SCHERER, JACQUELYN*, GARLAND R. UPCHURCH, JR., and MARGARET J. KNAUS. Department of Biology, Southwest Texas State University, San Marcos, TX 78666. - A laboratory exercise for teaching plant-climate relationships.
Students of Biology often ask questions such as, “How can anyone know
what the vegetation and climate were like millions of years ago?” A
related concept that many students find difficult is the role of
modeling in science. Paleobotanists estimate temperature and
precipitation for the distant geologic past through the functional
morphology of fossil plants, and in particular features that correlate
with modern climate, such as the shape and size of leaves. We
demonstrate the basis for inferring past climates, plus the role of
scientific modeling in paleobotany, through a laboratory exercise in
which students use the leaf physiognomy of modern vegetation to
estimate mean annual temperature and precipitation for their local
region. Students divide into working groups, collect samples of leaves
from a local forest, segregate their leaves into species, then
calculate: 1) the percentage of species with toothed margins, and 2)
average leaf size. Students then estimate local climate by fitting
their data to graphs that relate the percentage of species with
toothed margins to mean annual temperature (MAT), and the natural
logarithm of average leaf size to the natural logarithm of mean annual
precipitation (MAP). For San Antonio, Texas, students estimate a MAT
of 16 °C and MAP of 77 cm (average of 25 working groups), close to
average values of 20 °C and 76 cm derived from meteorological data.
The laboratory exercise demonstrates the basis for estimating past
climate from trends in living species and provides a venue for
discussing issues of study design, sampling error, and biases caused
by the misidentification of species. It is designed for the
high-school classroom but is adaptable to the university and younger
grade levels. Students develop an appreciation for how scientists
reconstruct the past and for the breadth of information that can be
inferred from fossil plants beyond simple identification.
Key words: climate, laboratory, modeling, plant, teaching