The litter-sifting lifestyle: Capturing ant diversity on Middle American mountains

Submitted by editor on 15 June 2018. Get the paper!
Fidel Vega, Saslaya National Park, Nicaragua, May 2011. Photo by Michael Branstetter.


By John Longino

MIGUEL! The shout echoes through the forest. It is dawn, in a cloud forest on an isolated group of mountains in eastern Nicaragua. Fidel Vega, a former soldier in the Sandinista army, is our Nicaraguan guide and expedition organizer, rousting our field crew from their scattered tents. "Miguel" is Michael Branstetter, my colleague and one of the co-creators of the project "Leaf Litter Arthropods of MesoAmerica". "FIDEL!" he shouts back, already up and bustling. Our crew includes students from Nicaragua, Canada, and the United States. They begin to emerge, groggily greeting each other with their developing Spanish and English, grateful that the violent electrical storm and downpour during the night didn't send any branches crashing down from the giant trees above our camp. Smoke from the cook tent draws us to breakfast, after which we gather sifters, machetes, tape measures, sample bags, gps units, and compasses and head out to our transect sites. By the end of a long day of attempting to walk straight lines in dense forest and rugged terrain, chopping and sifting square meter plots of leaf litter and rotten wood, carrying the litter samples back to camp, and loading the Winkler bags (a passive extraction device for collecting small arthropods), we have the 100 samples successfully suspended, tiny ants and beetles beginning to accumulate in each small sample bag.

Winkler bags extracting microarthropods from leaf litter samples, Saslaya National Park, Nicaragua, May 2011. Photo by Michael Branstetter.

Similar scenarios have played out over 50 times now, in wet forest sites from southern Mexico to Costa Rica, generating the dataset that appears in this Ecography paper. In tropical forests, the thin layer of leaf litter and rotting wood on the ground is home to a diverse community of tiny arthropods, what Mike Kaspari calls the "brown food web." In rainforests, about 60% of ant species occur in this zone, and it is clearly the evolutionary cradle for ants, with the greatest phylogenetic diversity. Our Winkler sampling provides a quantitative snapshot of this community for the entire Middle American corridor. This Ecography paper, showing a particular relationship of diversity to elevation, is an example of how a large-scale and sustained quantitative inventory like this can improve our knowledge of tropical diversity. The samples are a wellspring for research, and studies are underway that use DNA sequences from the sampled ants to examine the evolution of montane specialization across this large landscape.

Animated video on ant field work by Jennie Kunitake and Ryan Buck:​

The planning and execution of this sampling effort drove home for me the magnitude of the conservation imperative in this part of the world. Our goal was always to find sites of mature evergreen forest, from sea level to mountaintops. Choosing sites involved looking at Google Earth and finding whatever green patches we saw. Getting to them often involved days of travel through agricultural landscapes. Site selection was not based on some design principle, but rather on whatever was left. The litter fauna of these mature forest patches is far more diverse and with much higher regional endemism than the surrounding matrix of lands with high human impact. Large areas of evergreen forest were probably the norm for most of the Pleistocene, the context in which much of the species-level diversity evolved. The combined insults of interglacial warming, human arrival in the Americas and the introduction of fire, the accelerated clearing activities of the last 500 years, and now global climate change have reduced these distinctive mature forest communities to shrinking remnants. Regardless of whether or not we are successful at conserving or recovering patches of mature forest, this may be our last chance to get a clear picture of what biodiversity in the Americas looked like prior to human impact.

Border between mature cloud forest and cow pasture. Guatemala. Photo by Michael Branstetter.

Slash-and-burn agriculture in lowland rainforest, Guatemala. Photo by Michael Branstetter.

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