Physiological Ecology of Amphibians in Relation
to Susceptibility to Natural and Anthropogenic Factors
Christopher L. Rowe, Wiliam A. Hopkins, Christine M. Bridges
Introduction
In nature, animals must employ strategies that allow them to optimize
fitness under the range of environmental conditions to which they are
exposed. When conditions diverge significantly from the combinations that
are necessary for optimizing fitness, population- level changes may emerge.
The type of response that will occur at the level of the population will
depend upon genetic phenomena responsible for phenotypic plasticity and
the potential for or constraints acting against adaptation to new conditions.
Genetic aspects of populations relative to adaptability of amphibians
to changing environments will be dis- cussed in Chapter 2B. Here we are
concerned with characteristics of individuals that may make them susceptible
to or tolerant of certain environmental changes.
The causes and consequences of population declines cannot be examined
fully on the basis of only population or demographic trends because environmental
agents (biological, physical, or chemical) have their direct effects on
individuals, and the responses of individuals determine population dynamics
via changes to survival, growth, or reproduction. Hence, an examination
of processes occurring at the individual level is required so that some
mechanism for population changes in response to environmental changes
can be identified (see Figure 2A-1).
In contrast to most experimental situations, amphibians in field settings
are rarely faced with a single environmental challenge. Rather, numerous
chemical, physical, and biological factors may ultimately be modified
when anthropogenic or natural changes to the environment occur. For example,
human activities often result in chemical contamination of habitats by
complex mixtures of contaminants rather than by a single type of contaminant.
Terrestrial landscapes modified by human activities may present amphibians
with numerous challenges simultaneously, such as changes to temperature,
humidity/moisture, habitat heterogeneity, or prey base. Susceptibility
to pathogens may change with the presence of other chemical or physical
factors in the environment (e.g., Carey and Bryant 1995). Thus, interactions
with numerous and often disparate environmental variables requires that
individuals have the physiological capacities to respond to multiple challenges
in order to minimize deleterious effects (Figure 2A-2).
SREL Reprint #2765
Rowe, C. L., W. A. Hopkins and C. M. Bridges. 2003. Physiological ecology of amphibians in relation to susceptibility to natural and anthropogenic factors. p. 9-57. In Amphibian Decline: An Integrated Analysis of Multiple Stressor Effects, edited by G. Linder, S. Krest and D. Sparling. Society of Environmental Toxicology and Chemistry.
