The biological and physical mechanisms that establish and maintain species boundaries in the ocean are controversial. Contributing factors are offspring of species with planktonic larvae being physically transported outside their natal range, and adults thriving when transplanted into regions immediately beyond their natural distributions. It is unclear, however, why long-distance dispersal of a benthic organism's larva should persist on evolutionary timescales. There is more larval dispersal from natal habitat than would seem propitious. Furthermore, long larval duration is known to increase reproductive output for species persistence, makes population retention of favorable alleles less likely, and reduces the genetic diversity of the population.
The Co-PIs have shown that maintenance of range boundaries for a species are governed by a function analogous to that derived for allelic frequency/genetic clines in the coastal ocean. As with other recent advances in biodiversity theory, this work suggests a convergence between conditions that maintain the distribution of alleles within species and those that maintain the distribution of species themselves. This confluence of theory provides substantial opportunity for development of inter- and intra-species competition in an advective environment. It potentially would unify genetic and population-level theory, and create a holistic view of life in advective environs.
It is clear from preliminary work that a synthesis would depend critically on tradeoffs between dispersal mode and successful reproductive output. The theory would be developed both by pushing its analytical envelope, and by drawing upon extensive, existing databases to quantitatively constrain reproductive and dispersal tradeoffs. For example, although tradeoffs between larval quantity versus quality (i.e., many "energetically cheap" larvae versus few "highly provisioned" individuals) have long been the subject of qualitative models, they have not been quantitatively defined for life history characteristics of different benthic marine taxa. Combining analytical developments and observed life-history tradeoffs would provide 1) evolutionarily stable states for a range of dispersal strategies, 2) mechanisms that define species boundaries as a function of physical (e.g., temperature and alongshore variation in currents) and biological (like larval mortality) parameters and 3) quantitative origins of dispersal behaviors that would locally retain larvae, and result in relationships between inter- and intra-species fitness.
Such findings would predict species boundary locations and the presence/absence of various dispersal strategies as a function of local circulation, environmental conditions and their gradients. Predictions would be tested against data on species ranges gathered as part of an extensive literature and database search.
Broader impacts: This research would allow a better mechanistic understanding species' ranges that occur due to changes in the Earth's climate. For example, this study will test the hypothesis that warming favors species with longer larval planktonic duration. Therefore, high-latitude areas now dominated by species with direct development would shift to a mixture of planktonic dispersers and direct developers as the climate warms. The research would allow managers to understand how disruption to habitat can alter species ranges by changing alongshore sources and transport of planktonic larvae. A quantitative theory of species range will also help managers understand what sets the ultimate limits of recently introduced exotic species, allowing improvement of management strategies. This proposal includes the following education components. Two graduate students will be trained in cutting-edge techniques in the fields of quantitative phylogeography and biogeography. In addition, two undergraduate students each year will assist with all aspects of the project and will present their work at a national meeting. The students will be mentored to write REU proposals to NSF. Undergraduates will be recruited with the help of the Louis Stokes Alliance for Minority Participation, of which UGA is a flagship member. Undergraduates will also be recruited from the Research and Discovery Program at UNH, from colleges with limited opportunities for undergraduate research.
