Showing papers by "Donald L. DeAngelis published in 1994"

Competition and Coexistence: The Effects of Resource Transport and Supply Rates

Abstract: Classical resource competition theory can be generalized to apply to a variety of specific resource types and specific supply media (e.g., soil, water, or air). We develop a general model that relaxes the assumptions that (1) resources and organisms are sufficiently mixed that all organisms experience the same resource concentration and (2) the organisms themselves regulate the resource concentration of their shared environment. These assumptions are shown to apply to a limited subset of conditions in which the resource input rate is low and the resource transport rate in the environment is high. Under such conditions, the coexistence criteria of our general model converge with those of classical resource competition models. Such conditions may be met in some aquatic environments, but under other conditions, in which resource transport rates may be low or input fluxes high, the general model makes predictions that differ radically from those of the classical models. Specifically, our model predicts that, ...

Effect of periphyton biomass on hydraulic characteristics and nutrient cycling in streams.

Abstract: The effect of periphyton biomass on hydraulic characteristics and nutrient cycling was studied in laboratory streams with and without snail herbivores. Hydraulic characteristics, such as average water velocity, dispersion coefficients, and relative volume of transient storage zones (zones of stationary water), were quantified by performing short-term injections of a conservative tracer and fitting an advection-dispersion model to the conservative tracer concentration profile downstream from the injection site. Nutrient cycling was quantified by measuring two indices: (1) uptake rate of phosphorus from stream water normalized to gross primary production (GPP), a surrogate measure of total P demand, and (2) turnover rate of phosphorus in the periphyton matrix. These measures indicate the importance of internal cycling (within the periphyton matrix) in meeting the P demands of periphyton. Dense growths of filamentous diatoms and blue-green algae accumulated in the streams with no snails (high-biomass streams), whereas the periphyton communities in streams with snails consisted almost entirely of a thin layer of basal cells of Stigeoclonium sp. (low-biomass streams). Dispersion coefficients were significantly greater and transient storage zones were significantly larger in the high-biomass streams compared to the low-biomass streams. Rates of GPP-normalized P uptake from water and rates of P turnover in periphyton were significantly lower in high biomass than in low biomass periphyton communities, suggesting that a greater fraction of the P demand was met by recycling in the high biomass communities. Increases in streamwater P concentration significantly increased GPP-normalized P uptake in high biomass communities, suggesting diffusion limitation of nutrient transfer from stream water to algal cells in these communities. Our results demonstrate that accumulations of periphyton biomass can alter the hydraulic characteristics of streams, particularly by increasing transient storage zones, and can increase internal nutrient cycling. They suggest a close coupling of hydraulic characteristics and nutrient cycling processes in stream ecosystems.

Individual-Oriented Approaches to Modeling Ecological Populations and Communities

Abstract: At the level of ecological populations and communities, modelers have usually followed the state variable approach, in which a separate state variable equation is written for each species population. This approach has been extended to account for age and size structure within populations by dividing a population into classes, each repesented by a density. Similarly, to account for the spatial patchiness of populations, populations have been modeled as sets of subpopulations connected by migration, with a separate variable to describe each subpopulation. Still, the basic nature of even these more complex models involves variables representing highly aggregated components of populations.

Importance of landscape heterogeneity to wood storks in Florida Everglades

Abstract: Declines in populations of and reproductive success of wood storks and other wading birds have occurred in the Florida Everglades over the past several decades. These declines have been concurrent with major changes in the Everglades’ landscape characteristics. Among the plausible hypotheses that relate to landscape change are the following: (1) general loss of habitat; (2) heavy loss of specific habitat, namely, short-hydroperiod wetlands that provide high prey availability early in the breeding season; and (3) an increase in frequency of major drying out of the central slough areas, which can affect prey availability late in the breeding season. These three hypotheses were compared using an individual-based model of wood stork (Mycteria americana) reproduction. This model simulated the behavior and energetics of each individual wood stork in a breeding colony on 15-min time intervals. Changes in water depth and prey availability occurred on daily time steps. Simulation results showed a threshold response in reproductive success to reduction of wetland heterogeneity. Model comparisons in which (1) only short-hydroperiod wetlands were removed and (2) wetlands of both long and short hydroperiods were removed showed that, for the same loss of total area, the specific habitat removal caused a much greater reduction in wood stork reproduction, indicating hypothesis 2 may be a more likely explanation than hypothesis 1. Reduction of initial prey availability in the central slough areas (simulating frequent drying; hypothesis 3) reduced fledging success by an average of more than 90% in the model.

ATLSS: Across trophic level system simulation for the freshwater areas of the Everglades

Abstract: The Everglades of South Florida are characterized by complex patterns of spatial heterogeneity and temporal variability, with water flow being the major factor controlling the trophic dynamics of the system. A key objective of modeling studies is to compare the future effects of alternate hydrologic scenarios on the biotic components of the system. Due to the varying scales at which trophic interactions occur, and the importance of population structure and individual behavior for population prediction in higher trophic level organisms, use of a single modeling approach is not appropriate. We will describe a scheme to integrate three approaches for different trophic levels of the system: (1) process models for lower trophic levels (including benthic insects, periphyton and zooplankton), (2) structured population models for five functional groups of fish and macroinvertebrates, and (3) individual-based models for large consumers (wood storks, great blue herons, white ibis, American alligators, white-tailed deer, and Florida panther). These are integrated across the freshwater landscape of the Everglades and coupled to GIS maps for cover type. Spatial scales of resolution for the models are as small as 100 m, with the capability to vary this based upon the scale of available input data. The system is thenmore » coupled to a hydrology model, and used to assess the effects of alternative proposed restoration scenarios on trophic structure.« less