William R. Clark

Bio: William R. Clark is an academic researcher from Iowa State University. The author has contributed to research in topics: Population & Population density. The author has an hindex of 25, co-authored 55 publications receiving 1711 citations.

Predator selection of prairie landscape features and its relation to duck nest success

Abstract: Mammalian predation is a major cause of mortality for breeding waterfowl in the U.S. Northern Great Plains, and yet we know little about the selection of prairie habitats by predators or how this influences nest success in grassland nesting cover. We selected 2 41.4-km 2 study areas in both 1996 and 1997 in North Dakota, USA, with contrasting compositions of perennial grassland. A study area contained either 15-20% perennial grassland (Low Grassland Composition LGC]) or 45-55% perennial grassland (High Grassland Composition [HGC]). We used radiotelemetry to investigate the selection of 9 landscape cover types by red fox (Vulpes vulpes) and striped skunk (Mephitis mephitis), while simultaneously recording duck nest success within planted cover. The cover types included the edge and core areas of planted cover, wetland edges within planted cover or surrounded by cropland, pastureland, hayland, cropland, roads, and miscellaneous cover types. Striped skunks selected wetland edges surrounded by agriculture over all other cover types in LGC landscapes (P-values for all pairwise comparisons were <0.05). Striped skunks also selected wetland edges surrounded by agriculture over all other cover types in HGC landscapes (P < 0.05), except for wetland edges within planted cover (P = 0.12). Red foxes selected the edge and core areas of planted cover, as well as wetland edges within planted cover in LGC landscapes (i.e., they were attracted to the more isolated patches of planted cover). However, in HGC landscapes, red foxes did not select interior areas of planted cover (i.e., core areas of planted cover and wetland edges in planted cover) as frequently as edges of planted cover (P< 0.05). Red foxes selected core areas of planted cover more frequently in LGC than in HGC landscapes (P< 0.05) and selected pastureland more frequently in HGC than in LGC landscapes (P< 0.05). Furthermore, red foxes selected the isolated patches of planted cover more than pastureland in LGC landscapes (P< 0.05). Duck nest success was greater in HGC landscapes than in LGC landscapes for planted-cover core (P < 0.0001), planted-cover edge (P< 0.001) and planted cover-wetland edge (P< 0.001). Both the increased amount of planted-cover core area and the increased pastureland selection in HGC landscapes may have diluted predator foraging efficiency in the interior areas of planted cover and contributed to higher nest success in HGC landscapes. Our observations of predator cover-type selection not only support the restoration and management of large blocks of grassland but also indicate the influence of alternative cover types for mitigating nest predation in the Prairie Pothole Region.

Sampling Considerations for Disease Surveillance in Wildlife Populations

Abstract: Disease surveillance in wildlife populations involves detecting the presence of a disease, characterizing its prevalence and spread, and subsequent monitoring. A probability sample of animals selected from the population and corresponding estimators of disease prevalence and detection provide estimates with quantifiable statistical properties, but this approach is rarely used. Although wildlife scientists often assume probability sampling and random disease distributions to calculate sample sizes, convenience samples (i.e., samples of readily available animals) are typically used, and disease distributions are rarely random. We demonstrate how landscape-based simulation can be used to explore properties of estimators from convenience samples in relation to probability samples. We used simulation methods to model what is known about the habitat preferences of the wildlife population, the disease distribution, and the potential biases of the convenience-sample approach. Using chronic wasting diseas...

Population Ecology of Snowshoe Hares in the Central Rocky Mountains

Abstract: Measurements of natality rates, survival rates, movements, and densities were integrated to describe the mechanics of population balance for snowshoe hares (Lepus americanus) in Colorado (1969-71) and Utah (1972-73), near the southern extreme of this species' range. Adult home-range size averaged eight hectares in spruce (Picea spp.)-fir (Abies spp.) forest, the preferred habitat. Juveniles used unforested habitat more frequently than adults. Population density remained stable throughout the duration of both studies; historical accounts also indicate population densities have remained fairly stable in the Rocky Mountain region. Hares commenced breeding from mid-April to mid-May. Females surviving an entire reproductive season produced an average of 2.1-2.3 litters annually. Later-litter sizes, averaging 4.8 in Colorado and 5.9 in Utah, were larger than most litter sizes reported from higher latitudes. The annual natality rate was 8.2 and 11.5 young per female surviving an entire reproductive season in Colorado and Utah, respectively. Annual survival rate for adults in Colorado was 0.45. About 16 percent of juveniles born each summer needed to survive until the following breeding season to balance the population density. Second-litter juveniles had a lower survival rate than did first-litter juveniles. We surmise the long-term stability of the hare population in the Rocky Mountains to be related to dispersal of juveniles into poor (open) habitats where survival is low. The discontinuity of preferred spruce-fir habitat allows dispersal into open habitat to occur readily, and this may be the main mechanism averting the potential population increase. J. WILDL. MANAGE. 39(3):535-549 The snowshoe hare is indigenous to boreal forests throughout North America. This species has long interested population ecologists because of its "cyclic" population fluctuations (Keith 1963); however, mechanisms of population regulation are still poorly understood. In particular, little is known about population characteristics of hares in the southernmost extension of its range in the Rocky and Appalachian Mountains in the United States. This paper helps fill this void by presenting information on the population ecology of snowshoe hares in the Rocky Mountains of central Colorado (1969-71) and northern Utah (197273). The study had three objectives: (1) to estimate local densities of snowshoe hares, (2) to examine natality rates, survival rates, and movements, and to describe the immediate mechanics of population balance and fluctuation, and (3) to compare these populat on parameters with those published from snowshoe hare studies conducted at higher latitudes in an effort to clarify mechanisms causing cyclic fluctuations. We gratefully acknowledge J. E. Gross and M. L. Wolfe for their guidance and interest. D. A. Hein, F. H. Wagner, F. A. Glover, H. S. Donoho, S. Dolbeer, and M. Laderach also provided timely assistance.

Site selection and nest success of ring-necked pheasants as a function of location in Iowa landscapes

Abstract: Wildlife managers in the midwestern United States implicitly recognize that large-scale changes in land use have been a major factor in the nesting ecology of the ring-necked pheasant (Phasianus colchicus), but they have lacked models that quantify the relation between nest success and landscape variables at multiple scales. We used data from 288 nests of radiomarked female pheasants during the 1990-94 breeding seasons in Iowa to study nest-site selection and nest success. We quantified habitat and landscape metrics within the 485-m radius of a home range around nests by using aerial imagery and FRAGSTATS. We screened potential landscape variables by using principal component and classification and regression tree (CART) analyses before developing logistic regression models to predict nest-site selection and success as a function of landscape conditions. A 5-variable logistic regression model incorporating nesting patch size, mean grassland patch size, landscape core area, landscape shape index, and distance to edge predicted nest-site locations at a 77% posterior concordant rate. The CART analyses suggested nest success was best modeled by splitting nest observations into nests in patches ≤15.6 ha and >15.6 ha. For nests in patches ≤15.6 ha, a logistic regression model with site cover type and mean core area index predicted nest success with a 73% posterior concordant rate (P 15.6 ha, a model with site cover type, core area standard deviation, and distance from the nest to the edge predicted nest success best (concordant rate = 64%, P = 0.069), although the effect of distance to edge was very slight (conditional odds ratio = 1.003, 95% CI = 0.997-1.009). Our models suggest managers should strive to provide undisturbed grassland blocks ≥15 ha for nesting pheasants, but our observation was that success was highest in fields 4 times that size. Furthermore, cover in several large grassland blocks within the nesting home range is preferable to concentrating cover in 1 large block. Landscape models like ours could be used to project the consequences of changes in agricultural policy on ring-necked pheasant populations.

Predator activity related to landscape features in northern Iowa.

Abstract: We studied mammalian predator activity in relation to patches of grassland habitat in the agricultural landscape of northern Iowa to understand the potential interactions with ground-nesting birds, including waterfowl and ring-necked pheasant (Phasianus colrhicus). We quantified presence and movement direction of striped skunk (Mephitis mephitis), raccoon (Procyon lotor), and red fox (Vulpes vulpes) using unbaited track stations placed along the edges of 100-ha blocks of grassland and at other locations throughout the surrounding landscape. We used logistic regression with repeated measures and Akaike weights to develop predictive models of predator presence as a function of landscape variables including distance from a grassland block, shape of grassland edges, and presence of woodlands, farmsteads, and wetlands. Predators were detected at track stations in the landscape near (≤500 m) grassland blocks 33.5% of the time, more frequently than at stations immediately adjacent to edges of blocks (22.6%), and much more frequently than at stations distant (>500 m) from blocks (13.6%). Striped skunk presence at a station decreased as distance from grassland patches increased and was positively related to the number of farmsteads; raccoon presence was positively related to presence of woody cover; and red fox presence increased with greater area of pastureland and greater isolation from farmsteads, and decreased with increasing amount of strip habitat in the landscape. Predicted predator presence at locations where duck nests were found ≤500 m from blocks of grassland (23.1%) was within 1 SE of the Mayfield nest mortality rate, whereas predicted presence at isolated nest locations (12.0%) was greater than observed nest mortality. Track stations indicated that predators moved into and out of grassland patches at corners of blocks (80% of the time) much more frequently than when they traveled along the straight sides of blocks (7%). If presence of predators is directly related to predation rate, our models predict that risk to nesting birds would be greatest in patches near large grassland blocks where corridors, corners, and smaller patches focus predator activity. We envision that wildlife biologists could use models of predator activity to predict the potential influence of landscape configuration on predation risk to nesting birds.

Temporal Variation in Fitness Components and Population Dynamics of Large Herbivores

Abstract: ▪ Abstract In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV 30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, ma...

Interspecific Killing among Mammalian Carnivores

Abstract: Interspecific killing among mammalian carnivores is common in nature and accounts for up to 68% of known mortalities in some species. Interactions may be symmetrical (both species kill each other) or asymmetrical (one species kills the other), and in some interactions adults of one species kill young but not adults of the other. There is a positive significant relationship between the body masses of solitary killer species and body masses of their victim species, and grouping species kill larger victims than solitary species. Interactions and consumption of the victim appear more common when food is scarce or disputed. In response to killers, victim species may alter their use of space, activity patterns, and form groups. Consequences of interspecific killing include population reduction or even extinction, and reduction and enhancement of prey populations, and may therefore have important implications for conservation and management of carnivores and their prey.

Toxoplasma gondii infection in humans and animals in the United States.

Abstract: This paper reviews clinical and asymptomatic Toxoplasma gondii infection in humans and other animals in the USA. Seroprevalence of T. gondii in humans and pigs is declining. Modes of transmission, epidemiology and environmental contamination with oocysts on land and sea are discussed.

Life History Evolution

Abstract: Life history biology sits on the interface between genetics and ecology, and both have made important theoretical and empirical contributions to our understanding. However, the connections between the disciplines have not always been as close as they might have been and this book takes some useful steps towards remedying this. It gives an excellent review of life history theory, and integrates this well with results from the empirical literature. After an 11-page introduction, Roff sets out ‘a framework for analysis’ in which he covers the necessary elements of quantitative and population genetics. This includes clear definitions of fitness in a range of circumstances, from density independent populations in constant environments through to the more complex situations of density and frequency dependence and environments that are spatially or temporally stochastic. Trade-offs are then examined, including a valuable analysis of potential pitfalls in studying them and ways that these can be avoided. The author then deals in turn with evolution in constant environments; stochastic environments and ‘predictable environments’. The last of these covers situations where there is environmental variation, but at least some information is available to allow individuals to make an adaptive response. The final chapter identifies 20 topics for future study. Some will find the book too dominated by theory. Others (but probably not readers of Heredity!) will find it contains too much genetics. But Roff does an excellent job of making the theory accessible, covering the essential issues and pointing to original sources for the details. Theory is related to a significant number of empirical studies, although there is room for another book reviewing the empirical literature on life histories in detail, and Roff’s book would provide a robust skeleton on which to hang this. To make my own assessment, I examined in detail Roff’s discussion of the question of fitness measures for density dependent populations in stochastic environments – an area in which I have been involved. I could not fault him – all the key references were there and the issues were made very clear without the more esoteric mathematics. I also examined some areas that I was less familiar with, and again the text was clear and easy to read. My only real criticism of the book would be that its very long chapters (more than 130 pages in one case) makes it difficult to find things. It would have been simple to address this by including the section headings on the contents pages. A minor personal quibble would be that the book usually expresses problems in terms of the intrinsic rate of increase, r, and the characteristic (Lotka) equation. A matrix formulation is often more tractable and is easier to generalise to density dependent populations and stochastic environments, so expanding on the relationship between the two would have been useful. But overall this is an excellent book. It brings together the key theory in a single place. It gives an invaluable route into the literature, with a bibliography of 1600 or so items. These features, and its identification of topics that need further study should make an important contribution to moving the field forward.