In order to undertake a critical review of the interface between plant microevolution and conservation, it is necessary to examine published information on a very wide range of topics. Current microevolution is illuminated by ecological studies, common garden and other types of experiment, and a variety of cytological and genetic investigations that increasingly employ molecular markers. Concerning the environmental and conservation context of the success or failure of species, there are many peer-reviewed papers in academic journals and books, together with official documents and statistics produced by national governments, international agencies, interest groups and professional conservationists etc. There is also a great deal of what is called grey literature, which, for reasons of confidentiality, is not publicly available. This includes, for example, consultants' reports, on which far-reaching conservation decisions are made. There is also a great deal of information on the Internet. In total there is a substantial body of knowledge about the conservation of communities and endangered species, based not only on the experience of habitat management, but also on experiments, field observations, mapping and surveys.

Technical advances in many fields have greatly enlarged our understanding of wider environmental issues. With the increasing use of aerial photography, satellite imagery and remote sensing, it has been possible to investigate land use in a way hitherto impossible from fieldwork alone. Google Earth – http://earth.google.com – provides an unrivalled opportunity to examine in great detail the impact of human activities on ecosystems (Biever, 2005).

Our current views on evolution in plants are firmly rooted in Darwin's theory of evolution by natural selection. Before Darwin and Wallace formulated their concept of evolution, it was assumed that species had been individually created in a single act of Special Creation. They fitted perfectly their environment, and any deviations in morphology that occurred were the result of accident. Species were essentially unchanging and unchangeable ‘ideal types’. Moreover, the world had been created very recently. Thus, by counting scriptural generations, Archbishop Ussher came to the conclusion that the Earth originated in 4004 BC (Mayr, 1991, 16).

The first critical appraisals of Special Creation predated Darwin's theory of evolution (Briggs & Walters, 1997), but Darwin provided the most formidable challenge to the former orthodoxy, by suggesting not only a plausible mechanism of evolution but also by assembling a wide array of evidence. The naturalist Wallace independently arrived at the concept of natural selection, but with different emphases (Sheppard, 1975). In 1858, before Darwin had published his ideas, Wallace sent him an essay on evolution by natural selection. The question of priority was resolved by Darwin's friends, who arranged a meeting at the Linnean Society of London in July 1858 at which Wallace's essay was presented and Darwin's ideas were represented by unpublished extracts from his writings. Then, over the next few months, Darwin (1901) wrote an extended account of his work: On The Origin of Species by Means of Natural Selection. The main strands of the concept are as follows.

Microevolution and conservation: Darwin's insights

Darwin provided not only the major element of our present understandings of microevolution through his theory of natural selection, but also key insights into particular issues relevant to the themes of this book – the nature of species, the co-evolutionary relationships between species, the evolution of humankind, the insights into domestication processes, the vulnerability of rare species, the impact of invasive species, and the evolutionary responses to climate change etc. Also, in his approach to testing hypotheses, Darwin was a major figure in the development of experimentation. For all these contributions, and many others not mentioned here, there is cause to celebrate the 200th anniversary of Darwin's birth and the 150th anniversary of the publication of On the Origin of Species in 2009.

Cultural landscapes

Historically, the initial influence of humans on the biosphere was likely to have been very small, but, as populations migrated across the world and increased in numbers, humankind has become a major, indeed decisive, force, influencing all the world's ecosystems. In the future, human impact is certain to increase, as population growth is predicted to increase dramatically.

There has been a complex transition from a ‘natural world’, in which humans played an insignificant role, to a world of cultural landscapes, where human activities dominate. Archaeologists are discovering that areas of apparent wilderness have been subjected to major human impacts in the past. In addition, such areas are increasingly being influenced by human activities.

So far in this book we have been looking for an answer to the following general question: If we know which species exist in the species pool, and we know their functional traits, can we predict the relative abundance of each species in different environmental contexts? What happens if we don't know which species – or even how many species – are in the species pool? Clearly, if we don't know which species are in the pool then we are in no position to predict their relative abundances. Even if we do know that a particular species is in the pool we still can't predict its relative abundance if we don't know how many other species are in the pool; after all, relative abundance is a proportion from a total. Therefore, if we don't know the composition of the species pool then we can't possibly answer the central question posed in this book.

However, even when missing this vital information about the composition of the species pool, we can ask a different, but related, question. Since we can't inquire about the abundance of species i, we might want to know how many species will have a given abundance. We can ask, for example: how many species will have only one individual or unit of biomass? How many species will be a little less rare and have two individuals, or units of biomass, and so on?

Theory can be dangerously seductive. Once one has built up an argument that is internally consistent, and once conclusions appear to follow inexorably from premises through clean lines of logic, it is sometimes enticing to conflate logical argument with reality. A good defense against such logical seduction is to let Nature into the conversation. A proper empirical evaluation of the method presented in Chapter 4 would involve an accurately measured environmental gradient involving all of the relevant environmental variables driving natural selection plus measured values of the key functional traits that respond to this selection of all species in the regional pool. This would be replicated in different localities along with evidence of quantitative generality of the community-aggregated traits. Hopefully, this book will have sufficiently convinced you of the potential of the approach that you will contribute to the hard work of assembling such empirical information. When this is done then we will know if the model actually works.

I'm easy to seduce. I think that it will work. However, I'm old enough to know the difference between seduction and commitment and I have had enough experience with field ecology to know that it might not work after all. I certainly won't hang myself in the barn if the model fails. As Thomas Henry Huxley famously pointed out, many beautiful theories have been killed by ugly facts.

Analogies are a vital part of science because they help us to imagine the unknown with reference to that which we already understand. Although vital, analogies become dangerous when they become so entrenched that we confuse the analogy with reality. The danger, when this happens, arises because we are prevented from conceiving of nature in any other way. In medieval discourse the organizing Aristotelian analogy was nature-as-an-organism. Natural phenomena were seen to possess a life cycle: birth, growth, old age and death. Processes in the natural world were made intelligible in this way and were understood by comparison with the inherent desire (the “nature”) of sentient organisms to attain goals (teleology). Cats hunt mice. Why? Because a cat is a predator and it is in the nature of predators to hunt. A stone falls to the ground rather than flying up into the air. Why? Because it is in the nature of heavy objects (i.e. objects made of “earth” rather than “air”) to move down. To know the nature of a thing was to know the thing itself (Dear 2007).

This analogy was replaced in the seventeen century, by people like Descartes, Galileo and Newton, with a new one: the analogy of nature-as-a-machine. The hand of a mechanical clock doesn't move around the face because it is in its “nature” to do so – place the hand alone on a table and it remains stationary.

Throughout this book I have contrasted “neutral” processes with “selective” processes that are based on trait-based environmental filtering. If “neutral” is interpreted in its strict sense of requiring exactly equivalent fitness between all individuals of all species then community assembly is either neutral or it is not. As I have already argued, such a strict conception of neutral community assembly makes no sense, except as a benchmark to measure departures, because it makes natural selection impossible. If “neutral” is interpreted more loosely, as any process that is independent of functional trait differences and that affects population dynamics by affecting realized rates of survival, reproduction or immigration, then community assembly almost surely occurs through an interplay of both “neutral” and “selective” processes. This looser meaning of “neutral” would include the stochastic demographic effects of birth, death and immigration that are especially important when population sizes are small but would also include all those dispersal limitations, including landscape features and history, which prevent propagules from moving between local communities and which are not related to functional traits. In what follows I will use “neutral” in this less rigid sense. In real ecological communities traits are not enough because such neutral processes always exist. Some communities might be predominantly structured by neutral processes while others might be predominantly structured by selective processes. The relative importance of these two groups of processes will determine whether or not the model developed in this book will have good predictive ability or not.