Hi Sonia, just some elaboration on what Madelon said, who made some very good points. Usually we measure what we call "soft" traits, i.e. some more or less easily measurable properties of the plants, that are thought to represent physiological responses to the environment. Given that the whole approach is based on the existence of niches, it seems to make sense to make a distinction between alpha and beta niche, where the beta niche is defined by environmental conditions that make up the habitat in which different species can coexist (i.e. environmental filtering) and the alpha niche is defined by the small scale variation in resource availability (like light and soil nutrients; i.e. limiting similarity).

https://www.researchgate.net/publication/6866464_Phylogeny_and_the_hierarchical_organization_of_plant_diversity?ev=srch_pub

However, given traits could be a response to either of the two opposing mechanisms, in which case it becomes really important what spatial scale (grain size) is being considered, as already mentioned by Madelon. So in response to your question, I would say that yes, it is possible that both mechanisms simultaneously act on a species even if the same trait is considered.

Another important thing to consider is how you are defining your species pool. If you just pool the species of your samples it is possible to detect trait convergence even if the process is competition.

https://www.researchgate.net/publication/44798124_Opposing_effects_of_competitive_exclusion_on_the_phylogenetic_structure_of_communities?ev=srch_pub

A possible solution to this is to define your regional species pool not by pooling samples but by considering also species that can potentially live in the habitat but are not present in the samples (i.e. the dark diversity)

https://www.researchgate.net/publication/233786824_Functional_species_pool_framework_to_test_for_biotic_effects_on_community_assembly?ev=srch_pub

Hope this makes sense and is helpful.

Article Phylogeny and the hierarchical organization of plant diversity

Article Opposing effects of competitive exclusion on the phylogeneti...

Article Functional species pool framework to test for biotic effects...

Your question is very general. It is likely that limiting similarity and environmental filtering affect all individuals in a community at all times. However since one cannot directly measure these processes we infer them from the outcomes that these processes may have caused. If traits of co-occurring individuals are more similar than you would expect by chance, this is interpreted as a consequence of environmental filtering, or better to say that environmental filtering has had a larger effect on plant performance for these individuals than limiting similarity. But, this also depends on the spatial scale of the study; where smaller spatial scale makes it more likely to find limiting similarity, as well as on plant size; where larger trees are more likely to be affected by limiting similarity than smaller trees (see also Swenson et al 2007 Ecology).

Considerations also for selecting the trait: what resource are individuals likely to compete for and which trait may reflect acquisition of this resource? One may find different outcomes of assembly processes when assessing different traits.

Hope this helps!

Thanks, Medelon.

An ecological plant community is very complex and dynamic in nature. Predicting community assembly pattern is not so easy. Assembly process depends on spatial and temporal scale, species evolutionary characteristics, resource requirements, resource acquisition rate, niche partitioning and so on.

Hi Sonia, just some elaboration on what Madelon said, who made some very good points. Usually we measure what we call "soft" traits, i.e. some more or less easily measurable properties of the plants, that are thought to represent physiological responses to the environment. Given that the whole approach is based on the existence of niches, it seems to make sense to make a distinction between alpha and beta niche, where the beta niche is defined by environmental conditions that make up the habitat in which different species can coexist (i.e. environmental filtering) and the alpha niche is defined by the small scale variation in resource availability (like light and soil nutrients; i.e. limiting similarity).

https://www.researchgate.net/publication/6866464_Phylogeny_and_the_hierarchical_organization_of_plant_diversity?ev=srch_pub

However, given traits could be a response to either of the two opposing mechanisms, in which case it becomes really important what spatial scale (grain size) is being considered, as already mentioned by Madelon. So in response to your question, I would say that yes, it is possible that both mechanisms simultaneously act on a species even if the same trait is considered.

Another important thing to consider is how you are defining your species pool. If you just pool the species of your samples it is possible to detect trait convergence even if the process is competition.

https://www.researchgate.net/publication/44798124_Opposing_effects_of_competitive_exclusion_on_the_phylogenetic_structure_of_communities?ev=srch_pub

A possible solution to this is to define your regional species pool not by pooling samples but by considering also species that can potentially live in the habitat but are not present in the samples (i.e. the dark diversity)

https://www.researchgate.net/publication/233786824_Functional_species_pool_framework_to_test_for_biotic_effects_on_community_assembly?ev=srch_pub

Hope this makes sense and is helpful.

Article Phylogeny and the hierarchical organization of plant diversity

Article Opposing effects of competitive exclusion on the phylogeneti...

Article Functional species pool framework to test for biotic effects...

Dear Sonia,

This following paper might be interesting for you:

Spasojevic, M. J. and Suding, K. N. (2012), Inferring community assembly mechanisms from functional diversity patterns: the importance of multiple assembly processes. Journal of Ecology, 100: 652–661. doi: 10.1111/j.1365-2745.2011.01945.x

In this paper they conclude that assuming filtering increases trait convergence in stressful environments, whereas from competition (as niche partitioning, limiting similarity) traits would be different in productive environments, ignores how important other mechanisms as facilititation and fuctional redundancy operating in multiple niche axes.

I hope this is helpful for you,

Greetings

Florencia