bluuebunny/crossref_metadata_2025_split huggingface dataset:
MODELING FOREST UNDERSTORY FIRES IN AN EASTERN AMAZONIAN LANDSCAPE
Authors: Alencar Ane A. C. , Solórzano Luis A. , Nepstad Daniel C. 
Published: June 2007

Forest understory fires are an increasingly important cause of forest impoverishment in Amazonia, but little is known of the landscape characteristics and climatic phenomena that determine their occurrence. We developed empirical functions relating the occurrence of understory forest fires to landscape features near Paragominas, a 35‐yr‐old ranching and logging center in eastern Amazonia. An historical sequence of maps of forest understory fire was created based on field interviews with local farmers and Landsat TM images. Several landscape features that might explain spatial variation in the occurrence of understory fires were also mapped and co‐registered for each of the sample dates, including: forest fragment size and shape, forest impoverishment through logging and understory fire, sources of ignition (settlements and charcoal pits), roads, forest edges, and others. The spatial relationship between forest understory fire and each landscape characteristic was tested by regression analyses. Fire probability models were then developed for various combinations of landscape characteristics. The analyses were conducted separately for years of the El Niño Southern Oscillation (ENSO), which are associated with severe drought in eastern Amazonia, and non‐ENSO years.Most (91%) of the forest area that burned during the 10‐yr sequence caught fire during ENSO years, when severe drought may have increased both forest flammability and the escape of agricultural management fires. Forest understory fires were associated with forest edges, as reported in previous studies from Amazonia. But the strongest predictor of forest fire was the percentage of the forest fragment that had been previously logged or burned. Forest fragment size, distance to charcoal pits, distance to agricultural settlements, proximity to forest edge, and distance to roads were also correlated with forest understory fire. Logistic regression models using information on fragment degradation and distance to ignition sources accurately predicted the location of >80% of the forest fires observed during the ENSO event of 1997–1998. In this Amazon landscape, forest understory fire is a complex function of several variables that influence both the flammability and ignition exposure of the forest.
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
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
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.
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.
EFFECT OF ROADSIDE BIAS ON THE ACCURACY OF PREDICTIVE MAPS PRODUCED BY BIOCLIMATIC MODELS
Authors: Kadmon Ronen , Farber Oren , Danin Avinoam 
Published: June 2007

Sampling bias is a common phenomenon in records of plant and animal distribution. Yet, models based on such records usually ignore the potential implications of bias in data collection on the accuracy of model predictions. This study was designed to investigate the effect of roadside bias, one of the most common sources of bias in biodiversity databases, on the accuracy of predictive maps produced by bioclimatic models. Using data on the distribution of 129 species of woody plants in Israel, we tested the following hypotheses: (1) that data collected on woody plant distribution in Israel suffer from roadside bias, (2) that such bias affects the accuracy of model predictions, (3) that the road network of Israel is biased with respect to climatic conditions, and (4) that the impact of roadside bias on model predictions depends on the magnitude of climatic bias in the geographic distribution of the road network.As expected, the frequency of plant observations near roads was consistently greater than that expected from a spatially random distribution. This bias was most pronounced at distances of 500–2000 m from roads, but it was statistically significant also at larger scales. Predictive maps based on near‐road observations were less accurate than those based on off‐road or “rectified” observations (observations corrected for roadside bias). However, the magnitude of these differences was extremely low, indicating that even a strong bias in the distribution of species observations does not necessarily deteriorate the accuracy of predictive maps generated by bioclimatic models. Further analysis of the data indicated that the road network of Israel is relatively unbiased in terms of temperature, and only weakly biased in terms of rainfall conditions. The overall results are consistent with the hypothesis that the impact of roadside bias on model predictions depends on the magnitude of climatic bias in the geographic distribution of the road network. We discuss some theoretical and practical considerations of bias correction in biodiversity databases.
A MODEL‐FRAMED EVALUATION OF ELEPHANT EFFECTS ON TREE AND FIRE DYNAMICS IN AFRICAN SAVANNAS
Authors: Baxter Peter W. J. , Getz Wayne M. 
Published: June 2007

There is a concern that high densities of elephants in southern Africa could lead to the overall reduction of other forms of biodiversity. We present a grid‐based model of elephant–savanna dynamics, which differs from previous elephant–vegetation models by accounting for woody plant demographics, tree–grass interactions, stochastic environmental variables (fire and rainfall), and spatial contagion of fire and tree recruitment. The model projects changes in height structure and spatial pattern of trees over periods of centuries. The vegetation component of the model produces long‐term tree–grass coexistence, and the emergent fire frequencies match those reported for southern African savannas.Including elephants in the savanna model had the expected effect of reducing woody plant cover, mainly via increased adult tree mortality, although at an elephant density of 1.0 elephant/km2, woody plants still persisted for over a century. We tested three different scenarios in addition to our default assumptions. (1) Reducing mortality of adult trees after elephant use, mimicking a more browsing‐tolerant tree species, mitigated the detrimental effect of elephants on the woody population. (2) Coupling germination success (increased seedling recruitment) to elephant browsing further increased tree persistence, and (3) a faster growing woody component allowed some woody plant persistence for at least a century at a density of 3 elephants/km2. Quantitative models of the kind presented here provide a valuable tool for exploring the consequences of management decisions involving the manipulation of elephant population densities.
IDENTIFYING THE MINIMAL DEMOGRAPHIC UNIT FOR MONITORING POND‐BREEDING AMPHIBIANS
Authors: Petranka James W. , Smith Charles K. , Floyd Scott A. 
Published: June 2007

Amphibians are declining globally, and efforts are underway to establish long‐term programs to monitor population trends. Because researchers are constrained to sampling a small subset of populations that occur across a landscape, monitoring units should be selected that maximize the statistical independence of population responses to environmental stressors. Breeding sites of pond‐breeding amphibians are often clustered locally, and habitat switching between neighboring ponds could significantly compromise both demographic and statistical independence. This raises a fundamental issue of whether the basic monitoring unit for trend analysis should be an individual pond or a cluster of local ponds. To help resolve the degree of demographic independence within a cluster of local ponds, we conducted a spatial‐scale analysis of breeding‐population synchrony of the wood frog (Rana sylvatica) and spotted salamander (Ambystoma maculatum) in four national parks in Kentucky, North Carolina, and Tennessee, USA. We used the number of egg masses deposited annually from 1993 through 2002 as an index of relative breeding‐population size and used correlation coefficients of annual percentage change in population size as an index of synchrony.Within parks, synchrony for both species was independent of the distance between ponds and was lower between paired ponds within a local cluster compared with paired comparisons of geographically isolated groups. These patterns indicate a lack of demographic independence within clusters and are consistent with field observations of wholesale shifting of local pond populations to adjoining ponds. Habitat shifting occurred primarily in response to beaver activity that created new ponds or allowed fish to invade fish‐free habitats. Ambystoma maculatum shifted habitats less frequently and exhibited higher levels of within‐cluster population synchrony than R. sylvatica. Turnovers occurred for local pond populations for both species and at higher rates for R. sylvatica. However, no local pond cluster experienced a turnover event during the study. Our data suggest that pond populations that are only a few hundred meters apart are not demographically independent and are best treated as subpopulations of the same monitoring unit. We discuss the implications of these findings for amphibian‐monitoring programs that are designed to assess population trends.
RAPID EVOLUTION OF AN INVASIVE PLANT
Authors: Maron John L. , Vilà Montserrat , Bommarco Riccardo , Elmendorf Sarah , Beardsley Paul 
Published: June 2007

Exotic plants often face different conditions from those experienced where they are native. The general issue of how exotics respond to unfamiliar environments within their new range is not well understood. Phenotypic plasticity has historically been seen as the primary mechanism enabling exotics to colonize large, environmentally diverse areas. However, new work indicates that exotics can evolve quickly, suggesting that contemporary evolution may be more important in invasion ecology than previously appreciated. To determine the influence of contemporary evolution, phenotypic plasticity, and founder effects in affecting phenotypic variation among introduced plants, we compared the size, fecundity, and leaf area of St. John's wort (Hypericum perforatum) collected from native European and introduced western and central North American populations in common gardens in Washington, California, Spain, and Sweden. We also determined genetic relationships among these plants by examining variation in amplified fragment length polymorphism (AFLP) markers.There was substantial genetic variation among introduced populations and evidence for multiple introductions of H. perforatum into North America. Across common gardens introduced plants were neither universally larger nor more fecund than natives. However, within common gardens, both introduced and native populations exhibited significant latitudinally based clines in size and fecundity. Clines among introduced populations broadly converged with those among native populations. Introduced and native plants originating from northern latitudes generally outperformed those originating from southern latitudes when grown in northern latitude gardens of Washington and Sweden. Conversely, plants from southern latitudes performed best in southern gardens in Spain and California. Clinal patterns in leaf area, however, did not change between gardens; European and central North American plants from northern latitudes had larger leaves than plants from southern latitudes within these regions in both Washington and California, the two gardens where this trait was measured. Introduced plants did not always occur at similar latitudes as their most closely related native progenitor, indicating that pre‐adaptation (i.e., climate matching) is unlikely to be the sole explanation for clinal patterns among introduced populations. Instead, results suggest that introduced plants are evolving adaptations to broad‐scale environmental conditions in their introduced range.
LONG‐TERM ASSESSMENT OF TEMPERATE OCTOCORAL MORTALITY PATTERNS, PROTECTED VS. UNPROTECTED AREAS
Authors: Coma Rafel , Pola Emilià , Ribes Marta , Zabala Mikel 
Published: June 2007

Coastal marine protected areas (MPAs) are usually established with an aim to protect areas of special ecological value. However, protected areas tend to attract more tourism and associated recreational activities, thereby exposing the biota to new risks such as high diving activity. The effects of these drawbacks are still little known for low‐dynamic systems such as one of the most characteristic and fragile Mediterranean communities, the coralligenous community. Mortality rates were assessed in both heavily dived and lightly dived areas to evaluate the effect of diving on the survival of the gorgonian Paramuricea clavata. The study was designed to distinguish human‐induced causes from natural causes of gorgonian mortality and to provide criteria for sustainable management of protected areas. We examined total and partial mortality of adult colonies (>10 cm in height) at four locations, two each representing one of the two situations, heavily dived (MPA) and lightly dived (control), annually over a 9‐yr period (1992–2000).High levels of recreational activity did not affect the degree of injury of the colonies. On average, the proportion of live tissue of the colonies remained steady at ∼91%. Colony death by detachment was the main source of mortality at the MPA, four times higher than death due to overgrowth. Mortality rate due to overgrowth remained constant at both areas with an average of 1.2%/yr. Natural mortality rate in sites with low diving activity was estimated to be about 2.7%/yr, whereas high diving activity was estimated to increase the natural mortality rate of the species by a factor of three, up to ∼7.4%/yr. The demographic characteristics of long‐lived low‐turnover structural components of ecosystems makes them especially vulnerable to disturbance events. Since an increase in diving activity seems to be unavoidably brought about by the creation of any MPA, strict regulation of recreational activity must be guaranteed in areas with low‐turnover communities.