Brett J. Goodwin

Is landscape connectivity a dependent or independent variable

With growing interest in landscape connectivity, it is timely to ask what research has been done and what re mains to be done. I surveyed papers investigating landscape connectivity from 1985 to 2000. From these papers, I determined if connectivity had been treated as an independent or dependent variable, what connectivity metrics were used, and if the study took an empirical or modeling approach to studying connectivity. Most studies treated connectivity as an independent variable, despite how little we know about how landscape structure and organism movement behaviour interact to determine landscape connectivity. Structural measures of connectivity were more common than functional measures, particularly if connectivity was treated as an independent variable. Though there was a good balance between modeling and empirical approaches overall – studies dealing with connectivity as a dependent, functional variable were mainly modeling studies. Based on the research achieved thus far, fu ture landscape connectivity research should focus on: (1) elucidating the relationship between landscape struc ture, organism movement behaviour, and landscape connectivity (e.g., treating connectivity as a dependent variable), (2) determining the relationships between different measures of connectivity, particularly structural and functional measures, and (3) empirically testing model predictions regarding landscape connectivity.

Spatiotemporal Variation in a Lyme Disease Host and Vector: Black-Legged Ticks on White-Footed Mice

We monitored population density of white-footed mice (Peromyscus leucopus), burdens of immature black-legged ticks (Ixodes scapularis) on mice, and infection prevalence of host-seeking ticks on six forest plots in southeastern New York State from 1995 through 1999. Despite densities of mice that fluctuated two orders of magnitude, average larval and nymphal tick burdens per mouse remained remarkably constant. Spatial variability in mouse density and tick burdens was modest. The total number of larval and nymphal ticks that fed on the mouse population each year depended strongly on population density of mice; a steady increase was observed in both mouse density and total tick meals on mice from 1996 through 1999. The result was a steady increase in the infection prevalence of nymphal and adult ticks with the etiological agent of Lyme disease, Borrelia burgdorferi, over this time. We suggest that fluctuations in population density of mice, combined with possible regulation of tick burdens on mice, may influence risk of human exposure to Lyme disease.

A PRESCRIPTION FOR LONGER LIFE? BOT FLY PARASITISM OF THE WHITE-FOOTED MOUSE

Investigation of host-parasite interactions typically reveals a negative impact of parasitism on the host species. In contrast, mounting evidence indicates that bot fly (Cuterebra sp.) infestation enhances the survival of white-footed mice ( Peromyscus leu- copus). We propose that life history trade-offs, namely, between reproduction and survival, can explain this counterintuitive observation. By using an extensive data set spanning a decade, 12 sites in two states, and over 30 000 mouse captures, we offer a new perspective on the effects of bot fly parasitism on white-footed mice. Analysis of persistence time corroborated earlier studies that showed significantly higher survival rates of infested mice. Although a higher proportion of infested than uninfested females were in breeding condition, secondary reproductive success appeared to be negatively impacted by parasitism via de- clines in the number of litters and the total number of offspring produced by infested females. Population growth rates were negatively correlated with infestation prevalence, further indicating a negative effect of parasitism. Based on the negative impact of parasitism on reproduction, we propose that enhanced survival of infested mice can be explained by the diversion of resources from reproduction to body maintenance. Parasite-induced life history shifts in which mice decrease current reproduction to promote future reproduction, such as increasing the age at maturity, may also contribute to the decline in population growth rate observed in years of high infestation prevalence.

Spatio-temporal patterns in county-level incidence and reporting of Lyme disease in the northeastern United States, 1990-2000

We present an exploratory analysis of reported county-specific incidence of Lyme disease in the northeastern United States for the years 1990–2000. We briefly review the disease ecology of Lyme disease and the use of risk maps to describe local incidence as estimates of local risk of disease. We place the relevant elements of local environmental and ecological variables, local disease incidence, and (importantly) local disease reporting in a conceptual context to frame our analysis. We then apply hierarchical linear models of increasing complexity to summarize observed patterns in reported incidence, borrowing information across counties to improve local precision. We find areas of increasing incidence in the central northeastern Atlantic coast counties, increasing incidence branching to the north and west, and an area of fairly stable and slightly decreasing reported incidence in western New York.

USE OF TRACK PLATES TO QUANTIFY PREDATION RISK AT SMALL SPATIAL SCALES

Abstract Spatial heterogeneity in risk is a critical component of predator-prey interactions. However, at small spatial scales, it is difficult to quantify predation risk without altering it. We used track plates to measure local predation risk created by white-footed mouse (Peromyscus leucopus) foraging activity on oak-forest plots in Millbrook, New York. Live gypsy moth pupae (Lymantria dispar) were placed at 2 heights on trees and monitored for predation. Pupae deployed on trees visited by mice were more likely to be eaten than those on trees not visited. Logistic regression indicated that predation rates on gypsy moth pupae were positively correlated with track activity, indicating that areas of concentrated mouse activity were areas of heightened risk for gypsy moths. Survival of individual oat grains placed on and 50 cm from track plates were not statistically different, indicating that mice exhibited no detectable behavioral reaction toward track plates. We conclude that track plates offer an economical and reliable means of quantifying local risk of attack by terrestrial mammals without substantially altering the spatial distribution of risk.

Quantifying a Dynamic Risk Landscape: Heterogeneous Predator Activity and Implications for Prey Persistence

Spatial heterogeneity in predation risk can ameliorate impacts on prey populations, particularly for prey of generalists. Spatially heterogeneous risk implies the existence of refugia, and the spatial scale of those refugia and their persistence over time affect whether prey can avoid predation by aggregating therein. Our objective was to quantify the magnitude, spatial scale, and temporal persistence of heterogeneity in risk of predation by white-footed mice (Peromyscus leucopus), an abundant generalist predator of gypsy moths (Lymantria dispar) and songbirds. We used track plates to measure white-footed mouse activity at > 170 trees in each of three forest plots in upstate New York during summers of 2003-2005. We quantified the mean and coefficient of variation of track activity among trees by fitting the beta-binomial distribution to data from each plot and study period. We measured temporal persistence by disattenuated autocorrelation, and spatial scale by fitting exponential variograms. Mice were much less abundant in 2005 than the other two years, leading to lower overall track activity but higher coefficient of variation among trees. Mouse track activity at individual trees was positively autocorrelated between monthly study periods in 2003 and 2004, and even between the two years, whereas temporal autocorrelation in 2005 was much weaker. Track activity showed positive spatial autocorrelation over lag distances from approximately 30 to > 1000 m. These findings indicate that mouse activity, and hence risk to their prey, varies substantially in space at spatial and temporal scales that appear responsive to mouse population dynamics. The spatial scale and temporal persistence of that variation imply that prey may benefit from returning to, or failing to disperse from, refugia.

Spatial selection and inheritance: applying evolutionary concepts to population dynamics in heterogeneous space.

Organisms in highly suitable sites generally produce more offspring, and offspring can inherit this suitability by not dispersing far. This combination of spatial selection and spatial inheritance acts to bias the distribution of organisms toward suitable sites and thereby increase mean fitness (i.e., per capita population increase). Thus, population growth rates in heterogeneous space change over time by a process conceptually analogous to evolution by natural selection, opening avenues for theoretical cross-pollination between evolutionary biology and ecology. We operationally define spatial inheritance and spatial selective differential and then combine these two factors in a modification of the breeders equation, derived from simple models of population growth in heterogeneous space. The modified breeders equation yields a conservative criterion for persistence in hostile environments estimable from field measurements. We apply this framework for understanding gypsy moth population persistence amidst abundant predators and find that the predictions of the modified breeders equation match initial changes in population growth rate in independent simulation output. The analogy between spatial dynamics and natural selection conceptually links ecology and evolution, provides a spatially implicit framework for modeling spatial population dynamics, and represents an important null model for studying habitat selection.

A prospective study of injury affecting competitive collegiate swimmers.

The purposes of this study were to determine the incidence and distribution of injuries affecting collegiate competitive swimmers and to test possible injury risk factors. A prospective cohort design was used to follow 34 swimmers (16M, 18F) from an NCAA Division I Midwest University over one academic year. Exposure-based injury rates were determined for both practice and competition. Risk of injury was assessed relative to gender, years swimming, and history of injury. Twenty of 34 swimmers sustained 31 injuries with overall injury rates of 5.55 injuries per 1000 athlete exposures and 3.04 injuries per 1000 hours exposure. Practice injury rates for female swimmers were higher than for womens practice injury rates in other NCAA sports. The most common injury locations were the shoulder, back, and knee. Risk factors that remained significant in the multivariate analysis were history of injury to the same anatomical location and history of injury at other anatomical sites.

Epidemiological Review of Injury in Pre-Professional Ballet Dancers.

The objective of this study was to provide an epidemiological review of the literature concerning ballet injuries affecting pre-professional ballet dancers. The literature search was limited to published peer-reviewed reports and involved an extensive examination of Scopus, SPORTDiscus, and CINAHL. The following search terms were used in various combinations: ballet, injury, epidemiology, risk factor, pre-professional, and intervention. Additional citations were located using the ancestry approach. Unlike some other athletic activities that have been the focus of recent intervention research, there is a paucity of intervention and translational research in pre-professional ballet, and sample sizes have often been small and have not accounted for the multivariate nature of ballet injury. Exposure-based injury rates in this population appear similar to those reported for professional ballet dancers and female gymnasts. A preponderance of injuries affect the lower extremity of these dancers, with sprains and strains being the most frequent type of injury reported. The majority of injuries appear to be overuse in nature. Injury risk factors have been tested in multiple studies and indicate a variety of potential injury predictors that may provide useful guidance for future research.

Risk Factors for Injury in Pediatric and Adolescent Sports

Analysis of sports injury risk factors in child and adolescent sport has produced a number of significant injury predictors including age, balance, body size, maturity status, gender (specific to sport and type of injury), previous injury, stressful life events, rules regarding body-checking in ice hockey, volume of training, and fatigue. There is also preliminary evidence that the growth spurt is associated with an increased risk of injury and that menstrual irregularity and low-energy availability may relate to increased risk of injury in younger adolescents. However, results of risk factor analyses in child and adolescent sports may suffer from one or more methodological limitations and therefore should be interpreted cautiously. Risk factors identified should be viewed as initial steps in the important search for predictor variables and may provide interesting characteristics for manipulation in other experimental designs.