Community recovery dynamics in the rocky intertidal: Patterns, mechanisms and simulations

Understanding the manner in which communities develop over time is a fundamental goal of ecology. Traditionally, successional dynamics are investigated using either empirical or theoretical techniques but not both. Although there has been a great deal of work investigating succession and recovery processes in both terrestrial and marine systems, the circumstances governing both the likelihood and rate of ecological convergence remain poorly understood.

Initiating experimental disturbances in the rockweed Silvetia zone.

As more ecosystems are threatened by anthropogenic impacts, quantitative knowledge of the factors that contribute to recovery time can aid in the placement of reserves or other management decisions. Much of the work predicting community recovery dynamics has operated upon the general premise that community processes from intact communities can be used to predict community response to a disturbance.My research aims to improve our ability to predict and understand recovery rates and trajectories by including information about the importance of propagule input, species life history characteristics (i.e. lifespan and dispersal capability), geographic location and species interactions in predictive models. This combination of empirical and modeling techniques will provide a more complete understanding of the relative importance of ecological variables and species interactions in driving patterns of ecological succession, a process that is ubiquitous in nature.

Methods

Mussel disturbances at Point Sierra Nevada

I combine field data of post-disturbance community development with Markov analyses to broaden our understanding of the mechanisms driving observed differences in successional rates and trajectories. I have calculated community recovery rates following an experimental disturbance of an array of sizes across a major biogeographic break on the California coast in four intertidal assemblages (zones) that are each dominated by a taxon with a unique combination of life history traits: The California mussel Mytilus californianus, the acorn barnacle Chthamalus dalli/fissus, the rockweed Silvetia compressaand the red turf seaweed Endocladia muricata .

results

 My results show lifespan significantly influences recovery rates such that the fastest recovery rates occur in the zones dominated by Chthamalus and Endocladia (both short-lived) and that the strength of recruitment-driven recovery rates varies significantly by biogeographic region for all assemblages. Predictive Markov analysis in the Endocladia zone shows that intact communities accurately predict the endpoint of succession but not early successional trajectories.
 
Counting barnacle recruits
Further, examining species interactions shows that the proportion of positive, negative and neutral interactions in recovering communities is fundamentally different from those in intact communities such that there are more facilitative interactions in disturbed communities across all three biogeographic regions for the seaweed Endocladia. Since human presence or use of an area nearly always leads to removal of biota, the process by which a disturbed area recovers is a key part of understanding the long-term consequences of human impacts to ecosystems. As more and more ecosystems are threatened by human impacts, quantitative knowledge of the factors that contribute to variation in recovery rates is becoming increasingly critical to obtain. My research combines empirical data on succession with the analytical power of Markov models. This multi-faceted approach to understanding successional dynamics will provide useful information to coastal resource managers regarding recovery potential for intertidal organisms while at the same time deepening and quantitatively refining our understanding of the process of succession.  
 
For more information on this project please contact:
Tish Conway-Cranos
831.459.4145
tish@biology.ucsc.edu

 

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