and maintenance of species diversity in plant communities 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

Jak definovat kompetici? Grace (1990): “The variety of possible definitions of competition were discussed and it is safe to say that there is no universally accepted definition.” 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)

Typy kompetice Obr. Connell

Negativní efekt zprostředkovaný ohněm (strategie: Ať mě chcípne koza, hlavně když sousedovi chcípne kráva!)

Allelopathy: release of toxic chemicals to the soil (to prevent germination and growth) Problems - how to demonstrate experimentally? Similar effect - production of litter with low decay rate

Apparent competition Low birches (Betula nana) are under higher herbivor pressure under congeneric Betula tortuosa.

Resource competition Resource must be limiting, in restricted amount, and in common use

Components of resource competition

Both relationships must operate simultaneously 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 Stable equilibrium if and 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 Tilman’s theory: the species with lower R* is the winner (i.e. species, able to growth in the lowest concentration of the resources)

Population Resource

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

Experimental approaches

Growing plants in monocultures and together Long tradition in agricultural research

Pot competition experiment with Holcus lanatus, Lychnis flos cuculi and their mixture at different nutrient levels

Additive design vs. replacement series

Transplant experiments - Prunella vulgaris

Clonal plant’s reaction to competition - increase of stolon length and orientation of stolons to “competition free” part

Lychnis flos cuculi Tradeoff between flowering (in competitive environment) and producing secondary rosettes (in gaps)

Removal of vegetation around target individuals Attempts to separate above- and belowground competition

Dominant removal from a community

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

What is medium depends on the productivity

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

Seedling recruitment of Gentiana pneumonanthe mown burned gap control