American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Incorporating the connectivity timescale in metapopulation partitioning”

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Christopher M. Aiken and Sergio A. Navarrete (Aug 2020)

A new subpopulation scheme that considers the number of generations is developed

Read the Article (Just Accepted)

The distribution of organisms across the landscape tends to be neither homogeneous nor neatly clumped, but rather somewhere in between. To be able to manage a species, however, it is often useful to divide the individuals into groups, based on how strongly they interact with their neighbours. This study, undertaken by scientists from the Coastal Marine Research Station in Las Cruces, Chile, takes a new look at how best to partition a group of individuals – a “metapopulation” – into some small number of “compartments” or “subpopulations”. The study's novelty resides in the consideration of generations – quantifying the degree of interaction between groups of individuals by the number of generations required for genes to get from one to another. By redefining the metapopulation partitoning problem following this basic concept, a consistent and simple way to calculate the compartments is shown to be possible. By way of example a simple and efficient algorithm is used to partition the deep ocean based on the time required to drift from one point to another, as determined from drifting ocean buoys. After multiple one year generations the initial complex pattern of deep ocean connectivity gives way to a remarkably coherent spatial pattern of groupings. The example is used to discuss challenges for conservation of the orange roughy fisheries of the northen and southern hemisphere, given the large number of generations required for genetic information to transit between the two subpopulations.


Abstract

The often complex spatial patterns of propagule dispersal across a metapopulation present a challenge for species management, motivating efforts to represent the connectivity in more simple but meaningful ways. The reduction of complexity may be achieved by partitioning the metapopulation into groups of highly connected patches, called “subpopulations”. In order to have relevance for management, these subunits must be defined from ecological or evolutionary principles. The probabilities of dispersal-mediated propagule interchange between sites, commonly organized into a connectivity matrix, entail a timescale that is usually ignored in subpopulation analyses, limiting their utility and possibly leading to misinterpretation and wrong management decisions. Recognition of the essentially dynamical role played by metapopulation connectivity leads naturally to the incorporation of the generational timescale into the partitioning analysis. An algorithm is proposed to determine the subpopulations – both their cardinality and composition – as a function of the generational timescale and of a limiting probability of connection, illustrated with a novel empirical estimate of mesopelagic connectivity. The proposed framework allows the unambiguous determination of the timescales corresponding to dispersal barriers, and the identification of effective ecological units across the spectrum of management-relevant time horizons.