Sample Proposal 1

Belowground ecosystem function in mantled howler monkey (Alouatta palliata) latrines

Panama, 2012


Problem Statement, Research Questions, and Research Objectives
Researchers have focused heavily on the role of neotropical primates in shaping forest growth and regeneration processes through seed dispersal. Recent studies have shown, however, that the organic waste that is deposited along with dispersed seeds increases belowground microbial activity (Neves et al. 2009), which may alter the functional performance of these soils. While often considered a “blackbox” of immeasurable interactions and thus underrepresented in ecosystem models, there is mounting evidence that soil microbial communities affect ecosystem functioning, creating feedback loops with aboveground flora and fauna (Strickland 2009, Wardle 2004). Examination of these cryptic communities is absolutely critical in order to understand the mechanistic processes that drive tropical biodiversity.

I request funding from the Tropical Resources Institute to study the functional significance of the belowground microbial communities within howler monkey (Alouatta palliata) latrines. My research will address the following questions:

(1) Do latrine soils exhibit altered belowground ecosystem function (e.g. mineralization, decomposition) relative to surrounding soils?

(2) Is microbial community composition in latrine soils taxonomically distinct from surrounding soils?

This project will serve as a pilot study for my dissertation research, which will address the localized effects of arboreal mammals on forest regeneration processes. Determining the functional significance (Q1) and taxonomic composition (Q2) of the belowground microbial community will lay the foundation for future projects that will focus on the effects of belowground activity on the seed competition.

Literature Review

In forest regeneration models, dispersal of seeds is often assumed to be even across the landscape or decrease with distance from the parent tree. In neotropical forests, however, up to 90% of tree species produce fruit and thus depend on vertebrates, primarily primates, to distribute seeds across the landscape in order to reproduce (Schupp et al. 2002). As a result, seed dispersal patterns are influenced by the behavioral ecology of the dispersers, including movement, resource selection and use, and defecation habits (Julliot 1997, Russo and Augsberger 2006, Lazo et al. 2010).

Howler monkeys (Alouatta palliata) alone may distribute up to 56 kg/ha of feces (Hanksi and Cambefort 1991). Because Alouatta tend to defecate as a group at the end of the day and upon arousal in the morning, the majority of this organic material is concentrated below sleeping sites (Julliot 1997, Neves et al. 2009, Hopkins 2010). Recent research on these group defecation sites (latrines) has shown that they exhibit greater diversity and density of seeds than surrounding soils, as well as increased rates of germination, seedling success, and sapling growth (Pouvelle et al 2009, Feeley and Terborgh 2005, Neves et al. 2009, Bravo 2011).

In addition to the distinct growth patterns in aboveground plant communities, latrine sites are also characterized by 50-150% greater soil respiration rates, indicating a more active microbial community. Soil microbial communities are responsible for a range of ecosystem functions, including mineralization of nutrients, carbon sequestration, litter decomposition, nutrient retention, and other processes that affect the physical properties of the soil. Recent research indicates that aboveground processes that influence belowground community composition andactivity (e.g. waste deposition, litterfall) can in turn affect the ecosystem functions that this community performs (Strickland 2009, Hawlena et al. upubl. data). These factors combined suggest that the emergent microbial communities at latrine sites may perform a distinct functional role in localized forest regeneration processes.

Field Site Selection and Justification

I will conduct this research at the Smithsonian Tropical Research Institute (STRI) on Barro Colorado Island (BCI) in Panama. BCI is an ideal location for this project because the ranging behavior of several A. palliata is well known from previous research (e.g. Milton 1982, Hopkins 2010). Furthermore, this project will add a belowground perspective to ongoing research on seed dispersal and competition, seedling success, and sapling growth.


This pilot study will begin with a field survey of resident Alouatta social groups. Through focal observations of uncollared animals, I will identify up to three latrine sites from which I will collect soil samples. For each latrine site I will identify an analogous non-latrine site to use as a control. Non-latrine sites will be similar in crown cover, plant growth, slope, soil type, light exposure, and litter composition. I will collect three 1L soil samples from each latrine and non- latrine site. I will use half of each sample for characterization of physical soil properties, and the remaining half for microbial community characterization.

Physical Soil Properties: I will characterize physical soil properties of latrine and non-latrine soils in order to get a baseline of nutrient content, pH, and soil respiration. I will dry and weigh each soil sample and measure soil nutrient content (N, C:N ratio) and pH of each sample using a CNH analyzer as described by Feeley and Terborgh (2005). Phosphorus content will be tested using an Olsen P test (Olsen et al. 1954). I will measure soil respiration of individual soil samples using procedures outlined by Neves et al. (2009), which will serve as a proxy for microbial activity.

Microbial Community Characterization: I will test the functional significance of microbial communities in latrine soils using the suite of tests outlined by Frey et al. (2004). I will divide the field samples into microcosm containers in order to test for properties relevant to ecosystem functioning, including active bacterial and fungal biomass, enzyme activity, microbial carbon sequestration, and mineralization. In order to determine taxonomic composition of the microbial communities, I will extract, amplify, and sequence DNA using a PowerSoil DNA Isolation kit (MoBio Laboratories, Carlsbad, CA) as outlined by Reed and Martiny (2007).

Personal Qualifications and Research Collaborations

I will conduct field sampling for this project following two consecutive seasons of field experience at the Smithsonian Tropical Research Institute. All sampling will be within the regulations outlined by the STRI Tropical Soils Laboratory. Physical soil characterization and ecosystem function testing will be conducted in collaboration with the Bradford Lab at the Yale School of Forestry and Environmental Studies. I will send samples away for DNA extractions and sequencing at the Smithsonian Genetics Program at the National Museum of Natural History.


Field work will take place during the 2012-2013 tropical dry season (November – April) in order to maximize observational periods and guarantee access to field sites.

December 2012

  • 20 - Arrive in Panama
  • 21-31 - STRI Field Training (Panama City, BCI)

January 2013

  • 1-15 - Focal Observations, Field Site Identification (BCI)
  • 15-22  - Field Site Identification (BCI) 23-30 Soil Collection and Storage (BCI)

February 2013

  • 1-13 - Processing of Soil Samples (Panama City)
  • 14-16 - Soil Processing, Packaging, and Shipping
  • 20 - Return to Yale

March 2013

  • 1-25 - Physical Properties, Ecosystem Function Testing (Bradford Lab, Yale)
  • 1-31 - DNA Analysis – Samples Sent Away (Genetics Program, Smithsonian)

April 2013

  • 1-30 - Data Analysis and Writing