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1.  Protists have divergent effects on bacterial diversity along a productivity gradient 
Biology Letters  2010;6(5):639-642.
Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity–diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity–diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators.
doi:10.1098/rsbl.2010.0027
PMCID: PMC2936128  PMID: 20219744
bacteria; productivity; biodiversity; protist; predation
2.  ‘Tales of Symphonia’: extinction dynamics in response to past climate change in Madagascan rainforests 
Biology Letters  2009;5(6):821-825.
Madagascar's rainforests are among the most biodiverse in the world. Understanding the population dynamics of important species within these forests in response to past climatic variability provides valuable insight into current and future species composition. Here, we use a population-level approach to analyse palaeoecological records over the last 5300 years to understand how populations of Symphonia cf. verrucosa became locally extinct in some rainforest fragments along the southeast coast of Madagascar in response to rapid climate change, yet persisted in others. Our results indicate that regional (climate) variability contributed to synchronous decline of S. cf. verrucosa populations in these forests. Superimposed on regional fluctuations were local processes that could have contributed or mitigated extinction. Specifically, in the forest with low soil nutrients, population model predictions indicated that there was coexistence between S. cf. verrucosa and Erica spp., but in the nutrient-rich forest, interspecific effects between Symphonia and Erica spp. may have pushed Symphonia to extinction at the peak of climatic change. We also demonstrate that Symphonia is a good indicator of a threshold event, exhibiting erratic fluctuations prior to and long after the critical climatic point has passed.
doi:10.1098/rsbl.2009.0428
PMCID: PMC2827988  PMID: 19605388
palaeoecology; competition; global change; population model; soil; threshold
3.  Moderation of pathogen-induced mortality: the role of density in Bacillus thuringiensis virulence 
Biology Letters  2008;5(2):218-220.
Virulence in pathogens may be increased or decreased in order to maximize reproduction and transmission. We investigated how reproduction and virulence in the entomopathogen Bacillus thuringiensis (Bt) changed with bacterial density. We predicted that virulence would be moderated at high pathogen densities because extended time to death allows more growth in hosts. We found that pathogen reproduction (spores produced per cadaver) peaked at an intermediate time to death and was lowest in hosts that die early. Manipulating spore density (spores per unit area of leaf) by combining pathogenic Bt spores with a non-pathogenic mutant confirmed our prediction: larval 5-day mortality was reduced at higher pathogen densities. Pathogen reproduction increased with the density of pathogenic Bt. We hypothesize that more effective reproduction at high density is a consequence rather than a cause of density-dependent virulence.
doi:10.1098/rsbl.2008.0610
PMCID: PMC2665808  PMID: 19033132
Bacillus thuringiensis; mass action theory; prudence; trade-off; tragedy of the commons; quorum sensing

Results 1-3 (3)