bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF AN HERBICIDE AND AN INSECTICIDE ON POND COMMUNITY STRUCTURE AND PROCESSES
Authors: Rohr Jason R. , Crumrine Patrick W.
Published: June 2007

Virtually all species live within complex food webs, and many of these organisms are exposed to contaminants. However, we know little about how community processes, such as competition and predation, influence susceptibility to contaminants or how different types of contaminants shape communities. The objective of our study was to determine how realistic concentrations of the herbicide atrazine and the insecticide endosulfan influence the structure of a pond community when the presence of common community members was manipulated. We employed a factorial design in mesocosms to evaluate the effects of pesticide treatments (25 μg/L of atrazine, 10 μg/L of endosulfan, solvent control; two pulses separated by two weeks) and the presence or absence of wood frog tadpoles (Rana sylvatica), adult snails (Planorbella trivolvis), and caged dragonfly larvae (Anax junius) on a freshwater community.

Tadpoles, snails, and chironomid larvae, Polypedilum sp. (Dipterans), all competed for periphyton. As a result, tadpoles reduced the survival, mass, and reproduction of snails; snails reduced the growth, development, inactivity, and dragonfly avoidance of tadpoles; snails and tadpoles reduced the abundance of chironomid larvae; and chironomid larvae reduced snail mass. The adverse effect of snails on tadpole growth and behavior was greater in the presence of the caged tadpole predator, A. junius. Neither pesticide affected dragonfly survival, but endosulfan directly reduced zooplankton (Daphnia), and atrazine indirectly reduced chironomid abundance. Atrazine also directly decreased periphyton, and endosulfan decimated chironomid larvae, resulting in indirect increases and decreases in competition for both snails and tadpoles, respectively. Consequently, relative to endosulfan, atrazine tended to decrease snail mass and reproduction and reduce tadpole mass, development, inactivity, refuge use, and dragonfly avoidance. However, the indirect effects of pesticides depended upon the presence of heterospecifics. The indirect benefit of endosulfan on snail mass was greater in the presence of caged dragonfly larvae, and endosulfan's indirect benefit on tadpole mass was greater in the absence of snails. The effect of pesticides on tadpole activity depended on both caged dragonflies and snails. Thus, environmentally realistic concentrations of pesticides directly and indirectly shaped species responses and community composition, but the initial composition of the community influenced these pesticide effects. These results emphasize the importance of quantifying the effects of contaminants within complex natural communities.
OPTICAL INSTRUMENTS FOR MEASURING LEAF AREA INDEX IN LOW VEGETATION: APPLICATION IN ARCTIC ECOSYSTEMS
Authors: van Wijk Mark T. , Williams Mathew
Published: June 2007

Leaf area index (LAI) is a powerful diagnostic of plant productivity. Despite the fact that many methods have been developed to quantify LAI, both directly and indirectly, leaf area index remains difficult to quantify accurately, owing to large spatial and temporal variability. The gap‐fraction technique is widely used to estimate the LAI indirectly. However, for low‐stature vegetation, the gap‐fraction sensor either cannot get totally underneath the plant canopy, thereby missing part of the leaf area present, or is too close to the individual leaves of the canopy, which leads to a large distortion of the LAI estimate. We set out to develop a methodology for easy and accurate nondestructive assessment of the variability of LAI in low‐stature vegetation. We developed and tested the methodology in an arctic landscape close to Abisko, Sweden.

The LAI of arctic vegetation could be estimated accurately and rapidly by combining field measurements of canopy reflectance (NDVI) and light penetration through the canopy (gap‐fraction analysis using a LI‐COR LAI‐2000). By combining the two methodologies, the limitations of each could be circumvented, and a significantly increased accuracy of the LAI estimates was obtained. The combination of an NDVI sensor for sparser vegetation and a LAI‐2000 for denser vegetation could explain 81% of the variance of LAI measured by destructive harvest. We used the method to quantify the spatial variability and the associated uncertainty of leaf area index in a small catchment area.
CONSERVING SPECIES IN A WORKING LANDSCAPE: LAND USE WITH BIOLOGICAL AND ECONOMIC OBJECTIVES
Authors: Polasky Stephen , Nelson Erik , Lonsdorf Eric , Fackler Paul , Starfield Anthony
Published: June 2007

Habitat loss and fragmentation are major threats to biodiversity. Establishing formal protected areas is one means of conserving habitat, but socio‐economic and political constraints limit the amount of land in such status. Addressing conservation issues on lands outside of formal protected areas is also necessary. In this paper we develop a spatially explicit model for analyzing the consequences of alternative land‐use patterns on the persistence of various species and on market‐oriented economic returns. The biological model uses habitat preferences, habitat area requirements, and dispersal ability for each species to predict the probability of persistence of that species given a land‐use pattern. The economic model uses characteristics of the land unit and location to predict the value of commodity production given a land‐use pattern. We use the combined biological and economic model to search for efficient land‐use patterns in which the conservation outcome cannot be improved without lowering the value of commodity production. We illustrate our methods with an example that includes three alternative land uses, managed forestry, agriculture, and biological reserve (protected area), for a modeled landscape whose physical, biological, and economic characteristics are based on conditions found in the Willamette Basin in Oregon (USA). We find that a large fraction of conservation objectives can be achieved at little cost to the economic bottom line with thoughtful land‐use planning. The degree of conflict between conservation and economic returns appears much less using our joint biological and economic modeling approach than using a reserve‐site selection approach, which assumes that species survive only inside of reserves and economic activity occurs only outside of reserves.
ECOLOGICAL RESEARCH IN THE LARGE‐SCALE BIOSPHERE– ATMOSPHERE EXPERIMENT IN AMAZONIA: EARLY RESULTS
Authors: Keller Michael , Alencar Ane , Asner Gregory P. , Braswell Bobby , Bustamante Mercedes , Davidson Eric , Feldpausch Ted , Fernandes Erick , Goulden Michael , Kabat Pavel , Kruijt Bart , Luizão Flavio , Miller Scott , Markewitz Daniel , Nobre Antonio D. , Nobre Carlos A. , Priante Filho Nicolau , da Rocha Humberto , Silva Dias Pedro , von Randow Celso , Vourlitis George L.
Published: June 2007

The Large‐scale Biosphere–Atmosphere Experiment in Amazonia (LBA) is a multinational, interdisciplinary research program led by Brazil. Ecological studies in LBA focus on how tropical forest conversion, regrowth, and selective logging influence carbon storage, nutrient dynamics, trace gas fluxes, and the prospect for sustainable land use in the Amazon region. Early results from ecological studies within LBA emphasize the variability within the vast Amazon region and the profound effects that land‐use and land‐cover changes are having on that landscape. The predominant land cover of the Amazon region is evergreen forest; nonetheless, LBA studies have observed strong seasonal patterns in gross primary production, ecosystem respiration, and net ecosystem exchange, as well as phenology and tree growth. The seasonal patterns vary spatially and interannually and evidence suggests that these patterns are driven not only by variations in weather but also by innate biological rhythms of the forest species. Rapid rates of deforestation have marked the forests of the Amazon region over the past three decades. Evidence from ground‐based surveys and remote sensing show that substantial areas of forest are being degraded by logging activities and through the collapse of forest edges. Because forest edges and logged forests are susceptible to fire, positive feedback cycles of forest degradation may be initiated by land‐use‐change events. LBA studies indicate that cleared lands in the Amazon, once released from cultivation or pasture usage, regenerate biomass rapidly. However, the pace of biomass accumulation is dependent upon past land use and the depletion of nutrients by unsustainable land‐management practices. The challenge for ongoing research within LBA is to integrate the recognition of diverse patterns and processes into general models for prediction of regional ecosystem function.
INFLUENCE OF BARRIERS TO MOVEMENT ON WITHIN‐WATERSHED GENETIC VARIATION OF COASTAL CUTTHROAT TROUT
Authors: Wofford John E. B. , Gresswell Robert E. , Banks Michael A.
Published: June 2007

Because human land use activities often result in increased fragmentation of aquatic and terrestrial habitats, a better understanding of the effects of fragmentation on the genetic heterogeneity of animal populations may be useful for effective management. We used eight microsatellites to examine the genetic structure of coastal cutthroat trout (Oncorhynchus clarki clarki) in Camp Creek, an isolated headwater stream in western Oregon. Our objectives were to determine if coastal cutthroat trout were genetically structured within streams and to assess the effects of natural and anthropogenic barriers on coastal cutthroat trout genetic variation. Fish sampling occurred at 10 locations, and allele frequencies differed significantly among all sampling sections. Dispersal barriers strongly influenced coastal cutthroat trout genetic structure and were associated with reduced genetic diversity and increased genetic differentiation. Results indicate that Camp Creek coastal cutthroat trout exist as many small, partially independent populations that are strongly affected by genetic drift. In headwater streams, barriers to movement can result in genetic and demographic isolation leading to reduced coastal cutthroat trout genetic diversity, and potentially compromising long‐term population persistence. When habitat fragmentation eliminates gene flow among small populations, similar results may occur in other species.
STOCHASTIC FLOOD AND PRECIPITATION REGIMES AND THE POPULATION DYNAMICS OF A THREATENED FLOODPLAIN PLANT
Authors: Smith Marian , Caswell Hal , Mettler-Cherry Paige
Published: June 2007

Boltonia decurrens is an endangered plant restricted to the Illinois River Valley. Its complex life cycle has evolved in response to the dynamics of the historic flood regime, which has changed dramatically in the last century due to the construction of navigation dams and agricultural levees. To explore the effects of these changes, we developed deterministic and stochastic matrix population models of the demography of Boltonia. We used periodic matrix models to incorporate intra‐annual seasonal variation. We estimated parameters as a function of the timing of spring flood recession (early or late) and of growing season precipitation (high or low). Late floods and/or low precipitation reduce population growth (λ). Early floods and high precipitation lead to explosive population growth. Elasticity analysis shows that changes in floods and precipitation alter the life history pathways responsible for population growth, from annual to biennial and eventually clonal pathways. We constructed and analyzed a stochastic model in which flood timing and precipitation vary independently, and we computed the stochastic growth rate (log λs) and the variance growth rate (σ2) as functions of the frequency of late floods and low precipitation. Using historical data on floods and rainfall over the last 100 years, we found that log λs has declined as a result of hydrological changes accompanying the regulation of the river. Stochastic elasticity analysis showed that over that time the contribution of annual life history pathways to log λs has declined as the contributions of biennial and clonal pathways have increased. Over the same time period, σ2 has increased, in agreement with observations of large fluctuations in local B. decurrens populations. Undoubtedly, many plant and animal species evolved in concert with dynamic habitats and are now threatened by anthropogenic changes in those dynamics. The data and analyses used in this study can be applied to management and development strategies to preserve other dynamic systems.
LOGGING STRATEGY INFLUENCES COLONIZATION OF COMMON CHLOROLICHENS ON BRANCHES OF PICEA ABIES
Authors: Hilmo Olga , Holien Håkon , Hytteborn Håkan
Published: June 2007

Increased knowledge about how lichen colonization responds to logging is a prerequisite for developing guidelines in forest management aimed to maintain biodiversity. Within an experimentally logged boreal spruce forest we studied effects of different logging strategies and distance to the forest edges on colonization of epiphytic chlorolichens. Within a fine‐grained (23 clearcuts, 0.2 ha each) and a coarse‐grained area (3 clearcuts, 2.25 ha each) we sampled 90 branches. In addition 20 branches were sampled in an untouched control area. The 15 youngest annual shoots along the main axes on each branch were analyzed.

Establishment of the dispersed diaspores, most of themHypogymnia, was mainly limited to shoot ages 4–6 where the needles also were present. Independent of logging strategy the occurrence of small lobules increased with increasing distance from the edges, indicating unfavorable conditions for establishment at the edges or a lower supply of diaspores. A distinct decrease in the number of thalli ofCavernularia hulteniiwas observed in the two logged areas compared to the control branches. The colonization ofHypogymniaspp. andPlatismatiaspp. was successful in the fine‐grained area, while a coarse‐grained pattern of logging caused a significant decrease in the number of thalli, from shoot age 5 forHypogymniaand shoot age 9 forPlatismatia. An early drop of needles in the coarse‐grained area, especially at the forest edges, supports the assumption that the occurrence of needles is important for a successful colonization. A higher rate of growth of these species in the coarse‐grained area, compared to the other two areas, illustrates that logging does not necessarily cause unfavorable conditions for growth of already established thalli.

In conclusion, establishment of the diaspores is less successful in logged areas. Thus, a fragmented logging pattern influences the colonization negatively, even for common chlorolichens. Moreover, the response to logging strategy is species‐specific. Development of management guidelines should be based on wide scientific knowledge about the species life‐history characteristics.
FEDERAL FOREST‐FIRE POLICY IN THE UNITED STATES
Authors: Stephens Scott L. , Ruth Lawrence W.
Published: June 2007

Forest‐fire policy of U.S. federal agencies has evolved from the use of small patrols in newly created National Parks to diverse policy initiatives and institutional arrangements that affect millions of hectares of forests. Even with large expenditures and substantial infrastructure dedicated to fire suppression, the annual area burned by wildfire has increased over the last decade. Given the current and future challenges of fire management, and based on analytical research and review of existing policies and their implications, we believe several changes and re‐emphases in existing policy are warranted. Most importantly, the actual goal of fuels‐management projects should be the reduction of potential fire behavior and effects, not the simple reduction of fuels. To improve safety and economic efficiency, fire‐suppression policies should recognize differences in the characteristics of wildfires, and strategies should be tailored to better respond to the unique demands of each fire. Where forest fires are burning large areas, as in the western United States, reducing the trend of increased amounts of burned area may require a diversity of treatments, including prescribed burning, mechanical fuels treatment, and increased use of the Wildland Fire Use Policy. Assessment of how fire is affecting forests would be enhanced if land‐management agencies reported the area burned by low‐, mixed‐, and high‐severity fire and what proportion is outside the desired trend or range of conditions for each forest type. Congress should provide an improved budgetary process for fire and fuels management, with a larger annual federal fire‐suppression budget. Additionally, reducing annual area burned will require long‐term coordinated efforts by federal and state governments, with robust partnerships between land‐management agencies and the public in collaborative planning and stewardship. Research and adaptive management are essential in allowing fire‐hazard‐reduction projects to move forward where proposed projects are met with uncertainty and mistrust. While legislative reform may be desirable, a strategy that is not entirely dependent on new legislation is needed. Building on existing programs that are consistent with a science‐based strategy will enable land‐management agencies to better utilize information in pursuit of the overall objective of reducing uncharacteristically severe wildfires.
LONG‐TERM EFFECTS OF UNGULATES ON PERFORMANCE, ABUNDANCE, AND SPATIAL DISTRIBUTION OF TWO MONTANE HERBS
Authors: Gómez José M.
Published: June 2007

Herbivores highly reduce the performance of many plant species. However, little empirical information exists on the real effect that these organisms have on plant populations. With a long‐term (seven‐year) ungulate exclusion experiment in two areas of southeastern Spain, I demonstrated that these organisms can affect not only individual performance, but also the population dynamics and spatial structure of two short‐lived monocarpic herbs, Erysimum mediohispanicum and E. baeticum. There was between‐year and among‐microhabitat variability in damage, with plants growing under shrubs being less damaged than those growing in open sites. Ungulates consumed flowers and fruits, severely decreasing plant reproductive output. The postdispersal seed predation rate increased after ungulates were excluded, presumably as a consequence of the relaxation of competition between seed predators and ungulates. The effect of ungulates on Erysimum early establishment was nonsignificant, although >50% of Erysimum seedlings died due to ungulate trampling. The exclusion experiment also revealed that, as a consequence of their impact on seed production, ungulates affected the population dynamics of their host plants; their removal produced a significant increase in the abundance of the two studied plant species. Furthermore, habitat distribution of plants was also influenced by the activity of ungulates. In control plots, most Erysimum individuals grew under the canopy of co‐occurring shrubs. In contrast, a dramatic spatial redistribution of plants occurred in ungulate‐excluded plots, where they started to colonize open sites. Consequently, the spatial structure of the plants excluded from ungulates significantly differed from that in control plots and became statistically similar to the structure expected according to the cover of every microhabitat. Finally, this experiment revealed that, for plants inhabiting heterogeneous landscapes, abundance and spatial structure are tightly related. Thus, I found that abundance increased in ungulate‐excluded plots due not to a general and homogeneous increase, but to a significant increase in those microhabitats inaccessible to ungulates in control plots. These findings suggest that herbivory effects on plants are intricate, affecting not only their performance or population dynamics, but also their habitat distribution and niche structure.
INVASIVE SPECIES ACCELERATE DECOMPOSITION AND LITTER NITROGEN LOSS IN A MIXED DECIDUOUS FOREST
Authors: Ashton Isabel W. , Hyatt Laura A. , Howe Katherine M. , Gurevitch Jessica , Lerdau Manuel T.
Published: June 2007

Invasive species can change decomposition rates within an ecosystem by changing the quality of the litter entering a system. It is not known, however, whether or not invasions can also change rates of decomposition irrespective of litter quality. We conducted an experiment to explore the differences in decomposition between leaf litter of native and exotic invasive woody plants and between invaded and uninvaded mesic hardwood forests on Long Island, New York, USA. We evaluated the mass and nitrogen loss rates from leaf litter of four pairs of native and exotic woody species. Litter from the exotic species decomposed and released nitrogen significantly faster than litter from the native species. The largest differences in decomposition and nitrogen loss occurred between the invaded and uninvaded sites rather than between native and exotic species, with litter of all species types decomposing substantially faster in invaded sites. These results suggest that the invasion of exotic species into hardwood forests alters decomposition and nutrient cycling, irrespective of species‐specific litter quality differences between natives and exotics.
MINIMUM OPENING SIZES FOR CANOPY RECRUITMENT OF MIDTOLERANT TREE SPECIES: A RETROSPECTIVE APPROACH
Authors: Webster Christopher R. , Lorimer Craig G.
Published: June 2007

Minimum opening sizes and time required for successful canopy recruitment of tree saplings are not well known because the gap capture process is slow and difficult to monitor. In this study, we investigated canopy recruitment in harvest openings created by group selection in hemlock–hardwood forests to determine if yellow birch (Betula alleghaniensisBritt.), a species with intermediate shade tolerance, could successfully reach the canopy via small openings. We measured gap trees in openings ranging from 40 to 1000 m2and up to 55 years old. Sample trees up to 25 m tall, spanning all stages of the gap capture process, were destructively sampled to determine height–growth rates, total age, and size at time of gap formation. Results indicate that yellow birch comprised >40% of the upper stratum of gap saplings in openings as small as 100–400 m2. The ultimately successful hardwood gap trees, on average, reached crown shoulder height of the mature gap border trees (73% of total canopy height) within 28–37 years after gap formation. Successful trees were mostly advance regeneration at the time of gap formation, but some gap colonists were also successful. Height increments in all hardwood species were strongly size dependent, with saplings reaching a maximum growth rate at a height of 10 m. Extrapolations of current height growth of saplings <3 m tall would substantially overestimate time needed for gap capture, but use of a size‐dependent height increment function provided accurate estimates. Results suggest that inclusion of relatively small openings (200–1000 m2) in uneven‐aged or multicohort harvest operations may be sufficient to perpetuate the diversity of shade‐tolerance classes currently present in these stands.
MORAN EFFECT ON NONLINEAR POPULATION PROCESSES
Authors: Royama T.
Published: June 2007

I investigate the efficacy of the Moran effect as applied to natural population processes. The Moran effect, the correlated density‐independent disturbances that bring independently oscillating local populations into synchrony, was originally conceived as an attribute of a linear model system. However, it applies only approximately to natural populations, as they are inherently nonlinear in their density‐dependent structure, given that no animal has an unlimited reproductive capacity. The degree of approximation, as measured by the degree of correlation among populations involved, is shown to depend, given the density‐dependent structure, on the variances of the random disturbances. In particular, if the unperturbed density‐dependent process converges to an equilibrium density, approximation is good when the variances are equal among the populations involved and comparatively small, but it worsens as the variances and their differences increase. For those processes that do not converge, when unperturbed, but exhibit bounded oscillations, the degree of approximation tends to deteriorate considerably, or may practically collapse, even if the disturbances are not large in variance. A sample correlation coefficient is often spurious if the observed population processes to be correlated are highly autocorrelated and limited in length. To detect spuriousness, the density‐independent disturbances must somehow be estimated from the data. Three methods (moving‐average, linear regression, and nonlinear regression) are considered, and their merits and demerits are discussed. Results of the present investigation are summarized with respect to the interpretations (or diagnoses) of sample cross‐correlation functions.
CONTROLS ON NITROGEN CYCLING IN TERRESTRIAL ECOSYSTEMS: A SYNTHETIC ANALYSIS OF LITERATURE DATA
Authors: Booth Mary S. , Stark John M. , Rastetter Edward
Published: June 2007

Isotope pool dilution studies are increasingly reported in the soils and ecology literature as a means of measuring gross rates of nitrogen (N) mineralization, nitrification, and inorganic N assimilation in soils. We assembled data on soil characteristics and gross rates from 100 studies conducted in forest, shrubland, grassland, and agricultural systems to answer the following questions: What factors appear to be the major drivers for production and consumption of inorganic N as measured by isotope dilution studies? Do rates or the relationships between drivers and rates differ among ecosystem types? Across a wide range of ecosystems, gross N mineralization is positively correlated with microbial biomass and soil C and N concentrations, while soil C:N ratio exerts a negative effect on N mineralization only after adjusting for differences in soil C. Nitrification is a log‐linear function of N mineralization, increasing rapidly at low mineralization rates but changing only slightly at high mineralization rates. In contrast, NH4+ assimilation by soil microbes increases nearly linearly over the full range of mineralization rates. As a result, nitrification is proportionately more important as a fate for NH4+ at low mineralization rates than at high mineralization rates. Gross nitrification rates show no relationship to soil pH, with some of the fastest nitrification rates occurring below pH 5 in soils with high N mineralization rates. Differences in soil organic matter (SOM) composition and concentration among ecosystem types influence the production and fate of mineralized N. Soil organic matter from grasslands appears to be inherently more productive of ammonium than SOM from wooded sites, and SOM from deciduous forests is more so than SOM in coniferous forests, but differences appear to result primarily from differing C:N ratios of organic matter. Because of the central importance of SOM characteristics and concentrations in regulating rates, soil organic matter depletion in agricultural systems appears to be an important determinant of gross process rates and the proportion of NH4+ that is nitrified. Addition of 15N appears to stimulate NH4+ consumption more than NO3− consumption processes; however, the magnitude of the stimulation may provide useful information regarding the factors limiting microbial N transformations.
STRUCTURAL AND FUNCTIONAL RESPONSES OF A SUBTROPICAL FOREST TO 10 YEARS OF HURRICANES AND DROUGHTS
Authors: Beard Karen H. , Vogt Kristiina A. , Vogt Daniel J. , Scatena Frederick N. , Covich Alan P. , Sigurdardottir Ragnhildur , Siccama Thomas G. , Crowl Todd A.
Published: June 2007

Little is known about ecosystem‐level responses to multiple, climatic disturbance events. In the subtropical forests of Puerto Rico, the major natural disturbances are hurricanes and droughts. We tested the ecosystem‐level effects of these disturbances in sites with different land use histories. From 1989 to 1992, data were collected to determine the effects of Hurricane Hugo and two droughts on litterfall inputs, fine‐root biomass, and decomposition rates in three topographic locations (stream, riparian, upslope) within two watersheds. From 1994 to 1998, we added a third watershed and an experiment in which coarse‐wood levels were manipulated to simulate hurricane inputs. Data were collected on tree and palm growth rates, litterfall inputs, fine‐root biomass, and decomposition rates. From 1994 to 1998, four hurricanes and three droughts were recorded.

Measured parameters had unique responses and recovery rates to hurricanes and droughts. Litterfall inputs returned to long‐term mean rates within one month following droughts and small‐to‐moderate hurricanes but required five years to recover after an intense hurricane. In contrast, fine‐root biomass recovered seven months after an intense hurricane but failed to recover after five years following a severe drought. Despite the dramatic effects of these weather events on some ecosystem parameters, we found that aboveground measures of tree and palm growth were more affected by preexisting site conditions (e.g., nitrogen availability due to past land use activities) than hurricanes or droughts. The addition of coarse woody debris increased tree and palm growth, fine‐root biomass, and litter production; however, in the case of tree and palm growth, this effect was least measurable in the sites with the highest productivity. We found that decomposition rates were more controlled by litter quality than weather conditions. In conclusion, we found that certain ecosystem structures (e.g., canopy structure and fine‐root biomass) generally recovered more slowly from disturbance events than certain ecosystem processes (e.g., plant growth rates, decomposition rates). We also found that past land use activities and disturbance legacies were important in determining the responses and recovery rates of the ecosystem to disturbance.
MODELING AVIAN ABUNDANCE FROM REPLICATED COUNTS USING BINOMIAL MIXTURE MODELS
Authors: Kéry Marc , Royle J. Andrew , Schmid Hans
Published: June 2007

Abundance estimation in ecology is usually accomplished by capture–recapture, removal, or distance sampling methods. These may be hard to implement at large spatial scales. In contrast, binomial mixture models enable abundance estimation without individual identification, based simply on temporally and spatially replicated counts. Here, we evaluate mixture models using data from the national breeding bird monitoring program in Switzerland, where some 250 1‐km2quadrats are surveyed using the territory mapping method three times during each breeding season. We chose eight species with contrasting distribution (wide–narrow), abundance (high–low), and detectability (easy–difficult). Abundance was modeled as a random effect with a Poisson or negative binomial distribution, with mean affected by forest cover, elevation, and route length. Detectability was a logit‐linear function of survey date, survey date‐by‐elevation, and sampling effort (time per transect unit). Resulting covariate effects and parameter estimates were consistent with expectations. Detectability per territory (for three surveys) ranged from 0.66 to 0.94 (mean 0.84) for easy species, and from 0.16 to 0.83 (mean 0.53) for difficult species, depended on survey effort for two easy and all four difficult species, and changed seasonally for three easy and three difficult species. Abundance was positively related to route length in three high‐abundance and one low‐abundance (one easy and three difficult) species, and increased with forest cover in five forest species, decreased for two nonforest species, and was unaffected for a generalist species. Abundance estimates under the most parsimonious mixture models were between 1.1 and 8.9 (median 1.8) times greater than estimates based on territory mapping; hence, three surveys were insufficient to detect all territories for each species. We conclude that binomial mixture models are an important new approach for estimating abundance corrected for detectability when only repeated‐count data are available. Future developments envisioned include estimation of trend, occupancy, and total regional abundance.
AMPHIBIAN UPLAND HABITAT USE AND ITS CONSEQUENCES FOR POPULATION VIABILITY
Authors: Trenham Peter C. , Shaffer H. Bradley
Published: June 2007

To predict the effects of habitat alteration on population size and viability, data describing the landscape‐scale distribution of individuals are needed. Many amphibians breed in wetland habitats and spend the vast majority of their lives in nearby upland habitats. However, for most species, the spatial distribution of individuals in upland habitats is poorly understood. To estimate the upland distribution of subadult and adult California tiger salamanders (Ambystoma californiense), we used a novel trapping approach that allowed us to model the spatial variation in capture rates in the landscape surrounding an isolated breeding pond. As expected, we found that captures of adults declined with distance from the breeding pond. However, captures of subadults increased steadily from 10 to 400 m from the breeding site, but there were no captures at 800 m. A negative exponential function fit to the adult capture data suggested that 50%, 90%, and 95% were within 150, 490, and 620 m of the pond, respectively. For subadults, the quadratic function fit to the data similarly suggested that 95% were within 630 m of the pond, but that 85% of this life stage was concentrated between 200 and 600 m from the pond. To investigate the population‐level consequences of reducing the amount of suitable upland habitat around breeding ponds, we used a stage‐based stochastic population model with subadult and adult survival parameters modified according to our empirical observations of upland distribution. Model simulations suggested that substantial reductions in population size are less likely if upland habitats extending at least 600 m from the pond edge are maintained. Model elasticities indicated that quasi‐extinction probabilities are more sensitive to reductions in subadult and adult survivorship than reproductive parameters. These results indicate that understanding the upland ecology of pond‐breeding amphibians, especially the distribution and survivorship of subadults, may be critical for designing protective reserves and land use plans.
THE LETHAL IMPACT OF ROUNDUP ON AQUATIC AND TERRESTRIAL AMPHIBIANS
Authors: Relyea Rick A.
Published: June 2007

The global decline in amphibian diversity has become an international environmental problem with a multitude of possible causes. There is evidence that pesticides may play a role, yet few pesticides have been tested on amphibians. For example, Roundup is a globally common herbicide that is conventionally thought to be nonlethal to amphibians. However, Roundup has been tested on few amphibian species, with existing tests conducted mostly under laboratory conditions and on larval amphibians. Recent laboratory studies have indicated that Roundup may be highly lethal to North American tadpoles, but we need to determine whether this effect occurs under more natural conditions and in post‐metamorphic amphibians. I assembled communities of three species of North American tadpoles in outdoor pond mesocosms that contained different types of soil (which can absorb the pesticide) and applied Roundup as a direct overspray. After three weeks, Roundup killed 96–100% of larval amphibians (regardless of soil presence). I then exposed three species of juvenile (post‐metamorphic) anurans to a direct overspray of Roundup in laboratory containers. After one day, Roundup killed 68–86% of juvenile amphibians. These results suggest that Roundup, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines.
CARBON, NITROGEN, AND PHOSPHORUS ACCUMULATION IN FLOODPLAINS OF ATLANTIC COASTAL PLAIN RIVERS, USA
Authors: Noe Gregory B. , Hupp Cliff R.
Published: June 2007

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3–6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content.

Mean C accumulation rates ranged from 61 to 212 g·m−2·yr−1, N accumulation rates ranged from 3.5 to 13.4 g·m−2·yr−1, and P accumulation rates ranged from 0.2 to 4.1 g·m−2·yr−1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes.
POPULATION DYNAMICS AND CONSERVATION OF A SPECIALIZED PREDATOR: A CASE STUDY OF MACULINEA ARION
Authors: Mouquet Nicolas , Thomas Jeremy A. , Elmes Graham W. , Clarke Ralph T. , Hochberg Michael E.
Published: June 2007

We employ an empirically motivated “case model” approach to investigate the theoretical foundations for the conservation of the endangered butterfly Maculinea arion. Maculinea butterflies have highly specialized larvae that sequentially exploit a plant and an ant species. Our study establishes that M. arion's specialized life cycle, including scramble competition for limiting resources, and the spatially discrete nature of its resources, make it more sensitive to environmental variation and more prone to local extinction than other univoltine phytophagous species. We find that the number and spatial distribution of the butterfly's resources are key factors in their population dynamics, especially for M. arion populations in habitats associated with high larval survival and high adult fecundity. Factors that increase juvenile competition have first a positive effect on adult population size, but beyond a threshold this effect becomes negative. In general, oscillatory dynamics emerge for high potential growth rates and spatially homogeneous juvenile competition. We discuss the relevance of our results to population management, investigate the consequences of environmental variation, and consider different scenarios of conservation. Our model, although based on the Maculinea genus, should apply to a broad range of species for which the form of competitive interactions changes predictably at distinct points in the life cycle. Complex life cycles can lead to negative feedbacks involving parameters that are usually thought to optimize population size. We suggest that conservation strategies are neither generalizable for the Maculinea genus nor for disparate populations of each species of Maculinea, and rather that management should be conducted on a case‐by‐case basis.
ANALYZING BETA DIVERSITY: PARTITIONING THE SPATIAL VARIATION OF COMMUNITY COMPOSITION DATA
Authors: Legendre Pierre , Borcard Daniel , Peres-Neto Pedro R.
Published: June 2007

Robert H. Whittaker defined beta diversity as the variation in species composition among sites in a geographic area. Beta diversity is a key concept for understanding the functioning of ecosystems, for the conservation of biodiversity, and for ecosystem management. This paper explains how hypotheses about the origin of beta diversity can be tested by partitioning the spatial variation of community composition data (presence– absence or abundance data) with respect to environmental variables and spatial base functions. We compare two statistical methods to accomplish that. The sum‐of‐squares of a community composition data table, which is one possible measure of beta diversity, is correctly partitioned by canonical ordination; hence, canonical partitioning produces correct estimates of the different portions of community composition variation. In recent years, several authors interested in the variation in community composition among sites (beta diversity) have used another method, variation partitioning on distance matrices (Mantel approach). Their results led us to compare the two partitioning approaches, using simulated data generated under hypotheses about the variation of community composition among sites. The theoretical developments and simulation results led to the following observations: (1) the variance of a community composition table is a measure of beta diversity. (2) The variance of a dissimilarity matrix among sites is not the variance of the community composition table nor a measure of beta diversity; hence, partitioning on distance matrices should not be used to study the variation in community composition among sites. (3) In all of our simulations, partitioning on distance matrices underestimated the amount of variation in community composition explained by the raw‐data approach, and (4) the tests of significance had less power than the tests of canonical ordination. Hence, the proper statistical procedure for partitioning the spatial variation of community composition data among environmental and spatial components, and for testing hypotheses about the origin and maintenance of variation in community composition among sites, is canonical partitioning. The Mantel approach is appropriate for testing other hypotheses, such as the variation in beta diversity among groups of sites. Regression on distance matrices is also appropriate for fitting models to similarity decay plots.
CONVERGENT PATTERNS IN THE SELECTION MOSAIC FOR TWO NORTH AMERICAN BIRD‐DISPERSED PINES
Authors: Siepielski Adam M. , Benkman Craig W.
Published: June 2007

The strength and outcome of interspecific interactions often vary across the landscape because of differences in community context. We investigated how the presence or absence of pine squirrels (Tamiasciurusspp.) influences the ecology and (co)evolution of seed‐dispersal mutualisms between Clark's Nutcrackers (Nucifraga columbiana) and limber (Pinus flexilis) and whitebark (P. albicaulis) pines. Nutcrackers are the primary seed dispersers of these pines. Therefore both nutcrackers and pines potentially benefit from the evolution of a cone structure that enhances seed harvest by nutcrackers. Pine squirrels are the dominant predispersal seed predator of these pines throughout the Sierra Nevada–Cascades and Rocky Mountains and do not disperse seeds, so that pines benefit from deterring seed harvest by pine squirrels. To determine whether pines have evolved in response to selection by nutcrackers and pine squirrels, we conducted studies in ranges with pine squirrels and in ranges in the Great Basin and northern Montana where populations of the pines have apparently evolved without pine squirrels for 10 000 years or more. Cone evolution was convergent between both pines and among phylogeographically independent populations with and without pine squirrels, consistent with variation in selection by nutcrackers and pine squirrels. Where pine squirrels were present, they out‐competed nutcrackers for seeds, nutcrackers were less abundant, and selection by pine squirrels constrained the evolution of cone and seed traits that facilitate seed dispersal by nutcrackers. In the absence of pine squirrels, nutcrackers were more than twice as abundant, selection by pine squirrels on cone structure was relaxed, and selection on cone structure by nutcrackers resulted in cones that increased the foraging efficiency of nutcrackers and improved their potential for seed dispersal.
MECHANISMS RECONCILING GREGARIOUS LARVAL SETTLEMENT WITH ADULT CANNIBALISM
Authors: Tamburri Mario N. , Zimmer Richard K. , Zimmer Cheryl Ann
Published: June 2007

Marine benthic invertebrates living in dense, intraspecific aggregations are important community members because they provide structural habitat for other species. Here, we determined the mechanisms that facilitate gregarious larval settlement and promote group living. Using suspension‐feeding oysters (Crassostrea gigas) residing in large assemblages (“reefs”), experiments were conducted under laboratory conditions that simulated critical aspects of natural estuarine habitats. Oyster larvae were attracted to the scent of their conspecific elders. In still‐water trials, they moved downward and settled after contacting a waterborne, adult chemical cue. Yet, mortality of larvae placed in the adult pallial cavity was very high (mean of 91.3%). This seeming paradox of larval attraction to adult cannibals was resolved via laboratory flume (2 cm/s and 6 cm/s flows) experiments. Suspension‐feeding activity did not significantly affect flow speeds or directions. Moreover, weak (mean of 1.65 mm/s) adult ciliary currents effectively entrained phytoplankton but rarely captured larvae. In fact, only a small percentage (≤4.6%) of settlers was cannibalized in flume trials, even when they passed within 1 mm of the inhalant opening, or “gape” (a narrow slit between two valves). Larvae cued by conspecifics potentially attach to any portion of the shell surface, but there is a low probability that they will land in or near the inhalant opening. On juvenile and adult oysters, for example, the mean ratio of gape to shell surface area was only 0.025. Furthermore, in surveys of juvenile/adult oysters at nine field sites (Hood Canal and eastern Olympic Peninsula, Washington, USA), the gape was ≤5.2% of the total plane surface area of the reef. Thus, an oyster larva settling onto a reef of suspension‐feeding adults is unlikely to be cannibalized. Given this low mortality risk at settlement, future fitness payoffs (e.g., improved fertilization success) may drive the evolution of a gregarious settlement cue that promotes group living.
A Method for Pattern Recognition
Authors: Brauer Donna J.
Published: June 2007

Although pattern is a dominant concept in nursing science, only Newman’s method for recognizing pattern has been fully articulated and widely used in research about the human health experience. This article proposes an alternative, less costly method to facilitate research with larger numbers of participants in clinical settings. Cluster analysis, a quasi-quantitative technique, and content analysis were combined to produce a technique for recognizing patterns of person–environment interaction. Results from two studies with persons experiencing a highly variable chronic illness, rheumatoid arthritis, indicated that this new approach identifies distinct common patterns of person–environment interaction. Sufficient detail about the nature of each pattern resulted to facilitate further knowledge development about the health experience and to provide guidance in structuring nursing care.