Table 1.
Ecological concepts underaddressed in the phyllosphere
| Concept | Relevance | Issues |
|---|---|---|
| Autecology | ||
| Niche | Core concept for predicting outcomes of interactions such as competition or facilitation | The term “niche” has repeatedly been used to refer only to a spatial location, while the classic niche definition applies to a combination of resources and environmental conditions that allow survival and reproduction (including space, but not exclusively) |
| Resource uptake | ||
| Optimal foraging theory | The patchily distributed resources in the phyllosphere are ideal to test whether micro- and macroorganisms have an equally optimal energy intake over time… | |
| Ideal-free distribution | …and build up population sizes proportional to the amount of resources in a patch | |
| Phenotypic plasticity | Contributes to the flexibility of the reaction to environmental changes such as climate change | |
| Trade-offs | Limit the flexibility of evolutionary responses to abiotic and biotic changes | |
| Population ecology | ||
| Allee effect | Mechanism causing overproportional reduction in survival and reproduction at small population densities | |
| Allelopathy | Mechanism similar to antibiosis that could enhance pre-emptive competition | The focus of the only available study (Vokou 2007) was on allelochemistry rather than the ecological mechanism |
| Competition | ||
| Density dependence | Regulation of intraspecific population dynamics with consequences for coexistence | Density-dependent processes such as mortality have been identified, but forms of density dependence (e.g. over- or undercompensating for density increase) have not yet been explored |
| Scramble/contest | Mechanisms of sharing resources among all competitors (typical for r-strategists) versus monopolizing resources by the best competitor (K-strategists, territoriality), particularly relevant under varying spatiotemporal conditions | |
| Apparent competition | Improving the ecological realism by studying more complex interactions such as competition mediated by an enemy attacking both competitors | |
| Competitive release | Scope for microecological corroboration of this strongly debated concept of niche expansion after release from competition | |
| Resource depletion zone | Exploring the zone of resource reduction by the consumer may provide spatial explanations for competitive outcomes | |
| Cycles | Widespread population dynamics in ecology affecting the type and degree of interactions, e.g. predator–prey cycles | Only the potential for population cycles has been highlighted based on seasonality of environmental conditions across temporal scales (Hirano and Upper 2000); a demonstration is lacking |
| Metapopulation | Spatiotemporal mechanism for the prevention of extinction based on a set of patchy subpopulations that are linked by dispersal | There have been no explicit tests yet, but some implicit treatments (Ives et al. 2004; Woody et al. 2007). A test requires patchy subpopulations that go extinct asynchronously due to demographic stochasticity, but which are linked by dispersal ensuring metapopulation persistence |
| Community ecology | ||
| Community assembly rules | Mechanisms underlying species presence and absence in space and time | Community assembly rules have been mentioned (Nix-Stohr et al. 2008), but a more explicit identification of community assembly rules is needed |
| Diversity theories | Explain diversity patterns and provide underlying mechanisms [e.g., neutral theory of biodiversity (Hubbell 2001), intermediate disturbance hypothesis (Connell 1978)] | |
| Ecosystem engineers and keystone species | Provide a focus for biological control research and for understanding an ecosystem | |
| Food web, food chain, multitrophic interactions, connectance | Enhancing the ecological realism of research and the likelihood of discovering mechanisms by including more complex biotic interactions | |
| Island biogeography | Explains diversity dynamics on islands such as leaves or habitable patches within leaves | To our knowledge, only one explicit test exists to date (Kinkel et al. 1987), the conclusions of which are mixed. To establish generality, more tests are needed |
| Patch dynamics | Scale-explicit spatiotemporal coexistence mechanism, probably enhancing biodiversity | |
| Specialization and omnivory | Determines the connectedness of communities that can influence community resilience and resistance | |
| Species (or rank) abundance curves | Patterns for the validation of diversity theories such as Hubbell’s (2001) neutral theory | Ellis et al. (1999) report lognormal species abundance curves. To establish the generality of a diversity theory, more patterns have to be evaluated |
| Species–area relationships | Basis for island biogeography theory; related to community assembly and diversity theories | Kinkel et al. (1987) did not find a relationship between number of species and area, but the tested fungal species were probably not limited by area. Hence, testing other species would be valuable to establish generality |
| Stability | Measure of the resilience or resistance of a community to perturbations such as invasions by exotic species | |
| Top-down and bottom-up regulation | Knowledge of the regulation of an organism via antagonists or via resources is a key to understanding and manipulating community organization | |
Issues are only mentioned if concepts have been addressed, but insufficiently for our purpose of testing or applying the respective concept in the phyllosphere. “Concept” is used here in the wider sense, including theories. For a definition of the ecological concepts, see the glossary of an ecological textbook, e.g. http://www.blackwellpublishing.com/begon/