Search

Mathematical model studies have been conducted to investigate the effect of excessive growth of wild grasses such as Paspalum distichum on the growth of other macrophytes in the wetland of the Keoladeo National Park, Bharatpur, India. The model parameters are determined by the regression analysis of the observed biomass data for the Paspalum distichum and other aquatic macrophytes. A good agreement of numerical solutions with the observed data shows the applicability of the model. The model results show fast growth or the Paspalum distichum to its carrying capacity and decay of other macrophytes to a low equilibrium density thus demanding proper management of the wetland. A non-linear stability analysis of the control model incorporating the effort of removal of the grasses establishes the unconditional stability of the model solutions. Applying the model to the Park's wetland, it is found that an increasing effort is required to control the wild grasses. It is also seen that an increased rate of depletion of the grasses not only reduces their equilibrium and peak densities but also helps in restoring other macrophytes to the initial state.

In this paper, a mathematical model is proposed to study the effect of ecological changes caused by the excessive growth of wild grasses such as Paspalum distichum on the existence of various species in the Keoladeo National Wetland Park, Bharatpur, Rajasthan, India. In the model the growth rate of several species, such as floating vegetation ( Nymphoides indicum, Nymphoides cristatum, Nymphaea nouchali and Nymphaea stellata ), fishes, waterfowl, etc. and the corresponding carrying capacity of the wetland are assumed to decrease with the increase in biomass density of wild grasses. By analysing the model it is shown that if the wild grasses are not controlled, the existence of various other species will be threatened. It is shown through the model study that if the growth of wild grasses is controlled, either by allowing a managed number of buffaloes to graze them or by using some other mechanism to remove them, then the other species in the wetland will boom. Keeping in view the growth of Paspalum distichum and using the corresponding parameters for this wetland in the model, the number of buffaloes to be permitted for grazing has also been calculated for management purposes.

This paper offers a contrasting view to Shukla and Dubey's model (Ecol. Model. 86, 91-99, 1996) which advocates the introduction of water buffalo in the Keoladeo National Park to remove wild grasses, specifically Paspalum distichum. Using their model based on logistic equations of plant growth, they predict that 1247 water buffalo are required to clear emergent vegetation, to create an open water environment dominated by water lilies (Nymphaea and Nymphoides sp.). The historical setting of the 'water buffalo' controversy stems from the removal of water buffalo from Keoladeo National Park in 1981. After this, Paspalum distichum began to dominate the vegetation, altering the appearance of the wetland. In contrast to Shukla and Dubey's model, research conducted by Iowa State University in the 1980's in this park suggest that the grasses are now eaten by native herbivores such as Greylag and Barheaded Geese, nilgai, and wild boar. Grazing by these wild herbivores creates openings in the emergent vegetation and is likely sufficient to maintain species richness in Keoladeo National Park. Shukla and Dubey's claim that the reintroduction of water buffalo in the park is necessary to maintain species richness is unsupported bv field research.