Tuesday, April 10, 2018

Focal Tree Method (FTM) of Observational Study (Clara B. Jones, 1976)


Focal Tree Method (FTM) of Observational Study (Clara B. Jones, 1976)


A standard procedure in studies of plant ecology and entomology is the use of the "focal tree" method (FTM) to obtain data on the behavior of trees themselves (e.g., phenophase and its variability through T, flower-opening T, changes over T in fruit, flower, or new leaf mass) and/or of insect density, abundance, and behavior in relation to tree behavior over T (and, sometimes, S). In general, trees in a given plot or area are sampled on some schedule, preferably, though not necessarily, random. The FTM is best employed whenever the distribution, abundance, behavior, etc. of the plant (tree, shrub, epiphyte, etc.) is expected to be an independent variable inducing dependent responses in other organisms [most commonly insects: e.g. Frankie et al., 1976; I learned the technique watching Gordon Frankie & his assistant, Bill Haber and transferred the method to mantled howler monkeys (Alouatta palliata Grey)]. Scientists have been slow to apply the FTM to vertebrates, perhaps because research on vertebrates generally entails following animals over T and S to record their behavioral interactions with conspecifics (social behavior) and making the focal animal him/herself the target of observation. While this research strategy may yield important information about foraging and other behaviors by individuals and groups, target animals and variations in their behaviors are the primary focus of data-collection, minimizing the influence of variations in plant behavior on animals as well as quantifiable events ongoing in plant food resources (e.g., variations in animal behavior as a function of tree size, species, and phenophase, variations in animal behavior as a function of competition with other organisms for plant tissues and other products such as nectar and pollen). In 1983, using the FTM, Jones reported selectivity of legume flowers (Pithecolobium saman: see image of flower) at flower-opening time by mantled howler monkeys. In 2005, the same author published results for selectivity by mantled howlers for legume flowers at anthesis with the FTM. In another research project (Jones, 1976, unpublished), the FTM was used to quantify howler density and order of entry into trees x monkey age and sex as a function of tree size, phenophase, species, and habitat (tropical dry forest riparian or deciduous: Frankie et al., 1976). One or more observers may be employed with the FTM, the latter approach used in studies recently reported by Vogel and Janson (e.g., 2011). Depending on the precise design of studies employing the FTM, data are amenable to mathematical simulation or other mathematical modeling after data are collected. Alternatively, the Vogel and Janson report cited uses a quantitative model to evaluate aggressive behavior in capuchins as a function of plot size. The success of the studies discussed herein and the rich information they provide highlight the value of the FTM for research with vertebrates using plants for food.

Frankie, G.W. et al. 1976. Foraging behavior of solitary bees: implications for outcrossing of a Neotropical tree species. J. Ecol. 64: 1049-1057.

Jones, C.B. 1983. Do howler monkeys feed upon legume flowers preferentially at flower-opening time? Brenesia 21: 41-46.

Jones, C.B. 2005. Discriminative feeding on legumes by mantled howler monkeys (Alouatta palliata) may select for persistence. Neotropical Primates 13(1): 3-8.

Vogel, E.R. & Janson, C.H. 2011. Quantifying primate food distribution and abundance for socioecological studies: an objective consumer-centered model. Int. J. Primatol. DOI: 10: 1077/s10764-011-9498-7