Date of Award
Open Access Dissertation
Thomas J. Hilbish
Population connectivity, particularly in open systems, is an important metric for understanding population-level processes on both ecological and evolutionary timescales. In coastal marine systems, adults are typically sedentary and dispersal occurs primarily during a larval stage when individuals are transported in ocean currents. Because coastal marine populations exist as networks of interconnected subpopulations, variation in the magnitude and extent of population connectivity can have profound effects on population dynamics and species distribution limits. Connectivity is a complex process, affected by a multitude of factors, including adult inputs and physical dispersal, which operate at multiple scales and may interact. This dissertation describes work on three research questions, which examine how variation in temperature and dispersal patterns drive variation in connectivity and subsequently affect species range boundaries. The project integrated a combination of field surveys, laboratory experiments, and computer simulations and addresses the specific questions: (1) How does temperature-induced variation in adult input into the larval pool affect population dynamics and range limits? (2) What is the effect of temperature on reproductive success in intertidal organisms? and (3)How do potential connectivity patterns vary over time and can we use physical dispersal models to predict the rate of recolonization after a local extinction event? This work uses the widely-distributed acorn barnacle Semibalanus balanoides as a study organism, and takes advantage of climate-induced variation in the fecundity of this species to examine the role of adult input into the larval pool in the field and laboratory. Multi-year field surveys at a local southern limit of S. balanoides indicated that recruitment of this species was greater following cold winters than following warm winters and recent cold winters have led to a range expansion of this species at a local southern range limit. Climate-induced variation in population connectivity also explains decadal-scale oscillations in population abundance and geographic distribution of S. balanoides at this range limit. Laboratory experiments demonstrated that temperature did not significantly affect larval development rate, but brooding individuals reared at cold temperatures had significantly greater reproductive mass than individuals reared at warm temperatures. This mass difference is caused by an over three-fold larger number of embryos surviving in the coldest treatment (7°C) compared to the warmest treatment (13°C). Temperature-induced variation in number of surviving embryos likely contributes to differences in recruitment following cold winters vs. warm winters. Computer-simulated estimates of potential connectivity predicted recolonization following local extinction at a comparable rate to that observed in the field. This work highlights the importance of adult input into the larval pool and physical dispersal in controlling population connectivity, as well as the significant role of climate variation in determining the range limits of marine organisms.
Rognstad, R. L.(2014). Marine Population Connectivity: Range Boundaries and Climate Change. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/2943