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Temporal Dynamics of a Rainforest Leaflitter Ant Community, Osa Biodiversity Center, Costa Rica

This site reports the results of repeated sampling of the leaf litter ant community in a mature lowland rainforest at the Osa Biodiversity Center, on the Osa Peninsula, Costa Rica.

A hallmark of tropical rainforests is their high species diversity. A single hillside may harbor hundreds of tree species, hundreds of bird species, dozens of mammal species, and tens of thousands of insect species. As is true everywhere, species vary in abundance, with some species being common and others being rare. Abundances of species also change over time. Ecologists have long been interested in describing and explaining patterns of abundance among species and over time.

The most thorough examination of tropical species abundance patterns has been of trees. Scientists have established 50 ha plots in rainforests around the world, documenting tree species diversity and abundance in each one. Some of the plots have been re-measured multiple times, providing insights into the dynamics of community structure. To establish and maintain these plots has been a large-scale international effort involving hundreds of scientists and continual funding. It is a challenge to obtain long-term ecological datasets because most funding options are directed at projects with immediate goals and short timeframes.

Undergraduate field courses can operate for many years, with repeated visits to the same field sites. Teaching and research can be combined in a way that allows students to experience field research while contributing to a long-term ecological dataset. The project reported here measures and monitors the diversity of the leaf litter ant community at the Osa Biodiversity Center, relying on the contributions of multiple student groups over time.

Why ants? Ants are one of the few groups of invertebrates that everyone knows, and they are the subjects of intensive scientific investigation. They are omnipresent in most terrestrial ecosystems, forming a mantle of nests and foragers. They make up a large proportion of the animal biomass, and they interact with the biota as predators, scavengers, prey, herbivores, and mutualists. Compared to trees, ant communities are expected to be more dynamic and respond more rapidly to climate change. 

Why leaf litter? The leaf litter layer in tropical wet forests is a phenomenal zone of compressed biodiversity, intense biotic interactions, and key ecosystem processes. It is where soil is formed, carbon stored or respired, nitrogen fixed or released, plant nutrients bound or made available. About 60% of the Neotropical ant fauna occurs in the litter and rotten wood, and it is the microhabitat in which ants first evolved and the most primitive forms are found. Many leaf litter taxa have a specialized way of life and feature adaptations such as reduced eye size and poor powers of dispersal. As such they can be expected to reflect patterns in diversity on a much more local scale than do more vagile taxa. Leaf litter also has the advantage of being easily accessible and sampled quantitatively with well-established techniques.

Wet forest litter ant communities are quantified with miniWinkler samples. One square meter of forest floor is chopped with a machete, the chopped material is placed in a sifter and shaken, the particulate matter that falls through the sifter (which includes most of the small insects and other arthropods) is saved and returned to a lab or shelter. There the sifted material is suspended in thin mesh sacks that are enclosed in an outer bag that tapers to a container of preservative. Over several days the small arthropods work their way out of the suspended material and drop into the preservative. These samples are later processed in the lab, extracting and identifying the ants. The ants are stored in permanent museum collections, allowing further examination and reidentification. A great video of the miniWinkler sampling process was made by students Jennie Russ and Ryan Buck.

Three sets of miniWinkler samples have been taken in the same location at the Osa Biodiversity Center. The plot is in primary forest, with 60 samples taken in a 50 x 250 m area. These first two sample sets were taken by the Tropical Rainforests class of the Evergreen State College, in 2008 and 2010. The 2014 samples were taken by the Tropical Field Biology course of the University of Utah. Details of the methods from each year's sampling can be found by navigating to those years in the sidebar.