By: Pedro A. C. Lima Pequeno
Graduate Program in Ecology, National Institute for Amazon Research, Manaus, Brazil
The abundance of organisms varies in space and time. The triviality of such observation tells little about its causes, though, and some people have spent a lot of their time trying to understand this and related questions: Why do some places in the world have so many different kinds of organisms, while other ones are seemingly lifeless? How do organisms affect the environment they live in, and how are they affected in turn? The list goes on, but why would anybody care about these things in the first place? It turns out that such interests can actually be very helpful: understanding biological phenomena allow us to make predictions about them in space and time and, eventually, control them.
Termites constitute a group of animals remarkably abundant and diverse in the tropics. Combining a diet based on the most copious biomolecule on Earth – cellulose – and a complex social organization, termites have achieved dominance in many environments. For instance, their collective biomass has been estimated in more than 1 ton/ha in a tropical rainforest in Cameroon, and they are responsible for the respiration of up to 38,7% of the local organic carbon stock in some African savannas.
Not bad for citizen roaches. It has been long believed that termites are closely related to cockroaches, based on their shared gut microorganisms and some morphological traits. However, recent studies of DNA relatedness strongly suggest that termites are not only roach cousins, they are roaches themselves – albeit very modified ones. Apparently, primitive termites looked a lot like today’s relict roaches in the genus Cryptocercus, which live in familial groups and feed on dead wood. Also interesting is the fact that the oldest known termite fossils come from the Lower Cretaceous (145 – 99 million years ago), which suggests an even earlier origin for the group. This makes termites the oldest social animals currently alive in the whole world!
Despite all these remarkable features, quantitative information on colonies and populations of termites, as well as other social insects (i.e. ants, some bees and wasps), is still scant. This is unfortunate since these levels of biological organization are perceived as directly related to important ecological/evolutionary processes such as growth, survival and reproduction. Most detailed research to date on termite interactions with their environment has been carried out in Africa, mainly by European researchers. This is probably why this continent is considered the richest in described termite species.
Other regions, such as South America and Southeastern Asia are also termite-rich, but research in these areas has also been comparatively less intensive. Namely, the Neotropical (i.e. South and Central Americas) termite fauna is the second largest in species richness, but still poorly known. Basic information on most species is inexistent. Nevertheless, the past decade has seen a renewal in the interest for termites in South America, especially in Brazil, the only country in the continent with a relatively well-established tradition in termite studies.
In South America, nests built by termites are numerous in several environments, especially savannas (e.g. the Venezuelan “llanos” and the Brazilian “cerrado”). Although less evident in denser vegetation, around 30% of all known termite species inhabiting South American rainforests build conspicuous structures. Among these is the Amazon rainforest, with its ca. 5,5 million km2 – over half the area still covered by such vegetation type worldwide. Most of the forest is in Brazilian territory, where the region is known as Amazônia.
Overview of the Amazon rainforest
Amazonian forests can be classified in two groups: those that experience annual flooding, and those that do not. The former include so-called igapó, swamp forests flooded by black rivers (i.e. with high content of organic acids) and várzea, plains with sparse tree vegetation flooded by white rivers (i.e. with high content of clay). Non-flooded forests are known as terra firme forests. In central Amazon, altitude varies from 60 m to 120 m, and this variation is strongly correlated with soil type: highlands are clayish, whereas valleys are sandy. The former are known as platô forests, and the later as baixio forests. The soil gradient imposes many other gradients of biological relevance: vegetation structure, animal assemblages and environmental processes such as decomposition all change along with the soil. The region is not only convered by rainforest, though; there are several patches of savannas, as well as sparse vegetation on sandy soils (known in Brazil as campinas). Besides, the Amazon rainforest itself stands on two distinct geological formations: most of it grows on the largest watershed in the world, the Amazon basin, which drains an extensive plain of about 7 million km2; its northern part, however, is on the highlands of the Guyana shield.
The Amazon harbors some 238 described termite species, almost half the Neotropical termite fauna and 8% of the world termite species. Since large parts of the region have never been surveyed for termites, these numbers are most probably underestimates. The American researchers Alfred Emerson and Thomas Snyder provided the foundations of Amazonian termitology (i.e. the study of termites) during the first decades of the 20th century, describing many (then) new species. Later, from the 1950s to 1978, the Brazilian biologist Renato Araujo assembled the termite collection of the Museum of Zoology at São Paulo University, Brazil, nowadays the largest one in Latin America. More recent work has been fostered by specialized research groups, such as the Laboratories of Termitology at Brasilia (http://vsites.unb.br/ib/zoo/catalog.html) and Viçosa (http://www.isoptera.ufv.br) Universities, both in Brazil.
Why are there so many termite species in the Amazon?
As with many other living groups, termites tend to be more diverse in tropical regions. Climate stability during long periods of time at low latitudes – low seasonality, with warm temperatures throughout the year – has likely helped organisms make their living, both allowing new species to arise and preventing older ones to go extinct.
Although termites are generally known as pests for obtaining cellulose from wood – “termite” comes from Latin termites (anciently termes or tarmes), “wood-eating worm” –, more than half of all termite genera feed on soil. Extracting recalcitrant cellulose from soil humus is no easy task, but termites have evolved terrific biochemical machinery that allows the gut pH of some species to be higher than 12 – the highest known alkalinity in the living world! This helps termites explore the thick humus layers under tropical rainforest canopies, and many of these soil-feeding species actually live in their food. Termites that inhabit and feed on soil generally have bodies that are softer than those of other species. This makes them especially susceptible to dehydration and easier to go extinct under deforestation effects. The German biologist Christopher Martius once (and somewhat poetically) entitled rainforest termites “dwellers in the darkness” – a clever title, since most termites are also eyeless.
There have been several termite surveys in the Brazilian Amazon; most studies have focused on describing new species and patterns of termite diversity. In Brazil, termites are known by two names: térmitas, introduced by the Portuguese, and cupins, as the natives called them. Cupim comes from kaapi, which means “mound” in the Tupi language. The Amazonian termite fauna is composed mainly by members of two families, Rhinotermitidae (a.k.a. subterranean termites) and Termitidae (the most diverse one), but mostly the later. Other groups, such as the Kalotermitidae (a.k.a. dry wood termites), are also present but much less abundant, often restricted to the core of tree trunks and dead branches in the canopy. Among the Termitidae, the subfamilies Nasutitermitinae, Syntermitinae, Termitinae and Apicotermitinae are present. Macrotermitinae species (i.e. fungus-growers), known from their large, easily spotted mounds in some other tropical regions, are absent from the New World.