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Invasive species frequently affect urban ecosystems, but few studies investigate primary and secondary mechanisms to determine overall ecological effects. Previous work demonstrates slugs can negatively affect seedling recruitment and vegetation biomass, and positively affect litter decomposition, nutrient cycling, and litter invertebrate populations. This study aimed to assess components of how invasive European black slugs (Arion rufus) affect native Cascade Oregon grape (Mahonia nervosa), in Pacific Northwest forests. We hypothesized that slug herbivory would decrease leaf area, but excretion of leaf and litter matter would enhance soil and litter conditions. Field experiments aimed to alter slug densities to measure effects on leaf area, litter biomass, soil nutrients, and non-slug litter invertebrates. Leaf area was lower in areas with high slug densities along with slight increases in non-slug invertebrate abundance; whereas leaf area, number of leaves, and branches per plant were higher in areas with low slug densities. However, slugs did not affect soil nitrate or litter decomposition significantly. Laboratory experiments found slugs consumed fresh leaves faster than litter but there were no differences in assimilation. By testing potential primary and secondary ecological mechanisms, our results suggest the overall effect of invasive slugs on a common forest understory plant is negative, as expected, but secondary positive effects on the litter invertebrate community, which could mitigate cumulative impact, are subtle and detection may require longer-term study.
Trochammina hadai Uchio, a benthic foraminifera native to Japanese estuaries, was first identified as an invasive in 1995 in San Francisco Bay and later in 16 other west coast estuaries. To investigate the timing of the arrival and expansion of this invasive species in Padilla Bay, Washington, we analyzed the distribution of foraminifera in two surface samples collected in 1971, in nine surface samples collected by Scott in 1972–1973, as well as in two cores (Padilla Flats 3 and Padilla V1/V2) obtained in 2004. Trochanimina hadai, originally identified as the native Trochammina pacifica Cushman in several early foraminiferal studies, dominates the assemblage of most of the surface samples. In the Padilla V1/V2 and Padilla Flats 3 cores, the species' abundance follows a pattern of absence, first appearance, rapid expansion commonly seen shortly after the arrival of a successful biological invasion, setback, and second expansion. Using Q-mode cluster analysis, pre-expansion and expansion assemblages were identified. Pb-210 dating of these cores proved unsuccessful. However, based on T. hadai's first appearance occurring stratigraphically well above sedimentological changes in the cores that reflect deposition of sediments in the bay due to previous diversions of the Skagit River, and its dominance in the early 1970s surface samples, we conclude that the species arrived in Padilla Bay somewhere between the late 1800s and 1971. Trochammina hadai may have been introduced into the bay in the 1930s when oyster culturing began there or, at a minimum, ten years prior to its appearance in San Francisco Bay.
Recent studies in Southeast Alaska suggest the ecology of Glaucomys sabrinus differs from populations in the Pacific Northwest. In Southeast Alaska, densities were the highest reported for the species, populations were not as closely linked to old-forest attributes, and individuals had a more diverse diet that was less dependent on mycophagy. Pacific Northwest communities are comprised of several arboreal rodents; Southeast Alaska has a depauperate mammal fauna. I hypothesized that Southeast Alaska populations had a broader realized niche because of competitive release. The red squirrel (Tamiasciurus hudsonicus) is the only other arboreal squirrel and it is absent from the southern outer islands of Southeast Alaska's Alexander Archipelago. I compared demography and body mass of G. sabrinus on Prince of Wales Island to a population in sympatry with T. hudsonicus on a separate island (Mitkof). Home ranges were larger and population density, breeding female density, and juvenile recruitment of G. sabrinus were all lower in sympatry with T. hudsonicus. In a companion study, G. sabrinus on Prince of Wales Island used cavities for denning relatively more frequently than in sympatry with T. hudsonicus on Mitkof Island. Female G. sabrinus depend on cavities for natal dens, and breeding female and population densities are positively correlated with large snag or tree density. The presence of T. hudsonicus may influence G. sabrinus populations by limiting availability of cavities. Furthermore, variation in vertebrate assemblages among islands may influence realized niches of resident species, which manifest unique demographic profiles compared to populations of different ecological communities.
Riparian systems in the western United States provide important habitat for bird communities during all times of the year. In recent decades, invasive plants, such as Russian olive (Elaeagnus angustifolia), have achieved broad distribution and local dominance in many western riparian areas, raising concerns over the loss of ecological function within these systems. In 2005 and 2006 we conducted avian point counts and surveyed vegetation cover at 95 points along the Snake and Columbia Rivers in southeastern Washington to investigate the effects of total woody vegetation cover and the relative proportion of Russian olive cover on breeding and wintering riparian bird communities. Our results indicated that riparian habitats dominated by Russian olive can support diverse and abundant bird communities, though cavity nesting species were noticeably sparse. Bird density and species richness were best explained by a quadratic relationship to total woody vegetation cover in both seasons, as was breeding bird community composition, with greatest density and richness in intermediate cover levels. We found no indication that the proportion of the woody vegetation comprised of Russian olive strongly influenced any of these bird community metrics. Given that Russian olive comprised 81.6% of the riparian vegetation in our study area, it is unclear from our results how Russian olive would affect bird communities in regions where native vegetation is more abundant. Regardless, complete eradication of Russian olive from riparian systems where the plant is a major component will reduce the overall habitat value for birds by eliminating significant structural complexity.
Within the United States (U.S.), state wildlife agencies are required to identify Species of Greatest Conservation Need (SGCN), the factors that impact these species, and the conservation actions needed to conserve these species through documentation of a Comprehensive Wildlife Conservation Strategy (CWCS). While the identification of SGCN represents an essential first step towards a comprehensive management strategy at the state level, the incorporation of this information into county level comprehensive plans will likely increase conservation efforts needed statewide. Our objective for this study was to use spatial data to delineate areas of human activity overlapping with areas rich in biodiversity to provide state wildlife agencies and local county planners recommended conservation actions to reduce biodiversity loss by human activities. Using the state of Idaho as an example, we delineated areas within the state where biodiversity hotspots for terrestrial and aquatic SGCN and human activities may be conflicting. We then identified counties within the state where these areas of conflict occur and identified conservation actions that may mitigate human activities to benefit SGCN. Our study used available geospatial data and a simple geographical information system (GIS) based approach which could be applied to other areas to support county-level land use planning for wildlife conservation.
In 2008, I surveyed bird populations in two riparian areas in western Montana using territory-mapping and compared the results with surveys done in 1968 and 1980. Bird populations were assessed by mapping territories of singing males. Overall vegetation height of the ground layer increased between 1980 and 2008. A major vegetation component, mountain alder (Alnus tenuifolia), suffered massive mortality due to a freezing event in February 1989. The death of the main trunks and re-sprouting of mountain alder changed the structure of the riparian vegetation. Mean height of alder was 1.4 m less in 2008 than in 1980 along Elk Creek. It was 3.4 m lower along the North Fork. Based on male habitat-use information collected in 1968, these structural changes may have negatively impacted the Hammond's Flycatcher, Warbling Vireo, Yellow-rumped Warbler, and American Redstart since males of these species were documented in 1968 to primarily use the upper level of the alder canopy for singing. The MacGillivray's Warbler may have benefitted from the change in alder structure. Bird species richness was similar over time. On Elk Creek, the Willow Flycatcher, Veery and Red-eyed Vireo disappeared, whereas the American Redstart declined from 19 territories to two in 2008. On the North Fork, the Warbling Vireo and American Redstart disappeared and the Hammond's Flycatcher declined from 10 territories (in 1980) to 2.5 in 2008. Bird population size and species composition varied between the two riparian areas. Riparian width of Elk Creek was significantly larger than the North Fork and this corresponded with higher bird species richness and abundance.