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Despite widespread and long-standing efforts to model wildlife-habitat associations using remotely sensed and other spatially explicit data, there are relatively few evaluations of the performance of variables included in predictive models relative to actual features on the landscape. As part of the National Gap Analysis Program, we specifically examined physical site features at randomly selected sample locations in the Southwestern U.S. to assess degree of concordance with predicted features used in modeling vertebrate habitat distribution. Our analysis considered hypotheses about relative accuracy with respect to 30 vertebrate species selected to represent the spectrum of habitat generalist to specialist and...
Alien plants invade many ecosystems worldwide, often having substantial negative effects on ecosystem structure and functioning. The apparent complexity of invasions has impaired the development of a predictive framework of alien plant spread. Such a framework requires both a conceptual understanding of the ecology of invasions and appropriate modelling tools. We demonstrate, using a simple conceptual model and illustrative examples from the literature, that a predictive understanding of invasions can be established. Potential modelling tools are reviewed by categorizing models of plant spread as either simple-demographic, spatial-phenomenological or spatial-mechanistic, based on the model's data inputs and outputs....
The ecological process model Image (a Image ccession Image del) has been adapted to whitebark pine (Pinus albicaulis) forests of the inland Northwest and Rocky Mountains, U.S.A. Image simulates tree establishment, growth, and mortality on a 400-m2 plot. Also modelled are live and dead fuel accumulations, fire behavior, fuel reduction, and insect and disease mortality. The following influences on tree establishment and growth are simulated in the model: temperature, water stress, site quality, and light conditions. An additional submodel in Image simulates the mutualistic relationship between the Clark's nutcracker (Nucifraga columbiana) and the whitebark pine. Seed caches made by the Clark's nutcracker are evidently...
We evaluated the effects of probabilistic (hereafter DESIGN) and non-probabilistic (PURPOSIVE) sample surveys on resultant classification tree models for predicting the presence of four lichen species in the Pacific Northwest, USA. Models derived from both survey forms were assessed using an independent data set (EVALUATION). Measures of accuracy as gauged by resubstitution rates were similar for each lichen species irrespective of the underlying sample survey form. Cross-validation estimates of prediction accuracies were lower than resubstitution accuracies for all species and both design types, and in all cases were closer to the true prediction accuracies based on the EVALUATION data set. We argue that greater...
The diversity of forest stands may be affected by landscape fragmentation during periods of climatic change. A modified version of the Image model of the dynamic processes of establishment, growth, and death of forest trees is used in a spatially explicit framework to elucidate differences in the effects of both spatial structure and spatial processes. In cases with and without climatic change, the effects of including random or structured fragmentation and successively lower dispersal probabilities (increased chance of long-distance dispersal) are examined in simulation experiments. The exclusion of very low dispersal probability (p < 0.001) has an important effect on species richness. Barriers and random fragmentation...
Interaction Assessment (INTASS) is a field and analytic methodology for constructing population dynamics models. Because data collected in generating a model for one species comprise much of the information needed for other species, a small increase in effort can result in simultaneous expressions for the dynamics of multiple species. These expressions can be used to simulate whole community responses to environmental change, including management actions. Since publication of the most recent paper in this series, the INTASS methodology has undergone a large number of developments. These include the use of conceptual models to direct field and modeling efforts and incorporation of an information theoretic approach...
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A Leslie matrix model was developed for a small gray wolf (Canis lupus) population recolonizing an area with abundant resources and uncontrolled by humans. The model was modified to describe population growth in a limited environment using a discrete form of the logistic equation. The density dependent Leslie matrix model was applied to investigate gray wolf population recovery in the Upper Peninsula of Michigan. Estimates from the density dependent matrix model were compared with published winter count estimates from the Michigan Department of Natural Resources. The gray wolf population in the Upper Peninsula of Michigan was projected to reach a total of 929 wolves by the year 2012 with a 95% confidence interval...
The reintroduction of gray wolves to Yellowstone National Park (YNP) provides a natural experiment regarding the effects of top predators on scavenger species. Fieldwork on the Northern Range of Yellowstone indicates that wolves facilitate carrion acquisition by scavengers, but it is unclear whether this represents a transient or permanent effect of wolf reintroduction. Here we present a wolf-elk model with human elk harvest and use it to investigate the long-term consequences of predator?prey dynamics and hunting on resource flow to scavengers. Our model shows that while wolves reduce the total amount of carrion, they stabilize carrion abundance by reducing temporal variation in the quantity of carrion and extending...
Global climatic change is expected to affect growth and survival of trees and will likely change the geographical distribution of many temperate and boreal tree species. Models that calculate the effects of environmental factors, as well as biotic factors, such as intra- and interspecific competition, on growth and survival of trees have been widely used to calculate the potential effects of temperature changes on tree populations. The methods to calculate thermal effects in such models are described and analyzed for the soundness and consistency of underlying assumptions. They are compared to the evidence from studies of tree physiology, growth, and biogeography. The use of thermal indices, especially temperature...
Often landmark conservation decisions are made despite an incomplete knowledge of system behavior and inexact predictions of how complex ecosystems will respond to management actions. For example, predicting the feasibility and likely effects of restoring top-level carnivores such as the gray wolf (Canis lupus) to North American wilderness areas is hampered by incomplete knowledge of the predator-prey system processes and properties. In such cases, global sensitivity measures, such as Sobol? indices, allow one to quantify the effect of these uncertainties on model predictions. Sobol? indices are calculated by decomposing the variance in model predictions (due to parameter uncertainty) into main effects of model...
Atmospheric deposition of sulfur and nitrogen species have the potential to acidify terrestrial and aquatic ecosystems, but nitrate and ammonium are also critical nutrients for plant and microbial productivity. Both the ecological response and the hydrochemical response to atmospheric deposition are of interest to regulatory and land management agencies. We developed a non-spatial biogeochemical model to simulate soil and surface water chemistry by linking the daily version of the CENTURY ecosystem model (DayCent) with a low temperature aqueous geochemical model, PHREEQC. The coupled model, DayCent-Chem, simulates the daily dynamics of plant production, soil organic matter, cation exchange, mineral weathering, elution,...
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We developed and applied a simple population model to examine the relation between abundance of wolves in a wilderness area and the numbers that emigrate into adjacent agricultural areas and that may need to be removed on an annual basis. The model was applied using Minnesota wolf (Canis lupus) data. The gray wolf is emigrating from northern wilderness areas in the State of Minnesota (USA) into adjacent agricultural and urban areas to the south, and the costs of both wolf control and compensation to farmers for lost livestock is increasing as the number of wolves increases. Emigration reduces the number of wolves on a refuge to about 85% of the carrying capacity, and the number of wolves that emigrate into the agricultural...
The management of canid populations has been at the forefront of wildlife management worldwide for much of the last century. Effective management depends on the ability to integrate species biology, the environmental aspects upon which those populations depend, and the factors controlling species abundance. Further, managing canid populations requires consideration of territoriality and dominance, which may have a significant effect on population dynamics. To better understand the effect of social structure on canid populations, we developed an individual-based computer model using Swarm to mimic natural coyote population dynamics. We selected the Swarm simulation environment because it is ideally suited for creating...
A generalized mathematical model for plant growth was developed to simulate primary productivity and response to grazing of cold desert shrubs. The model simulates root, shoot, and carbohydrate reserve biomass for periods of 5?20 y using a weekly time step and equations based on the principles of growth analysis. The effect of soil water on plant growth is simulated by an empirical relationship between average soil water content and annual production. A separate evaporation model simulates weekly soil water content using precipitation data. The plant model requires weekly average and maximum air temperatures. Other data requirements have been reduced so that the model can be adapted to different species and different...
Effective conservation of amphibian populations requires the prediction of how amphibians use and move through a landscape. Amphibians are closely coupled to their physical environment. Thus an approach that uses the physiological attributes of amphibians, together with knowledge of their natural history, should be helpful. We used Niche Mapper? to model the known movements and habitat use patterns of a population of Western toads (Anaxyrus (=Bufo) boreas) occupying forested habitats in southeastern Idaho. Niche Mapper uses first principles of environmental biophysics to combine features of topography, climate, land cover, and animal features to model microclimates and animal physiology and behavior across landscapes....
Despite fire cycles of increasing severity and frequency in the arid western U.S., very little empirical analysis has examined the success of plant seeding on arid rangeland following fire. This manuscript uses a unique dataset to assess causal factors underlying the measured densities, several years after fires, of: (1) unwanted invasive grasses, (2) seeded grasses, and (3) sagebrush, on rangeland in a western U.S. state. To accommodate various characteristics of the data, we employ trivariate tobit maximum likelihood estimation. Results indicate that the success of reseeding efforts is sensitive to the timing of and techniques used in reseeding, as well as whether grazing is allowed on the land. Our findings have...
Millions of acres of rangeland in the western United States are now dominated by introduced annual weeds such as cheatgrass (Bromus tectorum L.). The ability to germinate rapidly at low temperatures has been proposed as one of many mechanisms that confer a competitive advantage to this species. Previous studies of this phenomenon, however, have been limited to relatively simple comparisons of total germinability and germination rate under selected constant-temperature treatments. In this study, we germinated seeds of cheatgrass and two native perennial bunchgrass species, bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Löve] and big squirreltail [Elymus multisetus (J.G. Smith) M.E. Jones], over the temperature...
To aid in the management and conservation of Southwestern Willow Flycatcher (Empidonax traillii extimus, hereafter “Flycatcher�), we developed numerous models of flycatcher breeding habitat at Roosevelt Lake, AZ. For model development and testing, we compiled 10 years of flycatcher territory data that were obtained from intensive fieldwork between 1996 and 2005. We identified riparian vegetation annually in the project area from Landsat Thematic Mapper images, and extracted floodplain features from a digital elevation model. We created a novel class of temporal (i.e., multiyear) variables by characterizing the stability and variability in breeding habitat over a 6-year time interval. We used logistic regression...
The use of advanced modelling methods in ecology expands as ecological data accumulates and increases in complexity. Artificial neural networks (ANN), and in particular, the self-organising map (SOM), has become very popular for analysing particular kinds of ecological datasets. As SOM have become more utilised, it has become increasingly clear that the results of SOM models must be interpreted carefully. SOM have been used in a number of ecological studies to investigate the spatial distribution of species. When using presence–absence data of species distributions at given locations, the input vectors to a SOM are binary and the connection weights after learning are between 0 and 1. Using fuzzy set theory, we...
Beaver–willow (Castor-Salix) communities are a unique and vital component of healthy wetlands throughout the Holarctic region. Beaver selectively forage willow to provide fresh food, stored winter food, and construction material. The effects of this complex foraging behavior on the structure and function of willow communities is poorly understood. Simulation modeling may help ecologists understand these complex interactions. In this study, a modified version of the SAVANNA ecosystem model was developed to better understand how beaver foraging affects the structure and function of a willow community in a simulated riparian ecosystem in Rocky Mountain National Park, Colorado (RMNP). The model represents willow in...
    map background search result map search result map Density dependent matrix model for gray wolf population projection Modeling emigration of wolves from a wilderness area into adjacent agricultural regions Density dependent matrix model for gray wolf population projection Modeling emigration of wolves from a wilderness area into adjacent agricultural regions