Trapping Webs Research Articles

Within-Patch Structures Influence Small Mammal Abundance in Managed Forests of Northern California, USA

AbstractWe evaluated how forest type, vegetation structure in trapping webs, and proximate forest types influenced localized (~6.35 hectares) abundances for commonly captured small mammals in northern California, USA. We trapped from May to August of 2011–13 in 69 forest patches that represented: (1) clearcuts (3–5 years postharvest), (2) 10–20 year-old conifer plantations, (3) rotation-aged conifer stands, and (4) Watercourse and Lake Protection Zones. We captured 11 species; four in sufficient numbers for regression modeling. Our average abundance estimates for the study were 4.57 (standard error [SE] = 0.43), 0.32 (SE = 0.11), 0.90 (SE = 0.30), and 0.25 (SE = 0.09) individuals per web location (~0.75 hectares) for Peromyscus spp., Neotoma spp., California ground squirrels, and Allen’s chipmunks. We found that web-level ground cover (shrubs and grass), downed wood, and types of forests containing our trapping webs best described small mammal abundances, whereas proximate forest types were not important. Our results indicated that retaining localized structures in the form of understory shrub cover and downed wood positively influences small mammal abundance in intensively managed forests of northern California.

Effects of forest composition on trophic relationships among mast production and mammals in central hardwood forest

Abstract Oak-dominated forest has declined in the eastern United States as shade-tolerant mesophytic species (e.g., maple [Acer spp.]) replace oaks (Quercus spp.), sparking concern among ecologists regarding species that consume acorns. Our goal was to describe how increasing mesophication of oak forests may affect consumers in higher trophic levels. We investigated relationships among forest composition, mast production, small-mammal density, and carnivore occurrence in 8 stands representing a gradient of oak–hickory dominance in central hardwood forest in southern Illinois. We livetrapped small mammals for >24,000 trap-nights in June–August 2009–2011 with trapping webs to estimate population density of mice (Peromyscus spp.). We collected mast seeds during October–November 2009–2010 and calculated average dry biomass (g/m2) for each species and stand. During winters 2009–2011, we photographed carnivores using baited camera traps. We regressed mast biomass on measures of forest composition and regressed ...

ASSOCIATION BETWEEN MOVEMENT AND SIN NOMBRE VIRUS (BUNYAVIRIDAE: HANTAVIRUS) INFECTION IN NORTH AMERICAN DEERMICE (PEROMYSCUS MANICULATUS) IN COLORADO

Capture data from long-term, mark-recapture studies were used to evaluate movements of North American deermice (Peromyscus maniculatus) on mark-recapture webs in Colorado with respect to Sin Nombre virus (SNV) infection status, age, sex, and trapping site. Latitude and longitude coordinates for each capture during the approximately 12-yr study were used to produce an individual minimum convex polygon (MCP) area representing the movements (not home range) of an individual mouse over time. These MCP areas were compared by SNV infection status (as determined by the presence of antibody), age, and sex. Antibody-negative deermice had significantly larger mean MCP areas than did antibody-positive mice. No differences in MCP area were found between male and female mice (either positive or negative). The smaller MCP areas of antibody-positive mice correspond to decreased movement by SNV-infected deermice on the trapping webs. These findings may indicate that SNV has a negative effect on movement, perhaps by reducing the health of infected deermice.

Land Use and Small Mammal Predation Effects on Shortgrass Prairie Birds

ABSTRACT Grassland birds endemic to the central shortgrass prairie ecoregion of the United States have experienced steep and widespread declines over the last 3 decades, and factors influencing reproductive success have been implicated. Nest predation is the major cause of nest failure in passerines, and nesting success for some shortgrass prairie birds is exceptionally low. The 3 primary land uses in the central shortgrass prairie ecoregion are native shortgrass prairie rangeland (62%), irrigated and nonirrigated cropland (29%), and Conservation Reserve Program (CRP, 8%). Because shortgrass–cropland edges and CRP may alter the community of small mammal predators of grassland bird nests, I sampled multiple sites on and near the Pawnee National Grasslands in northeast Colorado, USA, to evaluate 1) whether small mammal species richness and densities were greater in CRP fields and shortgrass prairie–cropland edges compared to shortgrass prairie habitats, and 2) whether daily survival probabilities of ground‐nesting grassland bird nests were negatively correlated with densities of small mammals. Small mammal species richness and densities, estimated using trapping webs, were generally greater along edges and on CRP sites compared to shortgrass sites. Vegetation did not differ among edges and shortgrass sites but did differ among CRP and shortgrass sites. Daily survival probabilities of artificial nests at edge and CRP sites and natural nests at edge sites did not differ from shortgrass sites, and for natural nests small mammal densities did not affect nest survival. However, estimated daily survival probability of artificial nests was inversely proportional to thirteen‐lined ground squirrel (Spermophilus tridecemlineatus) densities. In conclusion, these data suggest that although land‐use patterns on the shortgrass prairie area in my study have substantial effects on the small mammal community, insufficient data existed to determine whether land‐use patterns or small mammal density were affecting grassland bird nest survival. These findings will be useful to managers for predicting the effects of land‐use changes in the shortgrass prairie on small mammal communities and avian nest success.

Spatial patterns of bee captures in North American bowl trapping surveys

Abstract. 1. Bowl and pan traps are now commonly used to capture bees (Hymenoptera: Apiformes) for research and surveys.2. Studies of how arrangement and spacing of bowl traps affect captures of bees are needed to increase the efficiency of this capture technique.3. We present results from seven studies of bowl traps placed in trapping webs, grids, and transects in four North American ecoregions (Mid‐Atlantic, Coastal California, Chihuahuan Desert, and Columbia Plateau).4. Over 6000 specimens from 31 bee genera were captured and analysed across the studies.5. Based on the results from trapping webs and distance tests, the per bowl capture rate of bees does not plateau until bowls are spaced 3–5 m apart.6. Minor clumping of bee captures within transects was detected, with 26 of 56 transects having index of dispersion values that conform to a clumped distribution and 39 transects having positive Green’s index values, 13 with zero, and only four negative. However, degree of clumping was slight with an average value of only 0.06 (the index ranges from −1 to 1) with only five values >0.15. Similarly, runs tests were significant for only 5.9% of the transects.7. Results indicate that (i) capture rates are unaffected by short distances between bowls within transects and (ii) that bowls and transects should be dispersed throughout a study site.

BRUSH MOUSE (PEROMYSCUS BOYLII ) POPULATION DYNAMICS AND HANTAVIRUS INFECTION DURING A WARM, DROUGHT PERIOD IN SOUTHERN ARIZONA

We monitored Limestone Canyon hantavirus (LSCV) antibody prevalence, host (brush mouse, Peromyscus boylii) abundance, and environmental variables (temperature and rainfall) in brush mice captured on three trapping webs in southern Arizona for 5 yr. Although seasonal patterns were subtle, we observed large multiyear variation in population abundance and antibody prevalence. Limestone Canyon hantavirus infection in brush mouse populations varied over time with prevalence ranging from 0% to 33%. At all trapping webs, evidence of infection disappeared completely for an extended period (up to 2 yr) and eventually reappeared, suggesting that dispersal may play a role in maintaining infection in brush mouse metapopulations. Weather during the study period was drier and warmer than average and these conditions, especially during spring through fall, may have contributed to low brush mouse population density and the local extinction of LSCV during the second year of the study. Nevertheless, population growth was associated with relatively warm, dry conditions during winter periods and a cool, wet spring and summer period in the fifth year of the study. After prolonged absence, LSCV infection was consistently detected only when brush mouse population abundance reached relatively high levels during that fifth year. Comparison of our results to similar studies suggests that stochastic events resulting in the loss or survival of a few infected mice in low-density host populations may result in local extinction of virus; reestablishment of infection may occur via immigration of infected individuals from adjacent populations, but may be successful only when populations are of sufficient density to support frequent rodent-to-rodent interactions and virus transmission.

Point transect sampling with traps or lures

SummaryThe ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widely used tool for such monitoring is distance sampling, in which distances of detected animals from a line or point are modelled, to estimate detectability and hence abundance. Nevertheless, many species still prove problematic to survey. We have developed two extensions to point transect sampling that potentially allow abundance to be estimated for a number of species from diverse taxa for which good survey methods have not previously been available.For each method, the primary survey comprises a random sample of points, or more usually a systematic grid of points, through the region of interest. Animals are lured to a point, or trapped at a point, and the number of animals observed at each point is recorded. A separate study is conducted on a subset of animals, to record whether they respond to the lure or enter the trap, for a range of known distances from the point. These data are used to estimate the probability that an animal will respond to the lure or enter the trap, as a function of its initial distance from the point. This allows the counts to be converted to an estimate of abundance in the survey region.We illustrated the methods using a lure survey of crossbillsLoxiaspp. in coniferous woodland in Scotland.Synthesis and applications.Two extensions of point transect sampling that use the same statistical methodology, lure point transects and trapping point transects, have been developed. Lure point transects extend the applicability of distance sampling to species that can be lured to a point, while trapping point transects potentially allow abundance estimation of species that can be trapped, with fewer resources needed than trapping webs and conventional mark–recapture methods.

A field test of two methods for density estimation

Density of wildlife populations is a key variable for management, yet reliable estimation is elusive. We tested one established method (trapping webs and distance analysis) and one novel method (inverse prediction from capture-recapture data) on a population of brushtail possums (Trichosurus vulpecula) whose density also could be determined by exhaustive removal. The study area was approximately 315 ha of coastal plantation for- est surrounded on 3 sides by sand and water. We placed 4 lines of 9 cage traps at 20-m spacing in a square to form a grid. We set 5 hollow grids, each comprising 36 traps, for 5 days; we tagged and released possums. We later set 5 trapping webs of 50 traps each at the same sites; we caught possums and removed them over 4 days. Wide- area removal used a combination of acute poisoning and leghold trapping. The estimate of density by inverse prediction (1.88/ha, SE = 0.26) was consistent with the removal esti- mate (2.27/ha), whereas estimates from trapping webs were positively biased (6.5 to 8.0/ha, depending on method of analysis). The inverse prediction method frees cap- ture-recapture from the straitjacket of conventional grids and should allow accurate land- scape-scale estimation of density once the requisite trapping effort is identified.

SPATIAL CLUSTERING OF MURID RODENTS INFECTED WITH HANTAVIRUSES: IMPLICATIONS FROM META‐ANALYSES

We applied a rigorous, quantitative methodology to the analysis of local‐scale spatial clustering of multiple murid mice (brush mice, Peromyscus boylii; deer mice, P. maniculatus; piñon mice, P. truei; western harvest mice, Reithrodontomys megalotis) infected or uninfected with hantaviruses. Rodents were sampled longitudinally from 1994 to 2001 on 23 trapping webs at 10 locations in the southwestern United States. This study provided an opportunity to apply meta‐analysis techniques to an important ecological question. There were sufficient captures by species on 199 occasions (three consecutive nights) to compare general use of space using multi‐response permutation procedures (MRPP). The MRPP results were then used in meta‐analyses by species to determine if overall effects of spatial clustering of hantavirus‐infected mice as well as categorical effects (elevation, season, site, and state) were present. Based on MRPP analyses, overall spatial clustering of hantavirus‐infected mice was most pronounced for brush mice, followed by the deer mouse. Meta‐analyses indicated significant overall effects of spatial clustering and varying categorical effects (elevation, season, site, state) of infected mice for each species compared. The overlapping space use by rodents might be an important factor affecting the local transmission of several hantaviruses.

Natural history of Sin Nombre virus in western Colorado.

A mark-recapture longitudinal study of immunoglobulin G (IgG) antibody to Sin Nombre virus (SNV) in rodent populations in western Colorado (1994-results summarized to October 1997) indicates the presence of SNV or a closely related hantavirus at two sites. Most rodents (principally deer mice, Peromyscus maniculatus, and pinyon mice, P. truei) did not persist on the trapping webs much beyond 1 month after first capture. Some persisted more than 1 year, which suggests that even a few infected deer mice could serve as transseasonal reservoirs and mechanisms for over-winter virus maintenance. A positive association between wounds and SNV antibody in adult animals at both sites suggests that when infected rodents in certain populations fight with uninfected rodents, virus amplification occurs. At both sites, male rodents comprised a larger percentage of seropositive mice than recaptured mice, which suggests that male mice contribute more to the SNV epizootic cycle than female mice. In deer mice, IgG antibody prevalence fluctuations were positively associated with population fluctuations. The rates of seroconversion, which in deer mice at both sites occurred mostly during late summer and midwinter, were higher than the seroprevalence, which suggests that the longer deer mice live, the greater the probability they will become infected with SNV.

Long-term studies of hantavirus reservoir populations in the southwestern United States: rationale, potential, and methods.

Hantaviruses are rodent-borne zoonotic agents that cause hemorrhagic fever with renal syndrome in Asia and Europe and hantavirus pulmonary syndrome (HPS) in North and South America. The epidemiology of human diseases caused by these viruses is tied to the ecology of the rodent hosts, and effective control and prevention relies on a through understanding of host ecology. After the 1993 HPS outbreak in the southwestern United States, the Centers for Disease Control and Prevention initiated long-term studies of the temporal dynamics of hantavirus infection in host populations. These studies, which used mark-recapture techniques on 24 trapping webs at nine sites in the southwestern United States, were designed to monitor changes in reservoir population densities and in the prevalence and incidence of infection; quantify environmental factors associated with these changes; and when linked to surveillance databases for HPS, lead to predictive models of human risk to be used in the design and implementation of control and prevention measures for human hantavirus disease.

Estimation of Density of Mongooses with Capture-Recapture and Distance Sampling

We captured mongooses ( Herpestes javanicus ) in live traps arranged in trapping webs in Antigua, West Indies, and used capture-recapture and distance sampling to estimate density. Distance estimation and program DISTANCE were used to provide estimates of density from the trapping-web data. Mean density based on trapping webs was 9.5 mongooses/ha (range, 5.9–10.2/ha); estimates had coefficients of variation ranging from 29.82–31.58% ( X = 30.46%). Mark-recapture models were used to estimate abundance, which was converted to density using estimates of effective trap area. Tests of model assumptions provided by CAPTURE indicated pronounced heterogeneity in capture probabilities and some indication of behavioral response and variation over time. Mean estimated density was 1.80 mongooses/ha (range, 1.37–2.15/ha) with estimated coefficients of variation of 4.68-11.92% ( X#x0304; = 7.46%). Estimates of density based on mark-recapture data depended heavily on assumptions about animal home ranges; variances of densities also may be underestimated, leading to unrealistically narrow confidence intervals. Estimates based on trap webs require fewer assumptions, and estimated variances may be a more realistic representation of sampling variation. Because trap webs are established easily and provide adequate data for estimation in a few sample occasions, the method should be efficient and reliable for estimating densities of mongooses.

Animal Density Estiamtion Using a Trapping Web Design: Field Validation Experiments

A recent developed trapping web sampling design (Anderson et al. 1983) and a series of four density estimation models were evaluated using known field populations of ground—dwelling darkling beetles (Tenebrionidae: Eleodes spp.) in a shrub—steppe ecosystem in southwestern Wyoming. Known densities (range 794—11 793 beetles/ha) of marked beetles were established annually in two circular enclosures (415.5 m2 each) from 1984 to 1987. After releasing the beetles, we sampled the marked populations in each enclosure, using 141 pitfall traps arranged in a web design. The resulting data were analyzed with four density estimation models (Fourier series, exponential power series, negative exponential, and half normal) using the program TRANSECT. We then evaluated each model's ability to estimate the true beetle density (D). We found that the negative exponential model was most reliable, estimating D "correctly" (i.e., the 95% confidence interval of D included D) in 100% of the trials (n = 11), and having a mean coefficient of variation (CV) of 20% and no detectable bias. The exponential power series and Fourier series also performed well, providing confidence interval coverage of D in 91 and 73% of the trials, respectively. However, the precision of the exponential power series model was extremely low, resulting in very wide confidence intervals. The half normal model consistently underestimated the true densities, and provided only 18% confidence interval coverage. Tests of the sampling design's assumptions (regarding animal capture probabilities and movements) using actual field data showed that, in most cases, all assumptions were satisfied; even when assumptions were violated, the there successful models continued to function well. An improved procedure for setting confidence intervals is also provided. Based on these analytical results, and considering the logistical and theoretical advantages of trapping webs over trapping grids, we recommend the use of the web design and distance measure analyses for estimating population densities of mobile small animals.