Geoscience Reference
In-Depth Information
ous statistical treatment of measured effects, results of such studies are of lim-
ited utility. Also, indices are sometimes used to infer direct effects (e.g., calcu-
lating capture-recapture rates to infer marking effects on survival), but if the
index also measures other aspects of species biology (e.g., dispersal), such infer-
ences might be spurious. Other evaluation studies are too short to derive
meaningful conclusions regarding long-term effects, even though the latter
effects may very well be the most demographically significant (see discussions
by Daly et al. 1992 and Berteaux et al. 1996). Finally, sometimes statistically
significant results are not considered to be biologically important because they
are too small or uncommon (Korn 1987). Each of these approaches reduces
the likelihood of identifying marker effects that may adversely affect the ani-
mal or the study results.
Our review of the marker evaluation literature reveals that a marker can
affect a variety of aspects of animal biology, and that different types of evalua-
tions provide different results. When biologists plan an evaluation of marker
effects or when they interpret and apply results from previous evaluations, they
must make decisions about which methods of evaluation are most appropriate
for their objectives and subject species. Also, they must decide which results
are most relevant to assessing the importance of an effect on the animals and
their study objectives. For example, a biomechanical analysis of the effect of a
marker provides an estimate of how much extra energy is needed to carry the
marker, but it does not determine whether that increase in energy expenditure
has other biological implications for the animal, such as reduced food delivery
to young. A metabolic measurement might not indicate a significant change in
O
2
or CO
2
between the marked and unmarked animals. Should we thus con-
clude there is no effect? Observations of behavior of the same animal might
reveal that the marked animals spend more time resting than unmarked ani-
mals. All these evaluations could produce “significant” results, and yet contra-
dict each other or provide different types of information. It is the responsibil-
ity of the researcher to conduct or consider the most appropriate marker
evaluations relevant to the study objectives and the well-being of the study ani-
mals. The biologist must decide which effects are important.
REVIEW OF CURRENT GUIDANCE AVAILABLE FOR CHOOSING MARKERS
Numerous criteria must be considered when selecting markers to be used in a
given ecological study, including potential effects of markers on animals (Mar-
ion and Shamis 1977; Day et al. 1980; Friend et al. 1994; Nietfeld et al. 1994;
Samuel and Fuller 1994). Researchers can review the literature, refer to col-
