Showing papers in "Ecological Applications in 2003"

The impact of marine reserves: do reserves work and does reserve size matter?

Abstract: Marine reserves are quickly gaining popularity as a management option for marine conservation, fisheries, and other human uses of the oceans. Despite the popularity of marine reserves as a management tool, few reserves appear to have been created or designed with an understanding of how reserves affect biological factors or how reserves can be designed to meet biological goals more effectively (e.g., attaining sustainable fish populations). This shortcoming occurs in part because the many studies that have examined the impacts of reserves on marine organisms remain isolated examples or anecdotes; the results of these many studies have not yet been synthesized. Here, I review the empirical work and discuss the theoretical literature to assess the impacts of marine reserves on several biological measures (density, biomass, size of organisms, and diversity), paying particular attention to the role reserve size has in determining those impacts. The results of 89 separate studies show that, on average, with the exception of invertebrate biomass and size, values for all four biological measures are significantly higher inside reserves compared to outside (or after reserve establishment vs. before) when evaluated for both the overall communities and by each functional group within these communities (carniv- orous fishes, herbivorous fishes, planktivorous fishes/invertebrate eaters, and invertebrates). Surprisingly, results also show that the relative impacts of reserves, such as the proportional differences in density or biomass, are independent of reserve size, suggesting that the effects of marine reserves increase directly rather than proportionally with the size of a reserve. However, equal relative differences in biological measures between small and large reserves nearly always translate into greater absolute differences for larger reserves, and so larger reserves may be necessary to meet the goals set for marine reserves. The quality of the data in the reviewed studies varied greatly. To improve data quality in the future, whenever possible, studies should take measurements before and after the creation of a reserve, replicate sampling, and include a suite of representative species. Despite the variable quality of the data, the results from this review suggest that nearly any marine habitat can benefit from the implementation of a reserve. Success of a marine reserve, however, will always be judged against the expectations for that reserve, and so we must keep in mind the goals of a reserve in its design, management, and evaluation.

Population genetics, demographic connectivity, and the design of marine reserves

Abstract: Genetic analyses of marine population structure often find only slight geo- graphic differentiation in species with high dispersal potential. Interpreting the significance of this slight genetic signal has been difficult because even mild genetic structure implies very limited demographic exchange between populations, but slight differentiation could also be due to sampling error. Examination of genetic isolation by distance, in which close populations are more similar than distant ones, has the potential to increase confidence in the significance of slight genetic differentiation. Simulations of one-dimensional stepping stone populations with particular larval dispersal regimes shows that isolation by distance is most obvious when comparing populations separated by 2-5 times the mean larval dispersal distance. Available data on fish and invertebrates can be calibrated with this simulation approach and suggest mean dispersal distances of 25-150 km. Design of marine reserve systems requires an understanding of larval transport in and out of reserves, whether reserves will be self-seeding, whether they will accumulate recruits from surrounding exploited areas, and whether reserve networks can exchange recruits. Direct measurements of mean larval dispersal are needed to understand connectivity in a reserve system, but such measurements are extremely difficult. Genetic patterns of isolation by distance have the potential to add to direct measurement of larval dispersal distance and can help set the appropriate geographic scales on which marine reserve systems will function well.

Propagule dispersal distance and the size and spacing of marine reserves

Abstract: This study compiled available information on the dispersal distance of the propagules of benthic marine organisms and used this information in the development of criteria for the design of marine reserves. Many benthic marine organisms release propagules that spend time in the water column before settlement. During this period, ocean currents transport or disperse the propagules. When considering the size of a marine reserve and the spacing between reserves, one must consider the distance which propagules disperse. We could find estimates of dispersal distance for 32 taxa; for 25 of these, we were also able to find data on the time the propagules spent dispersing. Dispersal distance ranged from meters to thousands of kilometers, and time in the plankton ranged from minutes to months. A significant positive correlation was found between the log-transformed duration in the plankton and the log-transformed dispersal distance ( r 5 0.7776, r 2 5 0.60, df 5 1, 25, P 5 0.000); the more time propagules spend in the water column the further they tend to be dispersed. The frequency distribution of the log-transformed dispersal distance is bimodal (kurtosis 52 1.29, t 52 4.062, P , 0.001) with a gap between 1 and 20 km. Propagules that dispersed ,1 km spent less time in the plankton (,100 h), or if they remained in the plankton for a longer period, they tended to remain in the waters near the bottom. Propagules that dispersed .20 km spent more than 300 h in the plankton. The bimodal nature of the distribution suggests that evolutionary constraints may reduce the likelihood of evolving mid-range dispersal strategies (i.e., dispersal between 1 and 20 km) resulting in two evolutionarily stable dispersal strategies: dispersal , 1k m or.;20 km. We suggest that reserves be designed large enough to contain the short-distance dispersing propagules and be spaced far enough apart that long-distance dispersing propagules released from one reserve can settle in adjacent reserves. A reserve 4-6 km in diameter should be large enough to contain the larvae of short-distance dispersers, and reserves spaced 10- 20 km apart should be close enough to capture propagules released from adjacent reserves.

Ecologically sustainable water management: managing river flows for ecological integrity

Abstract: Human demands on the world's available freshwater supplies continue to grow as the global population increases. In the endeavor to manage water to meet human needs, the needs of freshwater species and ecosystems have largely been neglected, and the ecological consequences have been tragic. Healthy freshwater ecosystems provide a wealth of goods and services for society, but our appropriation of freshwater flows must be better managed if we hope to sustain these benefits and freshwater biodiversity. We offer a framework for developing an ecologically sustainable water management program, in which human needs for water are met by storing and diverting water in a manner that can sustain or restore the ecological integrity of affected river ecosystems. Our six-step process includes: (1) developing initial numerical estimates of key aspects of river flow necessary to sustain native species and natural ecosystem functions; (2) accounting for human uses of water, both current and future, through development of a computerized hydrologic simulation model that facilitates examination of human-induced alterations to river flow regimes; (3) assessing incompatibilities between human and ecosystem needs with particular attention to their spatial and temporal character; (4) collaboratively searching for solutions to resolve incompatibilities; (5) conducting water management experiments to resolve critical uncertainties that frustrate efforts to integrate human and ecosystem needs; and (6) designing and implementing an adaptive management program to facilitate ecologically sustainable water management for the long term. Drawing from case studies around the world to illustrate our framework, we suggest that ecologically sustainable water management is attainable in the vast majority of the world's river basins. However, this quest will become far less feasible if we wait until water supplies are further over-appro- priated. Key words: adaptive management; biodiversity; dam operations; ecological flow assessment; ecosystem management; ecosystem monitoring; freshwater ecosystems; hydrologic alteration; instream flow; river management; sustainable water development; water resources management.

Improving precision and reducing bias in biological surveys: estimating false‐negative error rates

Abstract: The use of presence/absence data in wildlife management and biological surveys is widespread. There is a growing interest in quantifying the sources of error associated with these data. We show that false-negative errors (failure to record a species when in fact it is present) can have a significant impact on statistical estimation of habitat models using simulated data. Then we introduce an extension of logistic modeling, the zero-inflated binomial (ZIB) model that permits the estimation of the rate of false-negative errors and the correction of estimates of the probability of occurrence for false-negative errors by using repeated visits to the same site. Our simulations show that even relatively low rates of false negatives bias statistical estimates of habitat effects. The method with three repeated visits eliminates the bias, but estimates are relatively imprecise. Six repeated visits improve precision of estimates to levels comparable to that achieved with conventional statistics in the absence of false-negative errors. In general, when error rates are ≤50% greater efficiency is gained by adding more sites, whereas when error rates are >50% it is better to increase the number of repeated visits. We highlight the flexibility of the method with three case studies, clearly demonstrating the effect of false-negative errors for a range of commonly used survey methods.

Plugging a hole in the ocean: the emerging science of marine reserves1

Abstract: 2Department of Zoology, Oregon State University, Corvallis, Oregon 97331-2914 USA 3Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 USA 4Department of Ecology, Evolution and Marine Biology, University of California at Santa Barbara, Santa Barbara, California 93106 USA WNational Center for Ecological Analysis and'Synthesis, Santa Barbara, California 93101-5504 USA

White-tailed deer impact on the vegetation dynamics of a northern hardwood forest

Abstract: Considerable controversy has arisen over the management of white-tailed deer in eastern landscapes where there is evidence of damage to forest vegetation, crops, and wildlife habitat attributable to deer. We examined the impact of 4, 8, 15, and 25 deer/ km 2 on herbaceous layer abundance and tree seedling density, height development, species composition, and diversity for 10 yr in a repeated-measures randomized-complete-block experiment at four replicate cherry-maple forest sites in northwestern Pennsylvania, USA. At each 65-ha site, deer were placed in 13- or 26-ha fenced enclosures in which the landscape composition and forage production of a forest managed on a 100-yr rotation was simulated by clear-cutting 10% of each area and thinning 30%. Vegetation was sampled 0-1, 3, 5, and 10 yr after treatment (YAT). We analyzed vegetative treatment responses separately in each silvicultural treatment. Time was an important factor mediating responses at all deer densities. Rubus spp. abundance in all silvicultural treatments and the density of striped maple (STM) in clearcuts and birch (BI), American beech (AB), and red maple (RM) in thinnings showed negative trends with increasing deer density. As deer density increased, we found negative linear trends in the height of BI, RM, and AB in clearcuts; in the height of AB, RM, and STM in thinnings; and in the height of AB and RM in uncut stands. Species richness showed a negative linear trend with increasing deer density in all silvicultural treatments. Conversely, species avoided by deer or resilient to deer browsing increased with in- creasing deer density. Percent cover of ferns, grasses, and sedges showed positive linear trends with deer density in clearcuts and in thinnings. The percentage of plots dominated by black cherry (BC) increased with increasing deer density in cut and uncut stands. The net result of increased deer impact was an altered trajectory of vegetation development dominated by species avoided by deer or resilient to deer browsing. Negative effects on vegetation became significant at deer impact levels well below those observed in many eastern forests. Moreover, species not browsed or resilient to browsing may have indirect effects on vegetation development through plant-plant interactions and on wildlife habitat quality for small mammals, birds, and deer. Managing these impacts is important as pressures to harvest and fragment eastern forests accelerate.

Ecological criteria for evaluating candidate sites for marine reserves

Abstract: Several schemes have been developed to help select the locations of marine reserves. All of them combine social, economic, and biological criteria, and few offer any guidance as to how to prioritize among the criteria identified. This can imply that the relative weights given to different criteria are unimportant. Where two sites are of equal value ecologically; then socioeconomic criteria should dominate the choice of which should be protected. However, in many cases, socioeconomic criteria are given equal or greater weight than ecological considerations in the choice of sites. This can lead to selection of reserves with little biological value that fail to meet many of the desired objectives. To avoid such a possibility, we develop a series of criteria that allow preliminary evaluation of candidate sites according to their relative biological values in advance of the application of socioeconomic criteria. We include criteria that,. while not strictly biological, have a strong influence on the species present or ecological processes. Out scheme enables sites to be assessed according to their biodiversity, the processes which underpin that diversity, and the processes that support fisheries and provide a spectrum of other services important to people. Criteria that capture biodiversity values include biogeographic representation, habitat representation and heterogeneity, and presence of species or populations of special interest (e.g., threatened species). Criteria that capture sustainability of biodiversity and fishery values include the size of reserves necessary to protect viable habitats, presence of exploitable species, vulnerable life stages, connectivity among reserves, links among ecosystems, and provision of ecosystem services to people. Criteria measuring human and natural threats enable candidate sites to be eliminated from consideration if risks are too great, but also help prioritize among sites where threats can be mitigated by protection. While our criteria can be applied to the design of reserve networks, they also enable choice of single reserves to be made in the context of the attributes of existing protected areas. The overall goal of our scheme is to promote the development of reserve networks that will maintain biodiversity and ecosystem functioning at large scales. The values of eco-system goods and services for people ultimately depend on meeting this objective.

Principles for the design of marine reserves

Abstract: The theory underlying the design of marine reserves, whether the goal is to preserve biodiversity or to manage fisheries, is still in its infancy. For both of these goals, there is a need for general principles on which to base marine reserve design, and because of the paucity of empirical experience, these principles must be based on models. However, most of the theoretical studies to date have been specific to a single situation, with few attempts to deduce general principles. Here we attempt to distill existing results into general principles useful to designers of marine reserves. To answer the question of how fishery management using reserves compares to conventional management, we provide two prin- ciples: (1) the effect of reserves on yield per recruit is similar to increasing the age of first capture, and (2) the effect of reserves on yield is similar to reducing effort. Another two principles answer the question of how to design reserve configurations so that species with movement in various stages will be sustainable: (3) higher juvenile and adult movement lowers sustainability of reserves for biodiversity, but an intermediate level of adult move- ment is required for reserves for fishery management, and (4) longer larval dispersal distance requires larger reserves for sustainability. These principles provide general guidelines for design, and attention to them will allow more rapid progress in future modeling studies. Whether populations or communities will persist under any specific reserve design is un- certain, and we suggest ways of dealing with that uncertainty.

Comparing marine and terrestrial ecosystems: implications for the design of coastal marine reserves

Abstract: Concepts and theory for the design and application of terrestrial reserves is based on our understanding of environmental, ecological, and evolutionary processes re- sponsible for biological diversity and sustainability of terrestrial ecosystems and how hu- mans have influenced these processes. How well this terrestrial-based theory can be applied toward the design and application of reserves in the coastal marine environment depends, in part, on the degree of similarity between these systems. Several marked differences in ecological and evolutionary processes exist between marine and terrestrial ecosystems as ramifications of fundamental differences in their physical environments (i.e., the relative prevalence of air and water) and contemporary patterns of human impacts. Most notably, the great extent and rate of dispersal of nutrients, materials, holoplanktonic organisms, and reproductive propagules of benthic organisms expand scales of connectivity among near- shore communities and ecosystems. Consequently, the ''openness'' of marine populations, communities, and ecosystems probably has marked influences on their spatial, genetic, and trophic structures and dynamics in ways experienced by only some terrestrial species. Such differences appear to be particularly significant for the kinds of organisms most exploited and targeted for protection in coastal marine ecosystems (fishes and macroinvertebrates). These and other differences imply some unique design criteria and application of reserves in the marine environment. In explaining the implications of these differences for marine reserve design and application, we identify many of the environmental and ecological processes and design criteria necessary for consideration in the development of the ana- lytical approaches developed elsewhere in this Special Issue.

Considerations in estimating larval dispersal distances from oceanographic data

Abstract: Determination of larval dispersal distances and larval origins is a central challenge in contemporary marine ecology. In this work, the larval dispersal problem is discussed from the perspective of oceanography. Following formulation of the advection- diffusion model, the importance of scale is argued. When considering dispersion parameters at the appropriate population scales, advection is usually weaker than initially anticipated (and often used), and diffusion is stronger than typically used in model studies. Focusing attention on coastal populations, the importance of retention zones is described, and the more general existence of a coastal boundary layer is discussed. The coupling of cross- shore and alongshore dispersion results in a nonlinear relation between alongshore dispersal distance and larval planktonic period for dispersion in a sheared flow. Thus, small changes in cross-shore dispersal, whether due to environmental differences or larval behavior result in significant differences in alongshore dispersal. Finally, the interplay between advection and diffusion is explored, showing the importance of adequately representing the diffusive effects that mitigate alongshore advection. In most cases, diffusion acts to prevent ''wash- out'' of a population and allows for more flexibility in the size and spacing of effective marine reserves. Future challenges must bring oceanographers and ecologists together around specific dispersal problems if there is to be a significant improvement in the notable absence of hard data in this field of enquiry.

Population models for marine reserve design: A retrospective and prospective synthesis

Abstract: We synthesize results from existing models of marine reserves to identify key theoretical issues that appear to be well understood, as well as issues in need of further exploration. Models of marine reserves are relatively new in the scientific literature; 32 of the 34 theoretical papers we reviewed were published after 1990. These models have focused primarily on questions concerning fishery management at the expense of other objectives such as conservation, scientific understanding, recreation, education, and tourism. Roughly one-third of the models analyze effects on cohorts while the remaining models have some form of complete population dynamics. Few models explicitly include larval dispersal. In a fisheries context, the primary conclusion drawn by many of the complete population models is that reserves increase yield when populations would otherwise be overfished. A second conclusion, resulting primarily from single-cohort models, is that reserves will provide fewer benefits for species with greater adult rates of movement. Although some models are beginning to yield information on the spatial configurations of reserves required for populations with specific dispersal distances to persist, it remains an aspect of reserve design in need of further analysis. Other outstanding issues include the effects of (1) particular forms of density dependence, (2) multispecies interactions, (3) fisher behavior, and (4) effects of concentrated fishing on habitat. Model results indicate that marine reserves could play a beneficial role in the protection of marine systems against overfishing. Additional modeling and analysis will greatly improve prospects for a better understanding of the potential of marine reserves for conserving biodiversity.

Spatial patterns and controls on historical fire regimes and forest structure in the klamath mountains

Abstract: Fire exclusion in mixed conifer forests has increased the risk of fire due to decades of fuel accumulation. Restoration of fire into altered forests is a challenge because of a poor understanding of the spatial and temporal dynamics of fire regimes. In this study the spatial and temporal characteristics of fire regimes and forest age structure are recon- structed in a 2325-ha mixed conifer forest in the Klamath Mountains. Forests were multiaged and burned frequently at low and moderate severity, but forest age structure did not vary with aspect, elevation, or topographic position. Recently there has been an increase in forest density and a forest compositional shift to shade-tolerant species. Median fire return in- tervals (FRI) ranged from 11.5 to 16.5 yr and varied with aspect but not with forest composition or elevation. The median area burned was 106 ha, and the pre-Euro-American fire rotation of 19 yr increased to 238 yr after 1905. Intra-annual position of fire scars in the tree rings indicates that 93% of fires occurred during the dry midsummer through fall period. Spatial patterns of sites with similar fire dates were spatially coherent and separated from others by topographic features that influence fire spread. Thus, patterns of fire oc- currence tended to be fixed in space with timing of fires varying among groups of sites. Spatial and temporal patterns of fire occurrence suggest that managers using physical fea- tures to contain prescribed fire will create burn patterns consistent with historical fires in the Klamath Mountains.

Application of ecological criteria in selecting marine reserves and developing reserve networks

Abstract: Marine reserves are being established worldwide in response to a growing recognition of the conservation crisis that is building in the oceans. However, designation of reserves has been largely opportunistic, or protective measures have been implemented (often overlapping and sometimes in conflict) by different entities seeking to achieve dif- ferent ends. This has created confusion among both users and enforcers, and the proliferation of different measures provides a false sense of protection where little is offered. This paper sets out a procedure grounded in current understanding of ecological processes, that allows the evaluation and selection of reserve sites in order to develop functional, interconnected networks of fully protected reserves that will fulfill multiple objectives. By fully protected we mean permanently closed to fishing and other resource extraction. We provide a frame- work that unifies the central aims of conservation and fishery management, while also meeting other human needs such as the provision of ecosystem services (e.g., maintenance of coastal water quality, shoreline protection, and recreational opportunities). In our scheme, candidate sites for reserves are evaluated against 12 criteria focused toward sustaining the biological integrity and productivity of marine systems at both local and regional scales. While a limited number of sites will be indispensable in a network, many will be of similar value as reserves, allowing the design of numerous alternative, biologically adequate net- works. Devising multiple network designs will help ensure that ecological functionality is preserved throughout the socioeconomic evaluation process. Too often, socioeconomic cri- teria have dominated the process of reserve selection, potentially undermining their efficacy. We argue that application of biological criteria must precede and inform socioeconomic evaluation, since maintenance of ecosystem functioning is essential for meeting all of the goals for reserves. It is critical that stakeholders are fully involved throughout this process. Application of the proposed criteria will lead to networks whose multifunctionality will help unite the objectives of different management entities, so accelerating progress toward improved stewardship of the oceans.

Wildlife responses to recreation and associated visitor perceptions

Abstract: Outdoor recreation has the potential to disturb wildlife, resulting in energetic costs, impacts to animals' behavior and fitness, and avoidance of otherwise suitable habitat. Mountain biking is emerging as a popular form of outdoor recreation, yet virtually nothing is known about whether wildlife responds differently to mountain biking vs. more traditional forms of recreation, such as hiking. In addition, there is a lack of information on the "area of influence" (within which wildlife may be displaced from otherwise suitable habitat due to human activities) of different forms of recreation. We examined the responses of bison (Bison bison), mule deer (Odocoileus hemionus), and pronghorn antelope (Antilocapra americana) to hikers and mountain bikers at Antelope Island State Park, Utah, by comparing alert distance, flight distance, and distance moved. Within a species, wildlife did not respond differently to mountain biking vs. hiking, but there was a negative relationship between wildlife body size and response. We determined the area of influence along trails and off- trail transects by examining each species' probability of flushing as perpendicular distance away from a trail increased. All three species exhibited a 70% probability of flushing from on-trail recreationists within 100 m from trails. Mule deer showed a 96% probability of flushing within 100 m of recreationists located off trails; their probability of flushing did not drop to 70% until perpendicular distance reached 390 m. We calculated the area around existing trails on Antelope Island that may be impacted by recreationists on those trails. Based on a 200-m "area of influence," 8.0 km (7%) of the island was potentially unsuitable for wildlife due to disturbance from recreation. Few studies have examined how recreationists perceive their effects on wildlife, although this has implications for their behavior on public lands. We surveyed 640 backcountry trail users on Antelope Island to investigate their perceptions of the effects of recreation on wildlife. Approximately 50% of recreationists felt that recreation was not having a negative effect on wildlife. In general, survey respondents perceived that it was acceptable to ap- proach wildlife more closely than our empirical data indicated wildlife would allow. Recrea- tionists also tended to blame other user groups for stress to wildlife rather than holding themselves responsible. The results of both the biological and human-dimensions aspects of our research have implications for the management of public lands where the continued coexistence of wildlife and recreation is a primary goal. Understanding wildlife responses to recreation and the "area of influence" of human activities may help managers judge whether wildlife pop- ulations are experiencing stress due to interactions with humans, and may aid in tailoring recreation plans to minimize long-term effects to wildlife from disturbance. Knowledge of recreationists' perceptions and beliefs regarding their effects on wildlife may also assist public lands managers in encouraging positive visitor behaviors around wildlife.

Applying ecological criteria to marine reserve design: A case study from the california channel islands

Abstract: Using ecological criteria as a theoretical framework, we describe the steps involved in designing a network of marine reserves for conservation and fisheries man- agement. Although we describe the case study of the Channel Islands, the approach to marine reserve design may be effective in other regions where traditional management alone does not sustain marine resources. A group of agencies, organizations, and individuals established clear goals for marine reserves in the Channel Islands, including conservation of ecosystem biodiversity, sustainable fisheries, economic viability, natural and cultural heritage, and education. Given the constraints of risk management, experimental design, monitoring, and enforcement, scientists recommended at least one, but no more than four, reserves in each biogeographic region. In general, the percentage of an area to be included in a reserve network depends on the goals. In the Channel Islands, after consideration of both conservation goals and the risk from human threats and natural catastrophes, scientists recommended reserving an area of 30-50% of all representative habitats in each biogeo- graphic region. For most species of concern, except pinnipeds and seabirds, information about distributions, dispersal, and population growth was limited. As an alternative to species distribution information, suitable habitats for species of concern were used to locate potential reserve sites. We used a simulated annealing algorithm to identify potential reserve network scenarios that would represent all habitats within the smallest area possible. The analysis produced an array of potential reserve network scenarios that all met the established

Soil tillage affects the community structure of mycorrhizal fungi in maize roots

Abstract: In this study we tested whether communities of arbuscular mycorrhizal fungi (AMF) colonizing the roots of maize (Zea mays L.) were affected by soil tillage practices (plowing, chiseling, and no-till) in a long-term field experiment carried out in Tanikon (Switzerland). AMF were identified in the roots using specific polymerase chain reaction (PCR) markers that had been developed for the AMF previously isolated from the soils of the studied site. A nested PCR procedure with primers of increased specificity (eukaryotic, then fungal, then AMF species or species-group specific) was used. Sequencing of amplified DNA confirmed that the DNA obtained from the maize roots was of AMF origin. Presence of particular AMF species or species-group was scored as a presence of a DNA product after PCR with specific primers. We also used single-strand conformation polymorphism analysis (SSCP) of amplified DNA samples to check if the amplification of the DNA from maize roots matched the expected profile for a particular AMF ...

Climate change effects on vegetation distribution, carbon, and fire in California

Abstract: The objective of this study was to dynamically simulate the response of vegetation distribution, carbon, and fire to the historical climate and to two contrasting scenarios of climate change in California. The results of the simulations for the historical climate compared favorably to independent estimates and observations, but validation of the results was complicated by the lack of land use effects in the model. The response to increasing temperatures under both scenarios was characterized by a shift in dominance from needle-leaved to broad-leaved life-forms and by increases in vegetation productivity, especially in the relatively cool and mesic regions of the state. The simulated response to changes in precipitation were complex, involving not only the effect of changes in soil moisture on vegetation productivity, but also changes in tree-grass competition mediated by fire. Summer months were warmer and persistently dry under both scenarios, so the trends in simulated fire area under both scenarios were primarily a response to changes in vegetation biomass. Total ecosystem carbon increased under both climate scenarios, but the proportions allocated to the wood and grass carbon pools differed. The results of the simulations underscore the potentially large impact of climate change on California eco- systems, and the need for further use and development of dynamic vegetation models using various ensembles of climate change scenarios.

Soil carbon addition controls weeds and facilitates prairie restoration

Abstract: Soil nitrogen enrichment and consequent vigorous weed growth are thought to hinder the restoration of tallgrass prairie. Adding carbon to the soil may facilitate prairie restoration by inducing immobilization of plant-available nitrogen. Early attempts to use this method, however, have had mixed results. Success of C addition depends on three conditions: weeds must suppress prairie species in the absence of C addition, weeds must be nitrophilic relative to prairie species, and C addition must result in a large enough decrease in N to alter the balance of competition among weeds and prairie species. We examined these conditions by comparing productivity of 10 weeds and 11 tallgrass prairie species under 14 levels of C addition, ranging from 84 to 3346 g C/m 2 . Carbon was tilled into the soil prior to planting. To control for non-N effects of C addition, N was added to a subset of plots. Relative to untreated plots, the highest level of C addition resulted in an 86% decrease in available NO3 -N, a1 43 increase in early season light availability, a 54% decrease in weed biomass, and a sevenfold increase in prairie biomass. Nitrogen addition significantly reduced or reversed all of these effects. Significant species-specific responses to C addition included decreased biomass for six annual weeds and increased biomass for six prairie species, one annual weed, and three perennial weeds. These results suggest that C addition may be a useful tool for restoring N-limited plant communities.

Forest ecosystem carbon and nitrogen accumulation during the first century after agricultural abandonment

Abstract: Forests of the northeastern United States are expected to serve as a substantial sink for carbon (C) and nitrogen (N) as they recover from extensive clearing and agriculture. However, questions remain concerning the rate, distribution, and duration of this potential sink. We used a chronosequence approach to determine changes in ecosystem C and N during the first 115 years of forest development after agricultural abandonment in Rhode Island, USA. All sites had similar soils, climate, land-use history, and dominant overstory vegetation (Pinus strobus), but differed in time since agricultural abandonment. Total ecosystem C increased linearly across the chronosequence at a mean rate of 2.10 Mg C·ha–1·yr–1. Most of the C was sequestered into plant biomass (73%) with less stored in the forest floor (17%) and deep mineral soil (6%; 20–70 cm depth). Total ecosystem N did not change over time; instead N accumulated in the forest floor (11.6 kg N·ha–1·yr–1) and plant biomass (4.1 kg N·ha–1·yr–1), and these increas...

Dispersal potential of marine invertebrates in diverse habitats

Abstract: Life-history parameters were used to estimate the dispersal potential of 1021 marine macroinvertebrates recorded in species lists from 91 sites comprising rocky intertidal, subtidal, kelp forest, sandy beach, and soft-bottom habitats in Washington, Oregon, and California. Mean species richness was significantly greater in the California rocky subtidal habitat. Data on development mode, planktonic larval duration, rafting potential, and adult mobility were compiled, and summaries of the dispersal potentials of taxa within each habitat type were generated and compared. In summary, development mode was known or estimated for 76% of species; larval planktonic duration for 49%; adult mobility for 76%; and rafting potential for 46%. In comparisons of species' life-history traits among habitats, sand-dominated habitats were distinct from rocky habitats. In rocky habitats, ∼42% of species had planktonic feeding larvae, 43% had planktonic nonfeeding larvae, and 15% had nonplanktonic larvae. Sandy intertidal habitats had higher proportions of taxa with nondispersing, nonplanktonic larvae and lower proportions of planktonic feeding and nonfeeding larvae than all other sites. Soft-bottom subtidal communities had the highest proportion of taxa with planktonic feeding development and larvae with planktonic lifespans >30 d. Species in soft-bottom subtidal sites, therefore, have the greatest potential for extensive larval dispersal, whereas species in soft-bottom intertidal sites have the least potential for larval dispersal. In these sites with limited larval dispersal potential, there is greater potential for adult dispersal through adult movement and rafting. These differences in the dispersal potential of larvae and adults suggest that the effect of environmental changes and the effectiveness of reserves may differ between habitats. Conservation methods, including the use of marine reserves, must therefore be tailored to the habitat of interest if effective protection of community resources is to be achieved.

The pace of ecosystem development of constructed spartina alterniflora marshes

Abstract: Ecological attributes were measured along a chronosequence of 1- to 28-yr- old, constructed Spartina alterniflora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil devel- opment (sediment deposition, organic C, N, P, organic matter quality), and microbial pro- cesses (C mineralization) were compared among eight constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5-15 yr after marsh construc- tion. An exception was soil organic C and N pools (0-30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophylla, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1- to 3-yr-old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0-10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g N/m 2 (0.05- 0.1% N) to support emergent vegetation and 1000 g C/m 2 (0.5-1% C) to sustain the het-

Avoiding current oversights in marine reserve design

Abstract: The pun in the above title reflects two points. First, marine life cycles com- monly include a dispersive juvenile stage that is moved about by ocean currents. This stage often is the predominant, or only, means of dispersal that connects spatially disjunct pop- ulations. As a consequence, details of dispersal likely play a critical role in determining the effectiveness of marine reserves as a management and conservation tool. Curiously, however (and this is the second point of the title), although dozens of models for marine reserves now exist, few actually account explicitly for larval dispersal. Moreover, those that do include dispersal, do so almost exclusively by considering it to be a nondirectional spreading process (diffusion), ignoring the effects of directional transport by currents (ad- vection). Here we develop a population dynamical model for marine organisms with rel- atively sedentary adults whose larvae are transported in a simple flow field with both diffusive spreading and directional characteristics. We find that advection can play a dom- inant role in determining the effectiveness of different reserve configurations. Two of the most important consequences are: (1) with strong currents, multiple reserves can be mark- edly more effective than single reserves of equivalent total size; and (2) in the presence of strong currents, reserves can significantly outperform traditional, effort-based manage- ment strategies in terms of fisheries yield, and do so with less risk. These results suggest that successful reserve design may require considerable new efforts to examine explicitly the role of dispersal of young.

Predator cues and pesticides: a double dose of danger for amphibians

Abstract: Amphibians are declining globally, and biologists have struggled to identify the causes. Pesticides may play a role in these declines, but pesticide concentrations in nature often are low and considered sublethal. Past research has found that the globally common pesticide carbaryl can become more lethal under different environmental condi- tions including differences in temperature and competition. A recent study has found that predatory stress, a situation common for most amphibians, can make carbaryl 2-4 times more deadly to gray tree frogs (Hyla versicolor). To determine whether this is a general phenomenon in amphibians, I examined how carbaryl affected the survival of six amphibian species in the presence and absence of predatory stress. Higher concentrations of carbaryl caused higher mortality. In two of the six species, carbaryl became even more lethal when combined with predatory stress (up to 46 times more lethal). This suggests that apparently safe concentrations of carbaryl (and perhaps other pesticides with similar modes of action) can become more deadly to some amphibian species when combined with predator cues.

Biomass n:p ratios as indicators of nutrient limitation for plant populations in wetlands

Abstract: The conservation or restoration of seminatural vegetation often involves measures that influence the availability of nutrients and consequently the plant species composition. The ability to predict effects of modified nutrient availability on species composition would therefore help to choose appropriate management strategies. The aim of this study was to test whether short-term effects of nitrogen or phosphorus enrichment can be predicted from nutrient ratios in plant biomass. At 11 species-rich sites in Dutch fens and dune slacks, small plots were fertilized with N, P, N + P, or not fertilized (control). The aboveground biomass, N and P concentrations, and N:P ratios were compared between fertilized and control plots for all sufficiently abundant plant populations in the summers preceding and following fertilization. Of 121 populations, only 45 had their biomass enhanced significantly by fertilization. Populations enhanced by P fertilization had on average higher biomass N:P ratios than those enhanced b...

Fire and grazing impacts on plant diversity and alien plant invasions in the southern sierra nevada

Abstract: Patterns of native and alien plant diversity in response to disturbance were examined along an elevational gradient in blue oak savanna, chaparral, and coniferous forests. Total species richness, alien species richness, and alien cover declined with elevation, at scales from 1 to 1000 m2. We found no support for the hypothesis that community diversity inhibits alien invasion. At the 1-m2 point scale, where we would expect competitive interactions between the largely herbaceous flora to be most intense, alien species richness as well as alien cover increased with increasing native species richness in all communities. This suggests that aliens are limited not by the number of native competitors, but by resources that affect establishment of both natives and aliens. Blue oak savannas were heavily dominated by alien species and consistently had more alien than native species at the 1-m2 scale. All of these aliens are annuals, and it is widely thought that they have displaced native bunchgrasses. If true, this...

A Bt TRANSGENE REDUCES HERBIVORY AND ENHANCES FECUNDITY IN WILD SUNFLOWERS

Abstract: Gene flow from transgenic crops can introduce novel traits into related spe- cies, but the ecological importance of this process is unknown. Here, we report the first empirical evidence that wild plants can benefit from a bacterial transgene under uncaged, natural conditions. Cultivated sunflower ( Helianthus annuus) is known to hybridize fre- quently with wild sunflower ( H. annuus) in the western and midwestern United States. We studied a crop-developed Bacillus thuringiensis(Bt) transgene, cry1Ac, in backcrossed wild sunflower populations. Lepidopteran damage on transgenic plants was strongly reduced relative to control plants at our two study sites, while damage by several weevil and fly species was unaffected. Our results suggest that reduced herbivory caused transgenic plants to produce an average of 55% more seeds per plant relative to nontransgenic controls at the field site in Nebraska. A similar but nonsignificant trend was seen at the site in Colorado (14% more seeds per plant). In a greenhouse experiment the transgene had no effect on fecundity, suggesting that it was not associated with a fitness cost. If Bt sunflowers are released commercially, we expect that Bt genes will spread to wild and weedy populations, limit damage from susceptible herbivores on these plants, and increase seed production when these herbivores are common.

A systematic analysis of factors affecting the performance of climatic envelope models

Abstract: Effective application of species distribution models requires some knowledge concerning the accuracy of model predictions. Yet very few studies have attempted to systematically analyze factors affecting the predictive power of distribution models. This study fills this gap for Climatic Envelope Models, which have been applied extensively for a variety of conservation and management purposes. We hypothesized that model predic- tions are influenced by properties of the data (both quantity and quality) and distribution properties of the modeled species. Hypotheses concerning the effects of both types of factors were tested by analyzing distribution patterns of 192 species of woody plants in Israel. Analyses were based on Monte Carlo simulations and standard statistical tests. The total number of observations had a strong positive effect on model performance; but on average, 50-75 observations were sufficient to obtain the maximal accuracy. Climatic bias (the degree of sampling bias with respect to climatic conditions) had a significant negative effect on predictive accuracy. Climatic completeness (the degree to which the climatic range occupied by the species is covered by the observations) had a negative effect on model performance-a result contradicting our original hypothesis. Among the species properties, commonness had a positive effect while niche width had a negative one. Niche position with respect to rainfall and temperature was also important in determining the accuracy of model predictions. The overall results are discussed with respect to trade-offs between commission and omission errors and the potential implications of scale dependency.

Feedbacks between soil nutrients and large herbivores in a managed savanna ecosystem

Abstract: Small-scale fertilization experiments have shown that soil nutrients limit plant productivity in many semiarid grasslands and savannas, but linkages among nutrients, grasses, and grazers are rarely studied in an ecosystem context. We used hectare-scale heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna to examine relationships among soil nitrogen and phosphorus, above- ground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland. Increasing soil N and P content was consistently associated with increasing plant productivity and rainfall use efficiency in wet, dry, and drought years. A fertilization experiment and analyses of grass N:P ratios across sites indicated that N is the primary limiting nutrient on nutrient-rich glades, whereas N and P co-limit productivity on nutrient-poor bushland sites. Variation in ANPP among patches within the landscape was linearly correlated with consumption rates of large her- bivores. Grazing pressure was consistently high ( .60% of ANPP) at all but one site in a dry year (1999), and was greater in nutrient-rich glades (73 6 4% of ANPP) than in nutrient- poor bushland sites (43 6 7% of ANPP) in a wet year (2001). Grasses of nutrient-rich sites contained sufficient P concentrations to meet requirements for pregnant and lactating un- gulates, whereas grasses in nutrient-poor swards were P deficient. Even though native and domestic herbivores selectively used and intensively grazed nutrient-rich sites, productivity on these sites remained high throughout the study. Analyses of nitrogen budgets for nutrient- rich and nutrient-poor sites showed that large herbivores themselves caused a net N input to the former and a net N loss from the latter. Thus, large herbivores not only respond to heterogeneity in soil and plant nutrients across the landscape, but also play a role in maintaining the N-enriched status of highly productive and intensively grazed sites.

Comparing designs of marine reserves for fisheries and for biodiversity

Abstract: We compare and contrast the design of networks of marine reserves for two different, commonly stated goals: (1) maintaining high yield in fisheries and (2) conserving biodiversity, in an idealized setting using simple models. The models describe larval dispersal over a system of evenly spaced reserves of equal size, assuming sedentary adults. We initially demonstrate that, since populations in reserve systems can be sustained either by covering a minimal fraction of the coast with small reserves or by covering a smaller fraction of the coast with few large reserves, cost considerations dictate that the conservation goal would be best met by reserves as large as practically possible. In contrast, the fisheries goal of maximizing yield requires maximizing larval export outside of reserves, which we show means that reserves should be as small as practically possible. Meeting the fisheries goal is ultimately more costly because it suggests a larger area of the coastline should be in reserves, but it also improves on conservation goals by enhancing sustainability for species dispersing longer distances.