People consult biogeography to understand pattern or process in the distribution of life on our planet. Despite the obvious link between the two, most biogeographers tend to focus primarily on either pattern or process for their research. Each of these areas asks different questions. For pattern, the question is mainly about which species are found in which areas. This kind of science produces long and accurate lists of the biotas in particular regions. This is immensely valuable for studies on conservation and biosecurity, as well as identifying endemicity, natural regions and invasive species. For process, the questions are mainly around how each species ended up in a particular area and whether this process is common. This approach is valuable for understanding evolution and the history of an area. Occasionally, you can get a nice mix of both pattern and process.
Juan Morrone is a prolific biogeographer who has spent most of his research life working on the neotropics (basically the area running from Mexico to northern Argentina and Chile). His book ‘Neotropical biogeography: regionalization and evolution’ is the culmination of a huge amount of his own research and a synthesis of the work of many others. With that title one might expect that this will be about both pattern and process. That is not quite what we get.
Morrone opens with a short (8 pages) section on evolutionary biogeography where he talks through his views on how to analyse the biogeography of regions. This is an interesting chapter and it would have been useful to have developed this further as the ideas here provide a structure for the rest of the book. A chapter on the history of biogeographical study for the neotropical region follows. This is a useful chapter (27 pages) that traces the various ideas of carving the neotropics up into different regions over the last 170 years. What is missing is an in-depth discussion on whether the neotropics is a real region and why an idea developed in the nineteenth century is still relevant today (how does it benefit us to think about major chunks of the world being divided into regions?).
The bulk of the book then breaks the neotropics into subregions/dominions and their provinces. For each subregion there is information on the history of the naming of this area by different authors over the last 170 years, a description of the area, some endemic and characteristic taxa to be found there, examples of the dominant plant species, the biotic relationships with other provinces, an example of a species track in the region and a section on cenocrons (subsets of the taxa found in the province that share a biogeographical history). Rinse and repeat for all 10 dominions and 53 provinces (194 pages).
The book is a very dense presentation of facts. It is not really meant to be read from cover to cover but is there for when somebody wants to know about a particular region. As such the book is a good starting point for getting into the literature (there are around 600 references) on species found and the geology of different provinces. This is where the book shines.
However, there are a couple of elephants (or maybe, as this is the neotropics, giant sloths?) in the room. The first is methodological and the second is philosophical. Morrone is very keen on track analysis. Basically, distribution dots are placed on maps and joined by lines (assuming a minimal spanning tree) to give a track for a species/species group. This track then suggests something about how geology has interacted with the species history. A group of tracks that might coincide suggests a cenocron. In an age of dated molecular phylogenies this connecting of the dots seems decidedly old school. How are the dots selected to go on the map (many of the tracks are for a single species, which presumably has a relatively continuous distribution between the dots)? Why is the shortest distance between points the best way to connect the dots? Do coinciding patterns confirm a single biogeographical process? What would the null hypothesis be for a species distribution (for example Cuba is a long, thin island and it is not surprising that tracks run along the island!)? Given that many geological scenarios over the last 60 million years are presented for most provinces, how can we tie tracks to a particular scenario? And so on. Ultimately, track analysis does not invalidate Morrone’s approach (you can just think of the tracks as a way of showing distributions in each area), but I do not think it provides the evidence that he was hoping for.
The bigger question is whether books on regionalisations are still useful or valid. I could not help thinking as I read my way through the book that it would have worked a lot better as a webpage (even as entries in Wikipedia). Each province would have a page with links to all of the information about the region. More tracks, maps, species lists and links to references could be included. A larger question is whether regional units are still valid. To be fair, Morrone does ask this question in a two page epilogue. His response is that books like this are valuable because of ‘Simple! Communication! Whenever biogeographers communicate their ideas they need to refer to a regionalization, usually in the form of a map’ (p. 237). Perhaps (but a webpage approach would be just as useful and available to a greater number of people than this book).
Increasingly, biogeography (and phylogeography) are being done in a lineage specific manner. With increased sampling we realise that few species have the same distributions and that their biogeographic histories are a result of many different processes. For example, once it was thought that New Zealand’s biogeography could be explained by common vicariant processes. As we have studied more lineages we have begun to appreciate that there are multitudes of processes that influence the distribution of New Zealand species (from Gondwanan vicariance to recent long distance dispersal).
I am not sure about the future of books like this one. Having said that, this book on neotropical biogeography is well written, has clear and useful figures and maps, and contains a wealth of information that will be of use to researchers as a starting point for their studies of organisms in various neotropical regions, especially if one is interested in patterns. This is not a book for most researchers’ collections but it is a nice addition to university and research libraries.