bluuebunny/crossref_metadata_2025 huggingface dataset:
CONFLICTING MANAGEMENT GOALS: MANATEES AND INVASIVE COMPETITORS INHIBIT RESTORATION OF A NATIVE MACROPHYTE
Authors: Hauxwell Jennifer , Osenberg Craig W. , Frazer Thomas K.
Published: June 2007

Vallisneria americana is a native macrophyte in freshwater and oligohaline ecosystems, often forming meadows that significantly affect ecosystem carbon and nutrient cycling and provide structural habitat. Vallisneria has declined in abundance in several Florida lakes, rivers, and estuaries. We conducted an 11‐month field experiment in Kings Bay, Florida, USA, to determine factors that might affect successful transplantation of Vallisneria and to guide potential future restoration efforts by water resource management agencies. To determine the effects of herbivores and other primary producers on Vallisneria production, we conducted a 2 × 2 factorial experiment at three sites in which we allowed or denied: (1) relatively large herbivores (>3 cm) and (2) other primary producers (e.g., Myriophyllum spicatum, Hydrilla verticillata, Lyngbya sp.) access to 1.5 × 1.5‐m transplanted plots of Vallisneria. Within one month, Vallisneria disappeared from 80% of herbivore‐access plots due primarily to consumption by manatees. Vallisneria density was reduced a variable amount (0–50%) in response to competitors, due to site‐specific variation in natural abundance of other primary producers (at two sites, we observed extensive colonization by other primary producers and a strong treatment effect). Most of this competitive effect was attributable to Eurasian watermilfoil (Myriophyllum spicatum); after pooling Vallisneria density data across sites, we observed a negative exponential relationship between shoot density of Vallisneria and stem density of Myriophyllum for every sampling date. We observed variable recruitment of Vallisneria transplants into larger size classes among sites, but not between treatments, and large, established plants grew at similar rates whether in monospecific or mixed stands, with evidence for reduced mass‐specific growth in dense stands. Hence, a probable mechanism by which Myriophyllum reduces Vallisneria occurs via space limitation, and reduction in Vallisneria densities and/or recruitment and growth of new shoots. We conclude that two different management goals (restoration of Vallisneria and protection of manatees) are in conflict and must be simultaneously considered to devise effective and sustainable ecosystem management scenarios. Due to the highly managed nature of freshwater systems worldwide, the limitations of extrapolating experimental results and the importance of site‐specific pilot experiments should also be recognized.
WEASELS, VOLES, AND TREES: INFLUENCE OF MUSTELID SEMIOCHEMICALS ON VOLE POPULATIONS AND FEEDING DAMAGE
Authors: Sullivan Thomas P. , Sullivan Druscilla S. , Reid Donald G. , Leung Maria C.
Published: June 2007

The role of predators, particularly small mustelids, in regulating vole (Microtus spp.) populations has been the subject of much scientific inquiry over the past several decades. From a management perspective, voles cause economic damage by feeding on seedlings planted on cutover forest land in temperate and boreal zones. Because of the close relationship between small weasels (Mustela erminea and M. nivalis) and voles, could the indirect effect of weasel scent disrupt vole populations and reduce their damage to forest plantations? This study was designed to test the hypotheses that synthetic weasel odor would: (1) reduce abundance, reproduction, survival, and movement of montane (Microtus montanus) and meadow (M. pennsylvanicus) vole populations; (2) enhance the activity of small weasels; and (3) reduce feeding damage by voles to tree seedlings. Study areas were located near Summerland and Gavin Lake in south‐central British Columbia, Canada. Vole populations were intensively live‐trapped on replicate sites from April 1994 to May 1995 during a peak year in abundance. Synthetic weasel odor was continually present on treatment sites from early summer 1994 to spring 1995. Weasel activity was measured by the number of individuals captured in live‐traps and by the number of snow tracks on control and treatment sites. Overwinter mortality to planted lodgepole pine (Pinus contorta) seedlings from vole feeding was measured on all sites in May 1995.

Mean vole abundance (n = 4) was similar between control (32–121 voles/ha) and treatment (37–118 voles/ha) sites. Montane voles declined by 17–36% on treatment sites during early summer when trappability of this species declined dramatically at Summerland. This pattern was not observed for meadow voles at Gavin Lake. Recruitment of new voles was generally similar between control and treatment sites. Weasel odor had no effect on reproduction, in terms of number of successful pregnancies and index of early juvenile survival, or on total survival, movements, or body mass of voles. Activity of small weasels appeared to be higher on treatment than control sites at Gavin Lake. Weasel odor did not reduce mortality of tree seedlings caused by vole feeding.

This study is the first investigation of the population responses of free‐living voles to synthetic odor of the short‐tailed weasel, a principal predator of Microtus spp. Our results demonstrate that by the time voles have reached high densities, it is too late to reduce numbers or curtail feeding damage, regardless of weasel odor‐induced antipredatory behavior or enhanced activity of predators. Application of weasel odor during the low phase of the vole population cycle would be a critical test of the hypothesis that small mustelids could lengthen the period of low vole numbers and potentially protect forest plantations from vole damage.
ALIEN FISHES IN CALIFORNIA WATERSHEDS: CHARACTERISTICS OF SUCCESSFUL AND FAILED INVADERS
Authors: Marchetti Michael P. , Moyle Peter B. , Levine Richard
Published: June 2007

The literature on alien animal invaders focuses largely on successful invasions over broad geographic scales and rarely examines failed invasions. As a result, it is difficult to make predictions about which species are likely to become successful invaders or which environments are likely to be most susceptible to invasion. To address these issues, we developed a data set on fish invasions in watersheds throughout California (USA) that includes failed introductions. Our data set includes information from three stages of the invasion process (establishment, spread, and integration). We define seven categorical predictor variables (trophic status, size of native range, parental care, maximum adult size, physiological tolerance, distance from nearest native source, and propagule pressure) and one continuous predictor variable (prior invasion success) for all introduced species. Using an information‐theoretic approach we evaluate 45 separate hypotheses derived from the invasion literature over these three stages of the invasion process. Our results indicate that successful establishment is best predicted with our global model that includes all seven variables, suggesting an inherent multivariate nature to the establishment stage of the invasion process. Spread of introduced fishes is best predicted using measures of physiological tolerance and propagule pressure. Species integration and impact is best predicted using a measure of prior invasion success. The results from analyses like this will help guide and inform management decisions regarding current and future species introductions.
AGRICULTURAL PONDS SUPPORT AMPHIBIAN POPULATIONS
Authors: Knutson Melinda G. , Richardson William B. , Reineke David M. , Gray Brian R. , Parmelee Jeffrey R. , Weick Shawn E.
Published: June 2007

In some agricultural regions, natural wetlands are scarce, and constructed agricultural ponds may represent important alternative breeding habitats for amphibians. Properly managed, these agricultural ponds may effectively increase the total amount of breeding habitat and help to sustain populations. We studied small, constructed agricultural ponds in southeastern Minnesota to assess their value as amphibian breeding sites. Our study examined habitat factors associated with amphibian reproduction at two spatial scales: the pond and the landscape surrounding the pond. We found that small agricultural ponds in southeastern Minnesota provided breeding habitat for at least 10 species of amphibians. Species richness and multispecies reproductive success were more closely associated with characteristics of the pond (water quality, vegetation, and predators) compared with characteristics of the surrounding landscape, but individual species were associated with both pond and landscape variables. Ponds surrounded by row crops had similar species richness and reproductive success compared with natural wetlands and ponds surrounded by nongrazed pasture. Ponds used for watering livestock had elevated concentrations of phosphorus, higher turbidity, and a trend toward reduced amphibian reproductive success. Species richness was highest in small ponds, ponds with lower total nitrogen concentrations, tiger salamanders (Ambystoma tigrinum) present, and lacking fish. Multispecies reproductive success was best in ponds with lower total nitrogen concentrations, less emergent vegetation, and lacking fish. Habitat factors associated with higher reproductive success varied among individual species. We conclude that small, constructed farm ponds, properly managed, may help sustain amphibian populations in landscapes where natural wetland habitat is rare. We recommend management actions such as limiting livestock access to the pond to improve water quality, reducing nitrogen input, and avoiding the introduction of fish.
MODEL PROJECTIONS OF THE FISHERY IMPLICATIONS OF THE ALLEE EFFECT IN BROADCAST SPAWNERS
Authors: Lundquist Carolyn J. , Botsford Louis W.
Published: June 2007

There has been widespread concern that reduction in density of broadcast spawners by a fishery can have severe effects on reproduction. As fishing decreases density, fertilization efficiency declines, so that reproduction declines more rapidly than indicated by density, producing an Allee effect. However, this potentially precipitous decline in reproduction with declining density or stock size is not well understood at the population level. We used a simple deterministic model of the reproductive dynamics of a broadcast spawning invertebrate to show that the abrupt threshold often proposed as the form of this Allee effect is possible only when individuals are evenly spaced, and when sperm dispersal distribution is a constant out to a specified distance. When the spatial distribution is random and the sperm dispersal distribution is either Gaussian or exponential, fertilization success is linear up to 100%; thus, zygote production is quadratic up to this density. As the width of the dispersal function decreases, fertilization reaches 100% at higher densities, so that it may be beyond the highest density experienced by the population. In that case, zygote production is functionally linear. We then used a simulation model to assess the effects of aggregative behavior and stochastic variability in spatial patterns. We compared narrow and broad sperm dispersal distributions that were based on empirically determined fertilization of the green sea urchin, Strongylocentrotus droebachiensis, under two flow regimes. Zygote production exhibited a gradual nonlinear Allee effect as density decreased for the broader gamete dispersal distribution, but a functionally linear relationship with a much lower slope for the narrower sperm dispersal distributions. Increasing aggregation increased the slope of both fertilization and zygote production vs. density at the origin, but they remained linear for the narrower distribution. High interannual variability in zygote production due to different spatial configurations suggested that the geometric mean of recruitment is a better indicator of population consequences than the arithmetic mean, and it displays a sharper threshold than the arithmetic mean. Our results imply that potential Allee effects at low density in broadcast spawning populations rarely exhibit threshold behavior, and that these Allee effects may be too weak to be detected in stock–recruitment relationships.
FIRE AND VEGETATION HISTORY IN THE EASTERN CASCADE MOUNTAINS, WASHINGTON
Authors: Wright Clinton S. , Agee James K.
Published: June 2007

Dendrochronological techniques were used to reconstruct a 433‐yr fire history, and to characterize the historical fire regime (frequency, size, season, severity) of the Teanaway River drainage in the eastern Cascade Mountains of Washington, USA. General Land Office section corner data were used to reconstruct aspects of the late‐19th‐century structure and composition of the forests in the study area. Systematic fire‐scar surveys (∼30 000 ha; 92 sites; 257 fire‐scarred cross‐sections; 1569 individual fire scars) revealed that fire frequency was quite variable spatially; Weibull median probability intervals ranged from seven to 43 years. Fire extent also varied widely; most fires were relatively small (<1000 ha), although several large fires (>4000 ha) were detected. Mean and median fire sizes were 1795 ha and 988 ha, respectively. Large fires occurred every 27 years, on average (every 11 years, on average, between 1708 and 1889), and coincided with periods of annual and seasonal drought (Palmer Drought Severity Index and winter Southern Oscillation Index). Intervals from 1 to 37 years occurred between fires of >4000 ha. Over 80% of fires occurred late in the growing season, or after the onset of cambial dormancy. Sampling locations in dry forest types (dominated by ponderosa pine) yielded fire‐scarred cross‐sections with numerous fire scars leading us to infer that most historical fires were of low intensity, leaving the overstory structure intact. This inference is corroborated by the composition and structure of the historical forest, which was characterized by a preponderance of very large (>100‐cm diameter) ponderosa pines. Mesic forest types (dominated by grand fir and Douglas‐fir) likely exhibited a wider range of fire severities. Moderate and occasional high‐severity understory fires or crown fires did occur within the study area, as indicated by the scarcity or lack of fire‐scar evidence and the presence of relatively even‐aged forests at several mesic forest sites. Historical section corner data indicate that small amounts of these forest types occurred in the study area. Fire frequency and size declined dramatically circa 1900, coincident with the advent of commercial timber harvesting, although most fires, despite their reduced number and size, continued to burn in the late summer or fall.
REMOTE SENSING OF GYPSY MOTH DEFOLIATION TO ASSESS VARIATIONS IN STREAM NITROGEN CONCENTRATIONS
Authors: Townsend Philip A. , Eshleman Keith N. , Welcker Chris
Published: June 2007

Disturbance is an important mechanism controlling dissolved nitrogen (N) leakage to receiving streams, rivers, lakes, and estuaries from forested watersheds. In oak forests of the eastern United States, defoliation by the gypsy moth caterpillar represents a recurring disturbance regime that can impact water quality. Following an upsurge in gypsy moth activity in the mid‐Appalachian region in 2000–2001, we examined the relationship between defoliation and N export within the Fifteenmile Creek watershed in Maryland and Pennsylvania using intensive stream surveys and remotely sensed imagery. Concentrations of dissolved N species were determined six times during seasonal baseflow and once during stormflow conditions at the outlet of 35 randomly selected sub‐watersheds between April 2001 and June 2002. Summer Landsat images were used to characterize forest disturbance within each of the sub‐watersheds in 1999, 2000, and 2001. Quantitative differences in imagery between the defoliation years of 2000 and 2001 (and 1999, a non‐defoliation year) derived from change vector analysis provided indices of forest change. Dissolved N concentrations in the 35 reaches were dominated by nitrate‐N (average 61%, ranging 19–89% of total dissolved nitrogen), although dissolved organic nitrogen was present at measurable levels (0.03–0.16 mg/L). Percent non‐forested land cover accounted for only 8–33% of the spatial variation in nitrate‐N concentrations, while multivariate models that also included change vector statistics from satellite imagery (magnitude and angular direction of image change) accounted for 72–80% of the spatial variation in nitrate‐N concentrations. Measurements of defoliation during both the current and (when appropriate) previous year were statistically significant and indicated the importance of defoliation for increasing N inputs to the system at unseasonably high rates as a consequence of the deposition of caterpillar frass. Jackknifed residuals were within 25% of the actual measurements, indicating that remote sensing models could be used to predict variations in N concentrations for ungauged watersheds in the region. Our results provide more evidence that the remote sensing approach is a valuable component in predicting spatially varying relationships between ecosystem status and water quality conditions at the regional scale, thereby allowing assessments of watershed disturbances as part of land management.
RESPONSE OF AVIAN COMMUNITIES IN LARGE‐RIVER FLOODPLAINS TO ENVIRONMENTAL VARIATION AT MULTIPLE SCALES
Authors: Miller James R. , Dixon Mark D. , Turner Monica G.
Published: June 2007

Large‐river floodplains have been subjected to profound human‐caused alteration, but subsequent effects on landbirds in these habitats are largely unknown. To assess the extent to which landscape measures might serve as ecological indicators in these systems, we examined patterns of habitat use by forest birds along a 380‐km stretch of the Wisconsin River, USA. We surveyed forest bird communities during the breeding season in 1999 and 2000 at 48 sites divided among six reaches of the 100‐year floodplain. Several tree and bird species thought to be characteristic of floodplain forests in Wisconsin, based on earlier surveys, appear to have declined in abundance or were absent altogether, even in reaches located in a 150‐km undammed stretch of the river. Bird species richness was similar among reaches, but overall abundance was notably lower at the two northernmost reaches. The most widespread and abundant birds were those that are typically associated with forest edge habitats, but several species associated with forest interior conditions were also relatively abundant. A canonical correspondence analysis based on a model derived from the entire pool of environmental variables indicated that most of the variation in avian community structure was accounted for by geographic variables describing latitudinal changes and distance from potential source habitats along the Mississippi River. Partial ordinations and univariate variance partitioning, however, showed confounding among environmental variable sets and revealed that local‐habitat measures tended to explain somewhat more variation than geographic variables. Metrics describing landscape pattern and composition accounted for the least amount of independent variation among the three variables sets. Our results indicate that landscape measures are necessary, but not sufficient to describe patterns of habitat use by forest birds in the Wisconsin River floodplain. Moreover, our data suggest that, while maintaining habitat for forest birds is still possible in these areas, it may be more difficult to conserve species with an affinity for conditions that characterize floodplains. This study further demonstrates that, for some species, designations such as “forest interior” or “edge” are not always portable from one region to another or even over relatively short distances within a region.
A TEST OF THE ENVIRONMENTAL KUZNETS CURVE USING LONG‐TERM WATERSHED INPUTS
Authors: Gergel Sarah E. , Bennett Elena M. , Greenfield Ben K. , King Susan , Overdevest Christine A. , Stumborg Basil
Published: June 2007

The Environmental Kuznets Curve (EKC) postulates that environmental quality is initially degraded with increasing economic prosperity, until reaching some turning point where environmental quality improves with increases in wealth. Tests using environmental indicators beyond those that affect human health have been less supportive of the EKC idea. We hypothesize that environmental changes impacting human health are more likely to show evidence of an EKC than variables less directly related to human health. Furthermore, the EKC hypothesis assumes that ecological damage is reversible, and we argue that this assumption is not always valid. We test for evidence of an EKC in Dane County, Wisconsin, using non‐point‐source pollution time series data for Lake Mendota throughout the 20th century. We examine metals deposited in lake sediments (cadmium, chromium, copper, and lead), other non‐point‐source pollutants such as sulfur and dissolved reactive phosphorus (DRP), and water clarity (measured by Secchi disk depth). We relate changes in ecological variables to changes in real wealth per capita (RWPC) in Dane County over time. The EKC did not describe the relationship between all ecological and economic indicators tested; however, several variables were related to RWPC. Our strongest results (for Secchi depth, DRP, and copper) show increasing pollution with increasing wealth. Secchi depth and DRP are related to water quality and clarity, which have value to society but less direct, immediate health consequences. P pollution may also be fairly irreversible over short time scales. The best models and plots for cadmium, chromium, and lead suggest improvements in environmental quality with increases in RWPC, although these trends were not statistically significant. Results for sulfur were inconclusive. Overall, wealth did not explain much of the variability in any of the ecological variables examined here, suggesting that consideration of additional factors are necessary to explain their dynamics. Economic prosperity cannot be expected to improve all aspects of the environment, but may be biased toward aspects that are ecologically reversible phenomena or of concern to human health.
BIODIVERSITY INDICATOR GROUPS OF TROPICAL LAND‐USE SYSTEMS: COMPARING PLANTS, BIRDS, AND INSECTS
Authors: Schulze Christian H. , Waltert Matthias , Kessler Paul J. A. , Pitopang Ramadhanil , Veddeler Dorthe , Mühlenberg Michael , Gradstein S. Robbert , Leuschner Christoph , Steffan-Dewenter Ingolf , Tscharntke Teja
Published: June 2007

Tropical landscapes are dominated by land‐use systems, but their contribution to the conservation of biodiversity is largely unknown. Since changes in biodiversity in response to human impact are known to differ widely among taxonomic groups and guilds, there is a need for multidisciplinary collaboration of plant, vertebrate, and invertebrate experts. We used inventories of trees, understory plants, birds (subdivided into endemics, insectivores, frugivores/nectar feeders), butterflies (endemics, fruit feeders), and dung beetles in Sulawesi (Indonesia) to characterize a gradient from near‐primary to secondary forests, agroforestry systems, and annual crops. As expected, overall species richness tended to decrease within this gradient of increasing habitat modification, but, in contrast to previous studies, we found the species richness between most taxonomic groups to be significantly correlated (36 out of 38 pairwise comparisons). However, on average only 48% of the variance could be explained (within the five main groups), and only a few taxonomic groups/guilds turned out to be good predictors for others: for example, trees for fruit‐ and nectar‐feeding birds (88% explanation) and fruit‐feeding butterflies (83%), endemic birds for endemic butterflies (72%), and frugivorous/nectar‐feeding birds for fruit‐feeding butterflies (67%). Although biodiversity of land‐use systems showed taxonomic group‐ and guild‐specific differences, most groups were affected in a similar way by habitat modification. Near‐primary forest sites proved to be of principal importance for conservation; however, land‐use systems such as secondary forests (for understory plants, birds, and butterflies) and agroforestry systems (for butterflies) supported relatively high numbers of species and might play a significant role for biodiversity conservation in tropical landscapes.
FOLIAR NUTRITION, SITE QUALITY, AND TEMPERATURE INFLUENCE FOLIAR CHEMISTRY OF TALLOWWOOD (EUCALYPTUS MICROCORYS)
Authors: Moore Ben D. , Wallis Ian R. , Wood Jeff T. , Foley William J.
Published: June 2007

The distribution of marsupial folivores in Australian eucalypt forests is extremely patchy and, although distribution patterns are known to be partly determined by nutritional factors, the role of plant secondary metabolites (PSMs) has been little studied. We investigated variation in the foliar concentrations of five constituents: total phenolics (TP); the foliar component bound by polyethylene glycol (PEGBC); the formylphloroglucinol compound, sideroxylonal (a strong deterrent of mammalian herbivory); the terpene, cineole; and nitrogen (N). These constituents were analyzed using near infrared spectroscopy in 501 individual tallowwood (Eucalyptus microcorys) trees at 42 sites across a broad geographic range in eastern Australia. We tested three hypotheses: (1) trees with lower foliar N produce higher PSM concentrations; (2) PSM concentrations are greater at colder sites; and (3) PSM concentrations are higher at sites with low resource availability. Hypothesis 1 was true for all PSMs considered and was the result of variation that occurred within sites. This is consistent with the carbon/nutrient balance hypothesis and with the hypothesis that PSMs protect leaves from photodamage. Hypothesis 2 was upheld for all constituents. This was consistent with both the growth–differentiation balance hypothesis, and with the hypothesis that PSMs represent an evolutionary adaptation to greater risks of photodamage and frost damage in cold environments. Hypothesis 3 was rejected, with one PSM, sideroxylonal, being affected by resource availability in a manner opposite to that predicted. The optimal defense hypothesis offers an explanation for this result (as sideroxylonal concentrations increased along with the apparent nutritional quality of the foliage, possibly to provide defense against higher rates of herbivory). We found that trees associated with koala fecal pellets had lower concentrations of sideroxylonal and cineole. We discuss this finding and further implications for the herbivores ofEucalyptusof the patterns of plant defense that we detected.
POPULATION CYCLES IN THE PINE LOOPER MOTH: DYNAMICAL TESTS OF MECHANISTIC HYPOTHESES
Authors: Kendall Bruce E. , Ellner Stephen P. , McCauley Edward , Wood Simon N. , Briggs Cheryl J. , Murdoch William W. , Turchin Peter
Published: June 2007

The forest insect pestBupalus piniarius(pine looper moth) is a classic example of a natural population cycle. As is typical for populations that exhibit regular oscillations in density, there are several biological mechanisms that are hypothesized to be responsible for the cycles; but despite several decades of detailed study there has been no definite conclusion as to which mechanism is most important. We evaluated three hypotheses for which there was direct experimental evidence: (1) food quality (nutritional value of pine needles affected by defoliation); (2) parasitoids (trophic interactions with specialist parasitoids); and (3) maternal effects (maternal body size affects the performance of offspring). We reviewed the empirical evidence for each of these hypotheses and expressed each hypothesis in the form of a mechanistic dynamic model. We used a nonlinear forecasting approach to fit each model to three long‐term population time series in Britain that exhibit some degree of regular cycling, and we used parametric bootstrap to evaluate the significance of differences between models in their goodness of fit to the data. The results differed among the three forests: at Culbin, the parasitoid and maternal effects models fit equally well; at Roseisle, the food quality and maternal effects models fit equally well; and at Tentsmuir, the parasitoid model fit best. However, the best‐fit parasitism models required that the parasitism rate vary between nearly 0 and nearly 1 during a cycle, greatly exceeding the range of parasitism rates that have been observed in the field. In contrast, the required variation in the observable maternal quality variable (pupal mass) was within the range of empirical observations. Under mild constraints on the parasitism rate (though allowing a much wider range than has been measured inB. piniariusat any location), the fit of the parasitism model fell off dramatically. The maternal effects model then had uniformly strong support, outperforming the constrained parasitism model at all three sites and the food quality model at two; it performed slightly better than the food quality model at the remaining site. This represents the first system in which the maternal effects hypothesis for population cycles has been supported by both strong biological and dynamical evidence.
LANDSCAPE PALEOECOLOGY AND MEGAFAUNAL EXTINCTION IN SOUTHEASTERN NEW YORK STATE
Authors: Robinson Guy S. , Pigott Burney Lida , Burney David A.
Published: June 2007

Stratigraphic palynological analyses of four late Quaternary deposits comprise a landscape‐level study of the patterns and processes of megafaunal extinction in southeastern New York State. Distinctive spores of the dung fungus Sporormiella are used as a proxy for megafaunal biomass, and charcoal particle analysis as a proxy for fire history. A decline in spore values at all sites is closely followed by a stratigraphic charcoal rise. It is inferred that the regional collapse of a megaherbivory regime was followed by landscape transformation by humans. Correlation with the pollen stratigraphy indicates these developments began many centuries in advance of the Younger Dryas climatic reversal at the end of the Pleistocene. However, throughout the region, the latest bone collagen dates for Mammut are considerably later, suggesting that megaherbivores lasted until the beginning of the Younger Dryas, well after initial population collapse. This evidence is consistent with the interpretation that rapid overkill on the part of humans initiated the extinction process. Landscape transformation and climate change then may have contributed to a cascade of effects that culminated in the demise of all the largest members of North America's mammal fauna.
INCREASED COMPETITIVE ABILITY OF AN INVASIVE TREE MAY BE LIMITED BY AN INVASIVE BEETLE
Authors: Siemann Evan , Rogers William E.
Published: June 2007

Invasive plants are often more vigorous in novel habitats than in their native ranges.Sapium sebiferum(Chinese tallow tree) is a major invader of habitats in the southern United States. Long‐term common garden experiments in Texas and Hawaii (USA) withS. sebiferumgenotypes from its native range (Asia) and from areas in North America where it is invasive suggest that post‐introduction evolutionary changes may contribute to its invasiveness in Texas. In Texas, where there was uniformly low herbivory, fast‐growing, poorly defended invasive North American genotypes outperformed slower growing, better defended native Asian genotypes in common garden plots. In Hawaii, in contrast, an Asian herbivore,Adoretus sinicus(Chinese rose beetle) is abundant, andS. sebiferumis not invasive. In Hawaiian common garden plots,A. sinicuscaused greater damage to North American genotypes, and Asian genotypes were competitively superior. Our results suggest that exotic plants freed from herbivory can evolve greater competitive ability, allowing them to become much more abundant than in their native ranges. This did not seem to occur, though, if herbivores from the native range were abundant.
SOIL NITROGEN CYCLING UNDER ELEVATED CO2: A SYNTHESIS OF FOREST FACE EXPERIMENTS
Authors: Zak Donald R. , Holmes William E. , Finzi Adrien C. , Norby Richard J. , Schlesinger William H.
Published: June 2007

The extent to which greater net primary productivity (NPP) will be sustained as the atmospheric CO2 concentration increases will depend, in part, on the long‐term supply of N for plant growth. Over a two‐year period, we used common field and laboratory methods to quantify microbial N, gross N mineralization, microbial N immobilization, and specific microbial N immobilization in three free‐air CO2 enrichment experiments (Duke Forest, Oak Ridge, Rhinelander). In these experiments, elevated atmospheric CO2 has increased the input of above‐ and belowground litter production, which fuels heterotrophic metabolism in soil. Nonetheless, we found no effect of atmospheric CO2 concentration on any microbial N cycling pool or process, indicating that greater litter production had not initially altered the microbial supply of N for plant growth. Thus, we have no evidence that changes in plant litter production under elevated CO2 will initially slow soil N availability and produce a negative feedback on NPP. Understanding the time scale over which greater plant production modifies microbial N demand lies at the heart of our ability to predict long‐term changes in soil N availability and hence whether greater NPP will be sustained in a CO2‐enriched atmosphere.
RANKING HABITAT FOR MARBLED MURRELETS: NEW CONSERVATION APPROACH FOR SPECIES WITH UNCERTAIN DETECTION
Authors: Stauffer Howard B. , Ralph C. John , Miller Sherri L.
Published: June 2007

An essential element in the conservation of rare species is the ranking of some aspects of habitat quality. We developed a method to rank the importance of individual habitat patches to Marbled Murrelets (Brachyramphus marmoratus) in 26 old‐growth forest stands in northern California, using estimates of stand occupancy as an index of nesting activity. We used survey data collected in the stands from 1992 to 1997. The analysis was based on an adjustment that incorporates uncertainty of detection into a binomial model. Maximum likelihood estimators were used for the proportion P of the stands occupied by murrelets and the conditional probability p of detection with each visit to an occupied survey station, and bootstrapping methods were used for error estimates. We were able to rank a single stand most important, three other stands second in importance, and eight additional stands third in importance to murrelet nesting activity. For the murrelets in our study area, these results provided information useful in negotiations between government agencies and a private company in efforts to preserve some of the stands. Our methodology also has potential application for other flora and fauna of management concern, when sampling for presence or absence with uncertain detection. This technique can be applied at a variety of scales depending upon the species and habitat. Although conservation issues require consideration of many factors, including political, social, economic, and biological, our methods are helpful in providing science‐based information from sample data to assist in the decision‐making process.
HISTORICAL EVIDENCE FOR HABITAT CONVERSION AND LOCAL POPULATION DECLINE IN A NEW ZEALAND FJORD
Authors: Tallis Heather M. , Wing Stephen R. , Frew Russell D.
Published: June 2007

Although direct links between habitat conversion and human activities are often apparent, their causal mechanisms may be less obvious. We identified historic salinity change, attributed to freshwater input from a hydroelectric power plant, as a potential mechanism of intertidal habitat conversion and severe local decline of the New Zealand littleneck clam (Austrovenus stutchburyi) in Doubtful Sound, New Zealand. Live clams were abundant at sites distant from the power plant with relatively unaltered salinity regimes, and were absent from the inner fjord near the power plant outflow. Remnant shells indicate past habitation by A. stutchburyi at inner fjord sites. Historic salinity conditions inferred from oxygen isotope ratios in shell carbonates confirm that salinity previously reached higher values in the inner fjord, and that A. stutchburyi probably has not inhabited that area since salinity was at pre‐power‐plant levels. A laboratory experiment showed that A. stutchburyi from Doubtful Sound have a high tolerance for low salinity conditions, but that hyposaline conditions become lethal after extended exposure (37‐day LC50 = 2.5). In situ transplant experiments demonstrated that present salinity conditions in the inner reaches of Doubtful Sound are lethal to this species. Our findings suggest that the increased freshwater input maintained by the power plant has converted the habitat in the inner reaches of Doubtful Sound to one with sustained low salinity unsuitable for the survival of A. stutchburyi.
HIERARCHICAL ANALYSIS OF FOREST BIRD SPECIES–ENVIRONMENT RELATIONSHIPS IN THE OREGON COAST RANGE
Authors: Cushman Samuel A. , McGarigal Kevin
Published: June 2007

Species in biological communities respond to environmental variation simultaneously across a range of organizational levels. Accordingly, it is important to quantify the effects of environmental factors at multiple levels on species distribution and abundance. Hierarchical methods that explicitly separate the independent and confounded influences of environmental variation across several levels of organization are powerful tools for this task. Our study used a hierarchical approach to partition explained variance in an Oregon Coast Range bird community among plot‐, patch‐, and landscape‐level factors. We used a series of partial canonical ordinations to decompose species–environment relationships across these levels of organization to test four hypotheses about the importance of environmental control over community structure. We found that plot‐level factors were better predictors of community structure than patch‐ or landscape‐level factors. In addition, although landscape‐level variables contributed substantial independent explanatory power, there was little evidence that patch‐level environmental variability provided additional explanation of community structure beyond that provided by plot‐ and landscape‐level factors. At higher levels of the hierarchical analysis, we found that, among plot‐level factors, vegetation cover type was as powerful a predictor of community structure as detailed floristics, and more powerful than vegetation structure. At the landscape level, we found that landscape composition and configuration both provided substantial independent explanatory power, with landscape composition being the better overall predictor. Our results have a number of implications for sampling, analysis, and conservation. For example, misleading results could be obtained by studies conducted at a single organizational level. Also, the high degree of confounding among several levels of our analysis suggests that there is a lack of independence between the influences of environmental structure at different organizational levels. Due to this confounding, our results suggest that patch‐based studies of forest–bird ecological relationships in the Oregon Coast Range may be equivocal. In addition, the power of mapped cover class as a plot‐level predictor variable suggests that coarse‐filter, multiscale approaches utilizing remote sensing and GIS may be nearly as effective at predicting local patterns as expensive field surveys of habitat conditions at the plot level, and more effective at predicting patterns continuously across large regions.
FISH INVASIONS IN CALIFORNIA WATERSHEDS: TESTING HYPOTHESES USING LANDSCAPE PATTERNS
Authors: Marchetti Michael P. , Light Theo , Moyle Peter B. , Viers Joshua H.
Published: June 2007

An important goal of invasion biology is to identify physical and environmental characteristics that may make a region particularly receptive to invasions. The inland waters of California (USA) are highly invaded, particularly by fishes, although there is wide variation in numbers of nonnative fishes across the state's watersheds. Here we examine patterns of fish invasions in California watersheds and their associations with natural environmental characteristics, native fish diversity, and various measures of human habitat disturbance. Our analysis is based on an extensive data set on the distribution of freshwater fishes across California's watersheds and on GIS land‐use coverages for the entire state. We used canonical correspondence analysis to examine associations between environmental characteristics and the distributions of both native and nonnative fish species. We then employed an information–theoretic model‐selection approach to rank hypothesized models derived from the fish invasion literature with regard to how well they predicted numbers of nonnative fishes in California watersheds. Our results indicate that pervasive, anthropogenic, landscape‐level changes (particularly the extent of urban development, small‐scale water diversions, aqueducts, and agriculture) influenced spatial patterns of invasion. In addition, we find that deliberately stocked fishes have different habitat associations, including a strong association with the presence of dams, than other introduced fishes. In our analysis, watersheds with the most native species also contain the most nonnative species. We find no evidence that existing watershed protection helps to prevent fish invasions in California, but we suggest that restoration of natural hydrologic processes may reduce invasion impacts.
DID TRAWLING ON THE BROOD STOCK CONTRIBUTE TO THE COLLAPSE OF ALASKA'S KING CRAB?
Authors: Dew C. Braxton , McConnaughey Robert A.
Published: June 2007

The 1976 U.S. Magnuson‐Stevens Fishery Conservation and Management Act effectively eliminated the no‐trawl zone known as the Bristol Bay Pot Sanctuary, located in the southeastern Bering Sea, Alaska. Implemented by the Japanese in 1959, the boundaries of the Pot Sanctuary closely matched the well‐defined distribution of the red king crab (Paralithodes camtschaticus) population's mature‐female brood stock, thus affording a measure of protection to the reproductive potential of the stock. In 1980, the point at which the commercial harvest of Bristol Bay legal‐male red king crab reached an all‐time high after a decade‐long increase, domestic bottom trawling in the brood‐stock sanctuary began in earnest with the advent of a U.S.–Soviet, joint‐venture, yellowfin sole fishery. In the first year of trawling in the Pot Sanctuary, the Bering Sea/Aleutian Islands (BSAI) red king crab bycatch increased by 371% over the 1977–1979 average; in 1981 the BSAI bycatch increased another 235% over that in 1980, most of which were mature females. As the number of unmonitored domestic trawls in the brood‐stock area increased rapidly after 1979 and anecdotal reports of “red bags” (trawl cod‐ends plugged with red king crab) began to circulate, the proportion of males in the mature population (0.25 in 1981 and 0.16 in 1982) jumped to 0.54 in 1985 and 0.65 in 1986. It is unlikely that normal demographics caused this sudden reversal in sex ratio. Our hypothesis is that sequential, sex‐specific sources of fishing mortality were at work. Initially there were ten years (1970–1980) of increasing, male‐only exploitation in the directed pot fishery, followed by a drastic reduction in the male harvest after 1980 (to zero in 1983). Then, beginning around 1980, there was an increase in bottom trawling among the highly aggregated, sexually mature female brood stock concentrated near the western end of the Alaska Peninsula, an area documented by previous investigators to be the most productive spawning, incubation, and hatching ground for Bristol Bay red king crab. There has been considerable discussion about possible natural causes (e.g., meteorological regime shifts, increased groundfish predation, epizootic diseases) of the abrupt collapse of the Bristol Bay red king crab population in the early 1980s. The purpose of our study was to conduct a rigorous examination of existing data in order to evaluate the relative likelihood that the collapse was caused by human fishing instead of natural mortality. Our discussion focuses on the association between record harvests of male crab in the directed fishery, the onset of large‐scale commercial trawling within the population's primary reproductive refuge, and the population's collapse.
THE IMPACT OF INSECTICIDES AND HERBICIDES ON THE BIODIVERSITY AND PRODUCTIVITY OF AQUATIC COMMUNITIES
Authors: Relyea Rick A.
Published: June 2007

Pesticides constitute a major anthropogenic addition to natural communities. In aquatic communities, a great majority of pesticide impacts are determined from single‐species experiments conducted under laboratory conditions. Although this is an essential protocol to rapidly identify the direct impacts of pesticides on organisms, it prevents an assessment of direct and indirect pesticide effects on organisms embedded in their natural ecological contexts. In this study, I examined the impact of four globally common pesticides (two insecticides, carbaryl [Sevin] and malathion; two herbicides, glyphosate [Roundup] and 2,4‐D) on the biodiversity of aquatic communities containing algae and 25 species of animals.

Species richness was reduced by 15% with Sevin, 30% with malathion, and 22% with Roundup, whereas 2,4‐D had no effect. Both insecticides reduced zooplankton diversity by eliminating cladocerans but not copepods (the latter increased in abundance). The insecticides also reduced the diversity and biomass of predatory insects and had an apparent indirect positive effect on several species of tadpoles, but had no effect on snails. The two herbicides had no effects on zooplankton, insect predators, or snails. Moreover, the herbicide 2,4‐D had no effect on tadpoles. However, Roundup completely eliminated two species of tadpoles and nearly exterminated a third species, resulting in a 70% decline in the species richness of tadpoles. This study represents one of the most extensive experimental investigations of pesticide effects on aquatic communities and offers a comprehensive perspective on the impacts of pesticides when nontarget organisms are examined under ecologically relevant conditions.