Measuring connectivity: MPAs and metapopulation persistence

A discussion group of marine ecology graduate students and faculty at UC Davis led to a synthesis project where we reviewed empirical studies estimating marine population connectivity. We found that most studies failed to measure or report the necessary information to assess whether a given MPA design contributes to metapopulation persistence. We described how to measure larval connectivity and how it can be combined with demographic data, providing a “road map” for future empirical studies that can test whether existing or proposed MPAs can contribute to persistence. Below is a description of the project for the public, written by one of my coauthors.

Burgess, SC, Nickols, KJ, Griesemer, CD, Barnett, LAK, Dedrick, AG, Satterthwaite, EV, Yamane, L, Morgan, SG, White, JW, & LW Botsford. 2014. Beyond connectivity: how empirical methods can quantify population persistence to improve marine protected area design. Ecological Applications 24:257-270http://dx.doi.org/10.1890/13-0710.1

 

Marine Populations and Measuring the Right Thing

Not all of the marine biologists at UC Davis are in Bodega Bay. Some of us walk among you in land-locked Davis! We are scattered in various departments around campus and investigate a variety of questions from behavior, to genomics, to population dynamics of marine organisms.

In the spring of 2012, a mixed group of Ecology Graduate Group members and Center for Population Biology affiliates, graduate students and postdocs, Bodega residents and Davis residents got together to discuss factors that connect and maintain populations of coastal fishes and invertebrates. The meetings originally arose as a need to have a marine-focused discussion group, and soon took form as a graduate level discussion group (ECL 290) sponsored by Bodega’s Dr. Steven Morgan and our own local professor, Dr. Loo Botsford.

Following the conclusion of the formal discussion group, many members continued to meet with an eye toward creating some kind of a product from our collective conversations. Recently, a group of us, lead by Center for Population Biology Postdoctoral Fellow, Scott Burgess, published a manuscript advocating appropriate measurements of marine population connectivity. Here’s why.

porcelain_crab_larvaI’m lucky enough to do my field work on the beach, and like many ecologists, I spend about half of my time counting. In my case, it’s counting shore crabs. Not a bad way to escape the hot Davis summers. I’m interested whether larval crabs are coming back to their natal beaches in high numbers and what consequences that might have for evolutionary processes in the intertidal.

One usually hopes, howeveporcelain_crab_adultsr, the implications of their research are broad. A common assertion among marine biologists like me who study dispersal and population dynamics is that an understanding of these processes aids in the appropriate development and distribution of the many marine protected areas now being implemented around the world.

Northern California MPA MapThough many of us who study the seas *are* interested in conservation of the populations we study, we are often guilty of narrow-focused data collection, only answering the question at hand in our particular system of interest. Our assertion in the review article is that a simple column added to the data sheet or even a simple change of a numerator would provide relevant data to MPAs.

In both terrestrial and marine realms, populations can be maintained through different modes as represented simply in the figure below:

 

Fig2A

Fig2BFig2C

 

 

 

 

      Fig. 2  from Burgess et al. 2013, Ecological Applications

For organisms with a dispersing larval stage (many marine plants and animals), most real populations are maintained through a combination of locally produced young and immigrants from other sites (see figure above). Genetic assignment tests uncover these connections, allowing investigators to assign young to their site of origin. These data can be assembled into a “connectivity” matrix. In combination with population sizes and reproductive outputs, a model of population resilience begins to form.

In a review of recent literature that reported to have implications for marine reserve design or fisheries management, our team found that many studies fell just short of reporting the data needed to characterize the population dynamics of the system at hand. Many of the studies recorded most of the necessary data; the problem resided in the reporting and interpretation. In other cases the data would have been obtained with minimal additional effort.

 

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