bluuebunny/crossref_metadata_2025 huggingface dataset:
PREDICTING THE OCCURRENCE OF RARE MOLLUSKS IN NORTHERN CALIFORNIA FORESTS
Authors: Dunk Jeffrey R. , Zielinski William J. , Preisler Haiganoush K.
Published: June 2007

Terrestrial mollusks are important components of forest ecosystems, yet we know very little about the distribution and habitat of many of these species. We sampled for terrestrial mollusks in northern California with the goal of estimating the geographic ranges and developing predictive habitat models for five species that were assumed to be sensitive to land management activities. The species of interest wereAncotrema voyanum,Helminthoglypta talmadgei,Monadenia churchi,Monadenia fidelis klamathica, andM. f. ochromphalus. We randomly selected 308 plots for sampling from a grid of points across a 2.2 million‐ha study area. We used Generalized Additive Models to estimate each mollusk's geographic range and to develop predictive habitat models within their ranges. Models were developed at one microscale (1 ha) and six mesoscales (ranging from 12.5 to 1250 ha) using vegetation, physical, climatic, and spatial location covariates. Estimated geographic ranges varied from 4770 to 15 795 km2. Predictive habitat models explained from 40.8% to 94.5% of the deviance in models describing the species' occurrences. Models at the 1‐ha scale were generally better than models at larger spatial scales. Of the six mesoscales evaluated, the “best” models were often at very large scales. Spatial location and climatic variables contributed significantly to the predictions of occurrence for most species. Models for species with small geographic ranges generally appeared to be better than models for species with larger geographic ranges, possibly reflecting more restricted environmental conditions. Cross‐validation results, however, showed that models for species with more locations were more stable.A. voyanumwas more frequently associated with late‐successional forests andM. churchiwas found to be a habitat generalist. The remaining three species were not detected enough for us to make strong conclusions about their habitat associations. Our results provide important guidance to land managers who are responsible for determining the necessity for surveys and protective measures for these and other terrestrial mollusk species prior to land management activities.
MANIPULATING VINEYARD IRRIGATION AMOUNTS TO REDUCE INSECT PEST DAMAGE
Authors: Daane K. M. , Williams L. E.
Published: June 2007

Insect herbivore densities can respond to changes in host plant vigor. While many basic studies have described the generalized patterns and mechanisms of host plant influence on herbivore densities and biological traits, fewer studies have shown practical applications for the observed ecological patterns. We assessed the effect of different irrigation amounts on grapevine (Vitis vinifera L., cv. Thompson Seedless) condition and the resulting changes to an insect herbivore (the variegated leafhopper, Erythroneura variabilis Beamer). Water amounts delivered to vines were manipulated with respect to amounts delivered in a weighing lysimeter: 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 times that used by vines in the lysimeter. We then followed plant growth measurements and leafhopper density and biological traits throughout the growing season. By August and September, midday leaf water potential, mean shoot length, vegetative growth, and pruning mass were a positive linear function of applied water amounts. The amount of N per unit leaf area decreased as applied water amounts increased. Similar to measured levels of vine growth, there was a seasonal response of leafhopper density to applied water amounts. By August and September, leafhopper density was a positive linear function of applied water amounts. Dry mass of fifth instar leafhoppers, the numbers of marked and recaptured adults, and leafhopper egg deposition were also positively correlated to irrigation amounts. Our results indicate that the greatest influence of manipulated vine growth and irrigation amounts may be due to differences in adult leafhopper movement and reproductive potential, which has implications for dispersal of pests between vineyards. We demonstrated that applied irrigation amounts to vines can be manipulated to suppress insect herbivore density without negatively influencing crop yield. We discuss our results of insect herbivore response to changes in plant water stress within the context of the plant vigor hypothesis.
FLORISTIC QUALITY INDICES FOR BIOTIC ASSESSMENT OF DEPRESSIONAL MARSH CONDITION IN FLORIDA
Authors: Cohen Matthew J. , Carstenn Susan , Lane Charles R.
Published: June 2007

Evaluation of wetland ecological condition requires quantitative biological indices for measuring anthropogenic impairment. We implemented a modified floristic quality assessment index (FQAI) protocol for 75 isolated, depressional herbaceous wetland systems, exploring refinements of FQAI standard methods. Species encountered during sampling (n = 397) were assigned coefficients of conservatism (CC) by ten expert botanists working independently. A quantitative summary metric of adjacent site buffer (up to 100 m) land use intensity, called the landscape development intensity (LDI) index, was calculated for each wetland system to quantify expected anthropogenic impairment. The association between LDI and wetland community mean CC scores was strong and conditionally independent of ecoregion. Weaker associations with LDI were observed for other community summary metrics, including richness‐weighted FQAI. We inverted LDI to compute an intensity coefficient (IC), which quantifies observed buffer development intensity tolerated by each species. IC scores were significantly associated with CC scores on a species basis and strongly associated on a site mean basis. Growing interest in floristic quality assessment for regulatory purposes provides opportunities for formally linking expert opinion and ground observations of species‐specific disturbance tolerance.
A FRAMEWORK FOR ASSESSING THE RELATIVE VULNERABILITY OF SPECIES TO LAND‐USE CHANGE
Authors: Pereira Henrique M. , Daily Gretchen C. , Roughgarden Joan
Published: June 2007

Conversion of native habitat to human‐dominated uses is the main driver of global biodiversity loss, yet which species will be most impacted, and why, remain poorly known. There is thus an urgent need to develop frameworks for understanding, and predicting, the effect of habitat alteration on biodiversity. We develop an approach with three components: a demographic model, a regional database of life‐history traits, and a sensitivity analysis of the model predictions. We use a spatially explicit model that predicts the fate of individual species in a human‐dominated landscape. The model takes as parameters habitat affinity, population growth rate, annual dispersal, and dispersal behavior at the habitat edges. The model predicts the minimum area of native habitat that allows for persistence of a species. We apply the model to a regional community of species, the avifauna of Costa Rica. We gather life‐history data (body mass, clutch size, breeding season length, number of broods per year, age at first breeding, life span, and dispersal distance) for Costa Rican birds. When data are not available for Costa Rican species, inferences are made from North American and European birds. We use these data to estimate the model parameters for each species. Minimum patch sizes predicted by the model are used to specify the relative degree of threat faced by each species. We perform a sensitivity analysis of patch size and relative vulnerability predictions to model assumptions and gaps in the data. Our predictions of relative vulnerability are robust to changes in model assumptions and agree with an independently derived empirical assessment. Our framework thus appears to be useful for understanding, and influencing, the fates of neotropical birds and possibly other taxa worldwide.
THE ROBUSTNESS OF EDDY CORRELATION FLUXES FOR AMAZON RAIN FOREST CONDITIONS
Authors: Kruijt B. , Elbers J. A. , von Randow C. , Araújo A. C. , Oliveira P. J. , Culf A. , Manzi A. O. , Nobre A. D. , Kabat P. , Moors E. J.
Published: June 2007

We analyzed errors and uncertainties in time‐integrated eddy correlation data for sites in the Amazon. A well‐known source of potential error in eddy correlation is through possible advective losses of CO2 emissions during calm nights. There are also questions related to the treatment of low frequencies, non‐horizontal flow, and uncertainties in, e.g., corrections for tube delay and frequency loss, as well as the effect of missing data. In this study, we systematically explore these issues for the specific situation of flux measurements at two Amazon forest sites. Results indicate that, for this specific environment with tall forest and tall towers, errors and uncertainties caused by data spikes, delay corrections, and high‐frequency loss are small (<3% on an annual basis). However, sensitivities to the treatment of low frequencies and non‐horizontal flow can be large, especially if the landscape is not homogeneous. Given that there is no consensus on methodology here, this represents an uncertainty of 10–25% on annual total carbon uptake. The other large uncertainty is clearly in the nighttime fluxes. Two different ways to evaluate the validity of these fluxes resulted in at least a 100% difference of annual totals. Finally, we show that uncertainty (standard errors) associated with data gaps can be reduced to <0.5 Mg·ha−1·yr−1 if data are covering at least half of the time, with random spread. Overall uncertainty, on annual CO2 fluxes, excluding the nighttime dilemma, is estimated at ±12% (central Amazon site) to ±32% (southwest Amazon site). Additionally, the nighttime uncertainty is of similar magnitude as the time‐integrated fluxes themselves.
MULTIPLE TRAIT ASSOCIATIONS IN RELATION TO HABITAT DIFFERENTIATION AMONG 17 FLORIDIAN OAK SPECIES
Authors: Cavender-Bares Jeannine , Kitajima Kaoru , Bazzaz F. A.
Published: June 2007

Differentiation of species distributions along environmental gradients and phenotypic specialization help explain the co‐presence of 17 oak species that might otherwise be expected to competitively exclude one another. In an effort to understand the role of niche differentiation in the co‐presence of these congeneric species in north‐central Florida, we examined the community structure of oak‐dominated forests in this region in relation to environmental variables and a suite of life history and physiological traits. Landscape distribution patterns of oaks and other woody species were determined from randomly established plots in three state parks. Soil moisture, nutrient availability, and fire regime were found to be critical factors influencing community structure, and the distribution of oak species was strongly correlated with these gradients. Detrended correspondence analysis of species' distributions supported the grouping of oak species into three major community types: (1) hammock, (2) sandhill, and (3) scrub. Principal components of multiple traits also supported differentiation of oak species into these three groups.

There is clear evidence for ecological sorting among the oaks in these forests as species partition environmental gradients more than expected by chance, and most functional traits of species correspond to species distributions as predicted based on a priori understanding of trait function. Across phylogenetic lineages, species showed evolutionary convergence in function and habitat preference. In contrast, leaf‐level traits were conserved within phylogenetic lineages and were not well correlated with local habitat factors, but rather with the broader geographic distributions and northern range limits of species. The cumulative results reported here provide strong evidence that oak species specialize for particular niches via trade‐offs in functional traits, and such niche partitioning contributes to the high diversity of oak species at the landscape level. At smaller spatial scales, phylogenetic diversity among the oaks is likely to be important in promoting their coexistence through other mechanisms.
A NEIGHBORHOOD ANALYSIS OF TREE GROWTH AND SURVIVAL IN A HURRICANE‐DRIVEN TROPICAL FOREST
Authors: Uriarte María , Canham Charles D. , Thompson Jill , Zimmerman Jess K.
Published: June 2007

We present a likelihood‐based regression method that was developed to analyze the effects of neighborhood competitive interactions and hurricane damage on tree growth and survival. The purpose of the method is to provide robust parameter estimates for a spatially explicit forest simulator and to gain insight into the processes that drive the patterns of species abundance in tropical forests. We test the method using census data from the 16‐ha Luquillo Forest Dynamics Plot in Puerto Rico and describe effects of the spatial configuration, sizes, and species of neighboring trees on the growth and survival of 12 dominant tree species representing a variety of life history strategies. Variation in size‐dependent growth and mortality suggests a complex relationship between size, growth, and survival under different regimes of light availability. Crowding effects on growth and survival appear to be idiosyncratic to each individual species, and with the exception of pioneers, there is little commonality among species that share similar life histories.

We also explain the implications of differential susceptibility to hurricane damage on species' growth and survival and on their ability to respond to damage to neighboring trees. Tree species in the Luquillo Forest Dynamics Plot differ strikingly in both their susceptibility to hurricane disturbance and the nature of their recovery from wind disturbance, through response of both adult plants and juveniles to enhanced resource availability. At the stand level, intense competitive thinning of densely packed saplings that grew after hurricane damage accounted for the majority of post‐hurricane mortality, particularly for shade‐intolerant species. At the individual species level, effects of previous hurricane damage on growth and survival depended primarily on variation in the quantity and quality of hurricane damage sustained by target species and their interaction with life history characteristics of these individual species.

Finally, we compare models that make different assumptions about the effects of competing species on tree growth and survival (e.g., equivalence of competitors vs. distinct species‐specific effects). Size effects alone could not account for growth and survival for the majority of target species. Our results also demonstrate that competing species have distinct per capita effects on growth of dominant target species. In contrast, we found moderate support for a model that assumed functional equivalence of competitors on survival.
SEED MASS AND MAST SEEDING ENHANCE DISPERSAL BY A NEOTROPICAL SCATTER‐HOARDING RODENT
Authors: Jansen Patrick A. , Bongers Frans , Hemerik Lia
Published: June 2007

Many tree species that depend on scatter‐hoarding animals for seed dispersal produce massive crops of large seeds at irregular intervals. Mast seeding and large seed size in these species have been explained as adaptations to increase animal dispersal and reduce predation. We studied how seed size and seed abundance simultaneously influenced seed dispersal and predation by scatter‐hoarding rodents in the large‐seeded rain forest tree Carapa procera (Meliaceae) in French Guiana. We individually tracked the fates of 3000 seeds, using remote video monitoring and thread‐marking. Seed size was manipulated by broadly varying intraspecific seed mass, whereas effects of seed abundance were examined by tracking seeds in three seed‐rich years and two seed‐poor years. The hypotheses, that seed mass and seed abundance both enhance dispersal success and that seed abundance reinforces the effect of seed mass, were supported by the results. Most seeds were removed by the scatter‐hoarding rodent red acouchy (Myoprocta acouchy) and subsequently were buried in scattered, single‐seeded caches up to distances >100 m. Seeds that were not removed failed to establish seedlings. Seed removal was slower, pre‐removal seed predation was greater, and seed dispersal was less far in seed‐rich years than in seed‐poor years, suggesting poorer dispersal under seed abundance. However, this was more than counterbalanced by a disproportionally greater survival of cached seeds in seed‐rich years. The per capita probability of seed survival and seedling establishment was at least 4½ times greater under seed abundance. Large seeds were removed faster, were more likely to be scatter‐hoarded, and were dispersed farther away than smaller ones, resulting in a higher probability of seedling establishment for larger seeds. Size discrimination was greater under seed abundance, albeit only during seed removal. Overall, large seeds shed in rich years had the highest probability of seedling establishment. Hence, both larger seed size and greater seed abundance stimulate rodents to act more as dispersers and less as predators of seeds. We conclude that scatter‐hoarding rodents can select for both large seed crops and large seeds, which may reinforce mast seeding.
SPECIES INTERACTION STRENGTH: TESTING MODEL PREDICTIONS ALONG AN UPWELLING GRADIENT
Authors: Menge Bruce A. , Blanchette Carol , Raimondi Pete , Freidenburg Tess , Gaines Steve , Lubchenco Jane , Lohse Dave , Hudson Greg , Foley Melissa , Pamplin Jacque
Published: June 2007

A recent model predicts that species interactions in benthic marine communities vary predictably with upwelling regimes. To test this model, we studied thePisaster–Mytilusinteraction at 14 rocky intertidal sites distributed among three oceanographic regions along a 1300‐km stretch of the U.S. West Coast. Regions included an intermittent‐upwelling region (northern), a persistent‐upwelling region (central), and a region of weak and infrequent upwelling (southern). We quantified predation rates by the sea starPisaster ochraceuson its main preyMytilus californianusby transplanting mussels into the sea star's low‐zone foraging range and comparing the rate of mussel loss in +Pisasterplots to those in −Pisasterplots. To evaluate the relation between predation rates and key ecological processes and conditions, we quantified phytoplankton concentration and rates of mussel recruitment, mussel growth, mussel abundance, and sea star abundance.

Predictions of the model are expressed as responses of predator and prey abundance, and species interaction strength (per capita and per population or total impact at the population level). As predicted by theory,per capitapredation rates were independent of upwelling regime, with no variation with region. Contrary to expectation however, per‐population predation rates were similar between intermittent‐ and persistent‐upwelling regions but were greater under strong upwelling than under weak upwelling conditions. The greatest variation inper‐populationpredation rates was at the level of site within region. Also contrary to theory, average abundances of prey (mussel cover) and predators (sea stars) were similar among oceanographic regions and varied mostly at the site level.

As expected from theory, predation rate was high where sea star density was high, a condition that often coincided with a high food supply (phytoplankton) for filter feeders, including larvae, and high recruitment. With the exception of two sites having dense sea star populations and thus high predation, low values of either or both were associated with low predation, suggesting that the supply of prey often depended on conditions that favored subsidies of both phytoplankton and new larvae to prey populations. The occurrence of high predator density and high predation at sites of low inputs of particulate food and propagules suggests that understanding sea star life history is a key to a fuller understanding of variation in predation on a coastal scale. Evidence suggests that often sporadic recruitment of sea stars along the coast is balanced by great longevity, which tends to even out predation impact on coastal intertidal communities.
SEAWEEDS UNDER STRESS: MANIPULATED STRESS AND HERBIVORY AFFECT CRITICAL LIFE‐HISTORY FUNCTIONS
Authors: Dethier Megan N. , Williams Susan L. , Freeman Aaren
Published: June 2007

Terrestrial plants respond in complex ways to the interaction of stress and herbivory, but much less is known about responses of seaweeds. We studied the common intertidal rockweed Fucus gardneri to determine how stress and herbivory interact to influence its survival, growth, reproduction, and the concentration of phlorotannins, which can deter herbivory and constitute substantial mass. We manipulated stress and herbivory both in the field and in outdoor mesocosms over 2–4 months during spring and summer. In the field, disruptive stress was reduced in the upper range of the seaweed's distribution with awnings made of screen. Temperatures and relative humidities were more extreme in the no‐awnings locations. This treatment was crossed with a limpet‐removal treatment. In mesocosms, the tidal period was controlled so that half of the experimental thalli were exposed to air daily for 3–4 hours longer (greater limitation stress) than the other half, and three levels of isopod grazing were maintained. Grazing intensity was effectively reduced in the field and increased in the mesocosms. Net rates of photosynthesis were used as independent measures of seaweed stress.

Fucus gardneri in the locations without awnings exhibited significant reductions in net photosynthesis, survival, and final size compared to thalli under awnings. The mesocosm environment was more benign; all individuals survived longer and grew larger. However, results from both experiments were generally consistent. Stress resulted in slightly lower growth and substantially reduced phlorotannin mass. Severe stress had a negative effect on reproductive output in the field experiment, but mild stress had a small positive effect in the mesocosms. Herbivory resulted in reduced thallus mass, slightly reduced growth, and reduced reproduction, but it had no effect on phlorotannin levels in either experiment. Herbivory and stress thus influenced different performance indicators in Fucus. Stress had more dramatic effects on phlorotannins than it did on growth, whereas herbivory more strongly influenced growth and reproduction. Few interactive effects were found, unlike in many terrestrial studies. If stress and herbivory act largely independently, as they appear to do here and in the limited number of other seaweed studies, predicting the effects of changes in the intertidal physical environment and in herbivory might be simpler than anticipated. The physiological basis for the observed responses to stress and herbivory is suspected to involve trade‐offs in resource allocation among these key life‐history parameters.
DO HABITAT POTENTIAL, POPULATION DENSITY, AND FIRES INFLUENCE SCRUB‐JAY SOURCE–SINK DYNAMICS?
Authors: Breininger David R. , Oddy Donna M.
Published: June 2007

The concept of source and sinks can guide conservation, but empirical studies are needed to demonstrate that this concept applies to the real world. We investigated whether the source–sink concept could help to clarify the influence of habitat potential (scrub ridge characteristics), population density, and fires (shrub heights) on Florida Scrub‐Jay (Aphelocoma coerulescens) demography and dispersal. We mapped territories and measured survival, recruitment, emigration, immigration, and shrub heights annually for 12 years. We classified territories as oak if they overlapped well‐drained ridges, oak–palmetto if they overlapped poorly drained ridges >0.4 ha, and palmetto–oak if they only overlapped poorly drained ridges <0.4 ha. Territory size differed little among these categories but was negatively correlated with the annual number of breeding pairs, which ranged from 12 to 27. Scrub ridge characteristics influenced the locations of sinks and potential sources, whereas population density and fires caused temporal variation in demographic success. Oak territories were usually sources because they were net exporters of individuals and because recruitment exceeded mortality. Oak–palmetto territories sometimes functioned as sources but were often pseudo‐sinks because density dependence caused mortality to exceed recruitment. Palmetto–oak territories were true sinks because they were net importers of individuals and mortality exceeded recruitment regardless of population density. All scrub was short (<1.2 m) or medium height (1.2–1.7 m), but the spatial arrangement of these height classes changed regularly because fires occurred every 2–7 years. We observed a quadratic relationship between demographic success and the area of medium‐height scrub within territories. Territories that had 0.9–1.2 ha of medium‐height scrub had the highest demographic success. Applying source–sink concepts at the territory scale was useful to quantify habitat variation at a spatial scale relevant to population processes, reserve design, and habitat management. Our approach can be applied by using territory maps or geographic information systems to partition heterogeneous landscapes into territories and then by classifying territories into potential sources and sinks using scrub ridge characteristics and shrub heights.
SMALL‐SCALE EXPERIMENTS SUPPORT CAUSAL RELATIONSHIPS BETWEEN METAL CONTAMINATION AND MACROINVERTEBRATE COMMUNITY RESPONSES
Authors: Clements William H.
Published: June 2007

Routine biomonitoring studies that compare abundance of benthic macroinvertebrates upstream and downstream from contaminant discharges generally cannot be used to demonstrate causal relationships between stressors and biological responses. In this study I describe stream microcosm and field experiments designed to support results of a 12‐year monitoring project in the metal‐polluted Arkansas River, Colorado. Microcosm experiments established concentration–response relationships between heavy metals and several structural (abundance, richness) and functional (macroinvertebrate drift, community respiration) endpoints. EC10values, the metal concentration that reduced abundance or richness by 10%, were generally lowest for mayflies and stoneflies, indicating greater metal sensitivity for these groups. Macroinvertebrate drift and community respiration showed highly significant concentration–response relationships with heavy metals and were generally more sensitive than structural measures. Potential interactions among metals were investigated by comparing community‐level responses to Zn alone, Zn+Cd, and Zn+Cu+Cd. Results showed that macroinvertebrate responses to a mixture of three metals were generally greater than responses to either Zn alone or Zn+Cd. Long‐term monitoring in the Arkansas River (Colorado) before and after remediation of metal inputs provided correlative evidence that elevated heavy metal concentrations altered community composition and reduced abundance of metal‐sensitive organisms. However, these field data were not especially useful for estimating safe concentrations of heavy metals that would be protective of benthic communities. Microcosm and field experiments provided further support for the hypothesis that metals caused alterations in benthic community structure and provided more precise estimates of safe metal concentrations.
ESTIMATING SITE OCCUPANCY AND SPECIES DETECTION PROBABILITY PARAMETERS FOR TERRESTRIAL SALAMANDERS
Authors: Bailey Larissa L. , Simons Theodore R. , Pollock Kenneth H.
Published: June 2007

Recent, worldwide amphibian declines have highlighted a need for more extensive and rigorous monitoring programs to document species occurrence and detect population change. Abundance estimation methods, such as mark–recapture, are often expensive and impractical for large‐scale or long‐term amphibian monitoring. We apply a new method to estimate proportion of area occupied using detection/nondetection data from a terrestrial salamander system in Great Smoky Mountains National Park. Estimated species‐specific detection probabilities were all <1 and varied among seven species and four sampling methods. Time (i.e., sampling occasion) and four large‐scale habitat characteristics (previous disturbance history, vegetation type, elevation, and stream presence) were important covariates in estimates of both proportion of area occupied and detection probability. All sampling methods were consistent in their ability to identify important covariates for each salamander species. We believe proportion of area occupied represents a useful state variable for large‐scale monitoring programs. However, our results emphasize the importance of estimating detection and occupancy probabilities rather than using an unadjusted proportion of sites where species are observed where actual occupancy probabilities are confounded with detection probabilities. Estimated detection probabilities accommodate variations in sampling effort; thus comparisons of occupancy probabilities are possible among studies with different sampling protocols.
QUANTIFYING SPATIAL PATTERN WITH EVENNESS INDICES
Authors: Payne Laura X. , Schindler Daniel E. , Parrish Julia K. , Temple Stanley A.
Published: June 2007

Quantifying the spatial distributions of organisms in simple and meaningful ways is important for understanding the ecology and habitat needs of species subject to anthropogenic disturbances. Most multi‐species conservation and management programs do not yet account for the variation of space‐use patterns exhibited by species preferring the same habitat type. To measure species' space‐use patterns as a step toward determining habitat needs, we suggest using evenness indices. Although commonly used in characterizing communities (i.e., as a measure of species diversity), these indices are suitable for characterizing many other ecological patterns, including patterns of site use by individuals.

We investigate the statistical properties of five indices (Camargo's index of evenness, E′; Simpson's index of evenness, E1/D^; Lloyd's index of mean crowding, J; Smith‐Wilson index Evar; and Dispersion index, DL, a variant of the Shannon diversity index) to evaluate their utility for quantifying broad‐scale spatial patterns of migratory shorebirds. We use a Monte Carlo simulation approach to compare these indices for their (1) ability to characterize a wide range of spatial patterns (from even to patchy); (2) ability to discriminate among distributions; and (3) robustness to incomplete sampling. In addition, we compare the ability of these indices to characterize spatial dispersion for four species of shorebirds migrating through the United States: Killdeer (Charadrius vociferus), Semipalmated Plover (C. semipalmatus), Sanderling (Calidris alba), and Red Knot (C. canutus).

Overall, we recommend Camargo, Simpson, and Lloyd indices for quantifying spatial dispersion. All three indices gave precise and unbiased estimates once 35 or more sites (3.5% of 1000 simulated sites) were sampled randomly, regardless of the degree of patchiness. Nonrandom sampling resulted in biased estimates until a much greater proportion of sites (at least 30–50%) were sampled, highlighting the importance of site selection in sampling programs. Our analysis of shorebird spatial patterns revealed that evenness indices discriminate well among the species we considered, ranking Killdeer as most dispersed and Red Knot as most aggregated. Our results agree with earlier (independent) assessments of these species' migration strategies and illustrate how simple univariate metrics may be useful tools for characterizing complex spatial patterns.
THE EFFECTS OF HERBIVORY AND POLLEN LIMITATION ON A DECLINING POPULATION OF TRILLIUM GRANDIFLORUM
Authors: Knight Tiffany M.
Published: June 2007

In long‐lived organisms, it is often difficult to determine which environmental factors will have the largest effects on population dynamics. In this study, I incorporated the results of short‐term experiments and observations into a demographic matrix model to determine the effects of both herbivory and pollen limitation on the dynamics of a declining population of the perennial herb Trillium grandiflorum. While pollen supplementation experiments in both 1999 and 2000 revealed that plants produce fewer seeds as a result of pollen limitation, this pollen limitation had almost no effect on the growth rate of the population. White‐tailed deer (Odocoileus virginianus) consumed nearly half of the reproductive plants in this population in 2000 and 2001. Herbivory causes reproductive and large nonreproductive plants to regress in stage and have lower fecundity. In the absence of herbivory, demographic projections suggest that the population would shift from declining to growing, the proportional representation of new recruits would rise, and plants in larger stage classes would have higher reproductive values. Such shifts in the reproductive values and stable stage distribution result in shifts in elasticities. A life table response experiment demonstrated that, while herbivory affected six vital rates, two of these contributed disproportionately to the change in the population growth rate: reproductive plants remaining reproductive and large nonreproductive plants remaining nonreproductive. In this population, herbivores contribute more to its decline than pollinators. Thus, active long‐term management of deer populations appears necessary for the conservation of understory herbs such as Trillium grandiflorum.
AVIFAUNAL RESPONSES TO SINGLE AND RECURRENT WILDFIRES IN AMAZONIAN FORESTS
Authors: Barlow Jos , Peres Carlos A.
Published: June 2007

Although forest wildfires threaten to impoverish vast expanses of once fire‐resistant humid tropical forest, their effects on the vertebrate fauna remain poorly understood. We report results from a study in central Brazilian Amazonia examining a large area of terra firma (unflooded) forest that had been affected by fires during the 1997–1998 El Niño‐mediated dry season. By sampling 0.25‐ha forest plots both one and three years after fire disturbance, we noted that over time the bird community became increasingly dissimilar from that in unburned control plots. The influences of burn severity and recurrent fires were then examined across 28 plots that were all sampled three years after the fires. Foraging guilds differed in their responses to the gradient of increasing burn severity; most guilds declined, although arboreal granivores, frugivores, and nectarivores showed unimodal responses and arboreal gleaning insectivores increased. These responses were strongly correlated with associated changes in the habitat structure and reflected differences in resource abundance where this was quantified. Rates of species turnover were high, and there was virtually no species overlap between unburned forest plots and those that had burned in more than one El Niño dry season. Our results indicate that, unless conservation strategies can prevent a recurrent fire regime from becoming established in seasonally dry tropical forests, only nonforest and second‐growth bird species, which are of minimal conservation importance, will be able to persist in fire‐prone landscapes of the future.
APPLYING PLANT FACILITATION TO FOREST RESTORATION: A META‐ANALYSIS OF THE USE OF SHRUBS AS NURSE PLANTS
Authors: Gómez-Aparicio Lorena , Zamora Regino , Gómez Jose M. , Hódar Jose A. , Castro Jorge , Baraza Elena
Published: June 2007

After a millenarian history of overexploitation, most forests in the Mediterranean Basin have disappeared, leaving many degraded landscapes that have been recolonized by early successional shrub‐dominated communities. Common reforestation techniques treat these shrubs as competitors against newly planted tree seedlings; thus shrubs are cleared before tree plantation. However, empirical studies and theory governing plant– plant interactions suggest that, in stress‐prone Mediterranean environments, shrubs can have a net positive effect on recruitment of other species. Between 1997 and 2001, we carried out experimental reforestations in the Sierra Nevada Protected Area (southeast Spain) with the aim of comparing the survival and growth of seedlings planted in open areas (the current reforestation technique) with seedlings planted under the canopy of preexisting shrub species. Over 18 000 seedlings of 11 woody species were planted under 16 different nurse shrubs throughout a broad geographical area. We sought to explore variation in the sign and magnitude of interactions along spatial gradients defined by altitude and aspect. In the present work, we report the results of a meta‐analysis conducted with seedling survival and growth data for the first summer following planting, the most critical period for reforestation success in Mediterranean areas. The facilitative effect was consistent in all environmental situations explored (grand mean effect sized+= 0.89 for survival and 0.27 for growth). However, there were differences in the magnitude of the interaction, depending on the seedling species planted as well as the nurse shrub species involved. Additionally, nurse shrubs had a stronger facilitative effect on seedling survival and growth at low altitudes and sunny, drier slopes than at high altitudes or shady, wetter slopes. Facilitation in the dry years proved higher than in the one wet year. Our results show that pioneer shrubs facilitate the establishment of woody, late‐successional Mediterranean species and thus can positively affect reforestation success in many different ecological settings.
BROWN SHRIMP ON THE EDGE: LINKING HABITAT TO SURVIVAL USING AN INDIVIDUAL‐BASED SIMULATION MODEL
Authors: Haas Heather L. , Rose Kenneth A. , Fry Brian , Minello Thomas J. , Rozas Lawrence P.
Published: June 2007

In many coastal areas, natural habitats are being fragmented and lost to encroaching human development. These landscape changes can affect the production of recreationally and commercially important fisheries because many exploited species of fish and shellfish are estuarine dependent and utilize coastal marshes as nursery grounds. Brown shrimp are an example of a commercially exploited species that may be highly affected by changes in the spatial distribution of habitat types. We used a spatially explicit, individual‐based simulation model to explore the role of marsh vegetation and edge habitat in brown shrimp survival. The model simulated shrimp movement, mortality, and growth of individual shrimp from arrival as postlarvae to 70‐mm body length, when they emigrate offshore. Simulations were performed on 100 × 100 m spatial grid of 1‐m2 cells, with each cell labeled as “water” or “vegetation”. Predation mortality was influenced by shrimp size, movement, and habitat. Simulated shrimp growth depended on temperature, habitat, and local shrimp density. We examined the relationships between shrimp survival and marsh attributes (amount of vegetation and edge habitat) by simulating a series of four habitat maps that we created from aerial photographs. Biological parameters were derived from published estimates and from field data. We corroborated the model by comparing the simulated shrimp abundance with summary statistics from long‐term monitoring data, by comparing the simulated density with fine‐scale patterns observed in field studies, and by comparing simulated and measured stable‐isotope values. Surviving shrimp grew faster, moved less, spent more time in vegetation, and experienced slightly higher local densities than shrimp that died during the simulation. Habitat maps with more edge habitat invariably produced higher simulated shrimp survival rates. High‐edge habitats increased survival by providing shrimp more direct access to vegetation without additional movement‐related mortality and density‐dependent growth costs associated with low‐edge habitats. Model predictions were robust to higher numbers of initial postlarvae and to alterations to the movement rules. The results of this study suggest that the management of brown shrimp should be extended from protecting the spawning stock through catch regulations to also protecting the estuarine life stages through habitat conservation and restoration.
METHANE AND NITROUS OXIDE FLUXES FROM URBAN SOILS TO THE ATMOSPHERE
Authors: Kaye Jason P. , Burke Ingrid C. , Mosier Arvin R. , Pablo Guerschman Juan
Published: June 2007

Land‐use change is an important driver of soil–atmosphere gas exchange, but current greenhouse‐gas budgets lack data from urban lands. Field comparisons of urban and non‐urban ecosystems are required to predict the consequences of global urban‐land expansion for greenhouse‐gas budgets. In a rapidly urbanizing region of the U.S. Great Plains, we measured soil–atmosphere exchange of methane (CH4) and nitrous oxide (N2O) for one year in replicated (n = 3) urban lawn, native shortgrass steppe, dryland wheat– fallow, and flood‐irrigated corn ecosystems. All soils were net sinks for atmospheric CH4, but uptake by urban, corn, and wheat–fallow soils was half that of native grasslands (−0.30 ± 0.04 g C·m−2·yr−1 [mean ± 1 se]). Urban (0.24 ± 0.03 g N·m−2·yr−1) and corn (0.20 ± 0.02 g N·m−2·yr−1) soils emitted 10 times more N2O to the atmosphere than native grassland and wheat‐fallow soils. Using remotely sensed land‐cover data we calculated an upper bound for the contribution of lawns to regional soil–atmosphere gas fluxes. Urban lawns occupied 6.4% of a 1578‐km2 study region, but contribute up to 5% and 30% of the regional soil CH4 consumption and N2O emission, respectively, from land‐use types that we sampled. Lawns that cover small portions of the landscape may contribute significantly to regional soil–atmosphere gas exchange.
CARBON SEQUESTRATION AND PLANT COMMUNITY DYNAMICS FOLLOWING REFORESTATION OF TROPICAL PASTURE
Authors: Silver Whendee L. , Kueppers Lara M. , Lugo Ariel E. , Ostertag Rebecca , Matzek Virginia
Published: June 2007

Conversion of abandoned cattle pastures to secondary forests and plantations in the tropics has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere and enhance local biodiversity. We used a long‐term tropical reforestation project (55–61 yr) to estimate rates of above‐ and belowground C sequestration and to investigate the impact of planted species on overall plant community structure. Thirteen tree species (nine native and four nonnative species) were planted as part of the reforestation effort in the mid to late 1930s. In 1992, there were 75 tree species (>9.1 cm dbh) in the forest. Overall, planted species accounted for 40% of the importance value of the forest; planted nonnative species contributed only 5% of the importance value. In the reforested ecosystem, the total soil C pool (0–60 cm depth) was larger than the aboveground C pool, and there was more soil C in the forest (102 ± 10 Mg/ha [mean ± 1 se]) than in an adjacent pasture of similar age (69 ± 16 Mg/ha). Forest soil C (C3‐C) increased at a rate of ∼0.9 Mg·ha−1·yr−1, but residual pasture C (C4‐C) was lost at a rate of 0.4 Mg·ha−1·yr−1, yielding a net gain of 33 Mg/ha as a result of 61 years of forest regrowth. Aboveground C accumulated at a rate of 1.4 ± 0.05 Mg·ha−1·yr−1, to a total of 80 ± 3 Mg/ha. A survey of 426 merchantable trees in 1959 and 1992 showed that they grew faster in the second 33 years of forest development than in the first 22 years, indicating that later stages of forest development can play an important role in C sequestration. Few indices of C cycling were correlated with plant community composition or structure. Our results indicate that significant soil C can accumulate with reforestation and that there are strong legacies of pasture use and reforestation in plant community structure and rates of plant C sequestration.
MIGRATION AND SURVIVAL OF PARNASSIUS SMINTHEUS: DETECTING EFFECTS OF HABITAT FOR INDIVIDUAL BUTTERFLIES
Authors: Matter Stephen F. , Roland Jens , Moilanen Atte , Hanski Ilkka
Published: June 2007

We examined the migration and survival of the butterflyParnassius smintheusin a heterogeneous landscape consisting of 21 habitat patches imbedded in a matrix of meadow and forest habitat. We modified an existing mark–release–recapture model to account for multiple habitat types and fit the model to data for 839 and 873 individuals in two separate years. Migration was infrequent with only 24 and 27 observed movements between patches in each year. Daily within‐patch survival was moderate (>0.90) and did not vary greatly with patch isolation. Estimated mortality during migration was low, but increased markedly for isolated populations. Despite the limited data, the model showed that forest matrix habitat reduced migration distance to a greater degree than did meadow habitat, indicating that the effective isolation of populations depends on both the habitat type and the distance between populations. This result concurs with previous investigations of these data, demonstrating the utility of the model even when movement is infrequent. Studies of migration are often hampered by few observable events. Our model provides reasonable estimates given few migration events. The ecological results of this study illustrate the need for spatial population studies to account for the effects of different habitat types on the migration of individuals among habitat patches. Our results also suggest management options for the conservation of endangeredParnassiusspecies in other parts of the world.
MAPPING OF MARINE SOFT‐SEDIMENT COMMUNITIES: INTEGRATED SAMPLING FOR ECOLOGICAL INTERPRETATION
Authors: Hewitt J. E. , Thrush S. F. , Legendre P. , Funnell G. A. , Ellis J. , Morrison M.
Published: June 2007

Increasingly, knowledge of broad‐scale distribution patterns of populations, communities, and habitats of the seafloor is needed for impact assessment, conservation, and studies of ecological patterns and processes. There are substantial problems in directly transferring remote sensing approaches from terrestrial systems to the subtidal marine environment because of differences in sampling technologies and interpretation. At present, seafloor remote assessments tend to produce habitats predominantly based on sediment type and textural characteristics, with benthic communities often showing a high level of variability relative to these habitat types. Yet an integration of information on both the physical features of the seafloor and its ecology would be appropriate in many applications. In this study, data collected from a multi‐resolution nested survey of side‐scan, single‐beam sonar and video are used to investigate a bottom‐up approach for integrating acoustic data with quantitative assessments of subtidal soft‐sediment epibenthic communities. This approach successfully identified aspects of the acoustic data, together with environmental variables, that represented habitats with distinctly different epibenthic communities. The approach can be used, regardless of differences in data resolution, to determine location‐ and device‐specific relationships with the benthos. When such relationships can be successfully determined, marine ecologists have a tool for extrapolating from the more traditional small‐scale sampling to the scales more appropriate for broad‐scale impact assessment, management, and conservation.