Ranging Behavior of Marsh Rice Rats in a Southern Illinois Wetland Complex

The marsh rice rat (Oryzomys palustris) inhabits wetlands that are often fragmented and isolated by upland cover types. Persistence of marsh rice rat populations and metapopulations likely depends on their ability to enter and traverse the upland matrix, yet basic information, such as home-range size and landcover use patterns, is lacking. Our goal was to quantify home-range size and habitat selection by marsh rice rats in southern Illinois. Between March and November 2011, we radiocollared 21 male rice rats (8 subadults and 13 adults) that were each located 7 to 24 times each via triangulation and homing. We estimated home-range size, compared landcover composition within kernel home ranges to what was available in the surrounding landscape, and quantified daily movement distances. Mean (±SE) home ranges were 3.53 ± 0.66 ha based on 95% kernel isopleths and 1.85 ± 0.49 ha based on minimum convex polygons. Home ranges were largest for individuals followed in early summer, but home-range sizes were similar for adults and subadults. Rice rats’ use of emergent wetland vegetation was greater than availability, indicating they preferred emergent wetlands habitat at the home-range level. However, upland cover types made up \u3e40% of each home range, on average. Daily movements averaged 46.6 ± 3.4 m (maximum: 396 m), and rice rats were located up to 464 m from the nearest wetland. Based on by far the largest sample size (in individuals and locations per individual) available for space use of the marsh rice rat, our findings support the characterization of male rice rats as highly vagile and suggest that rice rats move through upland cover more frequently than previously described

Indirect Interactions among Dendrophages: Porcupines Predispose Pinyon Pines to Bark Beetle Attack

Discerning linkages among trophic levels and untangling indirect interactions is essential to understanding structuring of communities and ecosystems. Indeed, indirect interactions among disparate taxa are often essential to the functional role of these species. The goal of this research was to test the hypothesis that the relationship between 2 dendrophagous taxa, the North American porcupine (Erethizon dorsatum) and the pine engraver beetle (Ips hoppingi), is an asymmetric indirect interaction mediated by a common host. We proposed that damage by the porcupine predisposes the papershell pinyon pine (Pinus remota) to colonization by pine engraver beetles. We examined porcupine tree selection, pinyon pine physiology and physiognomy, and beetle-pine associations on a study area in the southwestern Edwards Plateau of Texas from June 1997 to August 1999. Although attacks by beetles were evident on both damaged and undamaged trees, successful colonization was greater on pines damaged by porcupines. Intensity of porcupine attack, indexed by number of feeding scars and area of bark removed, also was associated with subsequent colonization by beetles. Porcupines selected pinyon pines over more abundant species (P \u3c 0.001) and were selective at the level of morphology, whereas pine engraver beetles were selective of tree morphology and physiology. Trees colonized by beetles had phloem with higher concentrations of fructose and glucose and lower percent composition of limonene, sabinene, and terpinolene than uncolonized trees. Our findings supported our hypothesis of an indirect interaction between these dendrophages. We rejected alternative explanations (e.g., that these dendrophages preferred similar trees or that beetles facilitated porcupine damage) for this relationship based on the biology of Ips and their selection of host trees. We propose that release of volatile terpenes as a result of porcupine feeding and reallocation of carbon resources as a response to stress explains the facilitation of beetle colonization in porcupine-damaged trees. Our findings parallel those observed in other systems involving indirect effects and fit within the framework of theories explaining host plant-herbivore interactions

Survival, Habitat Selection, and Body Condition of the Woodchuck (\u3ci\u3eMarmota monax\u3c/i\u3e) across an Urban-rural Gradient

Urban-adapter species facultatively exploit human-subsidized resources in the urban and suburban matrix. We used the woodchuck (Marmota monax) to study how aspects of autecology in an urban-adapter can vary across a gradient of urbanization. We captured and monitored woodchucks by radiotelemetry in southern Illinois from summer 2007 to spring 2009. We captured 47 woodchucks (19 adults, 19 yearlings, 8 young-of-the-year) during the active seasons, and implanted radiotransmitters in 17 adults and 3 yearlings (13 F, 7 M). Overall annual survival was estimated to be 0.76 ± 0.12, with three confirmed mortalities during the study period. Survival and home-range size did not vary by % urban landcover in a buffer surrounding an individual\u27s home range. Habitat-selection analyses indicated that rural edge was the highest-ranked habitat at the home-range scale, whereas urban cover (specifically, developed areas with human structures) was most highly ranked at the within-home-range scale. Body condition was negatively related to % urban landcover. Overall, our findings indicated no clear relationship between woodchuck ecology and urbanization level within our study area. However, our data on body condition and adipose composition, although preliminary, suggested a possible mechanism for variation in overwinter survival across the urban-rural gradient

Comparing Permeability of Matrix Cover Types for the Marsh Rice Rat (Oryzomys palustris)

Context Matrix land cover types differ in permeability to animals moving between habitat patches, and animals may actually move faster across lesssuitable areas. Marsh rice rats are wetland specialists whose dispersal crosses upland matrix. Objectives Our objectives were to (1) compare matrix permeability for the marsh rice rat among upland cover types, (2) compare permeability within versus outside perceptual range of the wetland, and (3) explore intrinsic and extrinsic features influencing matrix use and permeability. Methods We quantified permeability of grassland, crop field, and forest to the marsh rice rat during 2011–2012, by marking rats in wetlands and estimating the slope of capture rate versus distance (0–95 m) into the matrix. We also compared permeability within (0–15 m) and beyond the perceptual range of rice rats, and tested whether age, sex, time, water depth, rice rat abundance, and vegetation density influenced matrix use and permeability. Results Permeability was greater for soybean fields than grassland or forest but did not appear to differ within versus beyond rice rats’ perceptual range. Matrix capture rates were higher early in the study and in times and locations with thick ground vegetation and high rice rat abundance in the wetlands. Rice rats captured in the matrix were younger than those in wetland patches. Conclusions Our findings expand known matrix use by marsh rice rats, and support permeability being high in matrix types dissimilar to suitable habitat. Studying individual movements will help identify mechanisms underlying enhanced permeability in crop fields

Spatial and Temporal Structure of a Mesocarnivore Guild in Midwestern North America

Carnivore guilds play a vital role in ecological communities by cascading trophic effects, energy and nutrient transfer, and stabilizing or destabilizing food webs. Consequently, the structure of carnivore guilds can be critical to ecosystem patterns. Body size is a crucial influence on intraguild interactions, because it affects access to prey resources, effectiveness in scramble competition, and vulnerability to intraguild predation. Coyotes (Canis latrans), bobcats (Lynx rufus), gray foxes (Urocyon cinereoargenteus), raccoons (Procyon lotor), red foxes (Vulpes vulpes), and striped skunks (Mephitis mephitis) occur sympatrically throughout much of North America and overlap in resource use, indicating potential for interspecific interactions. Although much is known about the autecology of the individual species separately, little is known about factors that facilitate coexistence and how interactions within this guild influence distribution, habitat use, and temporal activity of the smaller carnivores. To assess how habitat autecology and interspecific interactions affect the structure of this widespread carnivore guild, we conducted a large-scale, non-invasive carnivore survey using an occupancy modeling framework. We deployed remote cameras during 3-week surveys to detect carnivores at 1,118 camera locations in 357 2.6-km2 sections (3–4 cameras/section composing a cluster) in the 16 southernmost counties of Illinois (16,058 km2) during January–April, 2008–2010. We characterized microhabitat at each camera location and landscape-level habitat features for each camera-cluster. In a multi-stage approach, we used information-theoretic methods to evaluate competing models for detection, species-specific habitat occupancy, multi-species co-occupancy, and multi-season (colonization and extinction) occupancy dynamics. We developed occupancy models for each species to represent hypothesized effects of anthropogenic features, prey availability, landscape complexity, and vegetative land cover. We quantified temporal activity patterns of each carnivore species based on their frequency of appearance in photographs. Further, we assessed whether smaller carnivores shifted their diel activity patterns in response to the presence of potential competitors. Of the 102,711 photographs of endothermic animals, we recorded photographs of bobcats (n = 412 photographs), coyotes (n = 1,397), gray foxes (n = 546), raccoons (n = 40,029), red foxes (n = 149), and striped skunks (n = 2,467). Bobcats were active primarily during crepuscular periods, and their activity was reduced with precipitation and higher temperatures. The probability of detecting bobcats decreased after a bobcat photograph was recorded, suggesting avoidance of remote cameras after the first encounter. Across southern Illinois, bobcat occupancy at the camera-location and camera-cluster scale (local = 0.24 ± 0.04, camera-cluster cluster = 0.75 ± 0.06) was negatively influenced by anthropogenic features and infrastructure. Bobcats had high rates of colonization (= 0.86) and low rates of extinction (= 0.07), suggesting an expanding population, but agricultural land was less likely to be colonized. Nearly all camera clusters were occupied by coyotes (cluster = 0.95 ± 0.03). At the local scale, coyote occupancy (local = 0.58 ± 0.03) was higher in hardwood forest stands with open understories than in other areas. Compared to coyotes, gray foxes occupied a smaller portion of the study area (local = 0.13 ± 0.01, cluster = 0.29 ± 0.03) at all scales. At the scale of the camera-cluster, gray fox occupancy was highest in fragmented areas with high proportions of forest, and positively related to anthropogenic features within 100% home-range buffers. Red foxes occupied a similar proportion of the study area as gray foxes (local = 0.12 ± 0.02, cluster = 0.26 ± 0.04) but were more closely associated with anthropogenic features. Only anthropogenic feature models made up the 90% confidence set at all scales of analysis for red foxes. Extinction probabilities at the scale of the camera-cluster were higher for both gray foxes (= 0.57) and red foxes (= 0.35) than their colonization rates (gray fox = 0.16, red fox = 0.06), suggesting both species may be declining in southern Illinois. Striped skunks occupied a large portion of the study area (local = 0.47 ± 0.01, cluster = 0.79 ± 0.03) and were associated primarily with anthropogenic features. Raccoons were essentially ubiquitous within the study area, being photographed in 99% of camera clusters. We observed little evidence for spatial partitioning based on interspecific interactions, with the exception of the gray fox-coyote pairs, and found that habitat preferences were more important in structuring the carnivore community. Habitat had a stronger influence on the occupancy of foxes than did the presence of bobcats. However, the level of red fox activity was negatively correlated with bobcat activity at a camera cluster. Gray fox occupancy and the number of detections within occupied sites were reduced in camera-clusters occupied by coyotes but not bobcat occupancy. Overall, gray fox occupancy was highest at camera locations with fewer hardwood and more conifer trees. However, gray foxes were more likely to occupy camera locations in hardwood stands than conifer stands if coyotes were also present indicating that hardwood stands may enhance gray fox-coyote coexistence. The 2 fox species appeared to co-occur with each other at the local scale more frequently than expected based on their individual selection of habitat. Similarly, occupancy of camera-location by red foxes was higher when coyotes were present. These positive spatial associations among canids may be a response to locally high prey abundance or unmeasured habitat variables. Activity levels of raccoons, bobcats, and coyotes were all positively correlated. Overall, our co-occurrence and activity models indicate competitor-driven adjustments in space use among members of a carnivore community might be the exception rather than the norm. Nevertheless, although our results indicate that gray foxes and red foxes currently coexist with bobcats and coyotes, their distribution appears to be contracting on our study area. Coexistence of foxes with larger carnivores may be enhanced by temporal partitioning of activity and by habitat features that reduce vulnerability of intraguild predation. For instance, hardwood stands may contain trees with structure that enhances tree-climbing by gray foxes, a behavior that probably facilitates coexistence with coyotes. Efforts to enhance gray fox populations in this region would likely benefit from increasing the amount of mature oak-hickory forest. Additionally, the varying results from different scales of analyses underscore the importance of considering multiple spatial scales in carnivore community studies

Dynamics of a Black Bear Population within a Desert Metapopulation

Understanding metapopulation dynamics in large carnivores with naturally fragmented populations is difficult because of the large temporal and spatial context of such dynamics. We coupled a long-term database of visitor sighting records with an intensive 3-year telemetry study to describe population dynamics of recolonization by black bears (Ursus americanus) of Big Bend National Park in Texas during 1988–2002. This population, which occurs within a metapopulation in western Texas and northern Mexico, increased from a single pair of known breeding-age animals in 1988 to 29 bears (including 6 females of breeding age) in March 2000 (λ = 1.25/year). A migration and dispersal event in August–December 2000 reduced the population to 2 adult females and as few as 5–7 individuals. One-way movement distances from the study area during this event averaged 76 km for females (n = 7) and 92 km for males (n = 4), and 3 animals conducted migrations of at least 154, 178, and 214 km, respectively. Our observations exemplify the importance of stochastic events on demographics of small populations and highlight the potential scale of bear movement among montane islands of southwestern North America. They also provide insight into the use of dispersal data in parameterizing metapopulation models for large carnivores

Effects of Sex, Age, and Season on Plasma Steroids in Free-ranging Texas Horned Lizards (Phrynosoma cornutum)

The Texas horned lizard (Phrynosoma cornutum) is protected in several states due to its apparently declining numbers; information on its physiology is therefore of interest from both comparative endocrine and applied perspectives. We collected blood samples from free-ranging P. cornutum in Oklahoma from April to September 2005, spanning their complete active period. We determined plasma concentrations of the steroids, progesterone (P), testosterone (T), and corticosterone (CORT) by radioimmunoassay following chromatographic separation and 17β-estradiol (E2) by direct radioimmunoassay. T concentrations in breeding males were significantly higher than in non-breeding males. P showed no significant seasonal variation within either sex. CORT was significantly higher during the egg-laying season compared to breeding and non-breeding seasons for adult females and it was marginally higher in breeding than in non-breeding males (P = 0.055). CORT concentrations also significantly increased with handling in non-breeding males and egg-laying females. Perhaps most surprisingly, there were no significant sex differences in plasma concentrations of P and E2. Furthermore, with respect to seasonal differences, plasma E2 concentrations were significantly higher in breeding females than in egg-laying or non-breeding females, and they were significantly higher in breeding than in non-breeding males. During the non-breeding season, yearling males exhibited higher E2 concentrations than adult males; no other differences between the steroid concentrations of yearlings and adults were detected. In comparison to other vertebrates, the seasonal steroid profile of P. cornutum exhibited both expected and unexpected patterns, and our results illustrate the value of collecting such baseline data as a springboard for appropriate questions for future research

High-resolution Niche Models via a Correlative Approach: Comparing and Combining Correlative and Process-based Information

Correlative and process-based approaches to describing the ecological niche in a spatially explicit fashion have often been compared in an adversarial framework. We sought to compare niche models developed via classic (correlative only), niche (process-based information), and hybridized (correlative augmented with process-based derived information) approaches, with the goal of determining if the added effort of process-based model development yielded better model fit. Correlative data layers (i.e., habitat models) included vegetation community types, Euclidean distance statistics, neighborhood analyses, and topographically-derived information. Mechanistic data layers were estimates of thermal suitability derived from field-collected datasets and biophysical calculations, and estimates of prey biomass interpolated from monitoring stations. We applied these models at high resolution (1 m × 1 m pixel size) to habitat occupied by a population of Texas horned lizards (Phrynosoma cornutum) located in central Oklahoma. Results suggested that our treatment of process-based information offered dramatically better identification of suitable habitat when compared to correlative information, but that these results were likely due to low variability of niche variable pixel values. Niche layers nearly perfectly predicted lizard locations; the interpretation of these results suggest that lizards occupy habitat based on thermal suitability over the duration of a field season. Given the low variability observed in thermal suitability layers, we question the ecological reality of these predictions. Correlative models may accurately describe the niche at small spatial scales, and may suffice in situations where time and financial resources are limiting constraints on project goals. Process-based information continues to be an important part of the niche, and may offer additional predictive accuracy via correlative approaches when included in an ecologically meaningful context