Variation in performance is ubiquitous among individuals in nature and can be focused on particular life histories stages of different taxa. I have found that variability among individuals affects the size structure of populations, their extinction risk, and the quantitative tools we use to describe populations. I use both models and data to show how variation that is not distributed independently among individuals (autocorrelation exists) is important to quantitative descriptors of populations. Mei Wang in the Statistics Dept has collaborated with me on this and we have developed a simple matrix projection model to describe this phenomenon in kelp and other species (Pfister and Wang 2005).

I am generally interested in how organisms, through the structure of their life cycle, ameliorate variability in population growth rate.  This has been a long-standing theme in my own research, where I have documented the pattern that population growth is not very sensitive to stages of a life cycle that are highly variable (Pfister 1998). I am interested in comparisons among species in life histories in order to ask if there are generalities in how species will respond to environmental variation and climate change.  Kelp have been the focus of much of the empirical work related to these questions.  A working group on this topic of ‘stochastic demography’ was sponsored by the National Center for Ecological Analysis and Synthesis (NCEAS) at Santa Barbara and several comparisons among taxa have resulted (Doak et al. 2005, Morris et al. 2008).

Both genetic and demographic factors have been shown to effect extinction risk, though the relative contribution of each is uncertain.  In collaboration with Tim Wootton, Dick Hudson,we are exploring how both genetic and demographic factors affect the persistence of the sea palm, Postelsia palmaeformis via field experiments. We are also using microsatellite markers to understand dispersal distances and mating system in the sea palm and looking at the fate of populations with differing genetic backgrounds.

This research was funded by the National Science Foundation, OCE #01-17801.

A related interest is the mating systems of kelp and their implications. I am currently testing whether there are barriers to selfing or costs associated with selfing in the sea palm Postelsia and a number of other kelp species.  This work is in collaboration with an undergraduate in my lab, Allison Barner, and my graduate student Julie Collens.  Of particular interest is whether selfing is a mechanism of reproductive assurance and thus persistence for annual species such as Postelsia.

Although it is recognized that the upwelling of nitrogen-rich water is a source of productivity in the northeast Pacific, my experiments and observations are also revealing that animal excretion is a significant source of ammonium in coastal waters and tidepools. Algal productivity within tidepools is boosted several-fold by the presence of mussels (Pfister 2007) and seawater in close proximity to Tatoosh Island has elevated ammonium levels compared with seawater away from the Island (Pfister et al. 2007). In collaboration with Mark Altabet at UMass and David Post at Yale University, we are using stable isotopes in conjunction with experiments to quantify how regenerated nutrients supplied by animals affects microbial populations and coastal primary productivity.

Nitrification seems ubiquitous in these coastal areas and, in collaboration with researchers at nearby Argonne National Labs (Folker Meyer, Dion Antonopoulos), we have used 454 technology to sequence microbial populations of Tatoosh Island to understand both the identity and function of microbes in this system.

This work is funded, in part, by an NSF grant from Ocean Sciences, #09-28232 to Pfister, Altabet and Post. 

As CO2 concentrations in the atmosphere increase, the pH of ocean water is expected to decrease. Our long-term research on Tatoosh Island supports a scenario of decreasing pH through time (Wootton, Pfister & Forester 2008), and the declines we have measured are greater than those predicted by models.  Ongoing work will continue to quantify this pattern as well as understand the implications for calcium-bearing organisms and their role in the nearshore community. With funding from the SeaDoc Society, we are currently asking whether the shells of bivalves contain archival information on ocean chemistry.

Long-term data on the dynamics of nearchore fish recrutiment and adult abundancee reveal that the dominat species as a recruiot (Clinocottus globiceps) is always replacednumerically as an adult by Oligocottus maculosus. Based on previous experimental work demonstrating the competitive dominance of O. maculosus and the presence of density-dependence, post-recruitment processes appear to play a very important role (Pfister 2006).  A competition-colonization trade-off among the two dominant species is suggested and may contribute to the coexistence of these species. Colonization differences in the two species may be driven by the interplay between where larvae are located in the water column and the effects of oceanographic events such as the spring transition (Shanks & Pfister 2009)

Funding has been provided by the National Science Foundation, the Andrew Mellon Foundation, the SeaDoc Society, the University of Chicago, and the EPA (via the Center for Integrating Statistics and Environmental Science).

Life history responses to productivity gradients:  snails in New Zealand

In collaboration with Nicole Phillips at Victoria University of Wellington, New Zealand, we are asking whether life history traits of gastropods change over productivity gradients around the north island of New Zealand.  Scavenging and predatory species of whelks, including Cominella maculosa, C. virgata and Haustrum haustorium and H. scobina have direct developing hatchlings, though they encapsulate them in different ways. We are looking at constraints and plasticity in how egg capsules are packaged and how hatchlings perform in response to ocean productivity.   This work was funded by the Marsden Fund of New Zealand.

I am grateful to the Makah Tribal Nation for continued access to these sites. 

Funding has been provided by the National Science Foundation, the Andrew Mellon Foundation, the University of Chicago and the EPA (via the Center for Integrating Statistics and Environmental Science).