bluuebunny/crossref_metadata_2025 huggingface dataset:
SUCCESSIONAL MECHANISM VARIES ALONG A GRADIENT IN HYDROTHERMAL FLUID FLUX AT DEEP‐SEA VENTS
Authors: Mullineaux Lauren S. , Peterson Charles H. , Micheli Fiorenza , Mills Susan W.
Published: June 2007

Invertebrate communities inhabiting deep‐sea hydrothermal vents undergo substantial succession on time scales of months. Manipulative field experiments assessed the relative roles of environmental state and biotic interactions in determining temporal succession along a spatial gradient in vent fluid flux at three vent sites near 9°50′ N on the East Pacific Rise (2500 m water depth). Species colonization patterns on cubic basalt blocks (10 cm on a side) deployed by the submersible Alvin revealed both positive (facilitation) and negative (inhibition) biological interactions, in the context of established succession theory. Over a series of four cruises from 1994 to 1998, blocks were exposed to colonists for consecutive and continuous intervals in short‐term (5 + 8 = 13 mo) and longer‐term (8 + 29 = 37 mo) experiments. Colonists grouped into a mobile functional group were less abundant in the continuous interval (13 mo) than in the synchronous pooled‐consecutive intervals (5 + 8 mo) of the short‐term experiment, indicating that early colonists inhibited subsequent recruitment. Colonists grouped into a sessile functional group exhibited the opposite pattern, indicating facilitation. Similar trends, though not statistically significant, were observed in the longer‐term experiment. The character of species interactions varied along a gradient in hydrothermal fluid flux (and inferred productivity), with inhibitory interactions more prominent in zones with high temperatures, productivity, and faunal densities, and facilitative interactions appearing where temperatures, productivity, and densities were low. Analyses of primary succession on introduced basalt blocks suggest that biological interactions during early vent community development strongly modify initial patterns of settlement, even in the absence of sustained temporal change in the vent fluid flux.

Corresponding Editor: R. J. Etter
A LONG‐TERM STUDY OF COMPETITION AND DIVERSITY OF CORALS
Authors: Connell Joseph H. , Hughes Terence P. , Wallace Carden C. , Tanner Jason E. , Harms Kyle E. , Kerr Alexander M.
Published: June 2007

Variations in interspecific competition, abundance, and alpha and beta diversities of corals were studied from 1962 to 2000 at different localities on the reef at Heron Island, Great Barrier Reef, Australia. Reductions in abundance and diversity were caused by direct damage by storms and elimination in competition. Recovery after such reductions was influenced by differences in the size of the species pools of recruits, and in contrasting competitive processes in different environments. In some places, the species pool of coral larval recruits is very low, so species richness (S) and diversity (D) never rise very high. At other sites, this species pool of recruits is larger, and S and D soon rise to high levels. After five different hurricanes destroyed corals at some sites during the 38‐ year period, recovery times of S and D ranged from 3 to 25 years. One reason for the variety of recovery times is that the physical environment was sometimes so drastically changed during the hurricane that a long period was required to return it to a habitat suitable for corals. Once S and D have peaked during recolonization, they may either remain at a high level, or decline. In shallow water, with no deleterious changes in environmental conditions, S and D may not decline over time, because superior competitors cannot overtop inferior competitors without exposing themselves to deleterious aerial exposure at low tide. At other times and places, S and D did decline over time. One cause of this was a gradual deterioration of the physical environment, as corals grew upward into the intertidal region and died of exposure. S and D also fell because the wave action in hurricanes either killed colonies in whole or part, or changed the drainage patterns over the reef crest, leaving corals high and dry at low tide. At deeper sites, declines in S and D were sometimes caused by heavy wave action, or by interspecific competition, as some corals overgrew or overtopped their neighbors and eliminated them.
GRASSLAND RESPONSES TO THREE YEARS OF ELEVATED TEMPERATURE, CO2, PRECIPITATION, AND N DEPOSITION
Authors: Zavaleta Erika S. , Shaw M. Rebecca , Chiariello Nona R. , Thomas Brian D. , Cleland Elsa E. , Field Christopher B. , Mooney Harold A.
Published: June 2007

Global climate and atmospheric changes may interact in their effects on the diversity and composition of natural communities. We followed responses of an annual grassland to three years of all possible combinations of experimentally elevated CO2 (+300 µL/L), warming (+80 W/m2, +∼1°C), nitrogen deposition (+7 g N·m–2·yr–1), and precipitation (+50%). Responses of the 10 most common plant species to global changes and to interannual variability were weak but sufficiently consistent within functional groups to drive clearer responses at the functional group level. The dominant functional groups (annual grasses and forbs) showed distinct production and abundance responses to individual global changes. After three years, N deposition suppressed plant diversity, forb production, and forb abundance in association with enhanced grass production. Elevated precipitation enhanced plant diversity, forb production, and forb abundance but affected grasses little. Warming increased forb production and abundance but did not strongly affect diversity or grass response. Elevated CO2 reduced diversity with little effect on relative abundance or production of forbs and grasses. Realistic combinations of global changes had small diversity effects but more marked effects on the relative dominance of forbs and grasses. The largest change in relative functional group abundance (+50% forbs) occurred under the combination of elevated CO2 + warming + precipitation, which will likely affect much of California in the future. Strong interannual variability in diversity, individual species abundances, and functional group abundances indicated that in our system, (1) responses after three years were not constrained by lags in community response, (2) individual species were more sensitive to interannual variability and extremes than to mean changes in environmental and resource conditions, and (3) simulated global changes interacted with interannual variability to produce responses of varying magnitude and even direction among years. Relative abundance of forbs, the most speciose group in the community, ranged after three years from >30% under elevated CO2 + warming + precipitation to <12% under N deposition. While opposing production responses at the ecosystem level by different functional groups may buffer responses such as net primary production (NPP) change, these shifts in relative dominance could influence ecosystem processes such as nutrient cycling and NPP via differences between grasses and forbs in tissue chemistry, allocation, phenology, and productivity.

Corresponding Editor: S. Smith
INDIRECT EFFECTS OF AN INTRODUCED UNGULATE ON POLLINATION AND PLANT REPRODUCTION
Authors: Vázquez Diego P. , Simberloff Daniel
Published: June 2007

Herbivores can affect plants not only directly through browsing and trampling, but also indirectly through other species. For example, herbivores could affect the interaction between plants and their pollinators. Because plant population density may affect plant–pollinator interactions and plant reproductive success, we hypothesized that herbivores could affect pollination and plant reproduction indirectly by modifying plant population density. Unlike previous hypotheses, which concerned individual‐level effects on vegetative and reproductive traits, our hypothesis focuses on population‐level effects and involves a feedback mechanism. To test this hypothesis, we conducted field studies in the temperate forest of the southern Andes, where introduced ungulates are a major source of anthropogenic alteration. For 10 animal‐pollinated understory plants, we compared population density, pollinator visitation, pollen deposition in stigmas, and reproduction in four pairs of grazed and ungrazed sites. We found evidence of indirect effects of ungulates on pollination and reproduction only for the herbAlstroemeria aurea(Alstroemeriaceae). The general lack of evidence for indirect effects on most of the species may result from resistance to cattle browsing and trampling, or low statistical power. ForA. aurea, we present additional evidence from trampling and hand‐pollination experiments, plus path analyses of the effect of density on pollination and reproduction showing that: (1) cattle decrease the absolute and relative population density of this species through trampling; (2) density, particularly relative density, affects pollen deposition on stigmas; and (3) conspecific pollen deposition affects reproduction. Thus, our results indicate that, by directly reducing the population density ofA. aurea, cattle are indirectly affecting its reproduction.
HYBRIDIZATION BETWEEN A RARE, NATIVE TIGER SALAMANDER (AMBYSTOMA CALIFORNIENSE) AND ITS INTRODUCED CONGENER
Authors: Riley Seth P. D. , Bradley Shaffer H. , Randal Voss S. , Fitzpatrick Benjamin M.
Published: June 2007

Exotic species threaten native biodiversity through predation, competition, and habitat alteration, but also by hybridizing with native species. A lack of reproductive isolation between exotic and native species can lead to genetic swamping, loss of native genetic diversity, and, in rare or endangered species, extirpation or extinction. We examined hybridization between a declining native salamander, the California tiger salamander,Ambystoma californiense, and an introduced congener,A. tigrinum.Ambystoma californienseis restricted to central California whereA. tigrinumhas been deliberately introduced as fish bait. In the Salinas Valley, we sampled salamanders from four artificial ponds and two natural vernal pools. Based on mitochondrial DNA and two nuclear loci, we found that hybrids were present in all six ponds, and that these hybrids were viable and fertile. No potentially pureA. californiensewere present in three of the six ponds, and only one pond had more than 8% possibly pure native animals. Despite a relatively ancient split and wide genetic divergence between these taxa, they are interbreeding and threatening the genetic purity of the native species.

Our data also suggest that the extent of the genetic mixing depends on the breeding habitat. There is little evidence of barriers to gene exchange in the four artificial breeding ponds. However in the two vernal pools, we found significantly fewer larvae with hybrid genotypes and significantly more with pure parental genotypes than expected. Linkage disequilibria revealed positive associations between native alleles and genotypes, and negative associations between native and introduced alleles and genotypes in these two ponds. Despite rampant hybridization, these data provide evidence of some constraints on hybridization in the native breeding habitats. Our results suggest that habitat characteristics of native species should be exploited in management strategies to limit hybridization with exotics.
WHAT CAN HABITAT PREFERENCE MODELS TELL US? TESTS USING A VIRTUAL TROUT POPULATION
Authors: Railsback Steven F. , Stauffer Howard B. , Harvey Bret C.
Published: June 2007

Habitat selection (“preference”) models are widely used to manage fish and wildlife. Their use assumes that (1) habitat with high animal densities (highly selected habitat) is high quality habitat, and low densities indicate low quality habitat; and (2) animal populations respond positively to the availability of highly selected habitat. These assumptions are increasingly questioned but very difficult to test. We evaluated these assumptions in an individual‐based model (IBM) of stream trout that reproduces many natural complexities and habitat selection behaviors. Trout in the IBM select habitat to maximize their potential fitness, a function of growth potential (including food competition) and mortality risks. We know each habitat cell's intrinsic habitat quality, the fitness potential a trout in the cell would experience in the absence of competition. There was no strong relation between fitness potential and the density of fish in the IBM; cells where fitness potential was high but density low were common for all age classes, and fitness potential was not proportional to density. This result was consistent at high and low abundance and high and low overall habitat quality. We developed a statistical model of trout density observed in the IBM as a function of the four habitat variables that vary among cells. We then tested the ability of modeled mean density to predict population response to habitat changes resulting from stream flow modification. Modeled density partially explained population response to flow, but only at flows near the flow at which the density model was developed, and not for groups (e.g., juveniles) experiencing strong competition for habitat. Modeled density predicted population response opposite that observed for age‐0 trout and incorrectly predicted response of all age classes to major changes in flow. These results make sense if habitat selection is understood as an emergent property of (1) the mechanisms by which habitat affects fitness, (2) habitat availability, (3) population abundance and size structure, and (4) how individuals compete with each other. We identified eight reasons why animal density may not reflect habitat quality and several inherent limitations of habitat selection modeling.
IMMUNE AND GROWTH RESPONSE OF WESTERN BLUEBIRDS AND ASH‐THROATED FLYCATCHERS TO SOIL CONTAMINANTS
Authors: Fair Jeanne M. , Myers Orrin B. , Ricklefs Robert E.
Published: June 2007

During the past two decades, a critical need has developed to determine how exposure to contaminants in the environment affects individual and population processes. In this study, the immunocompetence of Western Bluebirds (Sialia mexicana) and Ash‐throated Flycatchers (Myiarchus cinerascens) was studied on a landscape–soil contaminant gradient at Los Alamos National Laboratory (LANL) in New Mexico during 1997–1999. A variety of contaminants (heavy metals, chemicals, insecticides, polychlorinated biphenyls, and radioactive isotopes) range across different spatial scales and concentrations on LANL land. The two species have similar life‐history traits, except that the Ash‐throated Flycatcher has a faster rate of development and fledges 4–5 days earlier than the bluebird. The number of active nest boxes increased from 1997 to 1998 and 1999 for the Western Bluebird, but not for the Ash‐throated Flycatcher. Survival of nestling flycatchers was lower in areas within 60 m of a potential contaminant release site, with a higher survivorship function associated with boxes farther away. The two species did not differ in their response to antigens, and there was no difference between locations for immunocompetence for either species. Flycatcher nestlings had a higher average cell‐mediated response than bluebird nestlings, as predicted by the faster rate of development of the flycatchers. Phytohemagglutinin response varied between locations for both species. The cell‐mediated effects were dynamic in that, in general, the same locations showed similar patterns for each year. Hematocrits steadily increased with age for both species and varied between locations for the bluebird, but not the flycatcher.
THE PACE OF ECOSYSTEM DEVELOPMENT OF CONSTRUCTED SPARTINA ALTERNIFLORA MARSHES
Authors: Craft Christopher , Megonigal Patrick , Broome Stephen , Stevenson Jan , Freese Robert , Cornell Jeff , Zheng Lei , Sacco John
Published: June 2007

Ecological attributes were measured along a chronosequence of 1‐ to 28‐yr‐old, constructed Spartina alterniflora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil development (sediment deposition, organic C, N, P, organic matter quality), and microbial processes (C mineralization) were compared among eight constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5–15 yr after marsh construction. An exception was soil organic C and N pools (0–30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophyll a, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1‐ to 3‐yr‐old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0–10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g N/m2 (0.05–0.1% N) to support emergent vegetation and 1000 g C/m2 (0.5–1% C) to sustain the heterotrophic community.
RESPONSE OF HERBS TO SHRUB REMOVAL ACROSS NATURAL AND EXPERIMENTAL VARIATION IN SOIL MOISTURE
Authors: Berlow Eric L. , D'Antonio Carla M. , Swartz Heather
Published: June 2007

Like many semiarid grasslands, large montane meadows of the Sierra Nevada Mountains, California (USA) have experienced widespread expansion of woody plants (here Rothrock sagebrush, or Artemisia rothrockii), a reduction in herbaceous species cover, and apparent aridification over the past century. Because soil moisture is an important limiting resource in this system, we investigated the interactive effects of shrub removal and soil moisture on herbaceous species recovery. We conducted replicated shrub removal experiments across four sagebrush habitats that differed in soil moisture, water table depth, and related characteristics (e.g., soil texture, initial total herbaceous cover, and initial shrub biomass). Changes in herb cover after shrub removal were monitored over four years that differed in spring snow pack, a critical source of water in this system. To more directly quantify the effects of soil moisture on shrub–herb competition, shrub removal was combined with experimental water addition in the most xeric habitat and monitored for two years. Total herb cover increased significantly with shrub removal, but the magnitude of this effect varied among years and habitats, and with experimental watering. Regardless of the source of soil moisture variation (i.e., experimental, spatial, or temporal variation), the absolute change in herb cover with shrub removal increased linearly with moisture at the dry end of the gradient (<15% gravimetric soil moisture). An apparent reversal of this trend under wetter conditions was not possible to evaluate due to few data points above 15% soil moisture. Sagebrush growth rates increased with surface soil moisture, suggesting that this woody species can use water sources similar to those used by herbaceous species. In xeric sites dominated by sagebrush, increasing water availability alone is unlikely to increase herb biomass because suppression by shrubs negates the positive effect of watering. Shrub removal alone has the potential to increase herb biomass at mesic sites or during wet years at xeric sites.
THE AGGREGATION OF IMPACTS: USING SPECIES‐SPECIFIC EFFECTS TO INFER COMMUNITY‐LEVEL DISTURBANCES
Authors: Weiss Jack M. , Reice Seth R.
Published: June 2007

The use of BACI (before–after, control–impact), comparisons to assess environmental impacts on communities requires strict adherence to the principles of good experimental design in order to derive unambiguous conclusions. Unplanned natural ecological experiments seldom meet these requirements. What unplanned experiments lack in rigor, they often make up for in an abundance of data that has the potential to make even weak signals detectable. To realize this potential the following conditions should be satisfied. (1) High taxonomic resolution is achieved in identification (species level if possible). (2) Species‐specific tolerance values are available for most of the collected taxa. (3) An individual measure of impact is obtained for each taxon at a site. (4) All taxa are used in impact assessment. As a practical illustration we examine the effect of sedimentation from construction runoff on the population levels of stream benthic macroinvertebrates. Our purpose is to assess the efficacy of erosion‐ and sedimentation‐control regulations and their enforcement in three North Carolina (USA) jurisdictions. Due to the asynchronous onset and duration of construction events, samples from different sites varied both in their timing and frequency. As a result, the benthos (both the kinds and numbers of taxa collected) overlapped so little between sites that the standard multimetric approaches to impact assessment were of little use. The typical multivariate methods of impact assessment examine changes at the community level. Our approach focuses on changes at the individual species level for all collected taxa. By correlating species‐level population changes with known species‐level tolerance values we are able to construct an impact score for each site along with a measure of its reliability. Impact scores are then used to test for jurisdiction differences using a weighted regression approach to analysis of variance. If the immediate goal of a study is not to assess the impact at a single site but to compare the degree of impact across a number of impacted sites and to relate this to one or more classification variables, then we believe this approach can be broadly applicable.
ENERGY, SPECIES RICHNESS, AND HUMAN POPULATION SIZE: CONSERVATION IMPLICATIONS AT A NATIONAL SCALE
Authors: Chown Steven L. , van Rensburg Berndt J. , Gaston Kevin J. , Rodrigues Ana S. L. , van Jaarsveld Albert S.
Published: June 2007

The maintenance of biodiversity rests on understanding and resolving conflict between patterns of species occurrence and human activity. Recent debate has centered on the relationship between species richness and human population density. However, conclusions have been limited by the lack of investigations of these relationships for individual countries, at which level most practical conservation actions are determined, and for a spatial resolution at which practical conservation planning takes place. Here, we report the results of the first such analysis, for birds in South Africa. Species richness and human density are positively correlated, apparently because both respond positively to increasing levels of primary productivity. High species richness is maintained by currently designated reserves, but the areas surrounding these have higher human population densities than expected by chance, placing the reserves under increasing external pressure. Not all species lie within protected areas, but the options are limited for building on the present network to generate a more comprehensive one, which protects all species and significantly reduces the conflict with human activities by designating new reserves in areas with lower human populations. Ultimately, the only solution to the conflict between biodiversity and people is likely to be individual‐based regulation of human population size.
PATTERNS AND CAUSES OF SPECIES ENDANGERMENT IN CANADA
Authors: Kerr Jeremy T. , Cihlar Josef
Published: June 2007

Few studies have addressed patterns and causes of species endangerment at different resolutions and geographical extents. Using newly developed remote sensing and species distribution data sets, we examined the influence of both natural and anthropogenic factors on the density of terrestrial endangered species in Canada at two spatial scales. The first was at a national extent and the second was within a region of Canada (the mixed wood plains) where there are particularly large numbers of endangered species. We also examined the distribution of protected areas throughout Canada to determine their capacity to shelter endangered species. Land use, which is measured by 1‐km resolution satellite data, is a strong predictor of endangered species densities at both scales of analysis. Land use integrates information on habitat loss to agriculture and land use intensity, an index of agricultural pollution. The amount of protected area in a region is unrelated to endangered species numbers except to the extent that areas with the most endangered species are, at best, nearly devoid of protected area. Newly legislated protections for endangered species are unlikely to bring much improvement to this conservation dilemma. Canada's endangered species legislation promotes cooperative conservation activities in areas where species endangerment is most pronounced but does little to protect remaining habitat.
RELATIONSHIPS OF STREAM INVERTEBRATE COMMUNITIES TO DEFORESTATION IN EASTERN MADAGASCAR
Authors: Benstead Jonathan P. , Douglas Michael M. , Pringle Catherine M.
Published: June 2007

Madagascar has been recently identified as a global hotspot for freshwater biodiversity. Loss of most of its eastern rain forest, combined with a high incidence of micro‐endemism and specialization to forest stream habitats, has likely led to extinction of many of the island's stream insect species. We compared habitat and macroinvertebrate community structure in three streams draining protected rain forest within Ranomafana National Park in eastern Madagascar and three agriculture streams draining the park's largely deforested peripheral zone. Multivariate analyses showed that macroinvertebrate communities differed between stream types. Forest streams were characterized by species‐rich, diverse communities composed primarily of collector–gatherers and collector–filterers belonging to the orders Trichoptera, Ephemeroptera, Plecoptera, and Diptera. In contrast, relatively depauperate agriculture stream communities were dominated by generalist collector–gatherer taxa mostly belonging to the order Ephemeroptera. Agriculture streams had 0–14% canopy cover, significantly higher mean and maximum water temperatures, and significantly lower benthic organic matter storage than forest streams (71–83% canopy cover). We found no evidence for higher sedimentation rates or nutrient concentrations in agriculture streams. Differences in thermal regime may be important in the declines of certain taxa in agriculture streams (e.g., Plecoptera). However, our data support the hypothesis that differences in stream communities are caused mainly by differences among taxa in ability to track shifts in basal resources (i.e., terrestrial detritus vs. in situ algal production) caused by deforestation. Community simplification and loss of endemic specialist taxa will continue if projections of future deforestation are proved correct. We recommend that stream biodiversity be considered in future conservation planning and propose the creation and maintenance of multiuse riparian forests that could serve both ecological and economic functions. Given that more than 5 × 105km of stream and river channel are affected by tropical deforestation annually, our results have potential applications in other tropical regions.
THE EFFECTS OF ELEVATED CO2 ON NUTRIENT DISTRIBUTION IN A FIRE‐ADAPTED SCRUB OAK FOREST
Authors: Johnson D. W. , Hungate B. A. , Dijkstra P. , Hymus G. , Hinkle C. R. , Stiling P. , Drake B. G.
Published: June 2007

Elevated carbon dioxide (CO2) caused greater accumulation of carbon (C) and nutrients in both vegetation and O horizons over a 5‐yr sampling period in a scrub oak ecosystem in Florida. Elevated CO2 had no effect on any measured soil property except extractable phosphorus (P), which was lower with elevated CO2 after five years. Anion and cation exchange membranes showed lower available nitrogen (N) and zinc (Zn) with elevated CO2. Soils in both elevated and ambient CO2 showed decreases in total C, N, sulfur (S), and cation exchange capacity, and increases in base saturation, exchangeable Ca2+, and Mg2+ over the 5‐yr sampling period. We hypothesize that these soil changes were a delayed response to prescribed fire, which was applied to the site just before the initiation of the experiment. In the ambient CO2 treatment, the increases in vegetation and O horizon C, N, and S were offset by the losses of soil total C, N, and S, resulting in no statistically significant net changes in ecosystem C, N, or S over time. In the elevated CO2 treatment, the increases in vegetation and O horizon C content outweighed the losses in soil C, resulting in a statistically significant net increase in ecosystem C content. Nitrogen and S contents showed no statistically significant change over time in the elevated CO2 treatment, however. Comparisons of vegetation contents and soil pools of potassium (K), calcium (Ca), and magnesium (Mg) suggest that a substantial proportion of these nutrients were taken up from either groundwater or deep soil horizons. This study demonstrates that changes in ecosystem C sequestration due elevated CO2 or any other factor cannot be accurately assessed in the absence of data on changes in soils.
SPECIES‐RICH PLANTINGS INCREASE BIOMASS AND NITROGEN ACCUMULATION IN A WETLAND RESTORATION EXPERIMENT
Authors: Callaway John C. , Sullivan Gary , Zedler Joy B.
Published: June 2007

Our test of the hypothesis that biomass and nitrogen would increase with more species‐rich plantings simultaneously vegetated a salt marsh restoration site and demonstrated that on average, randomly chosen, 6‐species plantings accumulated more biomass and nitrogen than the mean for 0‐ and 1‐species assemblages, with the mean for 3‐species assemblages being intermediate. In addition, we found that individual species (from the pool of eight native halophytes) differed in their functional capacity, withSalicornia virginica(Sv) andJaumea carnosacontributing the greatest biomass when planted alone, whileTriglochin concinnahad the highest tissue N concentrations. When planted alone, Sv accumulated comparable amounts of biomass and nitrogen as in the multispecies plots, indicating that individual species can have a large effect on particular functions. Soil TKN in the surface 0–5 cm was greater in 6‐species plots than unplanted plots in 1999, while both 3‐ and 6‐species plots were greater than unplanted plots in 2000; however, there were no differences at 5–20 cm depth and no species‐specific effects. Root and shoot biomass both increased with species richness, with total biomass of 6‐species plots averaging 995.6 ± 120.5 g/m2in 2000, compared to the mean for 1‐species plots (572.1 ± 90.3 g/m2) and unplanted plots (164.5 ± 24.7 g/m2). Still, at the age of three years, root biomass was only about one‐third that of the species‐rich reference site, and shoot biomass was one‐half to one‐fifth the maxima reported for reference salt marshes. Species‐specific effects were found for Sv, which had high biomass of both roots and shoots in the multispecies plots (55% of aboveground biomass in 3‐species plots and 41% in 6‐species plots) and the highest pool of N (52% of the N pool in 3‐species plots and 42% in 6‐species plots), even though only one‐eighth of the initial plantings were Sv. However, when plots with this species were excluded from the analysis, the species‐richness effect persisted. Thus, ecosystem function, as measured by biomass and N accumulation, increased with species richness regardless of dominance by the highly productive Sv. We conclude that manipulating the richness and composition of plantings offers ecosystem restorationists an effective tool for accelerating the rate of functional development.
COTTONWOODS, ELK, AND WOLVES IN THE LAMAR VALLEY OF YELLOWSTONE NATIONAL PARK
Authors: Beschta Robert L.
Published: June 2007

In September 2001, the diameter at breast height (dbh) of all cottonwood (Populus spp.) ≥5 cm in diameter was measured within a 9.5‐km2 section of the Lamar Valley (elevation ∼2000 m), in northeastern Yellowstone National Park. A total of 700 trees were measured of which 71% were narrowleaf cottonwood (P. angustifolia) and 29% were black cottonwood (P. trichocarpa). Slightly more than half of the narrowleaf trees were growing on point bar landforms at three major meander bends of the Lamar River, with the remainder occurring in small groves spread across various floodplain surfaces within the valley. Almost all of the black cottonwood occurred on point bars at only two of the meander bend locations. Tree diameters for both species ranged mostly between 30 and 110 cm with a nearly total absence of cottonwoods between 5 and 29 cm in diameter. Age vs. diameter relationships were developed and used as a basis for estimating establishment dates for all narrowleaf cottonwoods. These relationships, in conjunction with the dbh data, indicated an absence of cottonwood recruitment (i.e., growth of seedlings/suckers into ≥5‐cm diameters trees) over approximately the last 60 years. The paucity of cottonwood recruitment appears to have occurred independently of fire history, flow regimes, channel migrations, or factors affecting normal stand development, but over the same period of time that wolves (Canis lupus) had been extirpated from Yellowstone National Park. With the removal of this wide‐ranging and keystone predator, elk (Cervus elaphus) populations were able to browse riparian plant communities unaffected by wolves.
NATIVE OR NATURALIZED? VALIDATING ALPINE CHAMOIS HABITAT MODELS WITH ARCHAEOZOOLOGICAL DATA
Authors: Baumann Martin , Babotai Caroline , Schibler Jörg
Published: June 2007

Conservation of mammal species often requires the application of predictive habitat models. While empirical models can indicate the potential suitability and distribution of recent habitat, they may fail to depict native habitat and distribution. Therefore, we advocate validating such models with archaeozoological data.

To demonstrate the power of archaeozoological data in investigating native distribution patterns, we use the alpine chamois (Rupicapra rupicapra) as a model species. After experiencing a severe historical population bottleneck due to overexploitation, chamois populations recovered markedly during the last century. Fostered by humans and having profited from translocations, this alpine ungulate greatly expanded its range and began to invade forested areas both within and outside the Alps, where damage to vegetation was soon obvious. Consequently, a controversy arose concerning the natural distribution and habitat of chamois. To study the native habitat and distribution of alpine chamois in Switzerland, we focus on the Late Mesolithic and Neolithic period (6000–2200 BC). This period best suits our purpose because pristine forests then dominated the landscape and human influence was as yet minimal. We describe two opposing habitat models: the alpine model assumes that chamois had survived only in alpine areas, whereas the forest model assumes that they also roamed in steep, entirely forested areas. We validate these models with archaeozoological data. Because the probability of chamois bone occurrence in prehistoric settlements is expected to decrease with increasing distance from chamois habitat, the models differ in their geographical predictions of chamois bone records. Applying logistic regression models, only settlement proximity to chamois forest habitat explains recoveries of fossil chamois bones. The resulting function of catchment distances (i.e., the likelihood of hunting chamois depending on the distance between a settlement and the nearest chamois habitat) matches the spatial behavior of extant hunters within pristine forests.

We conclude that Holocene chamois range in Switzerland naturally included steep and entirely forested regions, like the Jura Mountains. The recent invasion of these areas by chamois thus constitutes repatriation of native habitat. Accordingly, we propose a shift in perspective toward landscape integration of chamois.
CHRONIC ORGANOCHLORINE CONTAMINANTS, ENVIRONMENTAL VARIABILITY, AND THE DEMOGRAPHICS OF A BURROWING OWL POPULATION
Authors: Gervais Jennifer A. , Anthony Robert G.
Published: June 2007

We studied a population of Burrowing Owls whose eggs contained the organochlorine compoundp,p′DDE and traces of other organochlorine contaminants to determine if the levels of contamination were associated with survival or reproduction when nonanthropogenic environmental and biological variables were also considered. Demographic data were collected in conjunction with sampling eggs for contaminants and analyzing pellets for dietary information. Levels ofp,p′DDE in eggs varied over four orders of magnitude during the study but were not by themselves associated with reproductive failure. However, contaminant concentrations in combination with low rodent abundance in the diet were related to reduced productivity. The variation within and among years in egg contaminants suggests that patterns of egg contaminants are the result of immigrating owls from more contaminated sites, and to a lesser extent, to annual patterns in prey availability. Even low levels of chronic pesticide exposure may be detrimental when combined with other stressors, and documentation of the existence of a persistent pesticide in a biotic system is not enough to either infer the origin of the contamination or its potential effects.
PHOTOSYNTHETIC AND HETEROTROPHIC IMPACTS OF NUTRIENT LOADING TO BLACKWATER STREAMS
Authors: Mallin Michael A. , McIver Matthew R. , Ensign Scott H. , Cahoon Lawrence B.
Published: June 2007

Blackwater stream systems are the most abundant type of freshwater lotic system on the Coastal Plain of the eastern United States. Many of these ecosystems drain watersheds that receive large anthropogenic nutrient inputs, whereas some blackwater systems remain relatively pristine. A series of nutrient addition experiments was carried out over a four‐year period to assess the roles of nitrogen and phosphorus loading on the phytoplankton, bacterioplankton, and respiration of two third‐order and two fifth‐order blackwater streams in southeastern North Carolina. Stream water was distributed into 4‐L containers, amended with various nutrient addition treatments, and incubated in gently agitated outdoor pools over a six‐day period. Chlorophyll a production, direct bacterial counts, ATP, and biochemical oxygen demand (BOD) were measured as response variables. Significant phytoplankton production over control occurred in most experiments involving nitrogen additions, regardless of whether it was in the form of ammonium, nitrate, or urea. Concentrations of nitrate or a urea–nitrate combination of 14.3 μM (0.2 mg N/L) or higher increased chlorophyll a production and significantly stimulated BOD. Organic or inorganic phosphorus additions did not stimulate phytoplankton production. Combined organic–inorganic phosphorus additions of 16.1–32.3 μM P (0.5–1.0 mg P/L) significantly stimulated bacterial abundance, ATP, and BOD on most occasions. Nitrogen inputs stimulate blackwater stream phytoplankton growth, which in turn dies and decomposes in deeper, higher order streams, becoming sources of BOD and lowering dissolved oxygen (DO). Phosphorus inputs directly stimulate bacterial growth, increasing BOD, and lowering stream DO. Thus, changes in nutrient loading stimulate two different biological pathways (photosynthetic and heterotrophic activity), which in turn reduce dissolved oxygen, potentially causing hypoxic conditions stressful to resident aquatic life. The low slope, slow summer flows, and naturally low summer DO conditions make Coastal Plain blackwater streams particularly susceptible to additional DO losses through BOD formation.
FUTURE WATER ALLOCATION AND IN‐STREAM VALUES IN THE WILLAMETTE RIVER BASIN: A BASIN‐WIDE ANALYSIS
Authors: Dole David , Niemi Ernie
Published: June 2007

Our research investigated the impact on surface water resources of three different scenarios for the future development of the Willamette River Basin in Oregon (USA). Water rights in the basin, and in the western United States in general, are based on a system of law that binds together all water rights in a basin in a potentially complex web of interactions. We therefore analyzed the scenarios using a basin‐wide approach, in which we simulated the allocation of surface water across all water rights in the entire basin. Our analysis focused on two particular issues: the impact of increased urban demand for water; and protecting ecological values through an existing program to conserve water and devote the savings to in‐stream water rights. The latter represented what key stakeholders in the basin felt was the greatest environmental protection that was politically feasible. The results of our simulations were inconsistent with all of our expectations. We found that the web of interactions was not extensive, and that a basin‐wide approach wasn't warranted. Increased urban demands had little impact on water allocation, but even an extensive application of the existing water conservation program was not sufficient to protect ecological values. As a result, we believe that protecting ecological values in the future will require sacrifices from more than water rights themselves, and involving society as a whole, in terms of not only the resources devoted to protecting the environment, but also the political will to make difficult changes.
ENVISIONING ALTERNATIVES: USING CITIZEN GUIDANCE TO MAP FUTURE LAND AND WATER USE
Authors: Hulse David W. , Branscomb Allan , Payne Susan G.
Published: June 2007

Spatially explicit landscape analyses are a central activity in research on the relationships between people and changes in natural systems. Using geographical information systems and related tools, the Pacific Northwest Ecosystem Research Consortium depicted historical (pre‐EuroAmerican settlement, circa 1850), current (circa 1990), and three alternative future (circa 2050) landscapes for western Oregon's Willamette River Basin. These depictions were used to better understand and anticipate trajectories of change in human occupancy and natural resource condition. During a 30‐month period, we worked with lay and professional citizen groups to create, map, and refine a set of value‐based assumptions about future policy in three scenarios concerning land and water use. The Plan Trend 2050 scenario represents the expected future landscape in 2050 if current policies are implemented as written and recent trends continue. Development 2050 reflects a loosening of current policies, to allow freer rein to market forces across all components of the landscape, but still within the range of what citizen stakeholders considered plausible. Conservation 2050 places greater emphasis on ecosystem protection and restoration, still reflecting a plausible balance among ecological, social, and economic considerations as defined by the stakeholders. For the Conservation scenario, natural resource managers and scientists provided estimates for the area of key habitats required to sustain, in perpetuity, the array of dependent species. Spatially explicit analyses identified locations biophysically suited to meet the area targets. These locations, titled the Conservation and Restoration Opportunity Areas, were mapped and then reviewed by a series of groups regarding the political plausibility of conserving or restoring them to the indicated vegetation types. The three alternative 2050 futures, as well as the 1850 past conditions, were then evaluated by an array of evaluation models described by others in this issue. The Conservation and Restoration Opportunities map from the Conservation 2050 scenario has been adopted by the group charged with salmon recovery in the basin as the centerpiece of its restoration strategy.
ECOLOGICAL IMPLICATIONS OF BOVINE TUBERCULOSIS IN AFRICAN BUFFALO HERDS
Authors: Caron Alex , Cross Paul C. , du Toit Johan T.
Published: June 2007

Following the recent invasion of bovine tuberculosis (BTB) into the Kruger National Park, South Africa, we conducted a study on the maintenance host, African buffalo, to investigate associations between BTB prevalence and calf:cow ratio, age structure, body condition, and endoparasite load. Statistical analyses compared herds of zero, medium (1–40%), and high (>40%) BTB prevalence. To control for ecological variation across the park we collected data in northern, central, and southern regions and restricted some analyses to particular regions of the park. Body condition declined over the course of the 2001 dry season, and buffaloes in the southern region of the park, with the highest BTB prevalence, were in worse condition than buffaloes in the northern region (which receives less annual rainfall but is still virtually BTB‐free). Herd‐level analyses of the entire park, the south and central regions, and just the southern region all indicated that herds of higher BTB prevalence were in worse condition and lost condition faster through the dry season than herds of lower BTB prevalence. Fecal endoparasite egg counts increased during the dry season and were associated with both decreased body condition and increased BTB prevalence. Although we did not detect any obvious effect of BTB on the age structure of the buffalo population, our findings indicate early symptoms of wider scale BTB‐related ecological disturbances: buffalo herds with high BTB prevalence appear more vulnerable to drought (because of a decrease in body condition and an increase in endoparasite load), and because lions selectively kill weak buffaloes their prey base is accumulating a disproportionately high prevalence of BTB, to which lions are susceptible.
A SPATIALLY EXPLICIT WATERSHED‐SCALE ANALYSIS OF DISSOLVED ORGANIC CARBON IN ADIRONDACK LAKES
Authors: Canham Charles D. , Pace Michael L. , Papaik Michael J. , Primack Avram G. B. , Roy Karen M. , Maranger Roxane J. , Curran Raymond P. , Spada Daniel M.
Published: June 2007

Terrestrial ecosystems contribute significant amounts of dissolved organic carbon (DOC) to aquatic ecosystems. Temperate lakes vary in DOC concentration as a result of variation in the spatial configuration and composition of vegetation within the watershed, hydrology, and within‐lake processes. We have developed and parameterized a spatially explicit model of lake DOC concentrations, using data from 428 watersheds in the Adirondack Park of New York. Our analysis estimates watershed loading to each lake as a function of the cover type of each 10 × 10 m grid cell within the watershed, and its flow‐path distance to the lake. The estimated export rates for the three main forest cover types were 37.7–47.0 kg C·ha−1·yr−1. The four main wetland cover types had much higher rates of export per unit area (188.4–227.0 kg C·ha−1·yr−1), but wetlands occupied only 11%, on average, of watershed area. As a result, upland forests were the source of ∼70% of DOC loading. There was evidence of significant interannual variation in DOC loading, correlated with interannual variation in precipitation. Estimated net in situ DOC production within the lakes was extremely low (<1 kg C·ha−1·yr−1). Many of the lakes have large watersheds relative to lake volume and have correspondingly high flushing rates. As a result, losses due to lake discharge generally had a larger effect on lake DOC concentrations than in‐lake decay. Our approach can be readily incorporated within a GIS framework and allows examination of scenarios such as loss of wetlands, alterations in forest management, or increases in conserved areas, as a function of the unique configuration of individual watersheds.