Sanz, A., Igual, J.-M., Genovart, M., Oro, D., and Tavecchia G. 2016.
Estimating recruitment and survival in partially-monitored populations Journal Of Applied Ecology. in press. DOI: 10.1111/1365-2664.12580
Summary: In evolutionary and ecological studies, demographic
parameters are commonly derived from detailed information collected on a
limited number of individuals or in a confined sector of the breeding
area. This partial monitoring is expected to underestimate survival and
recruitment processes because individuals marked in a monitored location
may move to or recruit in an unobservable site.
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| Photo: http://www.markeisingbirding.nl/ |
We
formulate a multi-event capture–recapture model using E-SURGE software
which incorporates additional information on breeding dispersal and the
proportion of monitored sites to obtain unbiased estimates of survival
and recruitment rates. Using simulated data we assessed the biases in
recruitment, survival and population growth rate when monitoring 10% to
90% of the whole population in a short and a long-lived species with low
breeding dispersal. Finally, we illustrate the approach using real data
from a long-term monitoring program of a colony of Scopoli's
shearwaters Calonectris diomedea.
We
found that demographic parameters estimated without considering the
proportion of the area monitored were generally underestimated. These
biases caused a substantial error in the estimated population growth
rate, especially when a low proportion of breeding individuals were
monitored.
The proposed capture–recapture model successfully corrected for partial monitoring and provided robust demographic estimates.
Synthesis and applications.
In many cases, animal breeding populations can only be monitored
partially. Consequently, recruitment and immature survival are
underestimated, but the extent of these biases depends on the proportion
of the area that remains undetected and the degree of breeding
dispersal. We present a new method to obtain robust and unbiased
measures of survival and recruitment processes from capture–recapture
data. The method can be applied to any monitored population regardless
of the type of nests (e.g. artificial or natural) or breeding system
(e.g. colonial or territorial animals) and it only relies on an estimate
of the proportion of the monitored area. The unbiased estimates
obtained by this method can be used to improve the reliability of
predictions of demographic population models for species’ conservation
and management.
