CONCLUSIONS
In this study we tested if sample counts allow the detection of
population trends in a wild mountain ungulate, using simulated and real
census data. We show that in most of the cases in which sampling the
entire area would be able to detect population trends, sample counts in
only half of the sectors have a sufficient statistical power to draw
reliable conclusions about the population trend. Furthermore, a very
small proportion of the total area is required to detect a strong trend
even in a short period. Therefore, in taxa such as mountain ungulates,
for which the cost of monitoring is high, sample counts could constitute
a viable alternative to reduce the amount of resources needed for
censuses, to monitor a higher number of populations of the species and
to detect rapid changes of conservation interest. The results can be
potentially extended to other species of mammals, especially those who
exhibit a long generation time, and sample counts could be used
successfully and extensively to reduce costs of monitoring.
Nevertheless, the applicability of the method to species that exhibit
high trend variability or with a short generation time should be
carefully evaluated. Furthermore, as estimating population trends under
high trend variability and weak trends on a short term is challenging,
long-term monitoring is fundamental to correctly assess population
dynamics of wild animals. At last, abundance extrapolated from sample
counts could be biased compared to that estimated with complete counts
in the entire target area, and for this reason sampling the entire area
is probably still a preferable option (where there are adequate
resources) to estimate abundance instead of the population trend.
Future developments of this study can include evaluating the
effectiveness of sample counts with real census data from other ungulate
and non-ungulate species, testing the applicability of the method to the
wider possible number of species, or investigating in other systems the
effect of detectability and of a biased sector selection, in order to
identify cheaper census procedures also in other species.