Megan Raby: The Tropical Origins of the Idea of Biodiversity

Megan Raby: American TropicsToday we welcome a guest blog post from Megan Raby, author of American Tropics:  The Caribbean Roots of Biodiversity Science.

Biodiversity has been a key concept in international conservation since the 1980s, yet historians have paid little attention to its origins. Uncovering its roots in tropical fieldwork and the southward expansion of U.S. empire at the turn of the twentieth century, Megan Raby in American Tropics details how ecologists took advantage of growing U.S. landholdings in the circum-Caribbean by establishing permanent field stations for long-term, basic tropical research. From these outposts of U.S. science, a growing community of American “tropical biologists” developed both the key scientific concepts and the values embedded in the modern discourse of biodiversity.

American Tropics is available now in both print and e-book editions.


The Tropical Origins of the Idea of Biodiversity

Today biodiversity is a key concept in biology and international conservation. It has even become something of a household word. In a narrow sense biodiversity simply refers to the number and variety of species in a given area. You can talk about the biodiversity of a particular site, of a region, or of the entire planet. These nesting scales carry subtle connotations. They situate local species––and the local loss of species––as part of a global biological heritage. Under threat, conservationists have argued, are not just particular wild places or even individual endangered species, but rather the diversity of life on earth itself.

Biodiversity has been so successfully framed as a global resource that it is tempting to see its intellectual history as abstracted from place. Most historical accounts have also focused on the period since the term biodiversity was coined in 1985. Yet older concepts, including direct predecessors like species diversity, were developed and refined over the course of the 20th century in conjunction with longstanding scientific efforts to understand the numbers and distribution of species––particularly in the tropics. My research on 20th-century tropical biological fieldwork led me to see direct connections between the development of field stations in the circum-Caribbean area and the rise of biodiversity as a scientific and conservation concept.

Beginning at the turn of the 20th century, with emergence of the science of ecology and, as I discussed in a previous post, the expansion of U.S. empire into the tropics, U.S. botanists and zoologists pushed for the development of stations for basic research on living tropical organisms in their natural environment. The first decades of the 20th century saw a spate of tropical station building as biologists adapted existing institutions or established new ones, including, Harvard’s Atkins Institution, Soledad, Cuba; the Cinchona Botanical Station, Jamaica; New York Zoological Society’s Kalacoon and Kartabo, Brit­ish Guiana (present-day Guyana); and Barro Colorado Island, Panama.

From a basic research standpoint, these stations were important because tropical species had largely been known to US and European scientists from dead specimens. In previous centuries, expeditions had allowed itinerant naturalists from the north to pass through the tropics, bringing back collections to the scientific centers of their home countries. But the new stations allowed researchers access to living tropical organisms in place, over time. This helped build up a much deeper knowledge of the natural history, behavior, and ecology of many tropical species previously little known to outsiders. Focused in situ research also enabled researchers to develop intensive monitoring and censusing practices. Camera trapping on Barro Colorado Island, Panama, in the 1920s and 1930s, for example, uncovered even very rare and hard to document species and helped to reveal population fluxes over time––significant given assumptions that tropical forests were ancient, stable, and unchanging.

Place-based fieldwork allowed biologists to study living organisms and populations, but taxonomic studies also remained quite important. In fact, it seemed that the closer biologists looked, the more species they found. Sifting through a pile of detritus gathered from four square feet of rainforest floor, naturalist William Beebe identified at least 500 worms, insects, and arachnids. He marveled at the vast number of creatures this must entail in a square mile, let alone the unbroken forest of the Amazon Basin. But to the nascent community of tropical biologists, the diversity of life always meant much more than just numbers of species. These scientists might count species, but their interests focused on uncovering life’s intricate adaptations to tropical environments and the range of behaviors and ecological relationships in which these species took part. Beebe’s experiment led him not to attempt to achieve a more rigorous count, but rather to lament how little scientists knew about the life histories of these animals.

The post-WWII period saw profound change in biological science, as experimental, physical, and quantitative approaches increasingly came to dominate. In this context one might expect a retreat to the laboratory or at least, perhaps, to relatively simple, species-poor communities in nature, such as those in the arctic. In fact, the rise of quantitative population biology and systems ecology after World War II was accompanied by and connected to an explosion of tropical field research. The infrastructure that enabled this research was, again, largely shaped by expanding U.S. government and corporate interests.

It is in this context that species diversity––the most immediate intellectual predecessor to biodiversity––emerged as a central theoretical concern in biology. Working in Costa Rica, Panama, Puerto Rico, and Brazil, biologists like Robert H. MacArthur, Howard T. Odum, and Theodosius Dobzhansky began to use species diversity as a quantitative index, capturing tropical life in a number that could be measured and modeled. Cutting through the complexity tropical environments, they examined a few mathematical variables––species diversity in relation to measures of foliage height, island size, or solar radiation, for example. Rather than exploring the lives of individual species and their complex interactions in a particular place, they formulated quantitative field techniques and abstract models that allowed researchers to make comparisons among ecological communities in the tropics and other regions. Tropical studies helped to fuel a new theoretical turn by the 1960s, as biologists asked themselves what ecological and evolutionary mechanisms could explain differences in species diversity that could be found across the globe.

As a scientific measure, the concept of species diversity found ready application in conservation beginning in the 1970s. Its specific, place-based origins largely forgotten, species diversity offered an abstract and apparently objective tool for making conservation priorities anywhere in the world. Conservationists could focus their efforts on the places with the most species. Yet, as the history of tropical biology suggests, numbers alone have not always been the primary way of viewing or valuing diversity in nature.


Megan Raby is assistant professor of history at the University of Texas at Austin.  You can read her earlier UNC Press blog post here.