High Road Density Research Articles

Winter selection of landscapes by woodland caribou: behavioural response to geographical gradients in habitat attributes

Summary 1. Understanding animal-habitat relationships is central to the development of strategies for wildlife management and conservation. The availability of habitat attributes often changes along latitudinal and longitudinal axes, and animals may respond to those changes by adjusting their selection. We evaluated whether landscape selection by forest-dwelling woodland caribou Rangifer tarandus caribou varied along geographical gradients in habitat attributes. 2. Centroids {n = 422) of track networks made by caribou in winter were recorded during aerial surveys conducted over 161 920 km2 of boreal forest in Qu?bec, Canada. Autologistic models were estimated by comparing the characteristics of landscapes (201 km2) centred on each centroid to an equal number of randomly located landscapes, with an autocovariate controlling for the non independence among caribou locations. 3. The availability of habitat attributes varied along longitudinal and latitudinal gradients, and caribou altered their landscape selection with respect to those gradients. 4. Information Theory provided substantial support for only one model. The model revealed that the probability of occurrence of caribou increased with the abundance of conifer forests over most of the study region, but this positive response gradually became negative towards the southern portion of the region. The association between caribou and lichens changed from being negative west of the study region to being positive in the eastern part. Availability of landscapes dominated by lichen decreased from west to east. Finally, caribou generally displayed an aversion to areas with high road density, a negative association that became positive in the southern part of the study region. 5. Synthesis and applications. Under current legislation in Canada, the critical habitat of woodland caribou must be defined, and then protected. Our autoregressive models can help to identify landscapes to prioritize conservation efforts. The probability of occurrence of caribou was related to different landscape characteristics across their range, which implies that the typical habitat of woodland caribou differs spatially. Such behavioural plasticity could be problematic for defining critical habitat, but we showed that spatial variation in landscape selection was organized along geographical gradients. Our study illustrates how geographical trends in habitat selection can guide management and conservation decisions.

Modelling habitat overlap among sympatric mesocarnivores in southern Illinois, USA

Few researchers have developed large-scale habitat models for sympatric carnivore species. We created habitat models for red foxes ( Vulpes vulpes), coyotes ( Canis latrans) and bobcats ( Lynx rufus) in southern Illinois, USA, using the Penrose distance statistic, remotely sensed landscape data, and sighting location data within a GIS. Our objectives were to quantify and spatially model potential habitat differences among species. Habitat variables were quantified for 1-km 2 buffered areas around mesocarnivore sighting locations. Following variable reduction procedures, five habitat variables (percentage of grassland patches, interspersion–juxtaposition of forest patches, mean fractal dimension of wetland patches and the landscape, and road density) were used for analysis. Only one variable differed ( P < 0.05) between red fox and coyote sighting areas (road density) and bobcat and coyote sighting areas (mean fractal dimension of the landscape). However, all five variables differed between red fox and bobcat sighting areas, indicating considerable differences in habitat affiliation between this pair-group. Compared to bobcats, red fox sightings were affiliated with more grassland cover and larger grassland patches, higher road densities, lower interspersion and juxtaposition of forest patches, and lower mean fractal dimension of wetland patches. These differences can be explained by different life history requirements relative to specific cover types. We then used the Penrose distance statistic to create habitat models for red foxes and bobcats, respectively, based on the five-variable dataset. An independent set of sighting locations were used to validate these models; model fit was good with 65% of mesocarnivore locations within the top 50% of Penrose distance values. In general, red foxes were affiliated with mixtures of agricultural and grassland cover, whereas bobcats were associated with a combination of grassland, wetland, and forest cover. The greatest habitat overlap between red foxes and bobcats was found at the interface between forested areas and more open cover types. Our study provides insight into habitat overlap among sympatric mesocarnivores, and the distance-based modelling approach we used has numerous applications for modelling wildlife–habitat relationships over large scales.

Ruffed grouse brood habitat selection at multiple scales in Pennsylvania: implications for survival

Declines in ruffed grouse ( Bonasa umbellus (L., 1766)) populations in the central and southern Appalachians may be linked to low brood survival. Therefore, managing for high-quality brood habitat could improve grouse numbers. Understanding how brood habitat selection affects survival and the spatial scale at which this occurs is therefore fundamental to developing effective habitat management strategies. From 1999–2002, we monitored 38 broods for 5 weeks post hatch and estimated utilization distributions (n = 28), site-scale habitat use (n = 21), and daily survival rate (mean = 0.966, range = 0.920–0.997, and n = 19). Relative to available habitat, broods selected sites with greater herbaceous ground cover and higher small (&lt;2.5 cm diameter at breast height, DBH) stem densities and landscapes containing higher proportions of road and young deciduous forest. Herbaceous ground cover provided arthropod prey and concealment from predators and was a primary factor driving habitat selection. High stem densities and early successional habitats provided increased security, but were only used if adequate ground cover was present. Broods strongly selected roads and experienced higher survival near edges. However, higher road densities were associated with lower survival at the landscape scale. This pattern reflects the differential scale at which grouse and their predators respond to edge.

Delimitating the store market field based on the metric of the city-block distance

In social and economic activities,people usually actualize their spatial activities on road networks.However,most research results were on the ideal condition that geographical space was a homogeneous one,and almost all spatial analysis methods are according to the metric of planar Euclidean distance,its drawback is quite obvious.This paper presents the principle and the constructing method of network Voronoi diagrams,and the application of ordinary Voronoi diagram and network Voronoi diagram to the delimitation of the market fields of 17 stores in Wuhan,Hubei Province,China.The main results are as follows:(1) The market fields in the inner city are quite small while the ones in the outer city are a little large.If the road density in a store trade region was low,its area would be small;conversely,provided the road density in a store trade region was high,its area would be quite large.(2) There is a more or less difference between the application results of the methods based on ordinary Voronoi diagram and network Voronoi diagram.If the road density of a region was high,the difference would be small;and vice versa,there was a great difference in a region with a low road density.This shows that the method of ordinary Voronoi diagram can be chosen as a substitute of network Voronoi diagram to define the market fields of a store system in case of a region with a high road density.

Growth, Foreign Direct Investment and Urban Concentrations: Unbundling Spatial Lags

Cross-country regressions suggest that urbanization and FDI are important drivers of growth. However, it is not clear that primacy eventually hurts growth performance. Since it is tough to interpret cross-country growth regressions, we provide detailed evidence on the determinants of outward FDI from the US. FDI is higher in countries that are close to the US and have good institutions, well developed financial systems, a high road density, a high income per capita and substantial natural resource exports. Countries also attract more FDI if they have more medium-sized cities and primacy is not too large. We show that good institutions in neighbouring countries are important drivers of FDI. FDI is higher if neighbours suffer from primacy. However, FDI is attracted if surrounding countries have fewer cities, restrictions on international trade and low market potential (income per capita). We tentatively conclude that cities are important drivers of FDI and growth and unbundling spatial lags matters. Robustness is verified by re-estimating our regressions with fixed effects and for the sample of OECD countries.

Timber Harvesting Characteristics on Forest Stewardship Properties and Non–Forest Stewardship Properties in Central West Virginia

Abstract A study was conducted in the Elk River watershed in central West Virginia to evaluate the impact of the US Forest Stewardship Program (FSP) on the physical attributes of primary road systems used in timber harvesting operations. On seven properties enrolled in the FSP and on eight non-FSP properties, road systems used for logging within a 5-year period before this study were mapped and measured. Twenty dependent variables relating to residual vegetation, forest road characteristics, erosion, and certain best management practices (BMP) were used to characterize timber harvesting operations that had been conducted on these properties. With the exception of road density and waterbar implementation, analysis of these dependent variables failed to detect any statistical differences among property types. BMPs observed in this study included waterbars, broad-based dips, turnouts, culverts, and inside ditches. Results suggest that landowner objectives may play a role in the use of alternatives to waterbars. Eighty-one percent of BMP practices other than waterbars were observed on stewardship properties. Higher road densities on non-FSP properties were likely caused by road patterns used on forest industry properties.

County‐Level Factors Contributing to Deer‐Vehicle Collisions in Arkansas

ABSTRACT Arkansas harbors a substantial white‐tailed deer (Odocoileus virginianus) population, boasts an expanding human population, and both enjoys and suffers the resulting consequences. A highly visible negative consequence is the occurrence of deer‐vehicle collisions (DVCs). Several studies have investigated site‐specific factors that may contribute to DVCs. However, few studies have explored the role of broader scale factors. In this study, we used an exploratory, multivariate approach to examine the influence of county‐level factors on the density (no./1,000 km) of reported DVCs in Arkansas, USA, during 1998–2001. Factors considered to contribute to DVCs in Arkansas included human and deer population densities, urban growth, various roadway characteristics, daily traffic counts, timber harvests, and landcover composition and spatial characteristics. Using principal components and regression analysis we determined that there were 2 important components contributing to DVC densities in Arkansas. Component 1 represented a predominantly forested matrix with high edge density and contrast. Component 2 described an urban environment, with high road densities, human population densities, and average daily traffic counts. These 2 components were strongly related to DVCs (r2 = 0.55, P &lt; 0.001), with component 2 explaining the most variation (71.4%). The identification and recognition of the contribution of these broad‐scale factors to DVCs provide insight useful in making informed decisions related to DVC mitigation.

Effect of road density on abundance of white-footed mice

While several studies have demonstrated that roads can act as barriers to small mammal movement, the relationship between road density and small mammal abundance has not yet been investigated. In southeastern Ontario, Peromyscus leucopus (white-footed mice) suffer high over-winter mortality rates, resulting in small springtime populations and frequent local extinctions. Peromyscus leucopus movement is known to be inhibited by roads, which should result in lower rates of immigration into and recolonization of habitats in landscapes with high road density. We tested two predictions: (1) Forest sites situated in landscapes with high road densities have a higher chance of P. leucopus being absent during the early spring than forest sites situated in landscapes with low road densities and (2) P. leucopus populations during the summer are smaller in forest sites situated in landscapes with high road densities than in landscapes with low road densities. We sampled P. leucopus in focal patches within nineteen landscapes (7 rural, low-road-density landscapes; 7 rural, high-road-density landscapes; 5 urban landscapes). There was no significant relationship between road density and the presence/absence of P. leucopus during the early spring. We found a significant positive effect of road density on P. leucopus relative abundance during the summer, even when we excluded the urban landscapes and based the analysis on only the 14 rural landscapes. Our results suggest that any negative effect of roads on P. leucopus populations, created by their inhibition to moving across roads, is far outweighed by some positive effect of roads on P. leucopus abundance. We suggest that the two most likely explanations are that roads are positively correlated with an important as-yet-undetermined component of habitat quality, or that roads positively affect P. leucopus by negatively affecting their predators.

Road edge effect on the abundance of the lizard Gallotia galloti (Sauria: Lacertidae) in two Canary Islands forests

Transportation infrastructure is a main cause of environmental change in forest landscapes worldwide. In the Canary Islands, a dense road system fragment the native Canarian pine and laurel forests causing potential changes in population densities of endemic lacertid lizards (genus Gallotia). Our aim was to assess road edge effects on relative abundance patterns of the endemic Gallotia galloti in both forests. We also explored the species–habitat relationships in this road-fragmentation context. We found that lizard relative density in relation to road edges differed between forests. Lizards were more abundant along edges and leeward interior, but virtually absent from the interior of the windward laurel forest. In the pine forest, lizards were present at three distances from edge, with a net decrease in abundance from edge to interior. These patterns may be explained partly by differences in vegetation structure regarding road proximity in each forest that potentially affect the helio- and thigmothermic character of G. galloti, and thus its habitat use. A general suggestion of this study is that road margins create corridors that may be used by native lizards for dispersal through inhospitable forest matrix. The high road density in Tenerife may have negative implications for the conservation of the genetic variability of G. galloti. At the island scale, increased communication between lizard populations through road corridors might increase homogenization of the gene pool. Ecological processes in which this lizard plays important roles may also experience changes along road edges.

Land Cover and Road Network Map for the Monarch Butterfly Biosphere Reserve in Mexico, 2003

Please click here to download the map associated with this article. To preserve the monarch butterfly (Danaus plexippus L.) overwintering sites in Mexico, the fir forests used for the main colonies have been protected by three presidential decrees, in 1980, 1986 and 2000. The territory of the current Monarch Butterfly Biosphere Reserve (MBBR) belongs mainly to communal properties (ejidos and indigenous communities). Contrary to expectation, this protected area is still facing severe disturbance and loss of forest cover, because of intensive illegal and legal logging, and subsistence farming activities. Roads are landscape elements well known as a cause of disturbance and deforestation. Therefore, the aim of this map is to illustrate the road network and land cover relationship in the MBBR, taking into account the land tenure. The roads vector layer was obtained by photointerpretation of one meter resolution digital aerial photograph mosaics from March 2003, and one meter resolution Ikonos pansharpened images from March 2004, as well as field work, using GPS georeferenced tracks. Land cover polygons were constructed by visual interpretation of January 2003 Landsat ETM+ color composites, simultaneously verified with the aerial photograph mosaics. The final 1:75000 map shows very high human pressures over the reserve forests. This is expressed by a high density road network, composed mainly of tertiary roads opened to wood extraction, in many cases illegally, and incompatible with the protection category of these forests.

A High Accuracy Fuzzy Logic Based Map Matching Algorithm for Road Transport

Recent research on map matching algorithms for land vehicle navigation has been based on either a conventional topological analysis or a probabilistic approach. The input to these algorithms normally comes from the global positioning system (GPS) and digital map data. Although the performance of some of these algorithms is good in relatively sparse road networks, they are not always reliable for complex roundabouts, merging or diverging sections of motorways, and complex urban road networks. In high road density areas where the average distance between roads is less than 100 m, there may be many road patterns matching the trajectory of the vehicle reported by the positioning system at any given moment. Consequently, it may be difficult to precisely identify the road on which the vehicle is travelling. Therefore, techniques for dealing with qualitative terms such as likeliness are essential for map matching algorithms to identify a correct link. Fuzzy logic is one technique that is an effective way to deal with qualitative terms, linguistic vagueness, and human intervention. This article develops a map matching algorithm based on fuzzy logic theory. The inputs to the proposed algorithm are from GPS augmented with data from deduced reckoning sensors to provide continuous navigation. The algorithm is tested on different road networks of varying complexity. The validation of this algorithm is carried out using high precision positioning data obtained from GPS carrier phase observables. The performance of the developed map matching algorithm is evaluated against the performance of several well-accepted existing map matching algorithms. The results show that the fuzzy logic-based map matching algorithm provides a significant improvement over existing map matching algorithms both in terms of identifying correct links and estimating the vehicle position on the links.

Effectiveness of Protected Areas in Mitigating Fire within Their Boundaries: Case Study of Chiapas, Mexico

Since the severe 1982-1983 El Niño drought, recurrent burning has been reported inside tropical protected areas (TPAs). Despite the key role of fire in habitat degradation, little is known about the effectiveness of TPAs in mitigating fire incidence and burned areas. We used a GPS fire database (1995-2005) (n=3590 forest fires) obtained from the National Forest Commission to compare fire incidence (number of fires) and burned areas inside TPAs and their surrounding adjacent buffer areas in Southern Mexico (Chiapas). Burned areas inside parks ranged from 2% (Palenque) to 45% (Lagunas de Montebello) of a park's area, and the amount burned was influenced by two severe El Niño events (1998 and 2003). These two years together resulted in 67% and 46% of the total area burned in TPAs and buffers, respectively during the period under analysis. Larger burned areas in TPAs than in their buffers were exclusively related to the extent of natural habitats (flammable area excluding agrarian and pasture lands). Higher fuel loads together with access and extinction difficulties were likely behind this trend. A higher incidence of fire in TPAs than in their buffers was exclusively related to anthropogenic factors such as higher road densities and agrarian extensions. Our results suggest that TPAs are failing to mitigate fire impacts, with both fire incidence and total burned areas being significantly higher in the reserves than in adjacent buffer areas. Management plans should consider those factors that facilitate fires in TPAs: anthropogenic origin of fires, sensitivity of TPAs to El Niñio-droughts, large fuel loads and fuel continuity inside parks, and limited financial resources. Consideration of these factors favors lines of action such as alternatives to the use of fire (e.g., mucuna-maize system), climatic prediction to follow the evolution of El Niño, fuel management strategies that favor extinction practices, and the strengthening of local communities and ecotourism.

The relationship between the characteristics of transportation energy consumption and urban form

In this paper, we analyze the relationship between the characteristics of transportation energy consumption and urban form elements that were actively argued along with Environmentally Sound and Sustainable Development (ESSD). This paper can be divided into two parts: an examination of the theories and a practical analysis of domestic, small-, and medium-sized cities. Firstly, in the examination of theories, we surveyed the arguments about the sustainable urban form. Secondly, we made some hypotheses about the relationships between transportation energy consumption, city size, density, and center distribution pattern. Thirdly, we tested those hypotheses and examined the suitability of policies for each alternative for small- and medium-sized cities in Korea. The main themes in this paper are as follows. Firstly, how does the city size, density, etc. affect the transportation energy consumption? Secondly, in an overcrowded Korean situation, which alternative is the more suitable sustainable urban form from the point of transportation energy consumption, i.e., concentration or decentralized concentration? Thirdly, we examined the argument that a densely centralized development can reduce the need for travel, increase the transit use, and decrease automobile use. From the results of the analysis, we found that as the population increases, transportation energy represented by yearly gasoline consumption per automobile and the average yearly energy consumption as a result of surface transportation per 1,000 persons tends to decrease. Further, if the degree of city’s concentration represented by Gini coefficient is high, energy efficiency tends to decrease. Besides, the influential factors on the transportation energy consumption among the indicators of urban form could be road ratio and density. Whereas the road ratio is not related to the transportation energy consumption, road density is. From the analyzed results, we can deduce planning implications concerned with Korean cities. Firstly, Korean cities are already highly centralized so a decentralization policy should be carried out to increase transportation energy efficiency. In any case, in the case of high-density cities, multinuclei cities are better than mononuclear ones. Further, to increase the transportation energy efficiency, policies for high road densities through the construction of new roads in spite of narrow road widths are more effective than those for high road ratio-widening existing roads.

Wolf habitat analysis in Michigan: an example of the need for proactive land management for carnivore species

Gray wolves (Canis lupus) likely will recolonize the northern Lower Peninsula of Michigan (NLP). As such, land managers would benefit from information on the amount, distribution, and quality of potential wolf habitat in this region. We estimated that 2, 198-4,231 km2 of favorable wolf habitat exist in the NLP, supporting an estimated population of 40–105 wolves. Favorable habitat was fragmented by road networks and was predominantly located in the northeastern part of the state on private land. We discuss the management of wolves in the NLP as a case study of wolf recolonization in a landscape that has a relatively high road density and agricultural lands that likely will be sources of conflict with wolves. We provide a hierarchical model for consideration in proactively managing landscapes that already or likely will contain several carnivore species concomitant with human land use. We suggest that this case study and our hierarchical model offer insight into how proactive land management should occur for wolves and other carnivores in the northern Great Lakes Region and other human-altered landscapes.

MONITORING AND HABITAT ANALYSIS FOR WOLVES IN UPPER MICHIGAN

Gray wolves (Canis lupus) in upper Michigan, USA, have been monitored since 1991 when breeding activity in mainland Michigan was documented for the first time since 1954. Based on winter track counts, the mean annual rate of increase in abundance was 19% from 1995 to 2002, with the population reaching an estimated 278 animals in 2002. Our objectives were to (1) increase the efficiency of wolf management in Michigan by evaluating alternative and less extensive sampling approaches for population estimation, and (2) evaluate habitat for wolves based on occupancy after a decade of recovery. For the first analysis, we created 22 discrete sampling units that cover upper Michigan, and we evaluated abundance estimates based on various sampling plans using known distribution and populations from the 2000–2002 winter track surveys. We evaluated each plan based on the precision, bias, and confidence interval coverage. A random sampling plan with regression estimator returned the most precise estimates, but a stratified sampling plan, using low, medium, and high wolf density strata had the greatest precision at lowest effort. For the habitat evaluation, we compared white-tailed (Odocoileus virginianus) deer density and road density between wolf pack locations from 1995 to 2001 to random locations outside of the current wolf range. We estimated white-tailed deer density by a spatial interpolation of pellet group counts. Our resource selection function indicated that probability of wolf occupation of an area was positively correlated with deer density, and it was relatively constant for road densities <0.4 km/km2 but declined sharply at higher road densities. For areas habitable by wolves in upper Michigan, we predict a road density threshold of 0.7 km/km2 and a deer density threshold of approximately 2.3–5.8 deer/km2. We believe that these results will aid managers who need to estimate wolf abundance and predict wolf distribution.

Landscape evaluation of female black bear habitat effectiveness and capability in the North Cascades, Washington

We used logistic regression to derive scaled resource selection functions (RSFs) for female black bears at two study areas in the North Cascades Mountains. We tested the hypothesis that the influence of roads would result in potential habitat effectiveness (RSFs without the influence of roads) being greater than realized habitat effectiveness (RSFs with roads). Roads consistently had a negative influence on black bear RSFs across seasons and study areas. Roads reduced habitat effectiveness during all seasons at both study areas and changes in the potential habitat values ranged from 1.7% to 16.9%. The greatest reduction in habitat values occurred during the early-season on the west-side study area due to high open road densities. These results support the hypothesis that roads reduce habitat effectiveness for black bears. The influence of roads could be reduced through road closures to reduce open road densities and limit traffic volumes. We then used the scaled RSFs in a habitat-based population model to assess the influences of timber harvest and roads on potential black bear population sizes. On the west-side study area the potential black bear population size was most influenced by moderate use roads and timber harvest during the early-season (41% reduction). On the east-side study area, low use roads had the greatest effect on potential black bear population during the early-season (10% reduction). During the late-season, in both study areas, roads had less influence on the potential population sizes as bears were able to access habitats away from roads. The habitat-population model provided reasonable estimates of bear densities compared to other study areas with similar habitats and could be extrapolated to estimate potential black bear populations in other areas with similar habitats. This approach may provide a useful link between the landscape ecology and population biology of black bears, and could eventually be useful in the development of habitat-based population viability analyses.

SPATIAL RESPONSES OF WOLVES TO ROADS AND TRAILS IN MOUNTAIN VALLEYS

Increasing levels of human activity in mountainous areas have high potential to inhibit animal movement across and among valleys. We examined how wolves respond to roads, trails, and other developments. We recorded the movements of two wolf packs for two winters by following their tracks in the snow and simultaneously recording positions with a hand‐held global positioning system. We then used matched case‐controlled logistic regression to compare habitat covariates of wolf paths (cases) to multiple paired random locations (controls). This analysis emphasized the differences within pairs of cases and controls, rather than differences in their overall distribution, making it useful to assess fine‐scale habitat selection and path data. Both packs selected low elevations, shallow slopes, and southwest aspects. They selected areas within 25 m of roads, trails, and the railway line and more strongly selected low‐use roads and trails compared to high‐use roads and trails. One pack strongly avoided distances between 26 and 200 m of high‐use trails; otherwise, the wolves weakly selected or avoided this distance class. Both packs avoided areas of high road and trail density. We concluded that roads and trails have a cumulative effect on wolf movement and that management of trails, in addition to roads, may be needed to retain high‐quality habitat for wolves, particularly in known movement corridors.

Conceptual model of sediment processes in the upper Yuba River watershed, Sierra Nevada, CA

This study examines the development of a conceptual model of sediment processes in the upper Yuba River watershed; and we hypothesize how components of the conceptual model may be spatially distributed using a geographical information system (GIS). The conceptual model illustrates key processes controlling sediment dynamics in the upper Yuba River watershed and was tested and revised using field measurements, aerial photography, and low elevation videography. Field reconnaissance included mass wasting and channel storage inventories, assessment of annual channel change in upland tributaries, and evaluation of the relative importance of sediment sources and transport processes. Hillslope erosion rates throughout the study area are relatively low when compared to more rapidly eroding landscapes such as the Pacific Northwest and notable hillslope sediment sources include highly erodible andesitic mudflows, serpentinized ultramafics, and unvegetated hydraulic mine pits. Mass wasting dominates surface erosion on the hillslopes; however, erosion of stored channel sediment is the primary contributor to annual sediment yield. We used GIS to spatially distribute the components of the conceptual model and created hillslope erosion potential and channel storage models. The GIS models exemplify the conceptual model in that landscapes with low potential evapotranspiration, sparse vegetation, steep slopes, erodible geology and soils, and high road densities display the greatest hillslope erosion potential and channel storage increases with increasing stream order. In-channel storage in upland tributaries impacted by hydraulic mining is an exception. Reworking of stored hydraulic mining sediment in low-order tributaries continues to elevate upper Yuba River sediment yields. Finally, we propose that spatially distributing the components of a conceptual model in a GIS framework provides a guide for developing more detailed sediment budgets or numerical models making it an inexpensive way to develop a roadmap for understanding sediment dynamics at a watershed scale.

MODELING SURVIVAL: APPLICATION OF THE ANDERSEN–GILL MODEL TO YELLOWSTONE GRIZZLY BEARS

Wildlife ecologists often use the Kaplan-Meier procedure or Cox proportional hazards model to estimate survival rates, distributions, and magnitude of risk factors. The Andersen–Gill formulation (A–G) of the Cox proportional hazards model has seen limited application to mark–resight data but has a number of advantages, including the ability to accommodate left-censored data, time-varying covariates, multiple events, and discontinuous intervals of risks. We introduce the A–G model including structure of data, interpretation of results, and assessment of assumptions. We then apply the model to 22 years of radiotelemetry data for grizzly bears (Ursus arctos) of the Greater Yellowstone Grizzly Bear Recovery Zone in Montana, Idaho, and Wyoming, USA. We used Akaike's Information Criterion (AICc) and multi-model inference to assess a number of potentially useful predictive models relative to explanatory covariates for demography, human disturbance, and habitat. Using the most parsimonious models, we generated risk ratios, hypothetical survival curves, and a map of the spatial distribution of high-risk areas across the recovery zone. Our results were in agreement with past studies of mortality factors for Yellowstone grizzly bears. Holding other covariates constant, mortality was highest for bears that were subjected to repeated management actions and inhabited areas with high road densities outside Yellowstone National Park. Hazard models developed with covariates descriptive of foraging habitats were not the most parsimonious, but they suggested that high-elevation areas offered lower risks of mortality when compared to agricultural areas.

The total number of naturalized species can be a reliable predictor of the number of alien pest species

In her recent paper, Shawna J. Dark (2004) concluded that the distributions of ‘invasive alien plants’ and ‘non-invasive alien plants’ in California were significantly correlated. She found the highest numbers of both ‘invasive’ and ‘non-invasive’ species in regions with low elevation, high road density, and high native species richness. Dark actually uses two definitions of ‘invasive’ in the paper; we discuss the implications of this on her conclusions. We point out that the most important message of Dark’s paper is that the total number of naturalized species can be, at least at some spatial scales, a reliable predictor of the numbers of exotic pest species. We also provide another example to support this conclusion. We follow the definitions of native, non-native, naturalized, casual, pest, and weed in Pysek et al . (2004) in this note unless otherwise specified. It is necessary to examine how Dark defined ‘invasive’ in her paper because the data she used include only a small number of plant species (78) classified as ‘invasive’ while the remaining 1097 naturalized species listed in the most recent statewide flora and online updates (total 1175; Hickman, 1993; http:// ucjeps.berkeley.edu/interchange.html) were classified as ‘non-invasive alien plants’. Dark first defines ‘invasive alien plants’ in the paper’s second sentence as ‘alien plants that produce offspring in very large numbers and at large distances from parent plants and thus have potential to spread over a considerable area (Richardson et al ., 2000)’. Later, however, we learn that species actually classified as ‘invasive’ for data analysis in this study are only those rated as ‘A’ and ‘B’ on the California Exotic Pest Plant Council’s (1999) list of ‘Exotic Pest Plants of Greatest Ecological Concern’ (Dark, 2004; text under Fig. 1; CalEPPC, 1999). CalEPPC (1999) in turn defines its A and B categories as covering species that