About 65 million years ago, life on Earth was stressed by global climate change and rising sea levels. At this time, two large asteroids struck the planet simultaneously in North and South America. The impacts threw a huge dust cloud into the atmosphere and blocked the sun for at least several months. They also coincided with the extinction of the large dinosaurs and profound changes in other life.

Biologist Peter Ward has called attention to similarities between that time and our own. Climate change and rising sea levels are stressing the world's biota again and, to use Ward's analogy, another ‘asteroid’ struck in Africa about 100000 years ago – the evolution of the human species. Ward argues that the rise of humans has meant the diminishment of the great diversity of life on Earth, in just the same way as the impacts of the earlier asteroids altered the direction of evolution.

In this first theme of Environmental Biology we examine why an understanding of our species is essential to understanding and conserving the diversity of life.

In introducing the discipline of conservation biology Gary Meffe, C. Ronald Carroll and Martha Groom stated three unifying principles:

1. Evolution unites all biology (the evolutionary play).

2. The ecological world is dynamic (the ecological theatre).

3. Humans must be included in conservation planning (people are part of the play).

Your study so far in Environmental Biology should leave you in no doubt about all three maxims, but we have not yet discussed how to integrate the human element with your understanding of evolution and ecology.

In this final theme of Environmental Biology we apply your knowledge and understanding from the earlier themes to solving applied conservation problems or to redressing environmental damage. Good scientific method is at the core of all solutions, complemented by a thorough understanding of biodiversity and the interactions of species through the application of evolutionary and ecological principles.

The main characteristics of organisms from the various kingdoms of life were selected through evolution because they adapt the organisms to their physical and biotic environments. As biologists Marc Johnson and John Stinchcombe point out, we now realise that genetic variation and evolution within a species influence not only that species but also others with which it interacts and the surrounding environment. Thus the study of the interactions within and between species and their environment, collectively called ecology, is also the study of evolution in action. This is the topic of this theme.

We consider interactions between organisms of the same species as they build up a population and then examine the interactions between different species living together and forming a community. Finally, we cover the main characteristics of marine, freshwater and terrestrial environments and how the interactions between the communities within them and the physical environment form characteristic ecosystems. We need different techniques to study the microbes, plants and animals in the ecosystems and we describe some of them, as well as some of the instruments available and the ways of analysing and presenting data.

There are many excellent introductory biology textbooks available, so why write another? The answer lies partly in the rapid expansion of modern biology and partly in the needs and aspirations of modern students.

The second half of the 20th century and the early 21st century have seen such major developments as the unravelling of the structure of DNA, the complete cataloguing of the genome of humans and other species, and the first successful cloning. These developments are reflected in university biology curricula, which offer new units and courses in subjects such as molecular genetics and biotechnology and a much greater prominence for molecular biology in introductory textbooks. Simultaneously, other biologists have noted with concern the impacts of climate change, increasing human populations and changing technologies on natural environments and other species. They note that the rate of extinction in species at present is well above the background extinction rate shown in the fossil record, suggesting that the world is in a period of human-caused mass extinction that is reducing our biological heritage. These realisations are reflected in the curricula too, with new courses and units in conservation biology and restoration biology, as well as chapters on conservation in introductory textbooks.

Students majoring in biology at university need a thorough grounding in all these new areas as well as the more traditional aspects of the discipline. They are well served by existing textbooks, but many non-majors lack the space in their crowded timetables to cover all the topics in such detail.

Early this century biologists recognised that some regions of the Earth were unusually rich in the number of unique species living there but also threatened by human activity. They called these regions ‘biodiversity hotspots’. Thirty-four are currently recognised, including the South-west Botanical Province in Western Australia. This area of about 360000 km2 is characterised by low soil fertility and a Mediterranean climate, with most rainfall during winter and dry summers. It is bounded to the south and west by ocean and by desert to the north and east. The climate, low soil fertility and isolation are the driving forces in the evolution of a diverse and unique biota. The province contains nearly 6000 described plant species (including about 4500 unique to the region) and 456 vertebrates (including 100 unique to the region). Although the invertebrate diversity is poorly described, it is likely to be extremely rich as well.

In this third theme of Environmental Biology we apply your understanding of the scientific method to the problems of classifying the diversity of life in biodiversity hotspots and elsewhere on Earth. You will also learn how the abundance and distribution of species is determined by interactions within and between species and between species and their environment.

From Theme 1 you understand the central place of the human species in environmental biology today. You also have a general understanding of science and how it might be applied to solving biological problems.

Biologist Hugh Gauch listed five key resources for research in the sciences:

1. equipment to collect data

2. computers and software for data analysis

3. infrastructure, including libraries, colleagues and internet access

4. technical training to use all the above, and

5. a knowledge of the scientific method.

He argued that good research was often most impeded by a poor understanding of the fifth point, the scientific method.

Therefore in this second theme of Environmental Biology we explore the nature of the scientific method in detail. We also examine two of its most important contributions to modern biology: the great unifying theories of the cell and of evolution.