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research project (Jones, 1976, unpublished), the FTM was used to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