Enclosed track plate stations are a common method to detect mammalian carnivores. Studies rely on these data to make inferences about geographic range, population status and detectability. Despite their popularity, there has been no effort to document inter-observer variation in identifying the species that leave their tracks. Four previous field crew leaders identified the tracks of carnivores and non-carnivores on 105 track sheets from enclosed track plate stations that were used in field studies in California. Because the identity of the species was unknown, we evaluated the consistency in identifications among the 4 observers. The observers were in agreement on the identity of tracks on 73.3% of the track sheets. Considering only the putative carnivore tracks, the agreement was higher (86.8%) and was higher still (95.4%) when the lowest quality carnivore tracks were excluded. American martens (Martes americana) and fishers (M. pennanti) are important species from a conservation perspective, and there was only one occasion of inter-observer disagreement. Observers were much less consistent in identifying non-carnivores, achieving consensus on only 37.1% of the opportunities. When observers have training and experience similar to those involved here, tracks should be considered a reliable method for verifying the identity of most of the species that visit track-plate stations. Our results indicate that inter-observer variation is unlikely to have affected conclusions from previously published reports about the distribution or abundance of carnivores. We caution, however, that observers refrain from identifying a track when the quality is poor and also to assign only the highest level of taxonomic resolution that is justified.

We conducted a radiotelemetry evaluation to determine if strobe lights could be used to decrease turbine entrainment of juvenile steelhead (Oncorhynchus mykiss) at Cowlitz Falls Dam, Washington. We found that radio-tagged juvenile steelhead approached and entered two spillbays (one lighted, one unlighted) in equal proportions. However, the presence of strobe lights was associated with decreased spillbay residence time of juvenile steelhead and increased passage through induction slots (secondary turbine intakes located upstream of the ogee on the spillway). Mean residence time of tagged fish inside the lighted spillbay was 14 min compared to 62 min inside the unlighted spillbay. Radio-tagged steelhead passed through induction slots at a higher proportion in the lighted spillbay (55%) than in the unlighted spillbay (26%). Recent studies have suggested that strobe lights can induce torpor in juvenile salmonids. We believe that strobe light exposure affected fish in our study at a location where they were susceptible to high flows thereby reducing mean residence time and increasing the proportion of tagged fish entering induction slots in the lighted spillbay. Our results suggest that factors such as deployment location, exposure, and flow are important variables that should be considered when evaluating strobe lights as a potential fish-deterring management tool.

We conducted a study that evaluated the likelihood of capturing food web relationships with stable isotopes using two dominant producers, red alder and Douglas-fir, in the Oregon Coast Range. Foliage from 10 riparian forests dominated by either red alder or Douglas-fir was analyzed for δ¹⁵N and δ¹³C to determine the isotopic variability within a forest stand and across stands. We then conducted a sensitivity analysis using the IsoError model (Phillips and Gregg 2001) to determine whether δ¹⁵N and δ¹³C could successfully discriminate between red alder and Douglas-fir in a food web study. We found greater δ¹⁵N variation within and across sites for Douglas-fir (within stand: ≤2.58‰, average across stands: 1.72‰) compared to red alder (within stand: 0.59‰, average across stands: 0.27‰). δ¹³C variation was similar for both species within and among forest stands. On average, δ¹⁵N and δ¹³C of red alder and Douglas-fir differed by <2.0‰ in our forests. The sensitivity analysis found δ¹⁵N had limited use for predicting the dietary contribution of Douglas-fir and red alder to a consumer due to the high variability of δ¹⁵N in Douglas-fir and small differences in δ¹⁵N between the species. We had greater success with δ¹³C where overall variability was lower, and source differences were higher, than δ¹⁵N. Despite physiological differences that led us to believe red alder and Douglas-fir would have distinct δ¹⁵N and δ¹³C values, our results demonstrated that it would be difficult to discriminate between food webs based on these producers.

Mechanisms of interspecific and intraspecific competition and survival between the agronomic species Kentucky bluegrass (Poa pratensis L. ‘Midnight’), with the native grass Nuttall's alkaligrass (Puccinellia nuttalliana (Schult.) Hitchc.) and the introduced grass weeping alkaligrass (Puccinellia distans (Jacq.) Parl) were assessed over a two year period. A matrix of competitive regimes was created consisting of 4 monoculture densities and 16 mixtures of all possible pair-wise combinations. Response surfaces and substitution analysis of the three species were generated within the matrix to study competition dynamics between the species. Plants were grown under natural conditions, on a pH neutral (6.9) silt loam site, with no added irrigation or fertilizer. In general, in year 1, weeping alkaligrass was more competitive than Nuttall's alkaligrass and both species were far more competitive than Kentucky bluegrass. Both weeping and Nuttall's alkaligrass exhibited low survival (40% and 60%, respectively) following harvesting. There was also a shift in competitive effects in Year 2, such that weeping alkaligrass was equally competitive with Kentucky bluegrass, and both were far more competitive than Nuttall's alkaligrass. Even though weeping alkaligrass had very low survival rates its affect on Kentucky bluegrass into year 2 was equal to that of year 1. Thus, the legacy effect of weeping alkaligrass will likely have long-term implications to a rotation of Kentucky bluegrass plants, even if removed in the first year. However, the notion of a legacy effect of competition should not be limited to an agricultural setting. It is highly likely that similar interactions are exhibited across plant communities and that long term competition studies are required to adequately address this issue.

In the Klamath-Siskiyou region of northern California and southwest Oregon, the mixed-severity fire regime and short fire return interval has created diverse vegetative landscape with frequent regenerating patches of forest vegetation. Considerable evidence from this region suggests that intense competition from neighborhood vegetation can greatly reduce the survival and growth of young conifers following severe site disturbance, including fire. However, relatively little information exists regarding the growing conditions one to three decades following disturbance, particularly in unmanaged stands. We measured the effects of neighbor-hood vegetation on regenerating Douglas-fir (Pseudotsuga menziesii) growth in northern California, 10-20 years following severe wildfires. Steep climatic gradients owing to complex topography in the region can cause significant variation in local temperatures, levels of precipitation, and solar radiation; thus our measurements were dispersed across two abiotic environmental gradients, elevation and heat load. We used a nested sampling design to elicit the tree-level effects of neighborhood vegetation, the plot-level effects of elevation and heat load, and the interactions among tree-level and plot-level variables on Douglas-fir growth. We used a combination of of hierarchical regression models and non-parametric, multiplicative regression modeling for 3-dimensional graphical data presentation. Our results indicate that conifers are exposed to both positive (facilitative) and negative (competitive) neighborhood interactions depending on location in the abiotic environmental landscape. However, growth appears to be much more sensitive to abiotic environmental conditions than to the effects of neighborhood interactions. Considering the spatially explicit patterns in our data, we suggest that site-specific conditions play a significant role in the development of post-fire forest management strategies in the Klamath-Siskiyou region.

We compared ground beetle (Carabidae) assemblages between spotted knapweed (Centaurea maculosa Lam.) -invaded (invaded) and un-invaded (native) habitats in Rocky Mountain savannas. Carabids play important roles in biotic communities and are known as a good indictor group of environmental change. Carabid species activity-abundance and diversity were estimated, and environmental measurements were taken at four transects at each of six study sites in 1999 and 2000. Data on carabid trap captures were analyzed at both the species and functional group level. We found that species belonging to specialist predator and omnivore functional groups were more abundant on transects at invaded sites, whereas generalist predator species were more abundant within native sites. Carabid species richness was similar between invaded and native sites; however, evenness was greater at invaded compared to native sites. Greater species evenness in invaded versus native sites was primarily due to an increase in activity-abundance of species in the omnivore and specialist predator functional groups and a decrease in activity-abundance of dominant species belonging to the generalist predator functional group. Our results suggest that spotted knapweed invasion results in an alteration of carabid community structure and leads to the homogenization of carabid assemblages in Rocky Mountain savannas. Biotic homogenization, the increase in taxonomic similarity of once-diverse communities, is often a direct outcome of exotic invasions and an important concern currently facing biodiversity conservation.

We compared the hyposalinity tolerances of black prickleback (Xiphister atropurpureus) and penpoint gunnel (Apodichthys flavidus) that were collected in an intertidal area during a low-tide near Bamfield, British Columbia. We found black pricklebacks completely removed from the ebbing tide where they may be exposed to hyposaline conditions for up to five hours. Conversely, penpoint gunnels were found in larger tidepools or subtidal areas where they are less likely to be exposed to hyposaline conditions. The tolerance of each species was determined by measuring oxygen consumption (µmol·g·h) and counting opercular beats (per minute) in full-strength (∼30 ppt) and dilute seawater (∼6 ppt). Black pricklebacks (N = 10) consumed oxygen at a significantly lower rate (P = 0.001) in dilute seawater when compared to full-strength seawater, whereas there was no significant difference in consumption rate by penpoint gunnels (N = 10). The rate of opercular beats for both species significantly decreased in dilute seawater. Black pricklebacks showed a greater decrease in breathing rate, and opercular beating stopped completely in nine of the ten dilute seawater trials for periods ranging from 10 – 60 minutes. The lower oxygen consumption and breathing rate of black pricklebacks suggests that this species may have the ability to depress metabolic activity to remain in the intertidal zone during an ebb tide. These findings indicate that physiological adaptations may be a factor in the habitat portioning between black pricklebacks and penpoint gunnels.

Our goal was to determine whether Botta's pocket gopher (Thomomys bottae) eats hypogeous oak-woodland fungi and potentially functions as a vector of mycorrhizal inoculum. Although field guides and species accounts describe T. bottae as strict herbivores, members of the family Geomyidae are possible vectors of mycorrhizal inoculum because many ectomycorrhizal fungi are hypogeous, fruiting underground where Geomyidae live. Some studies have documented that Thomomys species are mycophagous at least seasonally. We removed fecal pellets from the large intestines of three T. bottae trapped in the spring at Whetstone Savanna in southern Oregon and examined them for presence of ectomycorrhizal fungal spores. Using light microscopy, we found spores from eight genera of hypogeous ectomycorrhizal fungi associated with Quercus garryana. These findings confirm that T. bottae is mycophagous and support a role for T. bottae as a spore dispersal vector for oak-obligate fungi. Therefore, T. bottae is potentially important for the survival, woodland regeneration and range expansion of Q. garryana.