TY  - JOUR
A1  - Fussmann, Gregor F.
A1  - Ellner, Stephen P.
A1  - Shertzer, Kyle W.
A1  - Hairston, Nelson G.
T1  - Crossing the Hopf bifurcation in a live predator-prey system
N2  - Population biologists have long been interested in the oscillations in population size displayed by many organisms in the field and Laboratory. A wide range of deterministic mathematical models predict that these fluctuations can be generated internally by nonlinear interactions among species and, if correct, would provide important insights for understanding and predicting the dynamics of interacting populations. We studied the dynamical behavior of a two- species aquatic Laboratory community encompassing the interactions between a demographically structured herbivore population, a primary producer, and a mineral resource, yet still amenable to description and parameterization using a mathematical model. The qualitative dynamical behavior of our experimental system, that is, cycles, equilibria, and extinction, is highly predictable by a simple nonlinear model.
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Shertzer, Kyle W.
A1  - Ellner, Stephen P.
A1  - Fussmann, Gregor F.
A1  - Hairston, Nelson G.
T1  - Predator-prey cycles in an aquatic microcosm : testing hypotheses of mechanism
N2  - 1. Fussmann et al. (2000) presented a simple mechanistic model to explore predator-prey dynamics of a rotifer species feeding on green algae. Predictions were tested against experimental data from a chemostat system housing the planktonic rotifer Brachionus calyciflorus and the green alga Chlorella vulgaris. 2. The model accurately predicted qualitative behaviour of the system (extinction, equilibria and limit cycles), but poorly described features of population cycles such as the period and predator-prey phase relationship. These discrepancies indicate that the model lacked some biological mechanism(s) crucial to population cycles. 3. Here candidate hypotheses for the 'missing biology' are quantified as modifications to the existing model and are evaluated for consistency with the chemostat data. The hypotheses are: (1) viability of eggs produced by rotifers increases with food concentration, (2) nutritional value of algae increases with nitrogen availability, (3) algal physiological state varies with the accumulation of toxins in the chemostat and (4) algae evolve in response to predation. 4. Only Hypothesis 4 is compatible with empirical observations and thus may provide important insight into how prey evolution affects predator- prey dynamics.
Y1  - 2002
UR  - http://www.blackwell-synergy.com/Journals/issuelist.asp?journal=jae
ER  - 
TY  - JOUR
A1  - Ellner, Stephen P.
A1  - Fussmann, Gregor F.
T1  - Effects of successional dynamics on metapopulation persistence
N2  - The classical (Levins) metapopulation scenario envisions a species persisting in a network of habitat patches through a balance between frequent local (within-patch) extinctions and recolonizations. Although this is the dominant paradigm for species in fragmented habitats, empirical support is limited and it has been argued that very restrictive conditions on migration rates are required: high enough for recolonization to balance extinctions, but low enough that local populations do not fluctuate in synchrony. Through simulation and analysis of a stochastic spatial model, we argue that the likelihood of persistence via the classical scenario is strongly affected by some basic properties of within- patch successional dynamics whose importance has not been emphasized in metapopulation theory: the distribution of successional stage durations, and whether patches are "refractory" versus immediately available for recolonization after an extinction has occurred. These properties are tied to the biological causes of extinction (e.g., demographic accident versus regular successional changes) and patch recovery (e.g., recolonization by a host species versus regeneration of an exhausted resource base). Our results indicate that metapopulation theory needs to incorporate the patch-dynamics perspective of a landscape in a dynamic mosaic of successional states, with particular attention to links between colonization-extinction processes and local succession.
Y1  - 2003
ER  - 
TY  - JOUR
A1  - Yoshida, Takehito
A1  - Jones, Laura E.
A1  - Ellner, Stephen P.
A1  - Fussmann, Gregor F.
A1  - Hairston, Jr.
A1  - Nelson, G.
T1  - Rapid evolution drives ecological dynamics in a predator-prey system
N2  - Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.
Y1  - 2003
UR  - http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v424/n6946/full/nature01767_fs.html
ER  - 
TY  - JOUR
A1  - Fussmann, Gregor F.
A1  - Ellner, Stephen P.
A1  - Hairston, Nelson G.
T1  - Evolution as a critical component of plankton dynamics
N2  - Microevolution is typically ignored as a factor directly affecting on-going population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for > 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific yet reproducible plankton dynamics that are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.
Y1  - 2003
ER  -