Thus far, the focus of phyllosphere microbiologists has been predominantly on concepts from autecology and population ecology, such as fitness, habitat, niche, population dynamics, and competition, as listed in detail in Electronic supplementary material (ESM) 1 and 2. For instance, bacterial profiles of nutrient source utilization in vitro have been used to estimate niche overlap and to quantify the degree of ecological similarity or niche differentiation of bacterial species (Wilson and Lindow 1994). Among the autecological concepts, the application of life-history strategies to phyllosphere organisms is noteworthy. Originally designed for the classification of plants, concepts such as Grime’s (2001) C-S-R triangle theory on the trade-offs between competitiveness (C), stress tolerance (S), and a combination of high reproduction and low longevity (R, for ruderality) were applied to phyllosphere fungi (Nix-Stohr et al. 2008), for which generally an S strategy is assumed, which involves maximizing stress tolerance. Contrary to this expectation, however, these fungi were found to maximize the occupation and exploration of resources, thus implying R and C strategies instead (Nix-Stohr et al. 2008).
In phyllosphere population ecology, population dynamics and competition are the predominating concepts (ESM 2). Studies on population dynamics are plentiful, but very few identify spatiotemporal patterns or go beyond reporting static population densities. In one of the few studies that do (Ellis et al. 1999), populations of fluorescent pseudomonads were sampled from sugar beet leaves to reveal a dynamic, nonrandom and continuous turnover of ribotypes within that population. Such cyclic population dynamics and their underlying mechanisms are a highly debated topic in ecology (Turchin and Hanski 2001), which future phyllosphere studies may help to elucidate.
A recurring pattern in phyllosphere population dynamics that might benefit from further investigation is the great temporal variability in population sizes (Dreux et al. 2007; Nix et al. 2008). Only recently have techniques been developed that allow the quantification of the fate and reproductive success of individual bacteria on leaf surfaces. For example, Remus-Emsermann and Leveau (2010) showed that individual immigrants to leaf surfaces contribute unequally to population sizes.
Competition has not only been inferred from nutrient overlap indices (Wilson and Lindow 1994), but also from pre-emptive exclusion of competitors by primary colonizers of the leaf surface (Lindow and Leveau 2002; Lindow and Brandl 2003), which can be an important mechanism underlying the success of biocontrol against plant pathogens (Mohamed and Caunter 1995). This is particularly true when the pathogen is an r-strategist with a fast reproduction and low competitiveness (Marois and Coleman 1995), or wh