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Modeling the effect of colonial breeding in bubulcus ibis (Aves: Ardeidae) on biomass and energy flows of coastal mangrove

Abstract:

Introduction: The colonies of wading birds reach thousands of highly grouped nests, which have a marked influence on the characteristics of the soil or the water that surrounds them due to a hyperfertilization effect. This causes the harmful accumulation of nitrogen compounds altering the chemistry of the substrate and causing defoliation and death of vegetation. The impact of these colonies on the mangroves in Cuba has not been evaluated, due to the logistical difficulties involved and the complexity of their processes. Objective: Mathematical modeling is a useful tool in these situations, so in this work the estimation of the quantities of biomass, energy and nutrients mobilized in a colony of herons was carried out, through a bioenergetic model of system dynamics. Methods: We used 29 primary variables, 3 bioenergetic equations and the postnatal growth equation of this species, implemented in the STELLA 9.1.3 program. From the interaction of these variables, the energy required by the reproduction cycle, the biomass consumed and the nutrients deposited in the colony were obtained. A sensitivity analysis and an uncertainty analysis were carried out to explore the variables that have the most influence on the results. The model was validated by the consistency in the units, the test of extreme values and the comparison with values recorded in the literature. Finally, disturbances scenarios that can affect a real colony were simulated. Results: According to the model, each nestling require 10 219.2 kcal to growth. The colony must totally invest 6.71x106 kcal, which represents consumption close to 2.2 tons of dams. Due to this consumption, the nutrients deposited in the colony by the excreta were 49 kg of nitrogen, 7 kg of phosphorus and 56 kg of calcium. According to the sensitivity analysis, the variables that produce the strongest changes in the result are the number of adults in the colony and the average clutch size. The uncertainty analysis showed little influence of the variables selected on the response variables. The most harmful simulated disturbances for the colony were the affectations to the recruitment and the increase of the mortality of the nestlings.