Biodiversity

Introduction

It has been estimated that there are some 3-30 million extant (in existence) species within the Earth's biosphere, which is the total sum of ecosystems able to support life on earth. This variety of living organisms is described as biodiversity. Also commonly referred to as biological diversity, it can refer to the genetic diversity within a single species ('genetic biodiversity'), the range of species within a habitat ('species biodiversity'), or the variety of ecosystems within a region ('ecosystem biodiversity').

The Earth's biodiversity helps preserve the balance of nature on our planet. A habitat which has reached a balance between the number of species present and the natural resources available within it is called a 'habitat in equilibrium'. Such habitats, with their biodiversity largely unaltered, have a much greater chance of surviving threats than those with less biodiversity. This is because the ecosystem has more immunity to unnatural changes. Man-made threats such as deforestation, pollution and human settlement have led to many species becoming extinct in Australia. Many human activities can destroy a single species and thus break natural food chains, which reduces the overall biodiversity of an ecosystem.

Key human impacts affecting Australia's biodiversity

Since the arrival of Europeans in Australia in 1788, the physical environment has seen a significant reduction in biodiversity because of human impact. Within a short time frame, many habitats were destroyed and hundreds of species of flora and fauna became extinct as a result. The pristine forests of south-western Tasmania, virtually untouched since European settlement, form one of the last remaining regions in Australia to have been left in their natural state. Their intricate ecosystems are part of a rare few in Australia which have been able to maintain an extremely high level of biodiversity. See image 1

Population growth and settlement patterns

Australia has an extremely uneven population distribution. The vast majority of people reside in urban areas within 100 kilometres of the coast. This pattern of urban settlement has meant that the populations of our cities have mushroomed outward, producing what is known as an urban sprawl. The effects of this process upon biodiversity have been immense. Arable (productive) land that once surrounded cities has been replaced with houses, which has destroyed habitats, broken food chains and lead to plant and animal extinction. Overuse of natural water sources, such as the Murray-Darling River system in south-eastern Australia, has seen water supplies become degraded and has also destroyed many freshwater habitats. Increased amounts of sewerage, the use of household chemicals, large-scale vegetation loss, high traffic volumes and the use of heavy machinery for industrial purposes have similarly disrupted many ecosystems and reduced biodiversity.

Deforestation and agriculture

Over the past two centuries, enormous areas of Australia's bushland have been cleared (a process known as deforestation) so that timber can be harvested as a natural resource. Although since the early years of European settlement levels of deforestation have declined considerably (from approximately 500 000 hectares per year to 100 000), the use of forests to support our large timber and wood chipping industries continues to have a large impact on the preservation of natural ecosystems and biodiversity.

Agriculture has also had a negative effect on biodiversity. Land clearing to create crop and pasture fields has destroyed the habitats of many native plant and animal species, and the importation of cattle and sheep has had devastating effects on the physical environment. Hard-hoofed, large-mouthed farm animals are not suited to Australia's physical environment, which is designed for Australia's soft-footed, small-mouthed native animals. Introduced sheep and cattle have consequently damaged the soil (rendering it useless in some areas) and crushed fragile varieties of native vegetation. Certain types of imported weeds, naturally more resilient to cattle and sheep, have also begun to proliferate and wipe out natural vegetation. The agricultural processes that have led to dryland salinity and desertification (refer to Chapter 1) have also reduced biodiversity in rural Australia.

Interference with bushfire patterns

Although many people consider it an environmental threat, bushfire can serve important ecological purposes. Used extensively by Indigenous Aboriginal populations prior to European invasion, bushfires have played a role in the evolution of native flora and fauna in Australia. For many species, the smoke from a bushfire is the natural cue for germination (sprouting). For others, such as the Banksia, the intense heat of a bushfire enables their seeds to be released from closed canopies high up in the treetops of a forest. This is why fire, although potentially destructive in many ways, can also be considered a natural part of biodiversity maintenance. See image 2 

Pollution and climate change

Pollution and the predicted impacts of global warming and the greenhouse effect will continue to have negative impacts on biodiversity in Australia and around the globe. Progressively rising sea levels, for example, are a major cause for concern. Higher sea temperatures have already led to the extinction of many organisms in Australian coral reef zones. It has also been estimated that by the year 2030 most parts of terrestrial Australia could be warmer by up to two degrees Celsius. As a result of this, changes to soil moisture on the mainland may begin to affect plant species' abilities to survive. Future rainfall predictions are also of concern, with research suggesting that average rainfalls will drop substantially due to rising atmospheric temperatures and increasing evaporation levels.

Exotic species

Exotic species are organisms that disrupt and damage habitats by providing competition for naturally-occurring organisms. They could essentially be considered as invaders of ecosystems and can be placed into two main categories: pest animals and environmental weeds. Many exotic species have been introduced to Australia from other countries (to be used as hunting game or for the control of other pests). Others, however, are indigenous (native) to Australia but have spread to unnatural ecosystems.

Cane toads are an example of an introduced pest animal which has devastatingly infiltrated ecosystems in Queensland, northern NSW and parts of Kakadu National Park in the NT. They were originally introduced to control beetles which were hindering sugar cane growth, but they spread throughout north-eastern Australia at an unstoppable rate. See image 3 and animation 1

Genetically modified organisms

The advent of genetic modification (GM) in recent decades has led to an increased focus on studying genetic diversity within groups of species and the potential impacts, both positive and negative, that this could have on biodiversity. Maintaining a high level of genetic biodiversity is important because it enables species to continue evolving.

Genetically modified organisms (GMOs) are any organisms whose genetic make-up has been changed through a process of genetic engineering (GE). The stated purpose of GE is to produce new genetic compositions which may either help humans advance, or help rectify some of the problems humans have created. It is believed by some that GE could be used to create species that are resistant to land affected by salinity, or to help protect endangered species and restore disrupted ecosystems.

It is important to note, however, that the ecological impacts of GMOs are not that well-known. They are difficult to predict because they can be both direct and indirect and they may not cause overt (observable) problems for quite some time. One of the most common hazards posed by GMOs is when they present too much competition for natural organisms. Another danger is when GMOs that were designed to be toxic to particular pest or weed end, up killing non-target species.