AMER. ZOOL., 32:151-153 (1992)
Introduction to the Workshop: Biophysical Ecology:
Methods, Microclimates, and Models'
JAMES R. SPOTILA AND MICHAEL P. O ' C O N N O R
Department of Bioscience and Biotechnology, Drexel University,
Philadelphia, Pennsylvania 19104
and
Savannah River Ecology Laboratory, Aiken, South Carolina 29802
and thermal radiation that sets the physical
boundaries, the microclimate, within which
an animal must live. To use a baseball analogy, this is like placing the animal into the
ball park. By solving the energy budget
equation for various combinations of real
conditions measured in an animal's habitat
we can track its location within the climate
space through time (Morhardt and Gates,
1974; Scott et al, 1982; Standora, 1982).
This is like locating a baseball player in the
infield.
Beyond the climate space, biophysical
ecologists have used time dependent equations to predict behavioral limits for animals (Porter et al, 1973; Porter and James,
1979; Christian et al, 1983; and others).
Potential for predator-prey interactions can
also be predicted (Porter and Tracy, 1974;
Christian and Tracy, 1981). However, the
outcome of specific encounters depends not
only upon biophysics, but also upon physiological performance variables (see Pough
[1989] for review) and stochastic factors.
Thus, we may be able to define who is on
first, who is playing second, and who is
catching, but cannot predict the outcome of
an attempted steal or the final score of a
particular ball game. Nevertheless, it is easier to understand baseball if we know the
rules of the game and easier to predict the
winner of the World Series if we know, not
only the rules, but also the conditions under
which the games will be played (dome or
open stadium), and the abilities of the players on the two teams. Biophysical ecology
provides the equations (rules), and the
methods for defining the microclimates
(game conditions) within which animals
interact. Data from its sister field of physiological ecology provide information on
1
From the Workshop on Biophysical Ecology: Meth- physiological performance (abilities of the
ods, Microclimates, and Models presented at the Annual players). Combined, these provide a clearer
Meeting of the American Society of Zoologists, 27-30 understanding of ecological relationships
Although Charles Darwin carried out
experiments on the effects of sleep movements of plants on leaf temperature, the
application of physics to ecological studies
is a relatively recent phenomenon. Biophysical ecology dates to the 1950s when
Gates and Tantraporn (1952) examined
infrared reflectivity of plants and Raschke
(1956) investigated the energy exchange of
leaves. A generation of ecologists read
Energy Exchange in the Biosphere by Gates
(1962) and plant ecologists integrated biophysical measurements into their research
with great success. Animal ecologists, however, have more often treated biophysical
ecology as an arcane art practiced by a few
initiates, and as a group, have not integrated
biophysical assessments into studies of
competition, population dynamics, and
behavior. This is unfortunate because biophysical ecology has much to contribute to
other branches of ecology.
A knowledge of physics is essential to our
understanding of ecological processes. Plants
and animals exchange energy, gases, nutrients, and water with their environment and
the laws of physics set the stage upon which
the ecological play is acted out. The goal of
biophysical ecology is not to reduce biotic
interactions to mathematical formulae for
their own sake, rather it is to define the
physical boundaries within which organisms must operate. This was the reason the
"climate space" (Porter and Gates, 1969)
was developed. Using relatively simple
steady state equations an ecologist can produce a visual representation of the interaction of temperature, wind speed, and solar
December 1989, at Boston, Massachusetts.
151
152
J. R. SPOTILA AND M. P. O'CONNOR
and allow us to predict interspecific interactions on a population scale.
Biophysical ecology is no more mathematical than population ecology, no more
rigorous than physiological ecology, and no
less observational than behavioral ecology.
It can add to any ecological study by providing a quantitative description of microclimates and the ability to predict intra- and
interspecific interactions by using mathematical models with appropriate levels of
sophistication. The purpose of this Workshop, held at the ASZ Centennial Meeting
in Boston in December, 1989, was to make
the methods and models of biophysical
ecology more accessible to animal ecologists. In a series of formal presentations,
informal discussions, and a display of
instruments, participants shared information and approaches to biophysical problems. The peer reviewed articles presented
here are the completion of that Workshop
process.
The first four articles discuss how to do
biophysical ecology. Grant and Porter consider global models while O'Connor and
Spotila present an approach to modeling that
asks "When do short cuts matter?" One of
the most successful methods in biophysical
ecology has been the use of Te models to
measure operative temperatures of animals
(Bakken and Gates, 1975). This technique
evolved from the use of hollow copper models by Winslow et al. (1937) to measure the
thermal environment of humans. The techniques used to make the first copper lizards
were based on those used for plaster and
agar salamanders by MacMahon (1964) and
Spotila (1972). While most of us in Gates'
research group thought that Te models would
provide an economical alternative to the
expensive equipment needed to carry out a
full scale biophysical ecology study, none of
us anticipated the explosion of studies that
would make use of this technique. In his
article, Bakken reviews these studies and
provides new insights into the application
of Te models in ecology. Measurement of
radiant heat loads on animals is a particularly difficult task and has received increasing attention since the insightful work of
Cena and Monteith (1975). The fourth article, by Walsberg, considers some general
approaches to quantifying radiative environments and estimating radiative heat
loads on animals.
The last two articles consider the application of biophysical ecology to specific animal groups. Casey addresses the biophysical
ecology and heat exchange of insects and
demonstrates that a biophysical approach is
a powerful tool for predicting body temperatures of insects. Karasov discusses the
utility of energetic increments for activity
in time-energy budgets, thermal energy
budgets, and analyses of foraging economics. These two presentations demonstrate
the utility of biophysical ecology in answering specific questions about animal ecology.
None of the authors of this workshop proceedings model for the sake of modeling.
Biophysical ecology has an important role
to play in ecology now and in the future. It
provides a framework for asking questions
about the role of abiotic and biotic factors
in the ecology of animals and the tools necessary to answer those questions.
ACKNOWLEDGMENTS
This workshop was supported by grants
from the Department of Energy to the
Savannah River Ecology Laboratory (DEAC09-76SROO-819) and Drexel University (DE-FG02-88ER 60727), and by the
American Society of Zoologists.
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