bluuebunny/crossref_metadata_2025 huggingface dataset:
LAND SYSTEMS AS SURROGATES FOR BIODIVERSITY IN CONSERVATION PLANNING
Authors: Oliver Ian , Holmes Andrew , Dangerfield J. Mark , Gillings Michael , Pik Anthony J. , Britton David R. , Holley Marita , Montgomery Margaret E. , Raison Madeline , Logan Vicki , Pressey Robert L. , Beattie Andrew J.
Published: June 2007

Environmental surrogates (land classes) for the distribution of biodiversity are increasingly being used for conservation planning. However, data that demonstrate coincident patterns in land classes and biodiversity are limited. We ask the overall question, “Are land systems effective surrogates for the spatial configuration of biodiversity for conservation planning?” and we address three specific questions: (1) Do different land systems represent different biological assemblages? (2) Do biological assemblages on the same land system remain similar with increasing geographic separation? and (3) Do biological assemblages on the same land system remain similar with increasing land system isolation? Vascular plants, invertebrates, and microbiota were surveyed from 24 sites in four land systems in arid northwest New South Wales, Australia. Within each land system, sites were located to give a hierarchy of inter‐site distances, and land systems were classified as either “low isolation” (large and continuous) or “high isolation” (small patches interspersed among other land systems).

Each type of land system supported components of biodiversity either not found, or found infrequently, on other land systems, suggesting that land systems function as surrogates for biodiversity, and that conservation‐area networks representing land‐system diversity will also represent biological diversity. However, the majority of taxa were found on more than one land‐system type, suggesting that a large proportion of the plant, arthropod, and microbial biodiversity may be characterized by widespread species with low fidelity to particular land systems. Significant relationships between geographic distance among sites and differences among assemblages were revealed for all taxa except the microbiota. Therefore, as sites on the same land system were located farther apart, the assemblages at those sites became more different. This finding strongly suggests that conservation planning based on land‐system diversity should also sample the geographic range occupied by each land system. Land‐system isolation was not revealed to be a significant source of variation in assemblage composition. Our research finds support for environmental surrogates for biodiversity in conservation planning, specifically the use of land systems and similarly derived land classifications. However, the need for explicit modeling of geographic distance in conservation planning is clearly indicated.
USE OF POPULATION VIABILITY ANALYSIS AND RESERVE SELECTION ALGORITHMS IN REGIONAL CONSERVATION PLANS
Authors: Carroll Carlos , Noss Reed F. , Paquet Paul C. , Schumaker Nathan H.
Published: June 2007

Current reserve selection algorithms have difficulty evaluating connectivity and other factors necessary to conserve wide‐ranging species in developing landscapes. Conversely, population viability analyses may incorporate detailed demographic data, but often lack sufficient spatial detail or are limited to too few taxa to be relevant to regional conservation plans. We developed a regional conservation plan for mammalian carnivores in the Rocky Mountain region using both a reserve selection algorithm (SITES) and a spatially explicit population model (PATCH). The spatially explicit population model informed reserve selection and network design by producing data on the locations of population sources, the degree of threat to those areas from landscape change, the existence of thresholds to population viability as the size of the reserve network increased, and the effect of linkage areas on population persistence. A 15% regional decline in carrying capacity for large carnivores was predicted within 25 years if no addition to protected areas occurred. Increasing the percentage of the region in reserves from the current 17.2% to 36.4% would result in a 1–4% increase over current carrying capacity, despite the effects of landscape change. The population model identified linkage areas that were not chosen by the reserve selection algorithm, but whose protection strongly affected population viability. A reserve network based on carnivore conservation goals incidentally protected 76% of ecosystem types, but was poor at capturing localized rare species. Although it is unlikely that planning for focal species requirements alone will capture all facets of biodiversity, when used in combination with other planning foci, it may help to forestall the effects of loss of connectivity on a larger group of threatened species and ecosystems. A better integration of current reserve selection tools and spatial simulation models should produce reserve designs that are simultaneously biologically realistic and taxonomically inclusive.
MACROBENTHIC RECOVERY PROCESSES FOLLOWING CATASTROPHIC SEDIMENTATION ON ESTUARINE SANDFLATS
Authors: Thrush Simon F. , Hewitt Judi E. , Norkko Alf , Cummings Vonda J. , Funnell Greig A.
Published: June 2007

Land use can exacerbate the rate of sediment delivery to estuaries. In particular, for catchments with steep terrain and heavy, sporadic rainfall, changes in land use can increase the risk of catastrophic deposition of terrestrial sediment. One of the key issues in assessing the ecological significance of catastrophic sedimentation events is determining the rate of recovery of the macrobenthic community and understanding how physical and biological processes influence the recovery rate in different locations. We conducted a field experiment over 212 days to assess the impact of terrestrial sediment deposits at six sites on the intertidal sandflats of Whitianga Harbour (New Zealand). Differences in the sedimentary habitat as a result of the deposition of terrestrial sediment lasted for ∼50 d, although these effects varied between different sediment properties and between sites. The deposition of terrestrial sediment had an immediate and negative effect on resident macrofauna, although complete defaunation of the experimental plots did not occur. Macrobenthic recovery lagged behind the recovery of the sediment properties. Based on multivariate analysis, three sites never recovered over the duration of the experiment, while based on univariate analysis four sites never recovered. Macrofaunal assemblages living deep (2–15 cm) within the sediment were generally slower to recover than those found in the top 2 cm. A meta‐analysis of recovery rates for macrofauna was conducted on information generated in this study and in two similar experiments carried out in other New Zealand estuaries. This analysis revealed a consistent negative relationship between the magnitude of disturbance generated by the terrestrial sediment layer and the recovery of the macrobenthos. Measures of recovery at the community level emphasized the importance of site environmental factors reflecting increased wave disturbance, flow velocity, and the wetting and drying of the deposited terrestrial sediment in speeding recovery. Overall, our results indicate that the long‐term effects of catastrophic sediment disturbance are influenced by local hydrodynamic conditions and the composition of resident macrofauna living in sediments adjacent to disturbed areas. Given the long time scale of recovery from these experiments they indicate the potential for catastrophic sediment deposition to result in broad‐scale degradation of estuarine macrobenthic communities.
GRASS RESPONSE TO CLIPPING IN AN AFRICAN SAVANNA: TESTING THE GRAZING OPTIMIZATION HYPOTHESIS
Authors: Leriche H. , Le Roux X. , Desnoyers F. , Benest D. , Simioni G. , Abbadie L.
Published: June 2007

It has been suggested that grazing could stimulate the aboveground dry mass and/or nitrogen yields available to grazers (i.e., the grazing optimization hypothesis, GOH), but the actual importance of this effect is still controversial. The GOH has only been tested for a few grasslands and one savanna ecosystem, but not for the moistest and warmest grasslands and savannas of the world. The objectives of this study were to test the GOH in the humid savanna of Lamto (West Africa) by analyzing the growth of grasses in response to a field trial with three levels of clipping × two levels of fertilization. We quantified the effects of clipping and fertilization on the dry matter and nitrogen yields to grazers (i.e., mass or nitrogen amount in clipped‐off tissues during the experiment) and on the remaining yield (i.e., mass or nitrogen amount in residual phytomass at the end of the experiment) over a three‐month period. Total phytomass yield, the sum of yield to grazers, and the remaining yield was maintained under moderate clipping frequency and fertilization as compared to control conditions. Both clipping frequencies decreased the remaining phytomass yield as compared to control plots. Clipping frequency significantly increased nitrogen concentrations in the total yield, in the remaining yield, and in the yield to grazers. Total nitrogen yield and nitrogen yield to grazers were 65% and 91% higher on the plots experiencing moderate clipping frequency with fertilization as compared to control plots. The study shows that grazers in this humid savanna system could potentially modify ecosystem processes in such a way as to partly alleviate nutritional deficiencies, but only in the presence of increased nitrogen availability.
REGIONAL DYNAMICS OF WETLAND‐BREEDING FROGS AND TOADS: TURNOVER AND SYNCHRONY
Authors: Trenham Peter C. , Koenig Walter D. , Mossman Michael J. , Stark Stacey L. , Jagger Leslie A.
Published: June 2007

We used data from a statewide frog monitoring network to investigate population turnover and synchrony in eight wetland‐breeding species. We found that subpopulations at many sites turn over frequently, with breeding choruses absent or undetectable in most years. Frequencies of detection across sites were significantly associated with the density of wetland patches (all species) and the areal extent of several terrestrial land cover categories (seven species) within 1 km. Intraspecific population fluctuations were statistically synchronized between survey sites separated by up to 50–100 km, but synchrony was not strong. Anuran abundances were significantly correlated with rainfall 1–4 years earlier, indicating that rainfall influences population fluctuations. However, population synchrony was much weaker than rainfall synchrony. Managers attempting to maintain amphibian populations regionally should focus on maintaining landscapes with high densities of wetlands and sufficient upland habitat resources. The dynamic nature of amphibian populations at individual wetlands is well known, and our results suggest that species distributions at the landscape level are similarly dynamic.
GENE FLOW IN COMMERCIAL FIELDS OF HERBICIDE‐RESISTANT CANOLA (BRASSICA NAPUS)
Authors: Beckie Hugh J. , Warwick Suzanne I. , Nair Harikumar , Séguin-Swartz Ginette
Published: June 2007

Multiple herbicide resistance to glyphosate, glufosinate, bromoxynil, or imidazolinone in volunteer plants of canola (Brassica napus) has been attributed to pollen flow among cultivars with different resistance traits. A study was conducted in Saskatchewan, Canada, in 1999 and 2000 to assess gene flow in space and time in adjacent commercial fields of glyphosate‐ and glufosinate‐resistant canola, including (1) estimation of gene flow with distance; (2) frequency and distribution of volunteers, and effect on gene flow; (3) effect of adventitious double herbicide‐resistant seed presence in seedlots planted; and (4) a comparison of various marker systems to track gene flow events. At 11 sites in 1999, gene flow was determined by sampling seeds from plants located at 0, 50, 100, 200, 400, 600, or 800 m along a transect perpendicular to the common border in the paired fields, spraying seedlings with glyphosate and glufosinate, and confirming the presence of the transgenes using commercial test strips and PCR analysis. In the spring of 2000, putative double herbicide‐resistant volunteers that survived sequential herbicide applications were mapped at three of the sites using GPS and resistance in sampled plants was characterized. In 1999, gene flow between the paired fields was detected to a maximum distance of 400 m. Values ranged from 1.4% outcrossing at the border common to the paired fields to 0.04% at 400 m. In 2000, gene flow as a result of pollen flow in 1999 was detected to the limits of the study areas (800 m). Large variation in gene flow levels and patterns among the three sites was evident. Adventitious presence of double herbicide‐resistant seed in glyphosate‐resistant seedlots planted at two of the sites in 1999 contributed to the occurrence of double herbicide‐resistant volunteers in 2000. The results of this study suggest that gene stacking in B. napus canola volunteers in western Canada may be common, and reflects pollen flow between different herbicide‐resistant canola, presence of double herbicide‐resistant off‐types in seedlots, and/or agronomic practices typically employed by Canadian growers.
UNDERSTORY VEGETATION AND ENVIRONMENT RESPONSES TO TILLAGE, FOREST HARVESTING, AND CONIFER PLANTATION DEVELOPMENT
Authors: Ramovs B. V. , Roberts M. R.
Published: June 2007

Increasing demand to conserve biodiversity in managed forests necessitates better understanding of the impacts of forestry practices on the species‐rich herbaceous layer. We compared composition and diversity of understory vegetation, environmental features, and stand structure of forests in New Brunswick, Canada, under four different management scenarios, including: young (24–66 yr) naturally regenerated forests and conifer plantations (19–64 yr) established after clear‐cutting, mature (77–100 yr) naturally regenerated forests originating from natural disturbance (insect defoliation), and old‐field plantations (31–77 yr) established on abandoned agricultural fields. The objectives were to determine how plant composition, forest structure, and microenvironment differed among stand types and which environmental or structural features were related to understory species. Detrended correspondence analysis (DCA) and multiresponse permutation procedure (MRPP) indicated that stand types differed in species composition and environments. Plantations were significantly lower in density of snags, deciduous canopy cover, and leaf substrate, and higher in coniferous canopy cover and needle, twig, and moss substrates than the natural stands. Old‐field plantations had less cover of pits and mounds than all other stand types. Mature natural stands contained the greatest amount of coarse woody debris (CWD) in all decay classes and snags >14 cm diameter, and the lowest density of trees >5 cm diameter and moss cover. Canonical correspondence analysis (CCA) showed that species in both natural stand types are associated with decayed CWD, deciduous cover, and leaf substrate. Species in cutover plantations were associated with coniferous cover and needle substrate. Species composition in old‐field plantations was distinct, with the lowest species richness and diversity of all stand types. We present a conceptual model illustrating the initial direct effects of previous land use and harvesting or postharvest treatments and the subsequent indirect effects associated with plantation or natural stand development on environmental features and understory vegetation. We recommend extending plantation harvest cycles to facilitate reestablishment and expansion of plant populations and maintaining diverse tree canopy composition, coarse woody debris, and pit and mound topography to sustain critical habitat for vascular understory plant species in managed forests.
FEEDBACKS BETWEEN SOIL NUTRIENTS AND LARGE HERBIVORES IN A MANAGED SAVANNA ECOSYSTEM
Authors: Augustine David J. , McNaughton Samuel J. , Frank Douglas A.
Published: June 2007

Small‐scale fertilization experiments have shown that soil nutrients limit plant productivity in many semiarid grasslands and savannas, but linkages among nutrients, grasses, and grazers are rarely studied in an ecosystem context. We used hectare‐scale heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna to examine relationships among soil nitrogen and phosphorus, aboveground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland. Increasing soil N and P content was consistently associated with increasing plant productivity and rainfall use efficiency in wet, dry, and drought years. A fertilization experiment and analyses of grass N:P ratios across sites indicated that N is the primary limiting nutrient on nutrient‐rich glades, whereas N and P co‐limit productivity on nutrient‐poor bushland sites. Variation in ANPP among patches within the landscape was linearly correlated with consumption rates of large herbivores. Grazing pressure was consistently high (>60% of ANPP) at all but one site in a dry year (1999), and was greater in nutrient‐rich glades (73 ± 4% of ANPP) than in nutrient‐poor bushland sites (43 ± 7% of ANPP) in a wet year (2001). Grasses of nutrient‐rich sites contained sufficient P concentrations to meet requirements for pregnant and lactating ungulates, whereas grasses in nutrient‐poor swards were P deficient. Even though native and domestic herbivores selectively used and intensively grazed nutrient‐rich sites, productivity on these sites remained high throughout the study. Analyses of nitrogen budgets for nutrient‐rich and nutrient‐poor sites showed that large herbivores themselves caused a net N input to the former and a net N loss from the latter. Thus, large herbivores not only respond to heterogeneity in soil and plant nutrients across the landscape, but also play a role in maintaining the N‐enriched status of highly productive and intensively grazed sites.
VALIDATION OF SIMULATED RUNOFF FROM SIX TERRESTRIAL ECOSYSTEM MODELS: RESULTS FROM VEMAP
Authors: Gordon W. S. , Famiglietti J. S. , Fowler N. L. , Kittel T. G. F. , Hibbard K. A.
Published: June 2007

Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) Phase 2 model experiments investigated the response of biogeochemical and dynamic global vegetation models (DGVMs) to differences in climate over the conterminous United States. This was accomplished by simulating ecosystem processes using historical climate and atmospheric CO2 records from 1895–1993. We evaluated the behavior of six models (Biome‐BGC, Century, GTEC, LPJ, MC1, and TEM) by comparing simulated runoff in 13 watersheds to gauged streamflow from the Hydro‐Climatic Data Network. Metrics used to assess the “goodness of fit” between simulated and observed values were: (1) Pearson's r to evaluate the overall data set, (2) Kendall's τ to gauge seasonality trends as derived from a time‐series analysis of monthly runoff, and (3) three measures of absolute and relative error.

We found small differences in performance among the six models over all watersheds. However, the models yielded highly divergent results depending upon the watershed analyzed. Performance of the ensemble of models in a watershed was positively correlated with observed streamflow: models in the wettest watersheds in this study were associated with the highest model correlations and largest absolute errors, and models in the driest watersheds were associated with the lowest correlations and smallest absolute errors. Mean relative error was small and nearly constant across watersheds. A bias estimator showed that the models tended to underestimate runoff in wet watersheds and overestimate runoff in dry watersheds. Analysis of long‐term trends in runoff using a moving‐average approach demonstrated the ability of the models to reproduce temporal variation in observed data, even though quantitative differences among models were large.

Models relying on prescribed vegetation (Biome‐BGC, Century, and TEM) outperformed the two DGVMs (LPJ and MC1); GTEC gave the poorest fit to observations due to the absence of an evaporation function and a snow routine. Across all 13 watersheds, TEM ranked the highest in model performance. The validation results presented here suggest that improvements in the simulation of hydrologic processes in land‐surface models will come, in part, from a more realistic representation of subgrid‐scale soil moisture and from a more detailed understanding and representation of subsurface processes.
LARVAL SALAMANDER RESPONSE TO UV RADIATION AND PREDATION RISK: COLOR CHANGE AND MICROHABITAT USE
Authors: Garcia Tiffany S. , Stacy Jodi , Sih Andrew
Published: June 2007

Adaptations to avoid or cope with harmful ultraviolet radiation (UVR) have evolved in many amphibian species. Sublethal levels of UVR can select for simple responses in larval amphibians, such as dark pigmentation or preference for UVR‐protected microhabitats (i.e., under cover or in deep water). This study focuses on color response to UVR, and whether avoidance behaviors like refuge use and depth choice depend on larval body color. We quantified responses to ambient levels of UVR in four experiments in semi‐field conditions using two sister species of salamander larvae that differ in their evolutionary history of UVR exposure. Both Ambystoma barbouri and A. texanum larvae darkened in response to UVR, and when given the choice of refuge, significantly increased the proportion of time spent in hiding. Additionally, both species used deeper microhabitats when exposed to UVR, but only A. barbouri larvae showed a preference for shallow waters when UVR was blocked out. Neither of these behaviors seemed to be color dependent, with larvae from both species taking refuge and preferring deep water in the presence of UVR, regardless of body color. Interesting behavioral trade‐offs arose when larvae were confronted with conflicting selection pressures from UVR and predation risk. Risk from predatory fish forces larvae to shallow areas, while UVR forces larvae into deeper water. Thus, the combination of the two selection pressures creates a conflict in optimal depth choice. Faced with this conflict, A. barbouri preferred deeper, risky areas to shallow water with high UVR exposure. Ambystoma texanum responded to predation risk with a preference for shallow water, but did not significantly alter depth in response to UVR. Given the opportunity to mediate exposure to UVR and predation risk by altering depth choices, neither species changed color in response to either UVR or predation risk. Overall, these changes in behavior and color may affect larval feeding, competition, and predation rates and could thus alter aquatic community structure.
EFFECTS OF TREE DENSITY AND STAND AGE ON CARBON ALLOCATION PATTERNS IN POSTFIRE LODGEPOLE PINE
Authors: Litton Creighton M. , Ryan Michael G. , Knight Dennis H.
Published: June 2007

Validating the components of the carbon (C) budget in forest ecosystems is essential for developing allocation rules that allow accurate predictions of C pools and fluxes. In addition, a better understanding of the effects of natural disturbances on C cycling is critical, particularly in light of alterations to disturbance regimes that may occur with global climate change. However, quantitative data about how postfire differences in ecosystem structure affect C allocation patterns are lacking. For this study, we examined how above‐ and belowground C pools, fluxes, and allocation patterns varied with fire‐initiated differences in tree density and stand age in lodgepole pine stands in Yellowstone National Park of four forest types: low (<1000 trees/ha), moderate (7000–40 000 trees/ha), and high tree densities (>50 000 trees/ha) in 13‐year‐old stands, and in ∼110‐year‐old mature stands. C pools in live biomass and detritus were estimated with allometric equations and direct sampling. Aboveground net primary productivity (ANPP) was estimated as aboveground biomass increment plus fine litterfall, and total belowground carbon allocation (TBCA) was estimated using a C balance approach. Our results indicate that the magnitude of C pools and fluxes varies greatly with fire‐initiated differences in tree density and stand age. Coarse woody debris and mineral soil carbon accounted for the majority of total ecosystem C in young stands (91–99%), in contrast to mature stands where the largest amount of C was found in live biomass (64%). ANPP and TBCA increased with tree density (mean ANPP was 59, 122, and 156 g C·m−2·yr−1, and TBCA was 68, 237, and 306 g C·m−2·yr−1for low‐, moderate‐, and high‐density young stands, respectively), and with stand age (ANPP was 218 g C·m−2·yr−1and TBCA was 382 g C·m−2·yr−1for 110‐year‐old stands). ANPP and TBCA were positively correlated, and both variables were well correlated with leaf area index. Notably, the ratio of TBCA to (TBCA + ANPP) remained remarkably constant (0.63–0.66) across extreme gradients of tree density and stand age, differing only slightly for the low‐density young stands (0.54). These results suggest that C allocation patterns in a postfire lodgepole pine ecosystem are independent of tree density and stand age.
PREDATOR CUES AND PESTICIDES: A DOUBLE DOSE OF DANGER FOR AMPHIBIANS
Authors: Relyea Rick A.
Published: June 2007

Amphibians are declining globally, and biologists have struggled to identify the causes. Pesticides may play a role in these declines, but pesticide concentrations in nature often are low and considered sublethal. Past research has found that the globally common pesticide carbaryl can become more lethal under different environmental conditions including differences in temperature and competition. A recent study has found that predatory stress, a situation common for most amphibians, can make carbaryl 2–4 times more deadly to gray tree frogs (Hyla versicolor). To determine whether this is a general phenomenon in amphibians, I examined how carbaryl affected the survival of six amphibian species in the presence and absence of predatory stress. Higher concentrations of carbaryl caused higher mortality. In two of the six species, carbaryl became even more lethal when combined with predatory stress (up to 46 times more lethal). This suggests that apparently safe concentrations of carbaryl (and perhaps other pesticides with similar modes of action) can become more deadly to some amphibian species when combined with predator cues.
EFFECTS OF AN INSECTICIDE ON AMPHIBIANS IN LARGE‐SCALE EXPERIMENTAL PONDS
Authors: Boone Michelle D. , Semlitsch Raymond D. , Fairchild James F. , Rothermel Betsie B.
Published: June 2007

We examined the effects of the insecticide carbaryl on larval amphibian communities in large‐scale experimental ponds. Tadpoles of two anurans, Woodhouse's toad (Bufo woodhousii) and southern leopard frog (Rana sphenocephala), were reared in ponds (800 m3 volume) to determine the effects of tadpole density and carbaryl exposure on mass at metamorphosis and on time and survival to metamorphosis. Exposure to carbaryl significantly affected toads at metamorphosis, but not leopard frogs. Carbaryl exposure nearly doubled toad survival compared to controls; this effect may be attributable to an indirect effect of carbaryl increasing algal food resources. The competitive environment (i.e., density) and carbaryl exposure significantly affected the trade‐off between mass and time to metamorphosis for toads. Our study is the first to demonstrate that in pond communities where predation and competition may be strong, short‐lived insecticides can significantly alter the community dynamics of amphibians.
SEABIRD ECOLOGY, EL NIñO ANOMALIES, AND PREDICTION OF SARDINE FISHERIES IN THE GULF OF CALIFORNIA
Authors: Velarde Enriqueta , Ezcurra Exequiel , Cisneros-Mata Miguel A. , LavÍn Miguel F.
Published: June 2007

Small pelagic fish constitute 25–40% of the fisheries landings in Mexico. More than 70% of these landings, predominantly Pacific sardine (Sardinops caeruleus), are captured in the Gulf of California. Small pelagic fishes are a key component of the Gulf's ecosystem; they are eaten by seabirds, sea mammals, and other fishes. The sardine fishery within the Gulf has been showing signs of overfishing since the early 1990s. To contribute to the sustainable management of this fishery, we developed two statistical models that use oceanographic conditions and seabird breeding and feeding data to predict total fishery catch and catch per unit effort (CPUE) of Pacific sardine in the central Gulf. Total catch was predicted with an accuracy of 54% by a linear model incorporating the Southern Oscillation Index (SOI), the clutch size of Heermann's Gulls (Larus heermanni), and the proportion of sardine mass in the diet of Elegant Terns (Sterna elegans). CPUE was predicted with an accuracy of 73% by a model based on the proportion of sardines in the diet of Elegant Terns, the reproductive success of Heermann's Gulls, and the springtime sea surface temperature anomaly in the Gulf region. Our results show that the reproductive ecology of seabirds is coupled to the global and local oceanographic conditions and that this information can be used to predict in advance the outcome of fishing efforts. We propose the use of models of this kind to reduce the effort of the fleet in years when it can be anticipated that CPUE will be low.
INTEGRATING REPRESENTATION AND VULNERABILITY: TWO APPROACHES FOR PRIORITIZING AREAS FOR CONSERVATION
Authors: Lawler Joshua J. , White Denis , Master Lawrence L.
Published: June 2007

Reserves protect biodiversity by ameliorating the threats to the persistence of populations. Methods for efficient, systematic reserve selection have generally been designed to maximize the protection of biodiversity while minimizing the costs of reserves. These techniques have not directly addressed the factors threatening species at specific sites. By incorporating measures of site vulnerability into reserve selection procedures, conservation planners can prioritize sites based on both representing biodiversity and the immediacy of factors threatening it.

Here we develop two complementary approaches for identifying areas for conservation based on species composition and potential threats facing the species. These approaches build on two established methods of systematic reserve selection. The first approach involves mapping irreplaceability (a statistic derived from reserve selection theory that measures the potential importance of a site for protecting all species) and the degree to which the area is vulnerable to threats from three basic anthropogenic factors (the percentages of a site devoted to agriculture, to urban and suburban development, and to open mines). We classified areas with respect to both irreplaceability and the three indicators of vulnerability, producing a continuous ranking of all sites based on these factors. Our second approach was to incorporate site vulnerability into a reserve selection algorithm. This approach allowed us to locate those sets of sites that protected all species and were most likely to be threatened by human activities. These two analyses can provide regional‐scale guidance for conservation in the Mid‐Atlantic region of the United States, and they demonstrate two potential tools for solving complex conservation‐planning problems.
NON‐TIMBER FOREST PRODUCT EXTRACTION: EFFECTS OF HARVEST AND BROWSING ON AN UNDERSTORY PALM
Authors: Endress Bryan A. , Gorchov David L. , Noble Robert B.
Published: June 2007

Despite the advocacy for non‐timber forest product (NTFP) extraction as a form of sustainable development, the population ecology of many NTFPs remains unstudied, making it difficult to assess the ecological impacts of extraction. We investigated the demography and population dynamics of the harvested, understory palm, Chamaedorea radicalis in the El Cielo Biosphere Reserve, Mexico. Our objectives were: (1) to describe patterns of C. radicalis abundance and population size structure, (2) to document C. radicalis demography, (3) to test experimentally how this demography was affected by different leaf harvest regimes and livestock browse intensities, and (4) to project their effects on transient and long‐term population dynamics.

Data on palm abundance and population size structure were collected from belt‐transects along hillsides. We also exposed 100 adult palms to each of five leaf harvest treatments (N = 500): control, harvest once per year, harvest twice per year, harvest four times per year, and a modified four times per year harvest where only one leaf was removed each harvest. Browse experiments were conducted to assess the effect of burro browse on demography. Experiments were monitored over two years, and results were incorporated with other demographic data to parameterize stage‐based (Lefkovitch) matrices for each year × treatment combination.

Topographic position influenced both population size structure and density, with a gradient from valleys (727 palms/ha) to upper slopes (5513 palms/ha). Palm demography was characterized by low mortality, low reproductive activity, and high seed germination rates. Leaf harvest increased adult mortality and reduced fecundity, and it was projected to reduce λ (finite rate of increase). However, λ for harvested populations did not differ significantly from 1. Browsing increased mortality of seedlings, juveniles, and small adults, resulting in populations projected to decline (λ < 1).

These findings indicate that browsing by free‐range livestock impacts C. radicalis populations more than leaf harvest and could explain the low density and skewed size structure in valleys. The modest impact of leaf harvest treatments is due in part to the reduction in the availability of marketable leaves. Detection of such feedbacks exemplifies how the incorporation of human management practices enhances the insights that experiments bring to studies of the population ecology of NTFPs.
THE IMPACT OF CHANGING FLOW REGIMES ON RIPARIAN VEGETATION AND THE RIPARIAN SPECIES MIMULUS GUTTATUS
Authors: Elderd Bret D.
Published: June 2007

Alteration of riparian stream flow through the damming of rivers and streams impacts not only river morphology but also the vegetation communities that exist within the confines of a river's banks. To examine changes in vegetation community composition and structure resulting from human control of water flow, I conducted a series of surveys on dammed and undammed streams in the Eastern Sierra Nevada Mountains of California. These surveys documented that areas below dams contain increased leaf litter and grass thatch deposition, increased grass species coverage, and an altered community of existing forbs as compared to sites with naturally flowing streams. There was also an increased woody species canopy coverage as distance from the stream increased. To examine the proximal causes of damming on herbaceous plants, I set up a factorial field experiment examining the impact of grass thatch, shading, and herbivory on a common riparian species, Mimulus guttatus, the common monkeyflower. M. guttatus germination was decreased in the thatch augmentation plots and under artificial shading. For seedlings, shading increased final plant height and thatch increased herbivory. In plots where herbivory was not controlled by insecticide, M. guttatus plants grew smaller and had lower reproduction. I also repeated this experiment in a more controlled greenhouse environment using two seed sources and two levels of shading coverage. Results from this experiment largely confirm patterns seen in the field, but also revealed a strong interaction between shading and thatch treatments for both germination and growth. Overall, my results suggest that altering riparian stream flow may impact plant performance through a cascading set of biotic interactions, and that controlled releases from dams that mimic bankfull or greater discharge events may be required to restore these important and diverse communities by resetting disturbance rates.
DIRECT AND INDIRECT EFFECTS OF EXOTIC BASS AND BLUEGILL ON EXOTIC AND NATIVE ORGANISMS IN FARM PONDS
Authors: Maezono Yasunori , Kobayashi Raita , Kusahara Miki , Miyashita Tadashi
Published: June 2007

Exotic largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) are thought to threaten native aquatic organisms worldwide, but few studies have demonstrated their community‐wide impacts, including the interaction between these fish and other exotic organisms. We tested the hypothesis that bass and bluegill in Japanese farm ponds will reduce some native organisms (fish, shrimp, odonates) as well as exotic crayfish (Procambarus clarkii) via top‐down effects, whereas other native organisms (chironomid larvae, oligochaetes, and macrophytes) will increase as a result of trophic cascades. To test this hypothesis, we conducted three types of field experiments. In the first experiment, we estimated predation pressure in ponds with and without bass and bluegills by using predator exclusion cages. This experiment revealed that predation on native odonates and exotic crayfish was greater in ponds with bass or bluegills, whereas predation on chironomids, oligochaetes, and macrophytes was lower in ponds with bass or bluegills. In the second experiment, we estimated the impact of bass and bluegills at the community level using four large mesocosms in a pond. Bass or bluegill were introduced into two mesocosms (treatment), but were absent in the other two mesocosms (control). We found that bass reduced native fish, exotic fish, shrimp, odonates, and exotic crayfish, while chironomids, oligochaetes, and macrophytes increased; however, introducing bluegill reduced only shrimp and odonates. In the third experiment, we established small mesocosms with and without exotic crayfish. This experiment showed that crayfish were responsible for a reduction of macrophytes. All three field experiments supported our hypothesis for bass effects, but not for most of the bluegill effects. The results provide important implications for strategies to eradicate exotic fish; when exotic crayfish are present, bass removal is likely to reduce macrophytes that perform important functions in freshwater ecosystems. To conserve macrophytes we propose that reduction of exotic crayfish should be considered when eliminating bass.
CARBON DYNAMICS ALONG A CHRONOSEQUENCE OF SLASH PINE PLANTATIONS IN NORTH FLORIDA
Authors: Clark Kenneth L. , Gholz Henry L. , Castro Mark S.
Published: June 2007

To determine factors controlling the carbon dynamics of an intensively managed landscape, we measured net CO2exchange with the atmosphere using eddy covariance and soil CO2fluxes using static chambers along a chronosequence of slash pine (Pinus elliottiivar.elliottii) plantations consisting of a recent clearcut, a mid‐rotation (10‐yr‐old) stand, and a rotation‐aged (24‐yr‐old) stand. Daytime net ecosystem exchange of CO2(NEEday) at the clearcut was not significantly different than zero during the growing season of the first year following harvest and reached levels that were ∼40% of those at the older stands during the second growing season. NEEdaywas similar at the mid‐rotation and rotation‐aged sites, reflecting the similar leaf areas of these stands. Nighttime net ecosystem exchange of CO2(NEEnight) was an exponential function of air or soil temperature at all sites. However, low decomposition rates of litter and flooding of the site following harvest likely constrained NEEnightat the clearcut, and drought affected rates at the mid‐rotation site. Annual net ecosystem exchange of CO2(NEEyr) was estimated at −1269 and −882 g C·m−2·yr−1at the clearcut, and 576 and 603 g C·m−2·yr−1at the mid‐rotation stand in 1998 and 1999, respectively. For comparison, NEEyrwas 741 and 610 g C·m−2·yr−1at the rotation‐aged stand in 1996 and 1997, respectively. In contrast, annual ecosystem respiration (Reco) was similar in magnitude at all sites during all years. AlthoughRecois similar in magnitude, NEEyris highly dynamic across this intensively managed landscape, with a maximum range of ∼2000 g C·m−2·yr−1. This range exceeds that across all the sites in both the Ameriflux and Euroflux networks and illustrates the need to include the range of stand ages and disturbance histories in landscape‐ to regional‐scale flux estimates.
POPULATION ECOLOGY OF AN INVASION: EFFECTS OF BROOK TROUT ON NATIVE CUTTHROAT TROUT
Authors: Peterson Douglas P. , Fausch Kurt D. , White Gary C.
Published: June 2007

Invasion by nonnative brook trout (Salvelinus fontinalis) often results in replacement of cutthroat trout (Oncorhynchus clarki) in the inland western United States, but the underlying mechanisms are not well understood. We conducted a four‐year removal experiment to test for population‐level mechanisms (i.e., changes in recruitment, survival, emigration, and immigration) promoting invasion success of brook trout and causing decline of native Colorado River cutthroat trout (O. c. pleuriticus). We chose 700–1200 m segments of four small mountain streams where brook trout had recently invaded cutthroat trout populations, two each at mid elevation (2500–2700 m) and high elevation (3150–3250 m), and annually removed brook trout from two streams (treatments), but not the other two (controls). We used depletion electrofishing, two‐way fish weirs, and mark–recapture methods to estimate abundance, movement, and survival of trout. At mid elevation, age‐0 and age‐1 cutthroat trout survived at 13 times and two times higher rates on average, respectively, where brook trout were removed. At high‐elevation sites, recruitment of cutthroat trout failed despite brook trout removals, apparently because of cold water temperatures. In contrast, age‐2 and older cutthroat trout survived at similar rates, whether brook trout were removed or not and regardless of elevation. Summer movement by cutthroat trout was unaffected by removal of brook trout. We conclude that brook trout depress cutthroat trout populations at mid elevation through age‐specific biotic interactions that reduce juvenile cutthroat trout survival, whereas populations restricted to high‐elevation sites by invasion continue to decline because an abiotic factor (low temperature) causes recruitment failure. In comparison, brook trout survived at the same or higher rates than same‐aged cutthroat trout. High immigration by brook trout recolonized depleted segments, and may help sustain invasions in sink habitats where environmental conditions limit recruitment. In streams similar to those we studied, eradication of brook trout is likely necessary to eliminate the threat to native cutthroat trout, but selective removal regimes that capture a high percentage of the brook trout population for least three consecutive years, repeated periodically, may permit cutthroat trout populations to persist with brook trout. To identify underlying mechanisms responsible for successful invasion by mobile, age‐structured vertebrates such as stream fishes, experiments conducted at realistic spatial and temporal scales and including multiple age classes will be required.
MACROALGAL (FUCUS VESICULOSUS) δ15N VALUES TRACE DECREASE IN SEWAGE INFLUENCE
Authors: Savage Candida , Elmgren Ragnar
Published: June 2007

Nutrient discharges from sewage treatment plants can contribute significantly to coastal and estuarine eutrophication. To counter anthropogenic nitrogen (N) loads in a Baltic Sea coastal embayment, improved (∼85%) N removal was implemented in a tertiary sewage‐treatment plant. This study used nitrogen stable‐isotope ratios (δ15N) in attached brown macroalgae, Fucus vesiculosus, to map the change in the spatial extent of the influence of sewage‐derived N. Elevated N content and δ15N values (δ15N = 8–9‰) suggest that sewage N was still traceable in algal tissues despite enhanced N removal from the effluent. However, the δ15N values decreased significantly with distance and approached background levels within 10–12 km of the outfall. Compared to a survey conducted in 1989, prior to enhanced N removal in the sewage treatment plant, macroalgae were 2.5–6‰ lower in δ15N values within 24 km from the outfall, demonstrating a decline in the importance of sewage‐derived nutrients to macroalgae, particularly in the inner reaches of the bay. Beyond 25 km from the outfall, δ15N values were at background levels (δ15N = 4‰). Two‐source mixing models estimate that the percentage sewage contribution to total algal N uptake in algae near the outfall was ∼40% in 1989 and ∼12% in 1999. Similarly, temporal variation in individual plants estimate that the percentage sewage N contribution to algae within 1 km from the outfall declined from >40% in the mid‐1990s to ∼20% in 2002. Nutrient budget calculations showed that F. vesiculosus is not an effective sink for N, assimilating only ∼3% of total annual N loads entering the bay.
NET CARBON FLUXES FROM FOREST CLEARANCE AND REGROWTH IN THE AMAZON
Authors: Steininger Marc K.
Published: June 2007

Estimates of net carbon exchange resulting from forest clearance and regrowth were made for three areas in the Brazilian and Bolivian Amazon. The study areas, ranging in size from 600 to 10 000 km2, include communities that practice a range of land uses from small‐scale, rotational agriculture to long‐term pasture. Carbon emissions from deforestation were estimated based on rates of deforestation derived from Landsat satellite data and published estimates of mature forest biomass. Estimates of carbon uptake by secondary forest regrowth were based on area estimates from the satellite data and biomass estimates from field surveys. Estimates of carbon emissions from the clearance of secondary forest were included. The total carbon emissions were partitioned into that immediately released by biomass burning during clearance and that from subsequent decomposition and burning of felled biomass. A range of net carbon fluxes from secondary forest regrowth and clearance was estimated by extrapolating land‐use patterns in each study area to the entire area of deforested landscape in Amazonian Brazil and Bolivia, and by varying average biomass accumulation rate of regrowing forest and fallow period.

Over 60 km2 of forest were cleared from 1988 to 1995 in each of the Brazilian study areas, and over 940 km2 were cleared from 1986 to 1996 in the Bolivian study area. This resulted in 30–200 Mg C/yr emitted from biomass burning during deforestation. If the carbon that is committed to subsequent burning and decomposition of felled biomass is included, total committed emissions of 75–650 Mg C/yr resulted from deforestation in each study area. The carbon uptake by secondary forests was 33–435 Mg C/yr. However, emissions from the reclearance of secondary forests were nearly as large: 17–365 Mg C/yr. Extrapolation of these results to the Brazilian and Bolivian Amazon suggests that, at the national level, carbon uptake by secondary forests offset less than one‐fifth of the carbon emissions from deforestation. Despite differences in land‐use pattern, average fallow period, and rate of biomass accumulation used in the extrapolation, net carbon uptake by secondary forests was consistently small when compared to the total emissions from deforestation.