bluuebunny/crossref_metadata_2025 huggingface dataset:
VOLE‐DRIVEN SUCCESSION IN EXPERIMENTAL WET‐PRAIRIE RESTORATIONS
Authors: Howe Henry F. , Lane Diana
Published: June 2007

A challenge of experimental restoration is to determine the reasons why restored communities develop as they do. Divergent successions in plantings of 16 tallgrass prairie species sown in equal densities in Wisconsin (USA) revealed strong effects of vole (Microtus pennsylvanicus) herbivory on vegetation initially protected for an establishment period of over 24 months, by which time all principal species were flowering and fruiting. Half of the plots were then subjected to 48 months of vole access. An otherwise common legume (Desmodium canadense) and grass (Elymus virginicus) were all but eliminated in 48 months of exposure: combined cover under protection was 43 ± 6%, but plummeted to <1% cover when voles had access. Dicots not eaten by voles (Pycnanthemum virginianum,Rudbeckia subtomentosa) averaged 40 ± 7% cover where voles were excluded, but 68 ± 8% after 48 months of vole access. Repeated‐measures analyses of variance revealed that net decreases (D. canadense,E. virginicus) or increases (P. virginianum,R. subtomentosa) in cover masked nonlinear effects reflecting vole‐driven transient dynamics during divergent successional processes. Diversities diverged for three years after vole access; a dramatic convergence of diversities in the fourth year leaves grossly similar communities with similar numbers of species and similar levels of equity, but distinctly different species compositions. Vole‐mediated effects on vegetation resemble those likely to occur in native prairies, without the catastrophic changes in cover and standing crop caused by rodents that occurred in some previous efforts of this research program.
HOW FINE SEDIMENT IN RIVERBEDS IMPAIRS GROWTH AND SURVIVAL OF JUVENILE SALMONIDS
Authors: Suttle Kenwyn B. , Power Mary E. , Levine Jonathan M. , McNeely Camille
Published: June 2007

Although excessive loading of fine sediments into rivers is well known to degrade salmonid spawning habitat, its effects on rearing juveniles have been unclear. We experimentally manipulated fine bed sediment in a northern California river and examined responses of juvenile salmonids and the food webs supporting them. Increasing concentrations of deposited fine sediment decreased growth and survival of juvenile steelhead trout. These declines were associated with a shift in invertebrates toward burrowing taxa unavailable as prey and with increased steelhead activity and injury at higher levels of fine sediment. The linear relationship between deposited fine sediment and juvenile steelhead growth suggests that there is no threshold below which exacerbation of fine‐sediment delivery and storage in gravel bedded rivers will be harmless, but also that any reduction could produce immediate benefits for salmonid restoration.
SPATIAL CLUSTERING OF MURID RODENTS INFECTED WITH HANTAVIRUSES: IMPLICATIONS FROM META‐ANALYSES
Authors: Root J. Jeffrey , Wilson Kenneth R. , Calisher Charles H. , Wagoner Kent D. , Abbott Ken D. , Yates Terry L. , Kuenzi Amy J. , Morrison Michael L. , Mills James N. , Beaty Barry J.
Published: June 2007

We applied a rigorous, quantitative methodology to the analysis of local‐scale spatial clustering of multiple murid mice (brush mice,Peromyscus boylii; deer mice,P. maniculatus; piñon mice,P. truei; western harvest mice,Reithrodontomys megalotis) infected or uninfected with hantaviruses. Rodents were sampled longitudinally from 1994 to 2001 on 23 trapping webs at 10 locations in the southwestern United States. This study provided an opportunity to apply meta‐analysis techniques to an important ecological question. There were sufficient captures by species on 199 occasions (three consecutive nights) to compare general use of space using multi‐response permutation procedures (MRPP). The MRPP results were then used in meta‐analyses by species to determine if overall effects of spatial clustering of hantavirus‐infected mice as well as categorical effects (elevation, season, site, and state) were present. Based on MRPP analyses, overall spatial clustering of hantavirus‐infected mice was most pronounced for brush mice, followed by the deer mouse. Meta‐analyses indicated significant overall effects of spatial clustering and varying categorical effects (elevation, season, site, state) of infected mice for each species compared. The overlapping space use by rodents might be an important factor affecting the local transmission of several hantaviruses.
EXOTIC EUROPEAN EARTHWORM INVASION DYNAMICS IN NORTHERN HARDWOOD FORESTS OF MINNESOTA, USA
Authors: Hale Cindy M. , Frelich Lee E. , Reich Peter B.
Published: June 2007

European earthworms are invading previously worm‐free hardwood forests across Minnesota and the Great Lakes region. In many of these forests, earthworm invasions have been associated with the loss of a previously thick forest floor. The ability of earthworms to alter and control ecosystem processes has been demonstrated in agricultural systems, but the dynamics and impact of these invasions in native forest ecosystems is largely unknown. The impacts of earthworm invasion are expected to be related to the size and species composition of the earthworm population because different species have different habitat and feeding preferences. We identified four sugar maple dominated forests in north central Minnesota in the Chippewa National Forest with active earthworm invasion. In each site a sample grid of 45 points (30 × 150 m) 10 m apart in three parallel transects with 15 points each was established that spanned a visible leading edge of invasion. Over four years earthworm populations and forest floor thickness were sampled across all transects, thus providing both a space‐for‐time assessment of decadal scale successional dynamics and a four‐year window into shorter time changes. We found a succession of earthworm species across the visible leading edge due to different patterns of colonization by different earthworm species. Marked increases in space and time in earthworm biomass were associated with the development of discrete transition zones where forest floor thickness decreases to zero in as little as 75 m from areas that have forest floor layers up to 10 cm thick with advancement of the visible leading edge of up to 30 m in four years at three of the study sites. The epi‐endogeic speciesLumbricus rubellusled to the most rapid removal of forest floor material during initial invasion. Epigeic and epi‐endogeic species of earthworms may facilitate the establishment of other species of earthworms leading to the establishment of stable populations of endogeic and anecic species, which prevent recovery of the forest floor.
FACTORS AFFECTING SPECIES DISTRIBUTION PREDICTIONS: A SIMULATION MODELING EXPERIMENT
Authors: Reese Gordon C. , Wilson Kenneth R. , Hoeting Jennifer A. , Flather Curtis H.
Published: June 2007

Geospatial species sample data (e.g., records with location information from natural history museums or annual surveys) are rarely collected optimally, yet are increasingly used for decisions concerning our biological heritage. Using computer simulations, we examined factors that could affect the performance of autologistic regression (ALR) models that predict species occurrence based on environmental variables and spatially correlated presence/absence data. We used a factorial experiment design to examine the effects of survey design, spatial contiguity, and species detection probability and applied the results of ten replications of each factorial combination to an ALR model. We used additional simulations to assess the effects of sample size and environmental data error on model performance. Predicted distribution maps were compared to simulated distribution maps, considered “truth,” and evaluated using several metrics: omission and commission error counts, residual sums of squares (RSS), and areas under receiver operating characteristic curves (AUC). Generally, model performance was better using random and stratified survey designs than when using other designs. Adaptive survey designs were an exception to this generalization under the omission error performance criterion. Surveys using rectangular quadrats, designed to emulate roadside surveys, resulted in models with better performance than those using square quadrats (using AUC, RSS, and omission error metrics) and were most similar in performance to a systematic quadrat design. Larger detection probabilities, larger sample sizes, contiguous distributions, and fewer environmental data errors generally improved model performance. Results suggest that spatially biased sample data, e.g., data collected along roads, could result in model performance near that of systematic quadrat designs even in the presence of potentially confounding factors such as contiguity of distributions, detection probability, sample size, and environmental data error.
VIABILITY OF BELL'S SAGE SPARROW (AMPHISPIZA BELLI SSP. BELLI): ALTERED FIRE REGIMES
Authors: Akçakaya H. Reşit , Franklin Janet , Syphard Alexandra D. , Stephenson John R.
Published: June 2007

We modeled the viability of a Bell's Sage Sparrow (Amphispiza bellissp.belli) metapopulation under different fire regimes in the foothills and mountains of San Diego County, California, USA. The approach integrates a landscape model, which predicts the vegetation composition and age under three fire regimes, a habitat model, which interprets the resulting landscape in terms of its suitability for the Sage Sparrow, and a metapopulation model, which predicts the viability of the species based on a dynamic spatial structure as determined by the landscape and the habitat models. Bell's Sage Sparrow depends on early‐successional shrubland (chaparral) habitat, especially when the availability of preferred open coastal subshrub vegetation is limited. The three fire rotation intervals (FRI) used in the landscape model were “current” (30‐yr), representing the effect of increased human ignitions; “natural” (90‐yr), representing the historic shrubland fire regime at higher elevations without the effect of human ignitions; and “long” (150‐yr), representing a hypothetical endpoint (very low fire frequency for southern California shrublands). The results indicated that the viability of the Sage Sparrow was highest under the “current” fire regime scenario, slightly lower (especially when population growth rate was low) under the “natural” scenario, and lowest under the “long” fire regime scenario.
REGIONAL ECOLOGY, ECOSYSTEM GEOGRAPHY, AND TRANSBOUNDARY PROTECTED AREAS IN THE ST. ELIAS MOUNTAINS
Authors: Danby Ryan K. , Slocombe D. Scott
Published: June 2007

This study characterizes the broad‐scale ecology of the St. Elias region of Yukon, Alaska, and British Columbia and assesses the implications for ecosystem‐based management of the region's protected areas, including Kluane, Wrangell‐St. Elias, and Glacier Bay National Parks, and Tatshenshini‐Alsek Provincial Park. An interdisciplinary, map‐based process was used to synthesize information, and the fields of regional ecology and ecosystem geography provided the foundation for analysis. Results illustrate that the protected areas share several regional‐scale ecosystem components with each other and with surrounding areas, including globally significant populations of large mammals and other wildlife species as well as vegetation communities that experience a full suite of natural disturbances with little human intervention. The valleys of the Tatshenshini, Alsek, and Copper Rivers serve as important links between coastal and interior areas as well as conduits for the movement of biota. However, connectivity is not distributed equally across the region, and the four core national parks have linkages with adjacent areas that are as strong, and in many cases stronger, than among themselves. The management challenge is not a matter of linking separate protected areas to create networks. Instead, it lies in integrating existing protected areas with each other and with surrounding areas and resisting small changes that have incremental and cumulative impacts. Interagency cooperation is seen as a key component in facilitating this, and some success has been achieved on the scale of single issues and specific resources. The challenge ahead is to build on this success by strengthening existing institutional frameworks and working toward more comprehensive efforts. Similar lessons can be derived for other complex mountain landscapes and northern regions where large protected areas and multiple land management agencies exist.
DEVELOPMENT OF TREE SIZE DISTRIBUTIONS IN DOUGLAS‐FIR FORESTS UNDER DIFFERING DISTURBANCE REGIMES
Authors: Zenner Eric K.
Published: June 2007

Two conceptual models describe the successional and structural development of mature and transitional stands toward old‐growthPseudotsuga menziesii(Mirbel) Franco forests in the Pacific Northwest. The “catastrophic/maturational” model is based on infrequent catastrophic disturbances that initiate the successional cycle, while the “chronic/ partial fire” model is based on low‐ to moderate‐severity fires which, over long periods of time, can create old‐growth conditions through multiple disturbances. Although both models can produce similar structural characteristics, quantitative differences in speed and pathways of structural development with respect to these models are not well understood. To elucidate these quantitative differences, diameter distributions of live trees were investigated in a chronosequence of mature, transitional, and old‐growth stands subjected to these two disturbance models. Stands characterized by the “catastrophic/maturational” model exhibited varying degrees of rotated sigmoid distributions up to 250–300 years of age because of long establishment periods and differential growth and mortality rates of the component species. They also showed a modest trend toward reverse‐J distributions with increasing stand age. Stands characterized by the “chronic/partial fire” model had a stratum of distinctly older emergent trees with younger cohorts ofPseudotsuga menziesii,Tsuga heterophylla(Raf.) Sarg., andThuja plicataDonn. and exhibited reverse‐J distributions within about 150–200 years after disturbance. These results suggest that reconsideration of current definitions of what constitutes old‐growth onTsugasites may be necessary. A conceptual model is presented, which links pathways of structural development to disturbance regimes. This model indicates that active management can hasten the development of old‐growth structure, even in some older forests.
ON THE IMPORTANCE OF LANDSCAPE HISTORY FOR ASSESSING EXTINCTION RISK
Authors: Schrott Gregory R. , With Kimberly A. , King Anthony W.
Published: June 2007

Assessment of extinction risk may depend not only upon the current state of the landscape and its projected trajectory of change, but also on its past disturbance history. We employed a spatially structured demographic model to evaluate extinction risk for several generic migratory songbirds within landscapes subjected to ongoing habitat loss and fragmentation. We generated different scenarios of dynamic landscape change using neutral landscape models, in which breeding habitat was systematically destroyed at various rates (0.5%, 1%, or 5% per year) and degrees of fragmentation, thus enabling us to determine the relative contribution of these factors to population declines. Extinction risk was assessed relative to thevulnerability threshold,the point where the change in population growth rate (Δλ) scaled to the rate of habitat loss (Δh) falls below −1% (Δλ/Δh= −0.01). Our model predicts that songbirds are likely to exhibit lagged responses to habitat loss in landscapes undergoing rapid change (5% per year). In such scenarios, the landscape changed more rapidly than the demographic response time of the population, such that population growth rates never exceeded the vulnerability threshold, even though these species inevitably went extinct. Thus, songbirds in landscapes undergoing rapid change might not be assessed as “at risk” until the population's demographic potential has been seriously eroded, which would obviously compromise the success of management actions aimed at recovering the population. Furthermore, our model illustrates how assessment of a species' extinction risk may vary widely among landscapes of similar structure, depending upon how quickly the landscape achieved its current state. Thus, information on the current landscape state (e.g., amount of habitat or degree of fragmentation) may not be sufficient for assessing long‐term population viability and extinction risk in the absence of information on the history of landscape disturbance.
GENETICALLY ENGINEERED ORGANISMS AND THE ENVIRONMENT: CURRENT STATUS AND RECOMMENDATIONS1
Authors: Snow A. A. , Andow D. A. , Gepts P. , Hallerman E. M. , Power A. , Tiedje J. M. , Wolfenbarger L. L.
Published: June 2007

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.
PESTICIDES AND AMPHIBIANS: THE IMPORTANCE OF COMMUNITY CONTEXT
Authors: Relyea Rick A. , Schoeppner Nancy M. , Hoverman Jason T.
Published: June 2007

The widespread application of pesticides has attracted the attention of ecologists as we struggle to understand the impacts of these chemicals on natural communities. While we have a large number of laboratory‐based, single‐species studies of pesticides, such studies can only examine direct effects. However, in natural communities, species can experience both direct and indirect effects. We conducted an outdoor mesocosm experiment on aquatic communities containing three tadpole species (Hyla versicolor,Bufo americanus, andRana pipiens), zooplankton, and algae. We then manipulated a factorial combination of predators (no predators; newts,Notophthalmus viridescens; and larval beetles,Dytiscussp.) and pesticides (no pesticides, the insecticide malathion, and the herbicide Roundup). We found that Roundup (1.3 mg of active ingredient/L) had substantial direct negative effects on the tadpoles, reducing total tadpole survival and biomass by 40%. However, Roundup had no indirect effects on the amphibian community via predator survival or algal abundance. Malathion (0.3 mg/L) had few direct effects on the tadpoles. Malathion caused no indirect effects with one of the predators (red‐spotted newts) but caused substantial positive effects on amphibians (a five‐fold increase in total tadpole survival and biomass) due to the sensitivity of the predatory beetles to the insecticide. Thus, while high concentrations of malathion can directly kill larval anurans, more ecologically relevant concentrations can have large positive effects in mesocosms by removing predatory insects. These results make it clear that pesticides can have both direct and indirect effects in natural communities and that these effects critically depend upon the composition of the community.
HAWAIIAN HONEYCREEPER HOME RANGE SIZE VARIES WITH HABITAT: IMPLICATIONS FOR NATIVE ACACIA KOA FORESTRY
Authors: Pejchar Liba , Holl Karen D. , Lockwood Julie L.
Published: June 2007

Reforesting degraded landscapes with native, high‐value timber trees may contribute to biodiversity protection while also increasing the economic value of the land. Ideally, reforested areas should have the habitat characteristics to support viable populations of native fauna. We investigated habitat use by Akiapolaau (Hemignathus munroi), an endangered Hawaiian honeycreeper, in three habitat types: a relatively intact old‐growth forest, an old‐growth forest with a long history of grazing, and a native Acacia koa plantation. We quantified habitat characteristics, calculated foraging preferences, mapped home ranges, measured territoriality, and determined reproductive success at all sites. We found that Akiapolaau were highly selective foragers, foraging primarily on A. koa despite its relative scarcity in the environment, and then secondarily on several subcanopy species. Home range size was significantly smaller at the intact old‐growth site and the A. koa plantation, the two sites with the greater cover of A. koa and of the subcanopy species preferred by Akiapolaau. Birds at these sites were also less territorial, supporting behavioral theory that predicts a nonlinear relationship between food availability and territoriality. Overall, our results show that the A. koa plantation, the site with the highest percentage of A. koa, the smallest Akiapolaau home ranges, and the least territoriality, supported the highest density of birds with no apparent reproductive cost. Because A. koa is an extremely high‐value hardwood and thus can be selectively harvested, there is tremendous potential for conservation advocates to work with landowners to grow A. koa for economic benefit while also enhancing biodiversity.
TEMPORAL VARIATION OF WOOD‐FUNGI DIVERSITY IN BOREAL OLD‐GROWTH FORESTS: IMPLICATIONS FOR MONITORING
Authors: Berglund Håkan , Edman Mattias , Ericson Lars
Published: June 2007

Monitoring programs that supply reliable and sufficient information on numbers and types of organisms are essential for following changes in biodiversity. In boreal Fennoscandia, forest‐dwelling species are threatened in managed forest landscapes and, thus, are of particular concern for conservation strategies. Wood fungi represent key ecological components in the boreal forest that are sensitive to forestry and widely used as indicators in large‐scale forest inventories for identifying valuable forest habitats. Knowledge of their natural dynamics is required for designing monitoring programs to assess the adequacy of conservation strategies. We studied the occurrence of corticoids (Corticiaceae) and polypores (Polyporaceae) over time at different spatial scales in unexploited boreal old‐growth forests. Data from 70 downed logs followed during an eight‐year period showed that the lifespan of fruit bodies of most species was shorter than four years. Even perennial species followed this pattern, although fruit bodies of some species (e.g.,Phellinusspp.) remained vital throughout the eight years studied. Both species richness and species composition on individual logs changed markedly over the eight years due to deterministic succession of species paralleling the wood decay. By contrast, data from the stand scale, i.e., seven 0.1‐ha plots, showed that species richness and species composition of polypores did not undergo any major changes during a six‐year period. A majority of all recorded polypore species (80%) were already present at the first inventory. However, although species richness remained constant at the stand scale, corticoid species composition differed between years, reflecting their short‐lived, annual fruit bodies. This study suggests that monitoring should be performed at stand scale and focus on species with durable fruit bodies, e.g., polypores. This will provide data that can be used both to detect future changes in biodiversity in old‐growth spruce forests and to evaluate conservation strategies.
HISTORICAL MARINE POPULATION ESTIMATES: TRIGGERS OR TARGETS FOR CONSERVATION? THE DUGONG CASE STUDY
Authors: Marsh Helene , De'ath Glenn , Gribble Neil , Lane Baden
Published: June 2007

Recent studies have estimated the historical abundance of large marine vertebrates to determine potential targets for conservation. We evaluated this approach using 1990s aerial survey estimates of dugong abundance and an estimate of the decline in dugong numbers since the 1960s based on changes in the catch per unit effort of dugong bycatch in a government shark control program on the east coast of Queensland, Australia. This analysis indicated that the catch rate of dugongs caught in shark nets, at six locations between latitudes 16.5° S and 28° S, declined at an average of 8.7% per year between 1962 and 1999. This represents a decline to 3.1% of initial catch rates over the sampling period. If the changes in the populations sampled by the shark nets and aerial surveys were equivalent, this result suggests that the region supported 72 000 dugongs in the early 1960s compared with an estimated 4220 dugongs in the mid‐1990s. The seagrass habitat in the region is currently insufficient to support 72 000 dugongs, suggesting that our hindcast estimate may be an unrealistic target for recovery. Nonetheless, the evidence of serious dugong decline from the shark‐net data and other sources has triggered significant conservation initiatives. This case study indicates that comparisons between historical and contemporary estimates of the abundance of large marine vertebrates can be powerful qualitative triggers for conservation action, but that quantitative targets for recovery require systematic testing of the assumptions underlying hindcast estimates, scientific evaluation of the current carrying capacity of the ecosystem for the target species, and consultation with a broad range of stakeholders. For some species, it may be more productive to set anthropogenic mortality targets that are designed to enable the population to recover to its optimum sustainable population than to set recovery targets per se.
EXPOSING EXTINCTION RISK ANALYSIS TO PATHOGENS: IS DISEASE JUST ANOTHER FORM OF DENSITY DEPENDENCE?
Authors: Gerber Leah R. , McCallum Hamish , Lafferty Kevin D. , Sabo John L. , Dobson Andy
Published: June 2007

In the United States and several other countries, the development of population viability analyses (PVA) is a legal requirement of any species survival plan developed for threatened and endangered species. Despite the importance of pathogens in natural populations, little attention has been given to host–pathogen dynamics in PVA. To study the effect of infectious pathogens on extinction risk estimates generated from PVA, we review and synthesize the relevance of host–pathogen dynamics in analyses of extinction risk. We then develop a stochastic, density‐dependent host–parasite model to investigate the effects of disease on the persistence of endangered populations. We show that this model converges on a Ricker model of density dependence under a suite of limiting assumptions, including a high probability that epidemics will arrive and occur. Using this modeling framework, we then quantify: (1) dynamic differences between time series generated by disease and Ricker processes with the same parameters; (2) observed probabilities of quasi‐extinction for populations exposed to disease or self‐limitation; and (3) bias in probabilities of quasi‐extinction estimated by density‐independent PVAs when populations experience either form of density dependence. Our results suggest two generalities about the relationships among disease, PVA, and the management of endangered species. First, disease more strongly increases variability in host abundance and, thus, the probability of quasi‐extinction, than does self‐limitation. This result stems from the fact that the effects and the probability of occurrence of disease are both density dependent. Second, estimates of quasi‐extinction are more often overly optimistic for populations experiencing disease than for those subject to self‐limitation. Thus, although the results of density‐independent PVAs may be relatively robust to some particular assumptions about density dependence, they are less robust when endangered populations are known to be susceptible to disease. If potential management actions involve manipulating pathogens, then it may be useful to model disease explicitly.
MOSQUITO HABITATS, LAND USE, AND MALARIA RISK IN BELIZE FROM SATELLITE IMAGERY
Authors: Pope Kevin , Masuoka Penny , Rejmankova Eliska , Grieco John , Johnson Sarah , Roberts Donald
Published: June 2007

Satellite imagery of northern Belize is used to examine the relationship between land use and habitats of the malaria vector, the Anopheles mosquito. A land cover classification based on multispectral Système Probatoire d'Observation de la Terra (SPOT) and multitemporal Radarsat images identified 11 land cover classes, including agricultural, forest, and marsh types. Two of the land cover types, Typha domingensis marsh and flooded forest, are habitats of immature Anopheles vestitipennis, and one, Eleocharis spp. marsh, is the habitat for immature Anopheles albimanus. Geographic information systems (GIS) analyses of land cover demonstrate that the amount of Typha domingensis in a marsh is positively correlated with the amount of agricultural land in the adjacent upland and negatively correlated with the amount of adjacent forest. This finding, coupled with field studies documenting higher soil phosphorus in wetlands adjacent to agricultural fields, supports the hypothesis that nutrient runoff is the cause of higher densities of Typha domingensis in marshes adjacent to fields in northern Belize. Thus, agricultural activities can potentially increase Anopheles vestitipennis habitat and thereby increase malaria risk across a broad region where Anopheles vestitipennis is a malaria vector.
SURVIVAL AND SELECTION OF MIGRATING SALMON FROM CAPTURE–RECAPTURE MODELS WITH INDIVIDUAL TRAITS
Authors: Zabel Richard W. , Wagner Tyler , Congleton James L. , Smith Steven G. , Williams John G.
Published: June 2007

Capture–recapture studies are powerful tools for studying animal population dynamics, providing information on population abundance, survival rates, population growth rates, and selection for phenotypic traits. In these studies, the probability of observing a tagged individual reflects both the probability of the individual surviving to the time of recapture and the probability of recapturing an animal, given that it is alive. If both of these probabilities are related to the same phenotypic trait, it can be difficult to distinguish effects on survival probabilities from effects on recapture probabilities. However, when animals are individually tagged and have multiple opportunities for recapture, we can properly partition observed trait‐related variability into survival and recapture components. We present an overview of capture–recapture models that incorporate individual variability and develop methods to incorporate results from these models into estimates of population survival and selection for phenotypic traits. We conducted a series of simulations to understand the performance of these estimators and to assess the consequences of ignoring individual variability when it exists. In addition, we analyzed a large data set of >153 000 juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) of known length that were PIT‐tagged during their seaward migration. Both our simulations and the case study indicated that the ability to precisely estimate selection for phenotypic traits was greatly compromised when differential recapture probabilities were ignored. Estimates of population survival, however, were far more robust. In the chinook salmon and steelhead study, we consistently found that smaller fish had a greater probability of recapture. We also uncovered length‐related survival relationships in over half of the release group/river segment combinations that we observed, but we found both positive and negative relationships between length and survival probability. These results have important implications for the management of salmonid populations.
RECRUITMENT IN DEGRADED MARINE HABITATS: A SPATIALLY EXPLICIT, INDIVIDUAL‐BASED MODEL FOR SPINY LOBSTER
Authors: Butler Mark J. , Dolan Thomas W. , Hunt John H. , Rose Kenneth A. , Herrnkind William F.
Published: June 2007

Coastal habitats that serve as nursery grounds for numerous marine species are badly degraded, yet the traditional means of modeling populations of exploited marine species handle spatiotemporal changes in habitat characteristics and life history dynamics poorly, if at all. To explore how nursery habitat degradation impacts recruitment of a mobile, benthic species, we developed a spatially explicit, individual‐based model that describes the recruitment of Caribbean spiny lobster (Panulirus argus) in the Florida Keys, where a cascade of environmental disturbances has reconfigured nursery habitat structure. In recent years, the region has experienced a series of linked perturbations, among them, seagrass die‐offs, cyanobacteria blooms, and the mass mortality of sponges. Sponges are important shelters for juvenile spiny lobster, an abundant benthic predator that also sustains Florida's most valuable fishery.

In the model, we simulated monthly settlement of individual lobster postlarvae and the daily growth, mortality, shelter selection, and movement of individual juvenile lobsters on a spatially explicit grid of habitat cells configured to represent the Florida Keys coastal nursery. Based on field habitat surveys, cells were designated as either seagrass or hard‐bottom, and hard‐bottom cells were further characterized in terms of their shelter‐ and size‐specific lobster carrying capacities. The effect of algal blooms on sponge mortality, hence lobster habitat structure, was modeled based on the duration of exposure of each habitat cell to the blooms. Ten‐year simulations of lobster recruitment with and without algal blooms suggest that the lobster population should be surprisingly resilient to massive disturbances of this type. Data not used in model development showed that predictions of large changes in lobster shelter utilization, yet small effects on recruitment in response to blooms, were realistic. The potentially severe impacts of habitat loss on recruitment were averted by compensatory changes in habitat utilization and mobility by larger individuals, coupled with periods of fortuitously high larval settlement. Our model provides an underutilized approach for assessing habitat effects on open populations with complex life histories, and our results illustrate the potential pitfalls of relying on intuition to infer the effects of habitat perturbations on upper trophic levels.
CORRIDORS CAUSE DIFFERENTIAL SEED PREDATION
Authors: Orrock John L. , Damschen Ellen I.
Published: June 2007

Corridors that connect disjunct populations are heavily debated in conservation, largely because the effects of corridors have rarely been evaluated by replicated, large‐scale studies. Using large‐scale experimental landscapes, we found that, in addition to documented positive effects, corridors also have negative impacts on bird‐dispersed plants by affecting seed predation, and that overall predation is a function of the seeds' primary consumer (rodents or arthropods). Both large‐seeded Prunus serotina and small‐seeded Rubus allegheniensis experienced greater predation in connected patches. However, P. serotina experienced significantly less seed predation compared to R. allegheniensis in unconnected patches, due to decreased impacts of rodent seed predators on this large‐seeded species. Viewed in light of previous evidence that corridors have beneficial impacts by increasing pollination and seed dispersal, this work demonstrates that corridors may have both positive and negative effects for the same plant species at different life stages. Moreover, these effects may differentially affect plant species within the same community: seeds primarily consumed by rodents suffer less predation in unconnected patches. By shifting the impact of rodent and arthropod seed predators, corridors constructed for plant conservation could lead to shifts in the seed bank.
RELATIVE STRENGTH OF TOP‐DOWN, BOTTOM‐UP, AND CONSUMER SPECIES RICHNESS EFFECTS ON POND ECOSYSTEMS
Authors: Wojdak Jeremy M.
Published: June 2007

Theory and experiments demonstrate that the number of species in a local area can determine rates of ecosystem processes, but we know little about how the strength of that control compares with other influences or how it might vary across ecological gradients. Here I report results of a pond mesocosm experiment where consumer (snail) species richness, predation intensity, and nutrient availability were crossed in a full‐factorial design. This design allowed a direct comparison of the strength of the different factors on food web properties and ecosystem functioning (i.e., system‐level fluxes of energy or matter), and an evaluation of how the factors may interact.

Systems with higher snail species richness had greater secondary production, consumer biomass, ecosystem respiration, and macrophyte stem growth, and lower epiphyton and periphyton biomass. However, snail species richness effects on periphyton and epiphyton were context dependent; predators reduced the effect of increasing snail richness on the biomass of attached algae. Species richness effects were most often the result of a biological mechanism (e.g., differential resource use), rather than being solely artifacts of the experimental design (e.g., sampling effects). The effects of nutrient enrichment and predation were mostly predictable from simple food chain models; increases in nutrient availability led to increased algal biomass, primary production, and snail biomass, while predators decreased snail biomass and indirectly augmented algae.

Snail species richness effects on the biomass of many functional groups were as strong or stronger than those of a substantial nutrient enrichment or of the addition of a voracious predator (Belostoma flumineum). Nutrient enrichment had the most pronounced effects on several system‐level processes (e.g., primary production, sedimentation). Species richness had weaker effects on ecosystem properties than on particular functional groups, probably because of compensatory responses among different producer functional groups. In summary, this experiment suggests that the number of consumer species in a system can have large and meaningful effects on the distribution of biomass in a food web, and that these effects can depend on ecological context.
HOW DO MAGELLANIC PENGUINS COPE WITH VARIABILITY IN THEIR ACCESS TO PREY?
Authors: Wilson Rory P. , Scolaro J. Alejandro , Grémillet David , Kierspel Mandy A. M. , Laurenti Sonia , Upton Jorge , Gallelli Hector , Quintana Flavio , Frere Esteban , Müller Gabriele , Straten Marion Thor , Zimmer Ilka
Published: June 2007

Movements of animals provisioning offspring by central place foraging extend from short, highly local trips where food is brought back essentially unchanged from its normal condition to extensive interseasonal movement where the offspring are nourished from body reserves built up during the adult's absence from the breeding site. Here, appropriate strategies for maximizing lifetime reproductive success depend on the abundance and location of prey in relation to breeding sites and the energetics and speed of travel of the animal. Magellanic PenguinsSpheniscus magellanicusundertake central place movements that are particularly variable during the incubation period; trips may last from a single day to over three weeks depending on colony locality. We reasoned that site‐specific variability in prey distribution and abundance is responsible for this. Remote‐sensing systems attached to 92 penguins from six different colonies over the species distributional range over the Patagonian Shelf were used to determine space use and foraging patterns in an attempt to understand the observed patterns. Birds in the north and south of the latitudinal range were essentially monophagic, feeding primarily on anchoviesEngraulis anchoitaand spratsSprattus fuegensis, respectively, both species that are to be found relatively close to the colonies. Penguins in the center of the distributional range, where these pelagic school fish prey are essentially absent at that time of the year, traveled either north or south, to the same regions utilized by their conspecifics, presumably to exploit the same prey. A simple model is used to clarify patterns and can be used to predict which movement strategy is likely to be best according to colony location. During chick rearing, southerly movement of anchovies and northerly movement of sprats mean that Magellanic Penguins in the center of the distributional range may benefit, although the abundance of these fish is considered to be less than that closer to the Magellanic Penguin range limits. The extensive time involved in the foraging trips during incubation coupled with the postulated poorer prey conditions during the chick‐rearing phase may help explain why Magellanic Penguin colony sizes in the center of the range are not elevated.
ECOHYDROLOGY IN A COLORADO RIVER RIPARIAN FOREST: IMPLICATIONS FOR THE DECLINE OF POPULUS FREMONTII
Authors: Pataki D. E. , Bush S. E. , Gardner P. , Solomon D. K. , Ehleringer J. R.
Published: June 2007

Populus fremontii (Fremont cottonwood) was once a dominant species in desert riparian forests but has been increasingly replaced by the exotic invasive Tamarix ramosissima (saltcedar). Interspecific competition, reduced flooding frequency, and increased salinity have been implicated in the widespread decline of P. fremontii. To elucidate some of the multiple and interacting mechanisms of this decline, we examined ecological processes in a control stand of P. fremontii along the Colorado River in Utah, USA, as well as a disturbed stand characterized by high groundwater salinity and invasion of T. ramosissima. Sap flux data showed that P. fremontii at the saline site experienced large reductions in afternoon canopy stomatal conductance relative to the control. Thus, average daily stand transpiration was 4.8 ± 0.1 mm/d at the saline site in comparison to 9.3 ± 0.2 mm/d at the control site over a two‐month period. Light‐saturated photosynthesis and apparent quantum yield were also reduced in saline P. fremontii. Stable isotope analysis indicated that trees at the saline site utilized evaporatively enriched groundwater that was likely derived from a nearby pond of irrigation runoff; this was also the probable source of high salinity. Interspecific competition for water at the saline site is unlikely, as T. ramosissima is still a minor species that is present only in the understory. However, reduced tissue N content in P. fremontii at the saline site suggested that physiological stress during salinity and halophyte invasion may be exacerbated by altered N relations.
A THEORY OF SPATIAL STRUCTURE IN ECOLOGICAL COMMUNITIES AT MULTIPLE SPATIAL SCALES
Authors: Harte John , Conlisk Erin , Ostling Annette , Green Jessica L. , Smith Adam B.
Published: June 2007

A theory of spatial structure in ecological communities is presented and tested. At the core of the theory is a simple allocation rule for the assembly of species in space. The theory leads, with no adjustable parameters, to nonrandom statistical predictions for the spatial distribution of species at multiple spatial scales. The distributions are such that the abundance of a species at the largest measured scale uniquely determines the spatial‐abundance distribution of the individuals of that species at smaller spatial scales. The shape of the species–area relationship, the endemics–area relationship, a scale‐dependent community‐level spatial‐abundance distribution, the species‐abundance distribution at small spatial scales, an index of intraspecific aggregation, the range–area relationship, and the dependence of species turnover on interpatch distance and on patch size are also uniquely predicted as a function solely of the list of abundances of the species at the largest spatial scale. We show that the spatial structure of three spatially explicit vegetation census data sets (i.e., a 64‐m2serpentine grassland plot, a 50‐ha moist tropical forest plot, and a 9.68‐ha dry tropical forest plot) are generally consistent with the predictions of the theory, despite the very simple statistical assumption upon which the theory is based, and the absence of adjustable parameters. However, deviations between predicted and observed distributions do arise for the species with the highest abundances; the pattern of those deviations indicates that the theory, which currently contains no explicit description of interaction mechanisms among individuals within species, could be improved with the incorporation of intraspecific density dependence.