Field Guide of Discovery-based Exercises for - Aseanipm ...

Section 4 • Integrated Insect and Rodent Pests Management
Exercise No. 4.16 162
RODENT POPULATION DYNAMICS: A GROUP
DYNAMICS EXERCISE AS WELL
BaCKGroUND aND raTIoNalE
A female rat specimen can be dissected to determine
incidence of pregnancy. This process can be used to
predict probable rodent population outbreaks even before
establishment of a vegetable crop. Scientists have provided
procedures for estimating annual productivity at pregnancy
and lactation of rodents (e.g., Rattus argentiventer and
Rattus rattus mindanensis) by employing these equations 163 :
• Incidence of pregnancy multiplied against mean litter size at gestation period (18 days) gives a
good estimate of a rodent’s potential productivity; and
• Incidence of lactation multiplied against average litter size at late weaning period (21 days)
gives an estimate of annual productivity of rodents.
However, rodents are known to regulate their own number in the presence of extreme numerical
abundance or increased competition for food and space resulting in population stress. Evidences
involving active self-regulation include delayed rate of maturity, obesity in mature females, absence
of sexually precocious young, reduce litter sizes, and severe drop in pregnancy and lactation. Selfregulation
as a function of survival may provide a reverse mechanism for depleted population,
including those resulting from reduction control programs, to recover their number to a level of their
carrying capacity 164 .
Nevertheless, rodent populations increase very rapidly because they, very often, have many
offspring. In FFS, a simulation exercise can be undertaken to visualize simple population growth
for one year. This activity was designed to understand rodent population dynamics.
162 Adapted from Callo, Jr. D.P., A.G. Castillo, and C.A. Baniqued (eds). 2001. Field Guide of Discovery-based Exercises for Corn Production. SEAMEO
Regional Center for Graduate Study and Research in Agriculture (SEARCA), College, Laguna, Philippines. pp360-362.
163 Davis, D.E. 1953. Characteristics of rat populations. Quar. Rev. Biol. 28(4): pp373-401.
164 Sumangil, J.P. 1990. Control of ricefield rats in the Philippines. In Quick, G.R. (ed). 1990. Rodents and Rice. Report and Proceedings of an Expert Panel
Meeting on Rice Rodent Control held on 10-14 September 1990 at International Rice Research Institute, Los Baños, Laguna, Philippines. pp35-48.
241
when is this exercise most
appropriate?
ɶ In FFS, TOT and VST
sessions, immediately
after crop establishment
in learning field; and
ɶ When farmers want to
learn and understand
rodent population
dynamics in their organic
vegetable fields.