Showing papers in "Ecological Applications in 2005"
TL;DR: A spatially detailed assessment of the wildland-urban interface across the United States is conducted to provide a framework for scientific inquiries into housing growth effects on the environment and to inform both national policymakers and local land managers about the WUI and associated issues.
Abstract: The wildland-urban interface (WUI) is the area where houses meet or intermingle with undeveloped wildland vegetation. The WUI is thus a focal area for human-environment conflicts, such as the destruction of homes by wildfires, habitat fragmentation, introduction of exotic species, and biodiversity decline. Our goal was to conduct a spatially detailed assessment of the WUI across the United States to provide a framework for scientific inquiries into housing growth effects on the environment and to inform both national policymakers and local land managers about the WUI and associated issues. The WUI in the conterminous United States covers 719 156 km? (9% of land area) and contains 44.8 million housing units (39% of all houses). WUI areas are particularly widespread in the eastern United States, reaching a maximum of 72% of land area in Connecticut. California has the highest number of WUI housing units (5.1 million). The extent of the WUI highlights the need for ecological principles in land-use planning as well as sprawl-limiting policies to adequately address both wildfire threats and conservation problems.
906 citations
TL;DR: In this paper, the authors synthesize the dominant spatial and temporal trends in population, agriculture, and urbanized land uses, using a variety of data sources and an ecoregion classification as a frame of reference.
Abstract: In order to understand the magnitude, direction, and geographic distribution of land-use changes, we evaluated land-use trends in U.S. counties during the latter half of the 20th century. Our paper synthesizes the dominant spatial and temporal trends in population, agriculture, and urbanized land uses, using a variety of data sources and an ecoregion classification as a frame of reference. A combination of increasing attractiveness of nonmetropolitan areas in the period 1970-2000, decreasing household size, and de- creasing density of settlement has resulted in important trends in the patterns of developed land. By 2000, the area of low-density, exurban development beyond the urban fringe occupied nearly 15 times the area of higher density urbanized development. Efficiency gains, mechanization, and agglomeration of agricultural concerns has resulted in data that show cropland area to be stable throughout the Corn Belt and parts of the West between 1950 and 2000, but decreasing by about 22% east of the Mississippi River. We use a regional case study of the Mid-Atlantic and Southeastern regions to focus in more detail on the land-cover changes resulting from these dynamics. Dominating were land-cover changes associated with the timber practices in the forested plains ecoregions and urban- ization in the piedmont ecoregions. Appalachian ecoregions show the slowest rates of land- cover change. The dominant trends of tremendous exurban growth, throughout the United States, and conversion and abandonment of agricultural lands, especially in the eastern United States, have important implications because they affect large areas of the country, the functioning of ecological systems, and the potential for restoration.
739 citations
TL;DR: In this article, the authors examined the patterns of biodiversity response and the ecological mechanisms that may underlie these responses and found that many native species have reduced survival and reproduction near homes, and native species richness often drops with increased exurban densities.
Abstract: Low-density rural home development is the fastest-growing form of land use in the United States since 1950. This ''exurban'' development ( ;6-25 homes/km 2 ) includes urban fringe development (UFD) on the periphery of cities and rural residential development (RRD) in rural areas attractive in natural amenities. This paper synthesizes current knowl- edge on the effects of UFD and RRD. We present two case studies and examine the patterns of biodiversity response and the ecological mechanisms that may underlie these responses. We found that many native species have reduced survival and reproduction near homes, and native species richness often drops with increased exurban densities. Exotic species, some human-adapted native species, and species from early successional stages often in- crease with exurban development. These relationships are sometimes nonlinear, with sharp thresholds in biodiversity response. These effects may be manifest for several decades following exurban development, so that biodiversity is likely still responding to the wave of exurban expansion that has occurred since 1950. The location of exurban development is often nonrandom relative to biodiversity because both are influenced by biophysical factors. Consequently, the effects on biodiversity may be disproportionately large relative to the area of exurban development. RRD is more likely than UFD to occur near public lands; hence it may have a larger influence on nature reserves and wilderness species. The ecological mechanisms that may underlie these responses involve alteration of habitat, ecological processes, biotic interactions, and increased human disturbance. Research on the patterns and mechanisms of biodiversity remains underdeveloped, and comparative and experimental studies are needed. Knowledge resulting from such studies will increase our ability to understand, manage, and mitigate negative impacts on biodiversity.
706 citations
TL;DR: In this paper, the authors used multiple sources of satellite data to estimate the extent of forest habitat and loss over the last 20 years within and surrounding 198 of the most highly protected areas (IUCN status 1 and 2) located throughout the world's tropical forests.
Abstract: 4 UNEP World Conservation Monitoring Centre, Cambridge, UK Abstract. Protected areas are one of the cornerstones for conserving the world's re- maining biodiversity, most of which occurs in tropical forests. We use multiple sources of satellite data to estimate the extent of forest habitat and loss over the last 20 years within and surrounding 198 of the most highly protected areas (IUCN status 1 and 2) located throughout the world's tropical forests. In the early 1980s, surrounding habitat in the 50- km unprotected or less highly protected ''buffers'' enhanced the protected areas' effective size and their capacity to conserve richness of forest-obligate species above the hypothetical case of complete isolation. However, in nearly 70% of the surrounding buffers, the area of forest habitat declined during the last 20 years, while 25% experienced declines within their administrative boundaries. The loss of habitat occurred in all tropical regions, but protected areas in South and Southeast Asia were most severely affected because of rela- tively low surrounding forest habitat in the early 1980s and high subsequent loss, particularly in dry tropical forests. The future ability of protected areas to maintain current species richness depends on integrating reserve management within the land use dynamics of their larger regional settings.
702 citations
TL;DR: In this article, a review of existing fire management policies and their impact on fire man- agement is presented, and several changes and re-emphases in existing policy are warranted.
Abstract: Forest-fire policy of U.S. federal agencies has evolved from the use of small patrols in newly created National Parks to diverse policy initiatives and institutional ar- rangements that affect millions of hectares of forests. Even with large expenditures and substantial infrastructure dedicated to fire suppression, the annual area burned by wildfire has increased over the last decade. Given the current and future challenges of fire man- agement, and based on analytical research and review of existing policies and their im- plications, we believe several changes and re-emphases in existing policy are warranted. Most importantly, the actual goal of fuels-management projects should be the reduction of potential fire behavior and effects, not the simple reduction of fuels. To improve safety and economic efficiency, fire-suppression policies should recognize differences in the charac- teristics of wildfires, and strategies should be tailored to better respond to the unique demands of each fire. Where forest fires are burning large areas, as in the western United States, reducing the trend of increased amounts of burned area may require a diversity of treatments, including prescribed burning, mechanical fuels treatment, and increased use of the Wildland Fire Use Policy. Assessment of how fire is affecting forests would be enhanced if land-management agencies reported the area burned by low-, mixed-, and high-severity fire and what proportion is outside the desired trend or range of conditions for each forest type. Congress should provide an improved budgetary process for fire and fuels manage- ment, with a larger annual federal fire-suppression budget. Additionally, reducing annual area burned will require long-term coordinated efforts by federal and state governments, with robust partnerships between land-management agencies and the public in collaborative planning and stewardship. Research and adaptive management are essential in allowing fire-hazard-reduction projects to move forward where proposed projects are met with un- certainty and mistrust. While legislative reform may be desirable, a strategy that is not entirely dependent on new legislation is needed. Building on existing programs that are consistent with a science-based strategy will enable land-management agencies to better utilize information in pursuit of the overall objective of reducing uncharacteristically severe wildfires. Key words: fire hazard; fire suppression; forest policy; fuels management; U.S. government
573 citations
TL;DR: A recent latitudinal and altitudinal expansion of the pine processionary moth, Thaumetopoea pityocampa, whose larvae build silk nests and feed on pine foliage in the winter is reported, attributed to increased winter survival due to a warming trend over the past three decades.
Abstract: Global warming is predicted to cause distributional changes in organisms whose geographic ranges are controlled by temperature. We report a recent latitudinal and altitudinal expansion of the pine processionary moth, Thaumetopoea pityocampa, whose larvae build silk nests and feed on pine foliage in the winter. In north-central France (Paris Basin), its range boundary has shifted by 87 km northwards between 1972 and 2004; in northern Italy (Alps), an altitudinal shift of 110–230 m upwards occurred between 1975 and 2004. By experimentally linking winter temperature, feeding activity, and survival of T. pityocampa larvae, we attribute the expansions to increased winter survival due to a warming trend over the past three decades. In the laboratory we determined the minimum nest and night air temperatures required for larval feeding and developed a mechanistic model based on these temperature thresholds. We tested the model in a translocation experiment that employed natural temperature gradients as spatial an...
530 citations
TL;DR: In this article, the authors used a stream-monitoring data set collected from the Coastal Plain of Maryland, USA to address analytical challenges presented by collinearity of land-cover class percentages, spatial autocorrelation of land cover and stream data, intercorrelations among and spatial auto-correlation within abiotic intermediaries that link land cover to stream biota, and spatial arrangement of landcover within watersheds.
Abstract: Watershed land cover is widely used as a predictor of stream-ecosystem condition. However, numerous spatial factors can confound the interpretation of correlative analyses between land cover and stream indicators, particularly at broad spatial scales. We used a stream-monitoring data set collected from the Coastal Plain of Maryland, USA to address analytical challenges presented by (1) collinearity of land-cover class percentages, (2) spatial autocorrelation of land cover and stream data, (3) intercorrelations among and spatial autocorrelation within abiotic intermediaries that link land cover to stream biota, and (4) spatial arrangement of land cover within watersheds. We focused on two commonly measured stream indicators, nitrate-nitrogen (NO3–N) and macroinvertebrate assemblages, to evaluate how different spatial considerations may influence results. Partial correlation analysis of land-cover percentages revealed that simple correlations described relationships that could not be separated from the effe...
515 citations
TL;DR: In this article, a modification of the original MSL model is proposed to encompass a wider range of real situations and to place it within the context of the state-and-transition (S-T) model.
Abstract: Two independent models concerning the effects of grazing on vegetation have gained wide acceptance in the last decade: Westoby et al.'s state-and-transition (S– T) model, and Milchunas et al.'s generalized model of the effects of grazing on plant community structure and diversity (MSL model). These two prevailing models, as they stand, are conceptually divergent. The MSL model implicitly assumes that, at a given site, for each grazing intensity there is a single equilibrium situation with a single diversity value. The S–T model suggests that rangeland dynamics include irreversible transitions and alternative equilibria. Here we propose a modification of the original MSL model, to encompass a wider range of real situations and to place it within the context of the S–T model. The four extreme cases proposed in the original MSL model are revisited, taking into account that (1) the “moisture” gradient can be generalized as a “productivity” gradient; (2) the selective pressure of herbivores on systems with lon...
418 citations
TL;DR: The authors explored the effect of burning on grazing activity, and the persistence of grazed patches, in a landscape-level experiment in a South African savanna, and showed that fire history was an important predictor of grazing-lawn distributions.
Abstract: The effects of fire–grazing interactions on grass communities are difficult to identify because fire and grazing influence each other on a landscape scale. Persistent heavy grazing can prevent the spread of fire by breaking up the grass layer. In contrast, frequent burning might inhibit the persistence of grazed patches by attracting grazers to the post-burn green flush. We explored the effect of burning on grazing activity, and the persistence of grazed patches, in a landscape-level experiment in a South African savanna.
We created 17 grazed patches by mowing grass in a 20 m diameter plot, with an adjacent un-mown control. We used dung counts as a measure of grazer visitation, and grass height as a measure of grazing intensity, at each of the sites over a year. Nearly all mowing treatments resulted in a rapid increase in grazing activity relative to controls (on average, 4–6 times more dung was found on mown sites). Subsequent fates of the grazed patches depended on their location with respect to fire. Burned areas drew animals off nearby unburned grazed patches, which then recovered lost biomass. Patches >1.5 km from burns remained grazed short. Frequent large fires might prevent areas of heavy grazing from persisting in the landscape, and thus limit the spread of grazing-adapted grasses.
Spatial information on fire frequencies in the park was used to explore the influence that the “magnet effect” of fire can have on grass communities. We mapped the distribution of tall, bunch grasslands and grazing-lawn grasslands using a 1999 Landsat TM satellite image. The extent of grazing lawns was directly related to fire return interval. Areas with a fire return of <4 years had less lawn grass than would be expected from the proportions of lawn grass in the park. A logistic regression analysis, which used various environmental variables known to influence grazing, showed fire history to be an important predictor of grazing-lawn distributions.
This work shows that, by influencing where, when, and for how long animals graze a patch, fire can influence the competitive balance between grazing-tolerant, and grazing-intolerant grass species and affect their distributions in the landscape. We discuss the implications of this research for the management of natural grazing systems and rangelands.
417 citations
TL;DR: Roundup, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines, including post-metamorphic amphibians.
Abstract: The global decline in amphibian diversity has become an international en- vironmental problem with a multitude of possible causes. There is evidence that pesticides may play a role, yet few pesticides have been tested on amphibians. For example, Roundup is a globally common herbicide that is conventionally thought to be nonlethal to amphibians. However, Roundup has been tested on few amphibian species, with existing tests conducted mostly under laboratory conditions and on larval amphibians. Recent laboratory studies have indicated that Roundup may be highly lethal to North American tadpoles, but we need to determine whether this effect occurs under more natural conditions and in post-meta- morphic amphibians. I assembled communities of three species of North American tadpoles in outdoor pond mesocosms that contained different types of soil (which can absorb the pesticide) and applied Roundup as a direct overspray. After three weeks, Roundup killed 96-100% of larval amphibians (regardless of soil presence). I then exposed three species of juvenile (post-metamorphic) anurans to a direct overspray of Roundup in laboratory containers. After one day, Roundup killed 68-86% of juvenile amphibians. These results suggest that Roundup, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines.
414 citations
TL;DR: It is shown that different management decisions may result when uncertainty in utilities and probabilities are considered in decision-making problems and the importance of a full assessment of uncertainty in conservation management decisions is highlighted.
Abstract: In conservation biology it is necessary to make management decisions for endangered and threatened species under severe uncertainty. Failure to acknowledge and treat uncertainty can lead to poor decisions. To illustrate the importance of considering uncertainty, we reanalyze a decision problem for the Sumatran rhino, Dicerorhinus sumatrensis, using information-gap theory to propagate uncertainties and to rank management options. Rather than requiring information about the extent of parameter uncertainty at the outset, information-gap theory addresses the question of how much uncertainty can be tolerated before our decision would change. It assesses the robustness of decisions in the face of severe uncertainty. We show that different management decisions may result when uncertainty in utilities and probabilities are considered in decision-making problems. We highlight the importance of a full assessment of uncertainty in conservation management decisions to avoid, as much as possible, undesirable outcomes.
TL;DR: In this paper, the authors presented maps of N deposition fluxes from site-network observations for the United States and Western Europe, and estimated dry N de-position fluxes by multiplying interpolated surface-air concentrations for each chemical species by model-calculated, spatially explicit deposition velocities.
Abstract: The documented acceleration of NH3 and NOx (NO NO2) emissions over the last 150 years has accelerated N deposition, compromising air and water quality and altering the functioning of terrestrial and aquatic ecosystems worldwide. To construct con- tinental-scale N budgets, we produced maps of N deposition fluxes from site-network observations for the United States and Western Europe. Increases in the rates of N cycling for these two regions of the world are large, and they have undergone profound modification of biospheric-atmospheric N exchanges, and ecosystem function. The maps are necessarily restricted to the network measured quantities and consist of statistically interpolated fields of aqueous NO3 and NH4, gaseous HNO3 and NO2 (in Europe), and particulate NO3 and NH4. There remain a number of gaps in the budgets, including organic N and NH3 de- position. The interpolated spatially continuous fields allow estimation of regionally inte- grated budget terms. Dry-deposition fluxes were the most problematic because of low station density and uncertainties associated with exchange mechanisms. We estimated dry N de- position fluxes by multiplying interpolated surface-air concentrations for each chemical species by model-calculated, spatially explicit deposition velocities. Deposition of the ox- idized N species, by-products of fossil-fuel combustion, dominate the U.S. N deposition budget with 2.5 Tg of NOy-N out of a total of 3.7-4.5 Tg of N deposited annually onto the conterminous United States. Deposition of the reduced species, which are by-products of farming and animal husbandry, dominate the Western European N-deposition budget with a total of 4.3-6.3 Tg N deposited each year out of a total of 8.4-10.8 Tg N. Western Europe receives five times more N in precipitation than does the conterminous United States. Estimated N emissions exceed measured deposition in the United States by 5.3- 7.81 Tg N, suggesting significant N export or under-sampling of urban influence. In Europe, estimated emissions better balance measured deposition, with an imbalance of between 0.63 and 2.88 Tg N, suggesting that much of the N emitted in Europe is deposited there, with possible N import from the United States. The sampling network in Europe includes urban influences because of the greater population density of Western Europe. Our analysis of N deposition for both regions was limited by sampling density. The framework we present for quantification of patterns of N deposition provides a constraint on our under- standing of continental biospheric-atmospheric N cycles. These spatially explicit wet and dry N fluxes also provide a tool for verifying regional and global models of atmospheric chemistry and transport, and they represent critical inputs into terrestrial models of bio- geochemistry.
TL;DR: GEOs should be evaluated and used within the context of a scientifically based regulatory policy that encourages innovation without compromising sound environmental management, and science-based regulation should subject all transgenic organisms to a similar risk assessment framework.
Abstract: The Ecological Society of America has evaluated the ecological effects of current and potential uses of field-released genetically engineered organisms (GEOs), as described in this Position Paper. Some GEOs could play a positive role in sustainable agriculture, forestry, aquaculture, bioremediation, and environmental management, both in developed and developing countries. However, deliberate or inadvertent releases of GEOs into the environment could have negative ecological effects under certain circumstances.
Possible risks of GEOs could include: (1) creating new or more vigorous pests and pathogens; (2) exacerbating the effects of existing pests through hybridization with related transgenic organisms; (3) harm to nontarget species, such as soil organisms, non-pest insects, birds, and other animals; (4) disruption of biotic communities, including agroecosystems; and (5) irreparable loss or changes in species diversity or genetic diversity within species. Many potential applications of genetic engineering extend beyond traditional breeding, encompassing viruses, bacteria, algae, fungi, grasses, trees, insects, fish, and shellfish. GEOs that present novel traits will need special scrutiny with regard to their environmental effects.
The Ecological Society of America supports the following recommendations. (1) GEOs should be designed to reduce environmental risks. (2) More extensive studies of the environmental benefits and risks associated with GEOs are needed. (3) These effects should be evaluated relative to appropriate baseline scenarios. (4) Environmental release of GEOs should be prevented if scientific knowledge about possible risks is clearly inadequate. (5) In some cases, post-release monitoring will be needed to identify, manage, and mitigate environmental risks. (6) Science-based regulation should subject all transgenic organisms to a similar risk assessment framework and should incorporate a cautious approach, recognizing that many environmental effects are GEO- and site-specific. (7) Ecologists, agricultural scientists, molecular biologists, and others need broader training and wider collaboration to address these recommendations.
In summary, GEOs should be evaluated and used within the context of a scientifically based regulatory policy that encourages innovation without compromising sound environmental management. The Ecological Society of America is committed to providing scientific expertise for evaluating and predicting the ecological effects of field-released transgenic organisms.
TL;DR: In this paper, the authors developed a spatially explicit model for analyzing the consequences of alternative land-use patterns on the per-sistence of various species and on market-oriented economic returns.
Abstract: Habitat loss and fragmentation are major threats to biodiversity. Establishing formal protected areas is one means of conserving habitat, but socio-economic and political constraints limit the amount of land in such status. Addressing conservation issues on lands outside of formal protected areas is also necessary. In this paper we develop a spatially explicit model for analyzing the consequences of alternative land-use patterns on the per- sistence of various species and on market-oriented economic returns. The biological model uses habitat preferences, habitat area requirements, and dispersal ability for each species to predict the probability of persistence of that species given a land-use pattern. The eco- nomic model uses characteristics of the land unit and location to predict the value of commodity production given a land-use pattern. We use the combined biological and eco- nomic model to search for efficient land-use patterns in which the conservation outcome cannot be improved without lowering the value of commodity production. We illustrate our methods with an example that includes three alternative land uses, managed forestry, agriculture, and biological reserve (protected area), for a modeled landscape whose physical, biological, and economic characteristics are based on conditions found in the Willamette Basin in Oregon (USA). We find that a large fraction of conservation objectives can be achieved at little cost to the economic bottom line with thoughtful land-use planning. The degree of conflict between conservation and economic returns appears much less using our joint biological and economic modeling approach than using a reserve-site selection ap- proach, which assumes that species survive only inside of reserves and economic activity occurs only outside of reserves.
TL;DR: In this article, the authors used 10-minute point counts and collected vegetation data from 13 burned and 13 unburned transects for five years before and three years after a severe fire in the Bitterroot Valley, Montana.
Abstract: Fire can cause profound changes in the composition and abundance of plant and animal species, but logistics, unpredictability of weather, and inherent danger make it nearly impossible to study high-severity fire effects experimentally. We took advantage of a unique opportunity to use a before-after/control-impact (BACI) approach to analyze changes in bird assemblages after the severe fires of 2000 in the Bitterroot Valley, Montana. Observers surveyed birds using 10-minute point counts and collected vegetation data from 13 burned and 13 unburned transects for five years before fire and three years after fire. We compared changes in vegetation variables and relative bird abundance from before to after fire between the set of points that burned and the set of points that did not burn. The magnitude of change in vegetation variables from before to after fire increased with fire severity. The relative abundances of nine bird species showed significantly greater changes from before to after fire at burned points compared with unburned points. Moreover, when burned points were separated by whether they burned at low, moderate, or high severity, an additional 10 species showed significant changes in relative abundance from before to after fire at one or more severities. Overall, almost twice as many bird species increased as decreased significantly in response to fire. We also found changes in abundance between one year after and two years after fire for most species that responded to fire. Thus, species that have been termed ''mixed responders'' in the literature appear to be responding dif- ferently to different fire severities or different time periods since fire, rather than responding variably to the same fire conditions. These findings underscore the importance of fire severity and time since fire and imply that both factors must be considered to understand the complexities of fire effects on biological communities. Because different bird species re- sponded positively to different fire severities, our results suggest a need to manage public lands for the maintenance of all kinds of fires, not just the low-severity, understory burns that dominate most discussions revolving around the use of fire in forest restoration.
TL;DR: In this article, the authors investigate the patterns of stream macroinvertebrate community structure along a gradient of agriculture to urban development, and the patterns among urban streams that vary in the amount of intact riparian buffer.
Abstract: The urbanization of agricultural lands is currently one of the dominant pat- terns of land use change in developed countries. In the United States and parts of Europe, this has led to the implementation of agricultural land preservation programs and riparian protection and replanting efforts along urban streams. The ecological benefits of such programs for the conservation of freshwater biodiversity have yet to be fully explored. We designed a study to investigate the patterns of stream macroinvertebrate community structure along a gradient of agriculture to urban development, and the patterns among urban streams that vary in the amount of intact riparian buffer. In 2001 and 2002, we sampled the 29 small headwater streams comprising the outlying tributaries of four watersheds just north of Washington, D.C., in Montgomery County, Maryland, USA. This region has had dramatic urban development over the last 50 years, yet significant efforts have been made to maintain riparian buffers and promote preservation of agricultural land. Macroinvertebrate richness was strongly related to land use, with agricultural streams exhibiting the highest macroinvertebrate diversity. Taxa richness was related negatively and linearly (no statistical threshold) to the amount of impervious surface cover. For the urban streams, there was a strong positive relationship between invertebrate diversity and riparian forest cover. Urban streams with high amounts of intact riparian forest exhibited biodiversity levels more comparable to less urban areas despite high amounts of impervious cover in their catchments. The agricultural headwater streams in this study were not only more diverse than the urban headwaters, but their levels of macroinvertebrate diversity were high compared to other published estimates for agricultural streams. These higher richness values may be due to widespread use of ''best management practices'' (BMPs), including no-till farming and the implementation of woody and herbaceous riparian buffers, which may alleviate many acute stressors caused by cultivation. These findings suggest that, if managed properly, the preservation of agricultural land from development may help conserve stream invertebrate biodiversity, and that maintenance of riparian forests even in highly urbanized watersheds may help alleviate ecological disturbances that might otherwise limit macroinvertebrate survival.
TL;DR: This study provides evidence consistent with density-dependent export of a planktivorous reef fish, Naso vlamingii, from a small no-take reserve at Apo Island, Philippines, and represents some of the best evidence available for density- dependent home-range relocation of fish from a no- take reserve.
Abstract: Spillover, the net export of adult fish, is one mechanism by which no-take marine reserves may eventually have a positive influence on adjacent fisheries. Although evidence for spillover has increased recently, mechanisms inducing movement of adult fish from reserve to fished areas are poorly understood. While density-dependent export is a reasonable expectation, given that density of fish targeted by fisheries should increase over time inside well-protected no-take reserves, no study to date has demonstrated development of the process. This study provides evidence consistent with density-dependent export of a planktivorous reef fish, Naso vlamingii, from a small no-take reserve (protected for 20 years) at Apo Island, Philippines. Mean density of N. vlamingii increased threefold inside the reserve between 1983 and 2003. Density approached an asymptote inside the reserve after 15–20 years of protection. Modal size in the reserve increased from 35 to 45 cm total length (TL) over 20 years of protection. In addition, both density and modal size increased outside the reserve close to (200–300 m), but not farther from (300–500 m), the reserve boundary over the 20 years of reserve protection. Movement of adult N. vlamingii across the boundaries of the reserve was rare. Aggressive interactions among adult N. vlamingii were significantly higher (by 3.7 times) inside than outside the reserve. This suggests that density-dependent interactions were more intense inside the reserve. When interacting adults differed in size, the larger individual usually chased away the smaller one. Furthermore, the mean size of adult fish captured by experimental fishing decreased from 35-cm TL 50– 100 m outside the boundary, to 32-cm TL 250–300 m outside the boundary. This represents some of the best evidence available for density-dependent home-range relocation of fish from a no-take reserve.
TL;DR: The results suggest that restoration might have little beneficial effect on biodiversity if the restoration schemes (and the original impact under amelioration) do not affect structural heterogeneity relevant to the target organisms.
Abstract: Restoration schemes often rely on the assumption that enhancing habitat complexity through addition of in-stream structures such as boulders and woody debris leads to increased biodiversity, but evidence for this assumption is scarce. We compared structural heterogeneity and fish and invertebrate diversity at restored, unrestored, and reference sites on tributaries of the Ume River, northern Sweden, where several kilometers of streams have been restored from channelization through placement of boulders into the channel. Structural heterogeneity at the study sites was assessed using a contour tracer at two spatial resolutions likely to be affected by restoration. These are the patch scale (0.7 m), reflecting substratum characteristics, and the reach scale (50 m), reflecting general channel topography. Fish and invertebrate samples collected via electroshocking were used to assess taxonomic richness, taxonomic density, evenness, and assemblage composition at the study sites. Measures of structural heterogeneity were substantially higher at restored relative to channelized sites; however, components of fish and invertebrate diversity were similar between these treatments. At restored sites, measures of structural heterogeneity and fish and invertebrate diversity were consistent with, or slightly exceeded reference levels. This implies that local (patch to reach) heterogeneity did not structure fish and invertebrate assemblages in the study streams. Our results suggest that restoration might have little beneficial effect on biodiversity if the restoration schemes (and the original impact under amelioration) do not affect structural heterogeneity relevant to the target organisms.
TL;DR: Evaluating binomial mixture models using data from the national breeding bird monitoring program in Switzerland, where some 250 1-km2 quadrats are surveyed using the territory mapping method three times during each breeding season finds eight species with contrasting distribution, abundance, and detectability.
Abstract: Abundance estimation in ecology is usually accomplished by capture–recapture, removal, or distance sampling methods. These may be hard to implement at large spatial scales. In contrast, binomial mixture models enable abundance estimation without individual identification, based simply on temporally and spatially replicated counts. Here, we evaluate mixture models using data from the national breeding bird monitoring program in Switzerland, where some 250 1-km2 quadrats are surveyed using the territory mapping method three times during each breeding season. We chose eight species with contrasting distribution (wide–narrow), abundance (high–low), and detectability (easy–difficult). Abundance was modeled as a random effect with a Poisson or negative binomial distribution, with mean affected by forest cover, elevation, and route length. Detectability was a logit-linear function of survey date, survey date-by-elevation, and sampling effort (time per transect unit). Resulting covariate effects and parameter est...
TL;DR: This article used matched case-controlled logistic regression to compare habitat covariates of wolf paths (cases) to multiple paired random locations (controls), emphasizing the differences within pairs of cases and controls rather than differences in their overall distribution, making it useful to assess fine-scale habitat selection and path data.
Abstract: Increasing levels of human activity in mountainous areas have high potential to inhibit animal movement across and among valleys. We examined how wolves respond to roads, trails, and other developments. We recorded the movements of two wolf packs for two winters by following their tracks in the snow and simultaneously recording positions with a hand-held global positioning system. We then used matched case-controlled logistic regression to compare habitat covariates of wolf paths (cases) to multiple paired random locations (controls). This analysis emphasized the differences within pairs of cases and controls, rather than differences in their overall distribution, making it useful to assess fine-scale habitat selection and path data. Both packs selected low elevations, shallow slopes, and southwest aspects. They selected areas within 25 m of roads, trails, and the railway line and more strongly selected low-use roads and trails compared to high-use roads and trails. One pack strongly avoided distances bet...
TL;DR: The results suggest that the invasion of exotic species into hardwood forests alters decomposition and nutrient cycling, irrespective of species-specific litter quality differences between natives and ex- otics.
Abstract: Invasive species can change decomposition rates within an ecosystem by changing the quality of the litter entering a system. It is not known, however, whether or not invasions can also change rates of decomposition irrespective of litter quality. We conducted an experiment to explore the differences in decomposition between leaf litter of native and exotic invasive woody plants and between invaded and uninvaded mesic hard- wood forests on Long Island, New York, USA. We evaluated the mass and nitrogen loss rates from leaf litter of four pairs of native and exotic woody species. Litter from the exotic species decomposed and released nitrogen significantly faster than litter from the native species. The largest differences in decomposition and nitrogen loss occurred between the invaded and uninvaded sites rather than between native and exotic species, with litter of all species types decomposing substantially faster in invaded sites. These results suggest that the invasion of exotic species into hardwood forests alters decomposition and nutrient cycling, irrespective of species-specific litter quality differences between natives and ex- otics.
TL;DR: Bee abundance was greatest in organic fields, followed by conventional fields, and lowest in GM fields, while pollination deficit was greatest on the other side of the spectrum, including organic fields and GM fields.
Abstract: The ecological impacts of agriculture are of concern, especially with genetically modified and other intensive, modern cropping systems, yet little is known about effects on wild bee populations and subsequent implications for pollination. Pollination deficit (the difference between potential and actual pollination) and bee abundance were measured in organic, conventional, and herbicide-resistant, genetically modified (GM) canola fields (Brassica napus and B. rapa) in northern Alberta, Canada, in the summer of 2002. Bee abundance data were collected using pan traps and standardized sweep netting, and pollination deficit was assessed by comparing the number of seeds per fruit from open-pollinated and supplementally pollinated flowers. There was no pollination deficit in organic fields, a moderate pollination deficit in conventional fields, and the greatest pollination deficit in GM fields. Bee abundance was greatest in organic fields, followed by conventional fields, and lowest in GM fields. Overall, there...
TL;DR: In this article, the authors compare a never-grazed grassland in Canyonlands National Park with two historically grazed sites with similar geologic, geomorphic, and geochemical characteristics that were grazed from the late 1800s until 1974.
Abstract: Many soils in southeastern Utah are protected from surface disturbance by biological soil crusts that stabilize soils and reduce erosion by wind and water. When these crusts are disturbed by land use, soils become susceptible to erosion. In this study, we compare a never-grazed grassland in Canyonlands National Park with two historically grazed sites with similar geologic, geomorphic, and geochemical characteristics that were grazed from the late 1800s until 1974. We show that, despite almost 30 years without livestock grazing, surface soils in the historically grazed sites have 38–43% less silt, as well as 14– 51% less total elemental soil Mg, Na, P, and Mn content relative to soils never exposed to livestock disturbances. Using magnetic measurement of soil magnetite content (a proxy for the stabilization of far-traveled eolian dust) we suggest that the differences in Mg, Na, P, and Mn are related to wind erosion of soil fine particles after the historical disturbance by livestock grazing. Historical grazing may also lead to changes in soil organic matter content including declines of 60–70% in surface soil C and N relative to the never-grazed sites. Collectively, the differences in soil C and N content and the evidence for substantial rock-derived nutrient loss to wind erosion implies that livestock grazing could have long-lasting effects on the soil fertility of native grasslands in this part of southeastern Utah. This study suggests that nutrient loss due to wind erosion of soils should be a consideration for management decisions related to the long-term sustainability of grazing operations in arid environments.
TL;DR: Results indicate that Camp Creek coastal cutthroat trout exist as many small, partially independent populations that are strongly affected by genetic drift, and in headwater streams, barriers to movement can result in genetic and demographic isolation leading to reduced genetic diversity, and potentially compromising long-term population persistence.
Abstract: Because human land use activities often result in increased fragmentation of aquatic and terrestrial habitats, a better understanding of the effects of fragmentation on the genetic heterogeneity of animal populations may be useful for effective management. We used eight microsatellites to examine the genetic structure of coastal cutthroat trout (Oncorhynchus clarki clarki) in Camp Creek, an isolated headwater stream in western Oregon. Our objectives were to determine if coastal cutthroat trout were genetically struc- tured within streams and to assess the effects of natural and anthropogenic barriers on coastal cutthroat trout genetic variation. Fish sampling occurred at 10 locations, and allele frequencies differed significantly among all sampling sections. Dispersal barriers strongly influenced coastal cutthroat trout genetic structure and were associated with reduced genetic diversity and increased genetic differentiation. Results indicate that Camp Creek coastal cutthroat trout exist as many small, partially independent populations that are strongly affected by genetic drift. In headwater streams, barriers to movement can result in genetic and demographic isolation leading to reduced coastal cutthroat trout genetic diversity, and potentially compromising long-term population persistence. When habitat fragmentation eliminates gene flow among small populations, similar results may occur in other species.
TL;DR: Environmental realistic concentrations of atrazine and endosulfan influence the structure of a pond community when the presence of common community members was manipulated but the initial composition of the community influenced these pesticide effects.
Abstract: Virtually all species live within complex food webs, and many of these organisms are exposed to contaminants. However, we know little about how community processes, such as competition and predation, influence susceptibility to contaminants or how different types of contaminants shape communities. The objective of our study was to determine how realistic concentrations of the herbicide atrazine and the insecticide endosulfan influence the structure of a pond community when the presence of common community members was manipulated. We employed a factorial design in mesocosms to evaluate the effects of pesticide treatments (25 mg/L of atrazine, 10 mg/L of endosulfan, solvent control; two pulses separated by two weeks) and the presence or absence of wood frog tadpoles (Rana sylvatica), adult snails (Planorbella trivolvis), and caged dragonfly larvae (Anax junius) on a freshwater community. Tadpoles, snails, and chironomid larvae, Polypedilum sp. (Dipterans), all competed for periphyton. As a result, tadpoles reduced the survival, mass, and reproduction of snails; snails reduced the growth, development, inactivity, and dragonfly avoidance of tadpoles; snails and tadpoles reduced the abundance of chironomid larvae; and chironomid larvae reduced snail mass. The adverse effect of snails on tadpole growth and behavior was greater in the presence of the caged tadpole predator, A. junius. Neither pesticide affected dragonfly survival, but endosulfan directly reduced zooplankton (Daphnia), and atrazine indirectly reduced chironomid abundance. Atrazine also directly decreased periphyton, and endosulfan decimated chironomid larvae, resulting in indirect increases and decreases in competition for both snails and tadpoles, respectively. Consequently, relative to endosulfan, atrazine tended to decrease snail mass and reproduction and reduce tadpole mass, development, inactivity, refuge use, and dragonfly avoidance. However, the indirect effects of pesticides depended upon the presence of heterospecifics. The indirect benefit of endosulfan on snail mass was greater in the presence of caged dragonfly larvae, and endosulfan's indirect benefit on tadpole mass was greater in the absence of snails. The effect of pesticides on tadpole activity depended on both caged dragonflies and snails. Thus, environmentally realistic concentrations of pesticides directly and indirectly shaped species responses and community composition, but the initial composition of the community influenced these pesticide effects. These results emphasize the importance of quantifying the effects of contaminants within complex natural communities.
TL;DR: In this paper, the authors used responses from 20 well-recognized ecologists throughout Australia to predict the impact of livestock grazing on birds using a statistical model using Bayesian methods, and found that the addition of expert data through priors strengthened results under at least one grazing level for all but one bird species examined.
Abstract: One of our greatest challenges as researchers is predicting impacts of land use on biota, and predicting the impact of livestock grazing on birds is no exception. Insufficient data and poor survey design often yield results that are not statistically sig- nificant or that are difficult to interpret because researchers cannot disentangle the effects of grazing from other disturbances. This has resulted in few publications on the impact of grazing on birds alone. Ecologists with extensive experience in bird ecology in grazed landscapes could inform an analysis when time and monetary constraints limit the amount of data that can be collected. Using responses from 20 well-recognized ecologists throughout Australia, we captured this expert knowledge and incorporated it into a statistical model using Bayesian methods. Although relatively new to ecology, Bayesian methods allow straightforward probability statements to be made about specific models or scenarios and the integration of different types of information, including scientific judgment, while formally accom- modating and incorporating the uncertainty in the information provided. Data on bird density were collected across three broad levels of grazing (no/low, mod- erate, and high) typical of subtropical Australia. These field data were used in conjunction with expert data to produce estimates of species persistence under grazing. The addition of expert data through priors in our model strengthened results under at least one grazing level for all but one bird species examined. When experts were in agreement credible intervals were tightened substantially, whereas, when experts were in disagreement, results were similar to those evaluated in the absence of expert information. In fields where there is extensive expert knowledge, yet little published data, the use of expert information as priors for ecological models is a cost-effective way of making more confident predictions about the effect of management on biodiversity.
TL;DR: In this article, the authors investigated the extent to which atmospheric and climatic variability may contribute to variability in annual area burned on 20 National Forests in Washington, Oregon, and Idaho.
Abstract: Wildland fire is an important disturbance agent in forests of the American Northwest. Historical fire suppression efforts have contributed to an accumulation of fuels in many Northwestern forests and may result in more frequent and/or more severe wildfire events. Here we investigate the extent to which atmospheric and climatic variability may contribute to variability in annual area burned on 20 National Forests in Washington, Oregon, and Idaho. Empirical orthogonal function (EOF) analysis was used to identify coherent patterns in area burned by wildfire in the Pacific Northwest. Anomaly fields of 500-hPa height were regressed onto the resulting principal-component time series to identify the patterns in atmospheric circulation that are associated with variability in area burned by wildfire. Additionally, cross-correlation functions were calculated for the Palmer drought severity index (PDSI) over the year preceding the wildfire season. Parallel analyses based on superposed epoch analysis focused only on the extreme fire years (both large and small) to discriminate the controls on extreme years from the linear responses identified in the regression analyses. Four distinct patterns in area burned were identified, each associated with distinct climatic processes. Extreme wildfire years are forced at least in part by an- tecedent drought and summertime blocking in the 500-hPa height field. However the re- sponse to these forcings is modulated by the ecology of the dominant forest. In more mesic forest types antecedent drought is a necessary precondition for forests to burn, but it is not a good predictor of area burned due to the rarity of subsequent ignition. At especially dry locations, summertime blocking events can lead to increases in area burned even in the absence of antecedent drought. At particularly xeric locations summertime cyclones can also lead to increased area burned, probably due to dry lightning storms that bring ignition and strong winds but little precipitation. These results suggest that fuels treatments alone may not be effective at reducing area burned under extreme climatic conditions and fur- thermore that anthropogenic climate change may have important implications for forest
TL;DR: Examination of local-scale relationships between native and exotic plant taxa in bunchgrass communities of western Montana, USA found that measures of biotic resistance, or the ability of communities to resist invasions, are weak.
Abstract: In response to the profound threat of exotic species to natural systems, much attention has been focused on the biotic resistance hypothesis, which predicts that diverse communities should better resist invasions. While studies of natural communities generally refute this hypothesis, reporting positive relationships between native species diversity and invasibility, some local-scale studies have instead obtained negative relationships. Most treatments of the topic have failed to recognize that all exotic invaders do not behave alike: while “weak” invaders become minor components of communities, “strong” invaders become community dominants at the expense of native species. At the same time, the specific impacts of strong invaders on communities are poorly documented yet critical to understanding implications of diversity loss. With these shortfalls in mind, we examined local-scale relationships between native and exotic plant taxa in bunchgrass communities of western Montana, USA. We found that measures of...
TL;DR: In this article, the authors used experimental fires together with measurements of micrometeorology (rainfall, vapor pressure deficit (VPD), wind velocity, and canopy attributes (leaf area index (LAI), canopy height), and fuel characteristics (litter moisture content (LMC) and mass) to identify the variables most closely associated with fire susceptibility in the east-central Amazon.
Abstract: Fire is playing an increasing role in shaping the structure, composition, and function of vast areas of moist tropical forest. Within the Brazilian Amazon, cattle ranching and swidden agriculture provide abundant sources of ignition to forests that become sus- ceptible to fire through selective logging, severe drought and, perhaps, fragmentation. Our understanding of the biophysical factors that control fire spread through Amazon forests remains largely anecdotal, however, restricting our ability to model the Amazon fire regime, and to simulate the effects of trends in climate and land-use activities on future regimes. We used experimental fires together with measurements of micrometeorology (rainfall, vapor pressure deficit (VPD), wind velocity), canopy attributes (leaf area index (LAI), canopy height), and fuel characteristics (litter moisture content (LMC) and mass) to identify the variables most closely associated with fire susceptibility in the east-central Amazon. Fire spread rates (FSR, m/min) were measured in three common forest types: an 8-yr-old regrowth forest, a recently logged/burned forest, and a mature forest. One hundred fires were set in each study area during the last two months of the 2002 dry season. VPD, recent precipitation history, wind velocity, and LAI explained 57% of the variability in FSR. In combination, LAI, canopy height, and recent precipitation history accounted for ;65% of the variability in VPD, the single most important predictor of FSR, and approximately half of the total observed variability in FSR. Using logistic regression we were able to predict whether a fire would spread or die 72% of the time based on LAI, canopy height, and recent precipitation history. An approximate threshold in fire susceptibility was associated with a LMC of ;23%, somewhat higher than previously reported (15%). Fire susceptibility was highest under low, sparse canopies, which permitted greater coupling of relatively hot, dry air above the canopy with the otherwise cool, moist air near the forest floor. Fire susceptibility increased over time after rain events as the forest floor gradually dried. The most important determinants of fire susceptibility can be captured in ecosystem and climate models and through remotely sensed estimates of canopy structure, canopy water content, and microclimatic variables.
TL;DR: In this paper, a network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3-6 years prior to sampling, and the sediment cores were collected from the material deposited over the clay pads, which was separated from the clay layer and then dried, weighed and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content.
Abstract: Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hy- drogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3-6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content. Mean C accumulation rates ranged from 61 to 212 g·m 22 ·yr 21 , N accumulation rates ranged from 3.5 to 13.4 g·m 22 ·yr 21 , and P accumulation rates ranged from 0.2 to 4.1 g·m 22 ·yr 21 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metro- politan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels