Positive interactions @ ESA100

Niche mediation/niche construction/niching: The dominant plant (shrub, cushion, tree, etc) can increases the suitable area for a plant species by reducing abiotic or biotic pressures. As E. McIntire has pointed out though, positive interactions generate more area with the same fundamental niche characteristics, rather than expanding the niche itself. Thus, removal of limiting factors on the beneficiary by the benefactor will not increase the realized niche beyond that of the fundamental niche. If biotic limitations are zero, then the realized niche will simply equal the fundamental niche.

Realized Niche = Fundamental niche – biotic limitations (sensu Hutchinson)

The dominant plant will therefore either 1) increase habitat availability by generating the same microclimatic conditions of the fundamental niche for a species; i.e. increasing the area of the fundamental niche or 2) Reduce biotic limitations, such as herbivory or competition, that prevent a species from occupying areas of their fundamental niche. Both these situations have the same perceived response (a range expansion), however, I believe they have different implications for ecology and conservation.

Semantics of facilitation: The original definition of facilitation stated, roughly, is a positive effect between two individuals that is non-trophic based. I think we have assumed that this means it remains within trophic level, but A. Liczner has pointed out that this may not be the reasoning behind the original definition. Instead, it may be to imply a positive effect that is not trophic. For example, a shrub would not be facilitating a deer by being eaten, but would facilitate a deer by providing shelter. I also think “facilitation” can be a challenging term because what would the opposite be for facilitation? Competition? But not all negative effects are competitive. For instance, a shrub deterring herbivory is often classed as facilitation, but if a shrub attracts herbivores what is it? I think the general classification of positive or negative interactions act as good umbrella terms, but not sure what to do when going more specific.

Beyond the stress gradient hypothesis: There was other semantic discussion on the term “stress” and how it may be time to move away from stress as if it were a quantifiable measure and instead discuss the gradient that is being measured (temperature, soil moisture, etc). Smit actually took this one step further and stated how we should also measure the response of stress on the plant. Simply correlating water availability with plant biomass or abundance is not sufficient to determine if a plant community is stressed, because these communities may have adapted different life-history traits (sensu Grime). Additionally, there should be a bigger push to study other approaches that are not singular mechanisms (similar to what I proposed in my review). Instead, as we concluded, there should be further work in other areas of research such as: animals, indirect interactions, “unpopular” mechanisms or mechanisms in combination.

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