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Functional Traits and Community Assemblage. What / Which Main Factors Drive Community Assembly (FTH)? Damien Bonal Functional traits and community assemblage. What / Which main factors drive community assembly (FTH)? Damien Bonal To cite this version: Damien Bonal. Functional traits and community assemblage. What / Which main factors drive community assembly (FTH)?. Species Interactions in Mixed Forest Ecosystems (MIXFOR). 2014 NFZ.forestnet Summer School, Aug 2014, Nancy, France. 53 p. hal-01268789 HAL Id: hal-01268789 https://hal.archives-ouvertes.fr/hal-01268789 Submitted on 5 Jun 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 3.4 Functional traits and community assemblage What / Which main factors drive community assembly (FTH)? D. BONAL 2 Plant ecologists seek to understand where plants grow and why they grow there 3 Which species, present in a larger geographical region, will be found at a local site? 4 What / Which main factors drive community assembly? How is it possible for a number of species to coexist in a relatively unstructured environments all competing for the same resources? How does high species diversity can be maintained within communities? How is it that so many species can co-exist? Why are some species common and others rare? 5 Questions at the interface of Functional Ecology and Community Ecology 1987 Functional Ecology … the relationships between the functions of biological systems and the environmental conditions To find the general rules that allow to explain … Community Ecology … the coexistence of species living together at a given place and at a given time 6 Questions at the interface of Functional Ecology and Community Ecology Why are these questions at this interface? Because: Mechanistic explanations of community assembly state that “community membership is constrained to those species with the appropriate functional traits to reach a site and establish under the circumstances set by the environment and other organisms” 7 Questions at the interface of Functional Ecology and Community Ecology Why are these questions at this interface? Because: In the framework of the Biodiversity-Ecosystem Function debate, the functional significance of biodiversity arises primarily from diversity of functional traits among the species in a community. 8 Functional Plant Diversity 9 Many ecologists believe that the key to understand these questions depends on our understanding of intra- and interspecific variation in plant functional traits Huge amount of research studies to characterize the functional diversity of species 10 Functional diversity of leaf traits 14 tree species in French Guiana 11 NOTE: Functional diversity measures at community level 12 Correlation and trade-off among traits Study on seedlings of 32 species in French Guiana Leaf functional and performance traits 1.0 20 0.8 ) -1 d -1 15 0.6 (mg g (mg 10 0.4 25% PAR 25% 5 0.2 RGR Understory Survival Rate Survival Understory 0.0 0 2 2 3 3 A 4 A 4 sat (umol 6m sat (umol 6m 2 8 2 8 -2 -2 10 s -1 10 s -1 ) 12 1 ) 12 1 14 N fol (%) 14 N fol (%) 0 0 Baraloto et al. in prep. Oecologia 13 Correlation and trade-off among traits There are fundamental differences among species in functional traits and in the trade-offs of these functions Functional traits provide an important tool in community ecology as they reflect trade-offs that determine species performance in a given environment and consequently species abundances along environmental gradients The quantification of these trade-offs as multivariate trait spectrums is consistent with the idea of Plant Strategies Plant strategies is central to developing a trait-based theory of community assembly and a general understanding of the dynamics and functioning of ecosystems 14 Plant strategies First edition in 1974 15 Plant strategies Grime introduced the CSR theory : “Each plant species has a blend of three strategies” : C (competitive), S (stress tolerant) and R (ruderal, or rapid propagation). Species differ in the “proportion” of these strategies This theory states that environmental stress and disturbance agents are providing the principal constraints on plant evolution and community structure. According to habitat, each species must adopt a predictable compromise with regard to how they use the resources in order to survive. The compromise involves the investment of resources in either the effort to acquire more resources, the tolerance of factors that reduce metabolic performance, or reproduction. 16 Ecological niche The ecological niche describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors Many definitions: A term used to describe a species’ habitat and distribution or a place in the environment that can be empty or filled? Hutchinson, 1957: Fundamental niche - hypervolume (>3 axes) within which a species can survive or reproduce The niche defines the total ecological space in which a species could survive http://bblonder.wordpress.com/2014/02/26/the-ecological-niche-and-the-n-dimensional-hypervolume/ 17 Community Assembly 18 Reminder : Mixture effect on ecosystem functioning 19 Community assembly 20 Community assembly Assembly rules: • Predators cannot invade a habitat where there are no prey • Abiotic conditions limit species ranges (e.g. temperature, presence of soil, etc) A lynx being a predator! A lynx just exercising! 21 Community assembly Assembly rules: • Predators cannot invade a habitat where there are no prey • Abiotic conditions limit species ranges (e.g. temperature, presence of soil, etc) • Priority rules: species that arrive first can potentially exclude later-arriving species 22 Community assembly Assembly rules: • Only some combinations of species exist, some never do • Stable combination types vary within a given environment 23 Community assembly Temporal variation in assembly Community assembly Keep in mind that … … a great uncertainty persists regarding the importance of different ecological processes in shaping species distribution in complex communities 25 Community assembly Theory of Community: Speciation, Drift, Extinction, Birth and Dispersal interact to determine community composition and dynamics across spatial scales Extinction Speciation Drift Metacommunity Birth Local community Dispersal Drift Death 26 Ecological processes in shaping species distribution Numerous studies show how plant functional traits affect the performance of individual species, but our ability to predict community assembly from these relationships is nevertheless limited. Community-level studies analyzing functional traits and species abundances have shown that niche-related processes clearly play a role in community assembly, while unpredictable chance events or the influence of local environmental conditions are also proposed to play a leading role … 27 Neutrality 28 Neutral theory The distribution of species in a given environment is related to stochastic processes operating at the different levels: 1967 2001 Extinction S.P. Hubbell Speciation Metacommunity Birth Local community All individuals in a community are strictly Dispersal equivalent regarding their prospects of reproduction and death This theory implies that biodiversity arises Death at random, as each species follows a “random walk” 29 Neutral theory The probabilities of immigration from the meta- community, and the probabilities of survival and reproduction of all species, are equal (demographic neutrality). Subsequent population dynamics in the local community are determined purely by random drift. “Surprisingly”, this theory is able to quite-well summarize a large array of empirical patterns of species abundance! Particularly in highly-diverse tropical rainforests So, even if one cannot rule out other potential mechanisms to explain patterns, why are these null models so well- describing some of the community assemblage? 30 Neutral theory - Example Example with tropical rainforest plots Gaussian model = Stochastic description of species distribution31 Environmental filtering Niche based 32 Environmental filtering Grime: A plant strategy is systematically associated with particular environmental conditions The most common trait values in a local community will be possessed by those individuals having the greatest probabilites of survival, reproduction and immigration. S ∑piti = twm Community mean trait value i=1 ofpassingfilters This average trait value will probability relative abundance~ relative reflect the selective A B C D E species advantage/disadvantage of this tA tB tC td tE traits of species trait in passing through the various abiotic and biotic filters 33 Environmental filtering Consequences of Grime’s ideas for community assembly: • Understanding how community functional composition varies across environmental gradients is necessary to understand community assembly • If environmental conditions strongly filter species among habitats, you can expect directional shifts in mean trait values among habitats and reductions in the range and variance of these traits at the community level 34 Environmental filtering The influence of environmental filtering
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