Mechanistic principles from engineering, meteorology, and soil physics are integrated with ecology and physiology to develop models for prediction of animal behavior. The Mojave Desert biome and the desert iguana are used to illustrate these principles.A transient energy balance model for animals in an outdoor environment is presented. The concepts and relationships have been tested in a wind tunnel, in a simulated desert, and in the field. The animal model requires anatomical information and knowledge of the thermoregulatory responses of the animal. The micrometeorological model requires only basic meteorological parameters and two soil physical properties as inputs. Tests of the model in the field show agreement between predicted and measured temperatures above and below the surface of about 2 to 3°C.The animal and micrometeorological models are combined to predict daily and seasonal activity patterns, available times for predator-prey interaction, and daily, seasonal and annual requirements for food and water. It is shown that food, water and the thermal environment can limit animal activity, and furthermore, the controlling limit changes with season. Actual observations of activity patterns and our predictions show close agreement, in many cases, and pose intriguing questions in those situations where agreement does not exist. This type of modeling can be used to further study predator-prey interactions, to study how changes in the environment might affect animal behavior, and to answer other important ecological and physiological questions.
Two types of rapid water table responses to rain were observed in a northern Michigan peatland. The first, called the Lisse effect, occurred during rains of high intensity when the infiltrating water acted as a tightly closing lid that forced the water table to rise to the level required to compensate for the pressure increase. The second, called the Wieringermeer effect, was a rapid rise of the water table to the surface due to the conversion of capillary to phreatic water and was always followed by an equally rapid decline after cessation of the rainfall. We simulated these phenomena in the laboratory and estimated the critical parameters that determine their occurrence. The recognition of the importance of the capillary fringe is essential in evaluating the role of wetlands in flood control and in wastewater treatment.
To examine nonclimatic factors controlling small-peatland development we expanded the classical model ofpeatland development by hypothesizing the existence of three horizontal zones. We then tested five predictions derived from the expanded model. Prediction 1: Peat Strata. There are two vertical strata of peat, an upper layer consisting of peat formed in the floating or grounded mat (mat peat) and a lower layer of peat formed in the floating mat, but dropped from the side or bottom of the mat (debris peat). Underlying these strata are lake sediments originating in the water column. Prediction 2: Strata Boundary. Chamaedaphne calyculata provides the framework for mat growth, and therefore stems and roots of this plant form the boundary between the two peat strata. The lower boundary of mat peat is continuous from the lake edge to the upland. Prediction 3: Strata Thickness. Thickness of mat peat increases as a function of the depth of the original basin and the length of time peat has been accumulating. Prediction 4: Peat Density. The density of peat increases with distance from the lake edge up to a zone in which peat has reached a maximum density and mean density is constant. Prediction 5: Vertical Accumulation Rate. The long-term rate of vertical accumulation (in grams per square metre per year) decreases with distance from the lake edge.To test these predictions we used data collected on peat stratigraphy, lake-edge vegetation, and peat age and density in Fallison Bog, a 5.5-ha peatland-lake system in northern Wisconsin, and to a lesser extent from 13 other peatlands in the region. Each prediction was confirmed, except that thickness of mat peat appears to be independent of peat accumulation time.We estimated the vertical growth rate of the mat by radiocarbon dating of C. calyculata stems. By dating twigs at different locations in the mat we estimated that the rate of vertical peat accumulation ranges from 34-75 g·m-2 ·yr-', depending on location within the peatland.The relationships among peat densities, vertical accumulation rates, and distance from the lake edge suggest that three horizontal zones occur in Fallison Bog: (I) a zone of thickening near the lake edge where vertical accumulation of organic matter thickens the floating mat, (2) a zone of compaction farther from the lake edge where vertical accumulation compacts underlying peat, and (3) a zone of equilibrium farthest from the lake edge where peat has reached a maximum density (100-110 kg!m 3 in Fallison Bog) and, in the absence of a perched water table, no peat accumulates. Our results underscore the importance of spatial dynamics in peatland development.
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