Distinguishing distribution dynamics from temporary emigration using dynamic occupancy models. Issue 12 (22nd July 2017)

• Record Type: Journal Article
• Authors: Valente, Jonathon J.; Hutchinson, Rebecca A.; Betts, Matthew G.
• Editors: Matthiopoulos, Jason
• Is Part Of: Methods in ecology and evolution. Volume 8:Issue 12(2017)
• Page Start: 1707
• Page End: 1716
• Publication Date: 2017-07-22
• Subjects: closure assumption -- colonization -- detection probability -- dynamic occupancy models -- extinction -- metapopulation -- Pollock's robust design -- temporary emigration; Ecology -- Periodicals; Evolution -- Periodicals; 577
• DOI: 10.1111/2041-210X.12840
• Languages: English
• ISSNs: 2041-210X

Abstract

Abstract: Dynamic occupancy models are popular for estimating dynamic distribution rates (colonization and extinction) from repeated presence/absence surveys of unmarked animals. This approach assumes closure among repeated samples within primary periods, allowing estimation of dynamic rates between these periods. However, the impact of temporary emigration (TE; reversible changes in sampling availability) on dynamic rate estimates has not been tested. Using simulated data, we investigated the degree to which TE could mislead researchers interested in quantifying dynamics. We then compared results from three avian point count datasets to evaluate the likelihood that TE confounds estimates of dynamics for 19 species under a popular sampling protocol. Simulated experiments indicated that when secondary periods were open to TE, presence of dynamics was correctly identified ≥95.1% of the time, and dynamic rate estimates were accurate. However, dynamic rate estimates were biased when secondary periods were closed to TE. In empirical datasets, dynamic occupancy models had greater support than closed models for all species when secondary sampling periods occurred in immediate succession (i.e. 3 samples within 10 min); however, our results suggest that this is because dynamic estimates were heavily influenced by TE. When counts within a primary period were separated by 24–48 hr, we found evidence of dynamics for less than half of these species. We recommend an alternative sampling approach that allows accurate estimation of dynamic rates when TE is of no interest, and introduce a novel model for estimating both processes simultaneously in rare cases where they are both of biological interest. Concern for violating the occupancy modelling closure assumption has led to widespread recommendations that samples within primary periods be conducted extremely close in time. However, this may not be the best approach when interest is in quantifying dynamic rates. While dynamic occupancy models provide estimates of "colonization" and "extinction, " these values do not inherently represent dynamics unless TE has been explicitly modelled or accounted for with sampling design. Naiveté to this fact can result in incorrect conclusions about biological processes.