Microbial viruses can control host abundances via density-dependent lytic predator-prey dynamics. Less clear is how temperate viruses, which coexist and replicate with their host, influence microbial communities. Here we show that virus-like particles are relatively less abundant at high host densities. This suggests suppressed lysis where established models predict lytic dynamics are favoured. Meta-analysis of published viral and microbial densities showed that this trend was widespread in diverse ecosystems ranging from soil to freshwater to human lungs. Experimental manipulations showed viral densities more consistent with temperate than lytic life cycles at increasing microbial abundance. An analysis of 24 coral reef viromes showed a relative increase in the abundance of hallmark genes encoded by temperate viruses with increased microbial abundance. Based on these four lines of evidence, we propose the Piggyback-the-Winner model wherein temperate dynamics become increasingly important in ecosystems with high microbial densities; thus 'more microbes, fewer viruses'.
Corals compete with other sessile organisms for the limited benthic surface. We hypothesized that resources available to fight at a coral’s perimeter depends on the coral’s surface area available for photosynthesis and heterotrophic feeding. To test this hypothesis, the perimeter to surface area ratio of over 50 coral colonies from the Caribbean island of Curaçao were analyzed. A physical and photo chain-link method was used to measure the perimeter length over multiple scales and surface area was calculated using a 3D, overlapping photo method. A visual score of the percentage of coral perimeter losing (%P- losing) the competition to other benthic organisms was also determined. Clade-specific positive relationships between perimeter to surface area ratio (P:SA) and %P-losing were observed in taxa belonging to three separate clades and a negative relationship was found in Montastraea cavernosa. Surface area had a significant negative correlation with %P-losing for all corals. All coral perimeters had a fractal dimension of 1 over a 1 mm – 1 m scale, suggesting that coral perimeters behave more like simple Euclidean shapes than fractal shapes. Together these results show that perimeter to surface area ratios predict competition outcomes for coral at a clade, and possibly guild, level. I propose that the Euclidean shape- like morphology of coral perimeter is a competition strategy to enhance coral success in the war for benthic space.