Prezentace na téma: "Kompetice rostlin and maintenance of species diversity in plant communities."— Transkript prezentace:
Kompetice rostlin and maintenance of species diversity in plant communities
Definice kompetice Důsledky přisedlého způsobu života Typy kompetice Komponenty kompetice o zdroje (resource competition) Modely Grime vs. Tilman Empirické studie - pozorování a manipulativní experimenty Species coexistence as violation of competitive exclusion principle Gradients of species diversity and their causes
Grace (1990): “The variety of possible definitions of competition were discussed and it is safe to say that there is no universally accepted definition.” Jak definovat kompetici? Možnosti: Podle efektu: interakce - - (obě populace jsou ovlivněny negativně. Velmi široká definice) Podle mechanismu: Grime: “The tendency of neighbouring plants to utilise the same resources” (velmi úzká definice) Řada dalších definic (někde mezi)
Rostlinná kompetice: Rostliny jsou sedentární, takže: Konkurence probíhá jen mezi sousedy - důležitost prostorové struktury a heterogenity Jsou ovlivněny heterogenitou prostředí (velká morfologická plasticita jako řešení) Zůstávjí během celého života na jednom místě Velikost individua je důležitější druhová identita (dospělý smrk lehce potlačí dospělou Calamagrostis ale dospělá Calamagrostis zahubí smrkový semenáč) Kompetice je velmi asymetrická (zvláště kompetice o světlo)
Both relationships must operate simultaneously. If not, there is no effect of one species on another
Plant affects both resource and non-resource characteristics (Tree decreases light by shading, but could protect from overheating) Effect is not always detrimental Facilitation (usually in stressed environments, or in stress periods) [Gap effect on transplant growth was highly positive during a wet year, but highly negative during dry year]
Classical Lotka-Volterra competition model and Stable equilibrium if i.e., when the inhibitive effect of each species on its own population is bigger than on the competitor (scaled by the corresponding K) => niche differentiation
Tilman’s theory: the species with lower R * is the winner (i.e. species, able to growth in the lowest concentration of the resources)
According to the theory, number of coexisting species can not exceed the number of limiting resources Plant compete for light and [water and nutrients] (and often tens of species coexist on a small area) Competition for pollinators, seed dispersers Competition for space - the aboveground space is far from being filled by plant mass. “Competition for space” - the way sedentary organisms attempt to monopolise the resources.
Grime vs. Tilman What is measure of competition success What are the trait of successful competitors (Grime - ability to capture the resources, high RGR, Tilman ability to grow at low resource levels, i.e. low R*) Importance of time scale
Empirical studies of competition 1. (Indirect) From (spatial) pattern 2. (Direct) Manipulative experiments a) planting (sowing) monocultures and mixtures b) transplanting (e.g. into a sward and into a gap) c) removal of vegetation in surrounding of target d) removal a species from a community
Regular (uniform) spatial patter is most probably consequence of increased mortality due to neighbours competition Aggregated (clumped) pattern has many causes, positive interactions being just one of less probable. (Most common: environmental heterogeneity, dispersal.) Changes in the pattern in the course of time are better evidence than static pattern.
Correlating the available space (or quantity of neighbours) with performance of the individual. [Danger of the confounding factors, reverse causality, etc.] Eccentricity of the root system
Species coexistence: can be seen as a violation of the competitive exclusion principle Competitive exclusion principle: two species can not coexist for indefinitely long time in a homogeneous environment The equilibrium and non-equilibrium explanations Equilibrium: Environment is not homogeneous (niche differentiation) Non-equilibrium: time is not sufficient
Medium disturbance hypothesis Repeated disturbance of medium intensity or frequency is able to prolong species coexistence
Density dependence - parasites & predators Janzen hypothesis - species diversity in tropics
Gradients of species diversity Tree species richness in Canada and the United States. Contours connect points with the same approximate number of species per quadrat. Quadrat size is 2.5˚ x 2.5˚ south of 50˚N, and 2.5˚ x 5˚ north of 50˚N (Currie and Paquin 1987).
Diversity usually decreases at very low and very high productivity Explanations of gradients of species diversity: 1. by community mechanisms 2. by species pool
Diversity decrease at high nutrient levels: some of the hypotheses - less species adapted to high nutrient levels - higher competition at high nutrients (Grime) - switch from underground competition to competition for light (which is more asymmetric) - suppressed seedling recruitment
mownburnedgapcontrol Seedling recruitment of Gentiana pneumonanthe