Bibliography - S. A. Sandin

1. Sandin, S. A., and Stephen W. Pacala, 2005: Demographic theory of coral reef fish populations with stochastic recruitment: comparing sources of population regulation. American Naturalist, 165(1), doi:10.1086/426674 107-119
   [ Abstract ]

   The effects of three forms of density-dependent regulation were explored in model coral reef fish populations: top-down (predation), bottom-up (competition for food), and pelagic (non-reefbased mechanisms) control. We describe the demographic responses of both biomass and numbers of adult fish, predicting the mean and the variance of temporal fluctuations resulting from stochastic recruitment of juveniles. We find that top-down control acts by suppressing variability of numbers of fish, which in turn suppresses the variability of biomass. Bottom-up control has no effect on fluctuations of numbers of fish, though it strongly reduces fluctuations of biomass. Because fecundity of fish is directly linked to body mass, the regulation of biomass tightly regulates reproductive output independently of the number of individuals in the population. Finally, populations under pelagic control experience bounded fluctuations of biomass and numbers directly proportional to the bounded fluctuations of recruitment. The demographic signatures predicted from both bottom-up and pelagic control are consistent with current evidence supporting the recruitment limitation hypothesis in reef fish ecology. We propose tests to discriminate the dominant mode of density-dependent regulation using qualitative trends in time series demographic data across environmental clines.

2. Sandin, S. A., and Stephen W. Pacala, 2005: Fish aggregation results in inversely density dependent predation on continuous coral reefs. Ecology, 86(6), doi:10.1890/03-0654 1520-1530
   [ Abstract ]

   Spatially density-dependent predation is a leading hypothesis describing mechanisms of population regulation in coral reef fish. However, studies supporting this hypothesis predominantly have been conducted on small, isolated patch reefs. Here, we searched for evidence of spatially density-dependent predation on the continuous reefs of the Netherlands Antilles in a study of a dominant planktivore, the blue chromis (Chromis cyanea). Across space, we quantified both the patterns of loss from site-attached aggregations of C. cyanea through time and the behavioral reaction of predators to these aggregations. Looking across C. cyanea densities, we found that loss from aggregations was not characteristic of direct density dependence, but instead was commonly inversely related to density. Individual C. cyanea in larger aggregations were less likely to be lost from the group than were individuals in smaller aggregations. Thus, the observed density dependence increased spatial heterogeneity of C. cyanea. Predators showed behaviors that were consistent with these demographic patterns. Using remote videography, we quantified predator visitation and strike rates across a range of C. cyanea aggregation sizes. Predators consistently visited and struck at individuals in C. cyanea aggregations in a pattern that was strongly inversely density dependent, suggesting that aggregation is an effective means of minimizing per capita risk of predation for prey reef fish. Differences in spatial distribution of resources for predators (i.e., prey fish) between continuous and patch reef habitats may explain the difference between these results and those of previous studies on patch reefs.

3. Sandin, S. A., and Stephen W. Pacala, 2004: Regulation in populations of coral reef fish: an exploration of models and data. Proceedings of the Ninth International Coral Reef Symposium, Bali, Indonesia, http://cmbc.ucsd.edu/content/1/docs/Sandin_Pacala_final_9ICRS.pdf, 455-462
   [ Abstract ]

   The study of population regulation in reef fish populations is confounded by large amounts of stochasticity obscuring patterns in the field. We analyze a series of population models, comparing equilibrial solutions under conditions of top-down and bottom-up regulation. We also treat patterns of population variance that will be expected as recruitment variance is propagated through to adult populations. We find that predators affect reef fish populations by absorbing recruitment variance across space and through time. Food limitation will instead reduce fluctuations of adult fish biomass through time. Our model suggests that the study of regulation cannot be conducted through counting fish alone, but requires measurement of biomass simultaneously. By surveying fish across natural and human-created clines of recruitment and mortality, we can focus fieldwork on testing focused predictions of regulation on coral reefs.

4. Hixon, M. A., Stephen W. Pacala, and S. A. Sandin, 2002: Population regulation: historical context and contemporary challenges of open vs. closed systems. Ecology, 83(6), doi:10.1890/0012-9658(2002)083[1490:PRHCAC]2.0.CO;2 1490-1508
   [ Abstract ]

   By definition, a population is regulated if it persists for many generations with fluctuations bounded above zero with high probability. Regulation thus requires density- dependent negative feedback whereby the population has a propensity to increase when small and decrease when large. Ultimately, extinction occurs due to regulating mechanisms becoming weaker than various disruptive events and stochastic variation. Population regulation is one of the foundational concepts of ecology, yet this paradigm has often been challenged, during the first half of the 20th century when the concept was not clearly defined, and more recently by some who study demographically open populations. The history of ecology reveals that earlier manifestations of the concept focused mostly on competition as the mechanism of population regulation. Because competition is often not evident in nature, it was sometimes concluded that population regulation was therefore also absent. However, predation in the broadest sense can also cause density dependence. By the 1950s, the idea that demographic density dependence was essential (but not sufficient) for population regulation was well established, and since then, challenges to the general concept have been short lived. However, some now believe that metapopulations composed of demographically open local populations can persist without density dependence. In particular, some recent manifestations of the Recruitment Limitation Hypothesis all but preclude the possibility of regulation. The theory of locally open populations indicates that persistence always relies on direct demographic density dependence at some spatial and temporal scale, even in models reportedly demonstrating the contrary. There is also increasing empirical evidence, especially in marine systems where competition for space is not self evident, that local density dependence is more pervasive than previously assumed and is often caused by predation. However, there are currently insufficient data to test unequivocally whether or not any persistent metapopulation is regulated. The challenge for more complete understanding of regulation of metapopulations lies in combined empirical and theoretical studies that bridge the gap between smaller scale field experiments and larger scale phenomena that can presently be explored solely by theory.

Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=4148