Competition (biology)

Summary

Competition is an interaction between organisms or species in which both require a resource that is in limited supply (such as food, water, or territory). Competition lowers the fitness of both organisms involved since the presence of one of the organisms always reduces the amount of the resource available to the other. In the study of community ecology, competition within and between members of a species is an important biological interaction. Competition is one of many interacting biotic and abiotic factors that affect community structure, species diversity, and population dynamics (shifts in a population over time). There are three major mechanisms of competition: interference, exploitation, and apparent competition (in order from most direct to least direct). Interference and exploitation competition can be classed as "real" forms of competition, while apparent competition is not, as organisms do not share a resource, but instead share a predator. Competition am

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The impact of flood variables on riparian vegetation

Katarína Dzubáková, Peter Molnar

The riparian vegetation of Alpine rivers often grows in temporally dynamic riverine environments which are characterized by pronounced meteorological and hydrological fluctuations and high resource competition. Within these relatively rough conditions, riparian vegetation fulfils essential ecosystem functions such as water retention, biomass production and habitat to endangered species. The identification of relevant flood attributes impacting riparian vegetation is crucial for a better understanding of the vegetation dynamics in the riverine ecosystem. Hence, in this contribution we aim to quantify the ecological effects of flood attributes on riparian vegetation and to analyze the spatial coherence of flood-vegetation interaction patterns. We analyzed a 500 m long and 300-400 m wide study reach located on the Maggia River in southern Switzerland. Altogether five floods between 2008 and 2011 with return periods ranging from 1.4 to 20.1 years were studied. To assess the significance of the flood attributes, we compared post-flood to pre-flood vegetation vigour to flood intensity. Pre- and post-flood vegetation vigour was represented by the Normalized Difference Vegetation Index (NDVI) which was computed from images recorded by high resolution ground-based cameras. Flood intensity was expressed in space in the study reach by six flood attributes (inundation duration, maximum depth, maximum and total velocity, maximum and total shear stress) which were simulated by the 2D hydrodynamic model BASEMENT (VAW, ETH Zurich). We considered three floodplain units separately (main bar, secondary bar, transitional zone). Based on our results, pre-flood vegetation vigour largely determined vegetation reaction to the less intense floods (R = 0.59-0.96). However for larger floods with a strong erosive effect, its contribution was significantly lower (R = 0.59-0.68). Using multivariate regression analysis we show that pre-flood vegetation vigour and maximum velocity proved to be the most significant variables impacting vegetation response. Generally, maximal flood attributes had more significant impacts than integrated attributes over the flood duration. Additional explanatory variables in the model should account for vegetation heterogeneity, groundwater conditions and different effects of lateral and surface erosion.

2016

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Questions What is the importance of root competition in the competitive abilities of dominant and subordinate species? Location Pair-wise greenhouse experiment based on field data from a semi-natural grassland community in the Swiss Jura Mountains (Col du Marchairuz, Switzerland). Methods The dominance hierarchy from a mountain wood-pasture ecosystem was used to identify five dominant and three subordinate species. These species were grown in pair-wise combinations under full competition and in the absence of root competition, enabling us to calculate indices of competitive effect and response and overall asymmetry. Results Root competition exclusion led to a decrease in the competitive abilities of dominants, whereas subordinates became overall more competitive. Total asymmetry also decreased, indicating reduced competition between the two species groups. The exclusion of root competition increased both below-ground and above-ground growth of subordinates, whereas for dominants below-ground growth was unaffected and above-ground growth decreased. Conclusions We demonstrate that root competition through rootshoot competition interactions is an important factor driving the competitive dominance of species and the structure of grazed grassland communities. Locally, reduction of root competition involved in gap creation might explain persistence of subordinate species within the vegetation community and lead to an aggregated spatial pattern of subordinates involved in species co-existence in grasslands.

Opulus Press2012

Effect of competing ions and complexing organic substances on the cadmium uptake by the soil bacterium Sinorhizobium meliloti

Rita Hajdu Schenk

In an effort to improve the understanding and prediction of Cd uptake by soil bacteria, adsorbed and intracellular Cd were determined in unpolluted and highly polluted model soil solutions within a concentration range spanning from 10-9 to 5  10-5 M of cadmium. In parallel, the free cadmium ion concentrations ([Cd2+]) were measured by a hollow fiber permeation liquid membrane. Obtained results demonstrated that Cd uptake by bacterium Sinorhizobium meliloti was related to [Cd2+] in the solution. Addition of different complexing organic substance reduced [Cd2+] in the bacterial medium and decreased both adsorbed and intracellular Cd. The adsorbed Cd was considerably reduced in the presence of 10-4 to 5  10-2 M [Ca] or [Mg]. No effect on Cd adsorption was observed in the presence of Zn or Mn, even at 100-fold excess. Intracellular Cd decreased in the presence of a high excess of Ca and Zn, while no significant effect was observed in the presence of Mg. An increase of dissolved Mn from 10-9 to 10-8 M resulted in a two-fold decrease of the intracellular Cd, but no clear trend was observed in the presence of 10-7 to 10-6 M of Mn. Based on complexation and competition studies, the stability constants, necessary for quantitative description of Cd uptake by S. meliloti and the development of the bacterial biotic ligand model for Cd, were derived and validated in the solutions containing mixtures of Cd , Zn, Ca and Mg. Further numerical simulations of Cd uptake by S. meliloti exposed to soil pore waters, demonstrated the importance of Zn competition and the insignificant influence of Ca and H on Cd uptake.

2009

The impact of flood variables on riparian vegetation

Katarína Dzubáková, Peter Molnar

2016