presence-absence

Monitoring changes in occupancy (i.e., probability a site has at least one individual of a species) across time is considered an inexpensive alternative to monitoring changes in abundance and can be used to monitor multiple species simultaneously across a watershed. Occupancy can be measured as the proportion of sites where a species is detected during surveys (i.e., naïve occupancy), but is more commonly modeled by surveying sites multiple times to estimate detection probability and address false-positive survey errors (sites that are occupied but with no survey detections of the species...

Determining population trends for many aquatic species is problematic for most resource agencies because little or no historical information is available on population size nor are resources available for contemporary population estimates. Managers often only have available to them presenceabsence data collected by qualitative surveys conducted at intermittent intervals. Changes in naïve occupancy can be used to detect population trends. Naïve occupancy is the ratio of number of sites where a species is detected to total number of sites surveyed, without correcting for imperfect detection...