Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8324
Title: Assessing spatial covariance among time series of abundance
Author: J. C. Jorgensen, E. J. Ward, M. D. Scheuerell, Richard W. Zabel
Publication Year: 2016
Journal: Ecology and Evolution
Volume: 6
Issue: 8
Pages: 2472-2485
Keywords: Chinook salmon, Columbia River, dynamic factor analysis, metapopulation, multivariate autoregressive state-space models, population spatial structure, species diversity,

For species of conservation concern, an essential part of the recovery planning process is identifying discrete population units and their location with respect to one another.  A common feature among geographically proximate populations is that the number of organisms tends to co-vary through time as a consequence of similar responses to exogenous influences.  In turn, high covariation among populations can threaten the persistence of the larger metapopulation.  Historically, explorations of the covariance in population size of species with many (> 10) time series has been computationally difficult. Here we illustrate how dynamic factor analysis (DFA) can be used to characterize diversity among time series of population abundances, and the degree to which all populations can be represented by a few common signals.  Our application focuses on anadromous Chinook salmon (Oncorhynchus tshawytscha), a species listed under the US Endangered Species Act, that is impacted by a variety of natural and anthropogenic factors. Specifically, we fit DFA models to 24 time series of population abundance and used model selection to identify the minimum number of latent variables that explained the most temporal variation after accounting for the effects of environmental covariates.  We found support for grouping the time series according to 5 common latent variables. The top model included two covariates:  the Pacific Decadal Oscillation in spring and summer.  The assignment of populations to the latent variables matched the currently established population structure at a broad spatial scale.  At a finer scale there was more population grouping complexity.  Some relatively distant populations were grouped together, and some relatively close populations—considered to be more aligned with each other—were more associated with populations further away.  These coarse– and fine–grained examinations of spatial structure are important because they reveal different structural patterns not evident in other analyses.

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Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.