the area can adversely effect some species, which could also reduce successful breeding rates.

Figure 6. Loss of habitat to mining activity.

Invasive species

Humans have moved species around the world for their use, such as crop plants and animals. How many of the foods you eat today have their origins in another part of the world?

Some species have been moved unintentionally such as stowaways within crops or in ballast waters of ships moving cargo around the world. Some of these invasive species have adapted to the new conditions and have and gone on to breed successfully. Problems have arisen when they degrade the habitat or out-compete local species for resources such as food.

Figure 7. Burmese Python from SE Asia introduced by the pet trade to the United States is now resident in the Florida everglades where it is a threat to native species.

Islands can be very vulnerable to invasive species. Local species, often also endemic lack the ability to adapt to hunting by humans or to the introduction of a new predator (e.g cats/dogs). Prior to colonization, Mauritius an island in the Indian Ocean had more endemic species than it does today.

Pollution

Aquatic habitats are being polluted through discharges of waste water including sewage and industrial effluent together with urban drainage and farm run-off. These inputs can degrade the habitat and decrease species diversity.

Disposal of waste on land, including fly tipping can contaminate the ground and degrade the habitat. The use and disposal of non-biodegradable material such as plastics has exacerbated this problem. Birds can become tangled up in plastic bags or plastic rings used for tin cans. Dumping of waste at sea can also cause problems from animals becoming tangled in waste or from ingestion of material that block their digestive system.

Figure 8. Dead turtle entangled in fishing nets.

Atmospheric pollution can occur from use of cars or production of electricity and can lead to a change in some localized groups of species such as lichen. Some species are intolerant to air pollution and therefore they will decline in number. Burning of fossil fuels leads to emissions of sulphur dioxide and nitrogen oxides that are the precursors of acid rain. Acid rain has devastated large areas of forest (e.g.in Sweden and Germany), changing the conditions in lake systems and reducing overall biodiversity.

Figure 9. Impact of acid rain - dead forest in Germany.

Climate change

Human activity has increased the amount of greenhouse gases such as carbon dioxide, methane and chlorofluorocarbons in the atmosphere. This is expected to cause an overall increase in global temperature, change in precipitation patterns and more extreme weather patterns. As a consequence, species which are unable to adapt to these changes or unable to migrate to more suitable conditions may die out. The causes and impacts of climate change are more fully discussed in subtopic 7.2.

The IPCC (2007) suggest that up to 30% of plants and animals are at risk from extinction as a consequence of climate change. Prediction of which areas may gain or lose plant species are illustrate in the figure below.

Figure 10. Estimated changes of plant species.

Source: UNEP/GRID-Arendal, 2009. Kirkup 2001.

Role of the IUCN Red List

Figure 1. IUCN Red List highlights species under threat.

The International Union for Conservation of Nature (IUCN) Red List aims: “to provide information and analysis on the status, trends and threats to species in order to inform and catalyse action for biodiversity conservation.” (IUCNredlist)

The following video provides a good overview -The IUCN Red List: Barometer of life.

The IUCN Red List uses a range of criteria to objectively evaluate whether a species is under threat and according to this level of threat is designated a specific category. The conservation status categories span from ‘least concern’ at one end of the spectrum to ‘extinct’ at the other end. Within the middle are the three threatened categories: vulnerable, endangered and critically endangered.

Figure 2: IUCN Red List categories.

Criteria used to determine the conservation status of species

Population size: number of mature individuals

Population size as considered by the Red List criteria is the number of mature individuals of a species. Mature individuals are counted as those that are able to reproduce. With a smaller population, the opportunity to successfully breed is lower and hence increasing the risk of extinction. Inbreeding is also more likely to occur in a small population increasing the probability of offspring suffering from genetic abnormalities.

Population size reduction

Population size reduction ie the loss of individuals within the population is calculated for a period of 10 years or three generations of the species. The greater the rate of decline in population size, the higher the risk that the species will become extinct.

Geographical range: extent of occurrence and area of occupancy

The area of occupancy is where the species can normally be found. The extent of occurrence is the boundary that can be drawn around the sites the species occupies. Hence the extent of occurrence includes the area of occupancy and may also contain habitats within the boundary not used by the species.

Examiner Tip

Ensure you can distinguish between ‘extent of occurrence’ and ‘area of occupancy’.

Number of locations

With the variety of threats to species and habitats discussed in the previous section, the number of locations a species is found in may decline. This problems is often most acute on islands and other areas with endemic species.

Extent of habitat fragmentation

Fragmentation of habitats often occur through human activities such as urban development and roads. Depending on the level of fragmentation subpopulations may become isolated and not have the critical numbers of mature individuals to successfully breed.

Quality of habitat

Organisms are dependent on their habitat for food and water. Hence the quality of habitat contributes to the survival and success of a species. If there is decline in the habitat (e.g. from logging activities) there may be a decline in available food.

Probability of extinction

This is the predicted likelihood of all the populations of the species in the wild dying out in the future.

(Source: IUCN Red List Criteria)

Additional factors contributing to species vulnerability

In addition to the above criteria, there are also various species characteristics which contribute to whether a species is more vulnerable to extinction, these include:

• The degree of specialization – for example, species with a very restricted diet. This includes pandas who are reliant on bamboo and therefore are more vulnerable than species that depend on a wider range of foods.

• Figure 3. Panda eating bamboo.
• Their trophic level – for example, organisms high up in a food chain may be exposed to higher levels of pollutants due to the process of bio-magnification and bio-accumulation.

Figure 4. Bio-accumulation within the food chain.

Case studies - extinct species

As discussed earlier in this subtopic, there are various human activities that cause species loss. This is demonstrated in the coming case studies which focus on:

• Species that have become extinct due to human activity.
• Species that are critically endangered.
• Species whose conservation status has been improved by intervention.

In this section, we consider two species that have become extinct, namely the Dodo and the Tasmanian tiger.

Dodo (Raphus cucullatus)

Figure 1. Dodo.

Today the Dodo is an iconic figure representing species which have become extinct. It was endemic on the island of Mauritius in the Indian Ocean, feeding on fruits and seeds from its forest habitat. Prior to human habitation, the numbers of dodos were high due to the lack of natural predators. This started to change when Dutch sailors settled on the island around the 1640s. The Dodo was a flightless bird and nesting on the ground made it easy prey to its new predators. Factors contributing to the extinction of the Dodo included:

• Hunting of the bird by humans for meat.
• Introduction of animals to the island by humans e.g. dogs, monkeys, pigs, and rats who attacked the nests eating the eggs and chicks.
• Human exploitation of forest resources, destroying the forest habitat.

By the start of the 17th century, the Dodo had become rare and the last Dodo was observed in 1681.

Tasmanian tiger (Thylacine cyncepphalius)

Figure 2. Tasmanian tiger.

The Tasmanian tiger historically occurred in Australia until about 2,000 years ago and thereafter appears to have been confined to Tasmania. It was a carnivorous marsupial bearing a pouch and also had similar characteristics to a dog. It fed on kangaroos, other marsupials, rodents and birds. After colonization by Europeans and the associated introduction of animal livestock, new prey such as sheep, were added to the Tasmanian tiger's diet. Its population was already considered to be low by the time Europeans arrived on the Island. Factors contributing to the extinction of the Tasmanian tiger included:

• Competition from dingoes and dogs.
• Hunting by humans to remove a livestock pest. Between 1888 and 1909 rewards were offered for killing each Tasmanian tiger.
• Habitat loss due to development of land for agriculture and for settlement.
• Population fragmentation caused by human induced fires.
• Possible disease epidemic in the 1920s which also affected the dingo population.

The last recorded Tasmanian tiger called ‘Benjamin’ died in captivity in 1936.

Case study - critically endangered species

In this section, we consider two examples of species that are categorized by the IUCN Red List as critically endangered, namely the Hawksbill turtle and the Sumatran orangutan.

Hawksbill turtle (Eretmochelys imbricate)

Figure 1. Hawkesbill turtle.

The hawksbill turtle resides in tropical oceans, predominately within coral reefs although its habitat varies according to its stage in its lifecycle. Eggs are incubated and hatch on sandy beaches and the hatchlings spend their first few years in the open sea before moving to coral reefs along coastal waters. They typically reach sexual maturity somewhere between 20 and 40 years old. When ready to lay the eggs, the female usually return to the same beach they hatched on.

The Hawksbill turtle is omnivorous eating algae, sponges, mollusc, crustaceans and fish. The turtle is in high demand for cultural and social reasons. They are used in traditional medicines and the shell is used in religious ceremonies or made into jewelry and ornaments as a symbol of wealth and social status. Presence of the Hawksbill turtle is also a key tourist attraction generating income. Reasons for a decline in species numbers include:

• Reduced nesting sites due to coastal development leading to loss of sandy beach and habitation by humans.
• Loss of feeding habitats e.g. loss of corals reef ecosystems due to pollution such as suspended solids blocking light penetration.
• Pollution e.g. ingestion of plastic debris resulting in blockage of digestive system and subsequent death.
• Climate change e.g. increase in temperature of nesting sites beyond tolerance levels for successful incubation or beach erosion caused by increase storm conditions.
• Accidental capture in fishing nets.
• Collection of eggs and the turtle for its flesh and shell. Despite being protected under Convention on International Trade in Endangered Species of Wild Fauna and Flora 1973 (CITES), the flesh is consumed around the world and trading of hawksbill shells and products has continued.

Sumatran orangutan (Pongo abelii)

Figure 2. Sumatran orangutan.

Humans often have a high affection for orangutans, to whom out of all other species in the world, we are most closely related. We share 96.4% of our DNA. Orangutans are highly intelligent apes, with a good memory and the ability to use tools. The name ‘Orang Hutan’ in Malay means ‘person of the forest’. Once found throughout the whole Island, Sumatran orangutans are now restricted to the provinces of North Sumatra and Aceh.

Orangutans are arboreal, living within the forest canopy. They build their nest in the trees and eat fruits such as figs. The loss of forests in Sumatra is estimated at about 50% over the past 25 years. Orangutans typically live for 45 years. Adult males usually live on their own and only meet up with females to mate. Young orangutans spent the first five years living with their mother. Females tend to reproduce every seven to eight years having up to three offspring, which potentially contributes to a slow rate of population growth. Estimates for the number of Sumatran orangutans in the wild varies between 6,600 and 7,300. Species loss has been driven by:

• Logging leading to habitat loss.
• Use of land for oil palm plantations and agriculture leading to habitat loss.
• Mining activity leading to habitat loss.
• Fire used to clear forest for other land uses, which can directly kill the slow moving orangutans.
• Capture of baby orangutans to be illegally traded as pets. Ownership of a young orangutan is considered a status symbol.
• Hunting of orangutans for meat.

Watch and make notes on the following video ‘Helping the orang-utan’ by the Natural History Museum:

Examiner Tip

Ensure you understand case studies sufficiently to apply that information to exam questions. For example, can you fully discuss the following statement:

'The fate of Sumatran orang-utans is inextricably linked to the islands fast disappearing forests. If we want to save the Sumartran orang-utan we have to save their forest home' Dr Barney Long (Asian Species Expert for WWF).

You should be able to discuss evidence that supports this statement i.e. habitat loss in addition to other factors that also contribute to the decline of the Sumatran orangutan populations such as the demand for baby orangutans as pets.

Case study - improved conservation status

In this section, we consider two species whose conservation status as categorized by the IUCN Red List has improved. This includes the Humpback whale whose status has improved from being classified as 'vulnerable' to 'least concern' and Lear's MaCaw whose status has changed from 'critically endangered' to 'endangered'.

Humpback whale (Megaptera novaeangliae)

Figure 1. Humpback whale.

Humpback whales inhabit all the world’s oceans. During the winter Humpback whales live and feed in polar waters and then move in the spring to warmer tropical waters at low latitudes, where they give birth to their calves. They feed on krill, fish and plankton. Humpback whales have been hunted since the 18th century for their meat, whalebone and oil. The level of hunting increased throughout the 19th century and intensified when improvements in technology led to use of explosive harpoons which made whaling easier.

In order to control levels of whaling the International Whaling Commission was set up in 1946. Most whaling nations signed up to adhere to set quotes and the use of restricted whaling times (open and close seasons). Nevertheless, the number of whales continued to fall and the International Whaling Commission prohibited commercial whaling of humpback whales in 1966. Whaling still continued in some areas into the 1970s. Environmental groups such as Greenpeace and Sea Shepherd have continued to highlighted illegal whaling activity, sometimes even risking their own lives by acting as human shields between the harpoons and whales.

Following the ban on whaling there has been partial recovery, with global Humpback whale numbers estimated at between 60,000 and 80,000. The status of humpback whales was reclassified in 2008 from vulnerable to least concern by the IUCN. Some countries have been granted temporary exemptions from the ban, which allows them to hunt a designated number of whales. This is typically in cases where whaling is considered to be part of the cultural heritage e.g. the Inuit people of Greenland.

Whale watching is a popular activity today that can attract significant numbers of tourist and therefore generates income for the area. It also helps to raise awareness of conservation including the vulnerabilities of other marine species.

Figure 2. Tourist whale watching.

Threats today include:

• Degradation of their marine habitat.
• Chemical pollution e.g. the bio-accumulation and bio-magnification of synthetic compounds such as pesticides.
• Noise pollution e.g. sonar form boats and military operations appear to disorientate whales and examination of beached whales indicate that sonar also causes physical trauma resulting in bleeding around the brain and other tissues.
• Entanglement in fishing nets.
• Lack of food e.g. due to overexploitation of fish stocks by humans.
• Hunting by humans (either legal or illegal).
• Strikes from boats.
• Harassment from boats with whale watchers getting too close.

Video: Canada removes Pacific Humpback whales from list of threatened species

Lear’s MaCaw (Anodorhynchus leari)

The two known colonies of Lear’s MaCaw are located in Toca Velha and Serra Branca, in Brazil.

Figure 3. The two known colonies of Lear’s MaCaw are located in Toca Velha and Serra Branca, in Brazil.

The parrots are known to eat Licuri palm nuts, flowers and maize. They typically nest in sandstone cliffs. Threats include:

• Capture of parrots for the pet trade.
• Reduction of Licuri palms (Syagrus coronate) and change to a grassland habitat.
• Grazing of its habitat by livestock leading to degradation.

Figure 4. Lear's MaCaw.

International trade of Lear’s Macaw is restricted by CITES Appendix I and II and is also protected by Brazilian national law. Action to reduce capture and trading of Lear’s MaCaw has seen some success. Action taken involved:

• Surveillance and monitoring the birds habitat, especially foraging and nesting sites.
• Enforcing legislation resulting in the arrest of poachers, smugglers, collectors together with confiscation of all birds found.
• Planting Licuri palms and protecting them from livestock grazing and trampling.
• Monitoring the health of the species and studying their natural history.
• Education and awareness programme.
• Working with local people and compensating farmers for crop losses.

Future plans under consideration include breeding in captivity and re-introduction of the parrot into its natural habitat. The numbers of Lear’s MaCaw in the wild improved from 70 birds in 1987 to more than 1,100 in 2010. The Red List status of this species has changed from critically endangered to endangered.

Biological hotspots

What are biological hotspots?

With so many species listed as endangered and limited resources and time, where do we want to focus our attention? In order to help with this decision making, in 1988 Norman Myers proposed the concept of biological hotspots which was then adopted by Conservation International. The two key elements to the concept are that these sites must have a high level of endemic species and also be under threat. Following further analysis and a global review Myers introduced quantitative thresholds. Conservation International now uses the following two criteria, both of which must be met for a site to be designated as a biological hotspot:

1. “It must have at least 1,500 vascular plants as endemics — which is to say, it must have a high percentage of plant life found nowhere else on the planet. A hotspot, in other words, is irreplaceable.
2. It must have 30% or less of its original natural vegetation. In other words, it must be threatened.”

Identification of biological hotspots allows conservation efforts to be focused in areas where it can protect the highest numbers of species. There are 34-35 global biodiversity hotspots, mostly located in the tropical rainforest. They occupy only 2.3% of the earth’s land area but contain approximately 50% of the earth’s endemic plant species and 42% of all terrestrial vertebrates (birds, mammals, reptiles and amphibians).

Figure 1. Location of biological hotspots.

Source: Berkeley

Watch the following video ‘What is a biodiversity hotspot?’ by CSIRO.

International-mindedness

Biodiverse regions of the world occupy vast areas and show no respect for country borders. Therefore, international scientific collaboration is essential. Think about or investigate how this is achieved.

Tropical rainforest biomes

Figure 2. Tropical rainforest.

These cover about 6% of the land surface and are the most rich and diverse biomes. As previously discussed in subtopic 3.1, the climate conditions are a result of their location near to the equator, which leads to high levels of productivity.

The largest regions of tropical rainforest are located in the Amazon basin, Congo basin and Indo-Malay region.

Figure 3. Location of tropical biomes.

Rainforest contain more than half the world’s plant and animal species. The high level of primary production supports an array of species. They are also the oldest biomes and have developed into climax communities with high levels of biodiversity.

As illustrated in the figure below, the rainforest can be divided into distinct vertical zones:

• The emergent layer which is the highest layer and consists of trees that extend beyond the general canopy.
• The canopy level that is fairly dense and significantly reduces light penetrating further into the forest.
• The understory layer below the canopy layer consisting of shrub plants and tree saplings.
• The forest floor or ground layer, which receives less than 2% of the light, so green plants are limited in number. Humidity is very high due to the limited air movement and high evaporation rates in the layer.

Each layer of the rainforest has different environmental conditions and hence contains its own unique community of species, adding to the overall biodiversity.

Figure 4. Vertical layers within a tropical rainforest.

The nutrient cycles within the tropical rainforest tend to be short. Nutrient levels in the soil are low as nutrients are easily leached out by the continual rain. Nutrients are mostly held within the biomass especially the root mats. Hence, removal of trees can cause nutrient levels within the ecosystem to decline rapidly.

Tropical rainforest also provide goods and services. Resources for humans include food, timber and medicines. Services include the absorption of carbon dioxide (carbon sink), production of oxygen, soil stability and filtration of water. Of course, tropical rainforest are significant for many other reasons which include intrinsic, cultural, spiritual, religious, aesthetical, education and scientific value.

Figure 5. Foraging in the forest.

Papua New Guinea

Papua New Guinea is home to one of the world's largest expanse of tropical rainforest. Today, this biological hotspot is under threat from:

• Commercial logging.
• Mining activity.
• Agriculture.
• Population growth.

Like many less economically developed countries (LEDCs) Papua New Guinea has welcomed multinational logging and mining companies, in exchange for economic growth. Some people believe that habitat degradation or habitat loss is a price worth paying for development. However, there have been cases where:

• Enforcement of legislation against illegal logging activities has been weak.
• Situations in which permits for logging have been gained under suspicious circumstances, with allegations of corruption against politicians and others in authority.

Figure 6. Logging activity leading to habitat destruction.

Watch and make notes on the following video ‘Chopping down trees to save the forest’ which considers tropical rainforest destruction in Papua New Guinea and approaches taken to ensure a more secure future.

Examiner Tip

Ensure you can apply different Environmental Value Systems (EVS) to the different choices made on whether or not to conserve natural resources such as habitats and species.

Using information in the table below, which EVS do:

1. The logging companies most align with?
2. The community based project most align with?

You should be able to fully justify the reasons for your choice.