bluuebunny/crossref_metadata_2025_split huggingface dataset:
Are epiphytes important for birds in coffee plantations? An experimental assessment
Authors: CRUZ‐ANGÓN ANDREA , GREENBERG RUSSELL 
Published: February 2005

Summary

Coffee is produced in tropical regions of the world, largely in Latin America. Coffee cultivation techniques range from traditional systems, where coffee grows under a diverse canopy of shade trees (shade‐coffee plantations), to modern systems, where coffee grows without any type of shade (sun‐coffee plantations). Shade‐coffee plantations provide refuge for forest fauna in otherwise deforested landscapes. The conservation value of these agro‐ecosystems depends upon their structural and floristic diversity.
The way coffee producers manage the vegetation, including the epiphytic component, may profoundly affect the value of plantations for conserving biological diversity. Shade‐coffee certification programmes have emerged to verify that coffee advertised as ‘shade grown’ is actually grown on highly biodiverse plantations. Although these programmes universally encourage epiphyte protection from pruning (a common practice), there has been no experimental evaluation of the importance of epiphytes in supporting faunal diversity. We report the effect of experimentally removing epiphytes on the bird assemblage in a shade‐coffee farm near Coatepec, Veracruz, Mexico.
We established two matching pairs of epiphyte removal and control plots. We compared bird diversity and abundance, based on daily censuses during the breeding and non‐breeding season. We used existing information on the way in which birds use epiphytes as foraging and nesting substrates to explain the presence of different species in plots with epiphytes.
Plots without epiphytes tended to be less diverse than plots with epiphytes, but rarefaction analysis and anova showed no significant differences in species richness between treatments in any of the seasons. Mean bird abundance was significantly higher in plots with epiphytes during both seasons, and a multidimensional scaling analysis showed that bird community structure differed between the two treatments.
Eighteen forest bird species were significantly more abundant in plots with epiphytes. Three non‐forest species were more common in plots without epiphytes. Resident bird species that used epiphytes as a nesting substrate were significantly more abundant in plots with epiphytes.
When epiphytes are removed, canopy cover, foraging substrates, nest sites and nest materials are eliminated and microclimatic conditions change. This could increase predation on adult birds and nests, increase intra‐ and interspecific competition, and decrease individual survivorship.
Synthesis and applications. This is the first experimental assessment of the importance of epiphytes for birds. Shade‐coffee plantations with epiphytes maintain higher abundance and diversity of the inhabitant bird fauna than plantations without epiphytes. This study reinforces the value of positive epiphyte management as an important factor in shade‐grown coffee certification, where the goal is to promote biodiversity conservation.
Non‐random species extinction and plant production: implications for ecosystem functioning
Authors: SCHLÄPFER F. , PFISTERER A. B. , SCHMID B. 
Published: February 2005

SummaryUnderstanding ecosystem responses to plant species loss is essential for the optimal management of grasslands. Recent studies have examined the effects of simulated random species loss in experimental plant communities but not those of realistic non‐random species loss resulting from transient extinction pressures in semi‐natural grasslands.To investigate the potential effects of non‐random species loss on grassland productivity, we established mesocosms with mixed communities comprising 15 plant species, and exposed them to 2 years of high‐intensity management (an extinction phase) followed by 2 years of low‐intensity management (a restoration phase) allowing recolonization from differentially managed neighbouring plots. In addition, monocultures of each component species were subject to the same extinction–restoration phases.During the extinction phase, species with high monoculture biomass had lower extinction probabilities in the mixed community than species with low monoculture biomass, but there was also species‐specific variation. The species that were most productive or most persistent during the extinction phase were not the same as those performing best in the restoration phase.No consistent effects of spontaneous recolonization from neighbouring communities on species richness or productivity of the focal communities were observed during the restoration phase.We estimated that extinction of all but the species with the lowest extinction risk reduced biomass productivity by 42–49%; loss of all but the four species with the lowest extinction risk reduced it by 2–35%. Identical calculations for a random extinction scenario yielded reductions of 52% and 26–54%, respectively.Synthesis and applications. Prediction of the effects of species loss on plant production and on other aspects of ecosystem functioning in semi‐natural grasslands must account for both specific non‐random extinction processes and post‐extinction conditions. For European mesic grasslands experiencing a shift from high‐intensity to low‐intensity management, our results suggest that recolonization by ‘missing’ species must be actively assisted if high production is a management objective.
Effects of timing of prescribed fire on the demography of an invasive plant, spotted knapweed Centaurea maculosa
Authors: EMERY SARAH M. , GROSS KATHERINE L. 
Published: February 2005

Summary

Prescribed burning is a key tool used in prairie and savanna restoration projects. The timing and frequency of prescribed fires are important variables to consider because they can differentially affect the survival of individual plant species, including noxious exotic species.
We used annual censuses and population matrix analysis to evaluate the demographic consequences of burning on populations of the invasive species spotted knapweed Centaurea maculosa in a Michigan, USA, prairie restoration experiment. We compared spring, summer and autumn burns at two frequencies: annually (2000–03) and in alternate years (2001, 2003). We examined the effects of different seasons and frequencies of prescribed fire on the survival, growth and reproduction of C. maculosa populations, and used life‐table response experiments and elasticity analyses to determine how season of fire affects population growth rates.
We found that annual summer burning was the only treatment that significantly reduced overall population growth rates.
The life‐table response experiment analysis indicated which life stages contributed the most to changes in population growth rates under the different treatments. The summer burn treatments reduced population growth by reducing reproduction.
The different burn treatments altered the elasticity structure of populations, but in general reproduction of adults as well as survival of non‐reproductive adults and juveniles remained important in all treatments. This indicates that future attempts to control C. maculosa should focus on combinations of treatments targeting these life stages.
Synthesis and applications. Management decisions regarding prescribed burning in grassland restoration projects should consider the responses of individual species already present in the system. In particular, it is important to consider the effects of burning on noxious invasive species that may or may not have different life histories and responses to fire compared with native species. Population matrix modelling provides a more complete picture of the effects of management on population responses compared with other measures based only on community composition and relative abundance. Depending on the goals of a restoration, non‐traditional management options, such as summer burning in mid‐west USA prairies, may be effective management tools for the control of invasive species.
Vegetation–site relationships of roadside plant communities in West Virginia, USA
Authors: RENTCH J. S. , FORTNEY R. H. , STEPHENSON S. L. , ADAMS H. S. , GRAFTON W. N. , ANDERSON J. T. 
Published: February 2005

Summary

In mountainous regions, road construction is accompanied by large‐scale physical disturbance associated with cut and fill operations that drastically alter the landscape. Cut operations remove soil and rock from the hillside above the proposed road, while soil and rock are deposited on the down‐slope area in fill operations. The resultant roadsides are highly disturbed habitats characterized by plant communities maintained at an early successional stage. They are often planted with non‐native species and frequently provide vectors for the introduction and spread of invasive species. Public transportation managers need to balance the rapid revegetation of roadsides with the goal of maximizing use of native species and minimizing the introduction of non‐native species.
This study examined vegetation–site relationships along 13 major four‐lane highways in West Virginia, USA, using analysis of variance, multiresponse permutation procedures and indicator species analysis.
Mean soil nutrient values showed some differences with respect to highway, but fewer when highway positions were compared. Similarly, when highway position was considered, there were no significant differences in mean plant species richness, evenness or diversity.
Results of multiresponse permutation procedures suggested that different highways may be characterized by distinct vegetation assemblages. This hypothesis was supported by indicator species analysis: 54 species showed a statistically significant (P < 0·05) affinity to one highway over all others. More than half of these were classified as non‐native and exotic invasive species. When highway position was considered, no significant differences in community composition were found, and indicator species analysis found only 25 species that exhibited a significant affinity to one type of position. Of these, only eight were exotic.
Of the 33 most abundant herbaceous species, 11 showed a significant relationship between cover and distance from pavement. For all but one, average cover declined in a linear fashion with increasing distance.
Synthesis and applications. Despite extensive topographic disturbance associated with highway construction, the resultant vegetative communities do not differ with respect to type of construction or resultant landform. This suggests that highway agencies can manage roadside vegetation using similar, standard techniques. Roadsides are optimal growing sites for exotic invasive species that out‐compete native vegetation. Management goals should therefore include techniques for limiting the establishment of these species, and substitution of non‐native species planted for erosion control with suitable native species.
Stable coexistence of an invasive plant and biocontrol agent: a parameterized coupled plant–herbivore model
Authors: BUCKLEY YVONNE M. , REES MARK , SHEPPARD ANDREW W. , SMYTH MATTHEW J. 
Published: February 2005

Summary

Coupled plant–herbivore models, allowing feedback from plant to herbivore populations and vice versa, enable us to predict the impact of biocontrol agents on their target weed populations; however, they are rarely used in biocontrol studies. We describe the population biology of the invasive plant Echium plantagineum and the weevil Mogulones larvatus, a biocontrol agent, in Australia. In order to understand the dynamics of this plant–herbivore system, a series of coupled models of increasing complexity was developed.
A simple model was extended to include a seed bank, density‐dependent plant fecundity, competition between weevil larvae and plant tolerance of herbivory, where below a threshold plants could compensate for larval feeding. Parameters and functional forms were estimated from experimental and field data.
The plant model, in the absence of the weevil, exhibited stable dynamics and provided a good quantitative description of field densities before the weevil was introduced.
In the coupled plant–herbivore model, density dependence in both plant fecundity and weevil larval competition stabilized the dynamics. Without larval competition the model was unstable, and plant tolerance of herbivory exacerbated this instability. This was a result of a time delay in plant response to herbivore densities.
Synthesis and applications. The coupled plant–herbivore model allowed us to predict whether stable coexistence of target plant and biocontrol agents was achievable at an acceptable level. We found this to be the case for the Echium–Mogulones system and believe that similar models would be of use when assessing new agents in this and other invasive plant biocontrol systems. Density dependence in new biocontrol agents should be assessed in order to determine whether it is likely to result in the aims of classical biocontrol: low, stable and sustainable populations of plant and herbivore. Further work should be done to characterize the strength of density dependence according to the niche occupied by the biocontrol agent, for example the strength and functional form of density dependence in stem borers may be quite different to that of defoliators.
Exposure of non‐target small mammals to rodenticides: short‐term effects, recovery and implications for secondary poisoning
Authors: BRAKES C. R. , SMITH R. H. 
Published: February 2005

Summary

Monitoring of exposure to pesticides in many countries shows extensive exposure of predators to anticoagulant rodenticides, which are used to control rats. Many predators and scavengers are declining in numbers, and exposure to rodenticides might therefore be of importance in conservation biology.
Predators and scavengers of poisoned rats are at most risk of secondary poisoning. However, several predatory species of conservation concern rarely eat rats, implicating non‐target small mammals as the major route of exposure. For the first time, this research investigated the importance of non‐target small mammals as routes of exposure to rodenticide for predators and scavengers in the UK.
Exposure studies of non‐target small mammals were carried out alongside routine rat control at five sites, around agricultural buildings (n = 2) and feed hoppers for game birds (n = 3).
Three non‐target rodent species fed on rodenticide from bait boxes during routine rat control treatments. A large proportion (48·6%) of individuals in local populations ate the bait: woodmice Apodemus sylvaticus were most exposed, followed by bank voles Clethrionomys glareolus then field voles Microtus agrestis.
Local populations of non‐target small mammals declined significantly following rodenticidal rat control but their relative proportions did not change significantly. Populations recovered partially after 3 months, depending on the time of the year relative to the breeding cycle.
Synthesis and applications. Our results clearly demonstrate that routine rat control reduced local populations of non‐target small mammals. This may limit the food supply of some specialist predators. Most importantly, this demonstrates a significant route of exposure of predators and scavengers of small mammals to secondary poisoning. Rodenticides are applied on farms and game estates across the UK. Hence the results of this study are indicative of non‐target rodenticide exposure nationally. Mitigation requires a shift from the current reliance on rodenticides to ecologically based rodent management, involving improvements in site management and the adoption of good farming practice.
Indirect negative impacts of radio‐collaring: sex ratio variation in water voles
Authors: MOORHOUSE TOM P. , MACDONALD DAVID W. 
Published: February 2005

SummaryRadio‐tracking is used ubiquitously in studies of wild vertebrates, a fundamental assumption being that tagged animals do not significantly differ, behaviourally or otherwise, from untagged animals.We studied two populations of water volesArvicola terrestris: one population was live‐trapped from April to September for 2 years (2000, 2001) and then concurrently radio‐tracked and trapped in a third year (2002). The second population was trapped only during 2002.During 2002, a substantial decline in female numbers in the radio‐collared population was recorded, apparently resulting from a male skew in the sex ratios of offspring born to this population. The mean numbers of males and females born duringtrappingonly were 25·7 (SD 2·1) and 29·0 (SD 7·0), respectively. Recruits to theradio‐trackedpopulation were skewed heavily in favour of males (43 : 13).Both hypotheses commonly invoked to explain mammalian sex‐ratio manipulation refer to the condition of mothers. The altered sex ratio resulted from a 48% decrease in numbers of females born, a decrease similar to the proportion (0·49) of the female population that was collared. No similar decline in male births occurred. This suggests that radio‐collaring of females caused male‐skewed sex ratios.Synthesis and applications. We conclude that the observed decline in female numbers resulted from male‐skewed recruitment sex ratios due to the attachment of radio‐collars to female water voles. These results question the assumption that the use of radio‐collars does not fundamentally affect the biology of collared water voles.
Predicting numbers of hauled‐out harbour seals: a mathematical model
Authors: HAYWARD JAMES L. , HENSON SHANDELLE M. , LOGAN CLARA J. , PARRIS CATHERINE R. , MEYER MATTHEW W. , DENNIS BRIAN 
Published: February 2005

SummaryIt was once assumed that commercially important fish make up significant portions of seal diets. As a consequence, prior to the 1970s many seal populations were dramatically reduced by rampant slaughtering. Today, seals and other marine mammals are valued components of marine ecosystems and their numbers are carefully managed. To facilitate management, government statutes mandate the systematic monitoring of seal populations. Population estimates are based on counts of hauled‐out seals obtained by aerial survey and radio and satellite telemetry; hence, considerable effort has been devoted to finding optimal times for such counts. We have developed a predictive mathematical model of seal haul‐out to assist resource managers in the selection of optimal census times.Haul‐out depends on a number of environmental variables. Some of these variables, such as wind speed, can be obtained only as historical data or short‐range predictions. Others, such as tide height, are deterministic and can be obtained as long‐range predictions.We used deterministic environmental variables to develop mathematical models that describe haul‐out dynamics of harbour sealsPhoca vitulinaduring the pupping season at a site in Washington, USA. A list of alternative hypotheses for environmental cues gave rise to a suite of competing models. We used information–theoretic model selection techniques to choose the best model. The selected model was a function of tide height and current direction, and explained 40% of the variability in hourly census data.An assumption that the system recovers rapidly after disturbance introduced two time scales. This allowed the differential equation model to be reduced to an algebraic equation.Synthesis and applications.This study demonstrates that resource managers can use a simple algebraic equation based on deterministic environmental variables to predict times at which to census maximal haul‐out in harbour seals. At the Washington site, maximal daily haul‐outs during pupping season are predicted to occur during receding tides, approximately midway between high and low tides. The largest maximal daily haul‐outs during the pupping season are predicted to occur in the last week of July. The environmental factors correlated with haul‐out are, however, site‐specific; therefore the model developed for the Washington site will not necessarily hold for other haul‐out areas. Managers should carry out the model selection procedure separately for each monitored haul‐out site. The general methodology employed in this study can be used to make long‐range predictions of diurnal movements for a variety of marine birds and mammals.
Power of monitoring programmes to detect decline and recovery of rare and vulnerable fish
Authors: MAXWELL DAVID , JENNINGS SIMON 
Published: February 2005

Summary

Abundance trends provide key guidance when setting conservation priorities, whether indicating population decline, stability or recovery. Knowledge of the power of surveys to detect trends is essential, as the consequences of not detecting a real trend can be profound.
Unfortunately, some surveys have been established with no assessment of power, and others are used to study species that were not their original focus. The latter is common in the marine environment, where rare fish are monitored using catch data from surveys that target more abundant commercially fished species.
We calculated the power of a large‐scale annual monitoring survey (the English North Sea bottom trawl survey) to detect decline and recovery of species that are vulnerable to fishing. As fisheries exploitation invariably precedes scientific investigation, the survey began after many vulnerable species had already been depleted.
The power of the survey to detect declines in the abundance of vulnerable species on time scales of < 10 years was low and the survey often failed to detect declines that would lead to listings under the IUCN A1 Red List criteria. Thus conservation prioritization based solely on survey data may fail to identify species at risk of regional extinction.
If conservation measures were effective, and vulnerable populations recovered at the maximum potential rate, 5–10 years of monitoring would often be required to detect recovery.
Power to detect trends in abundance was increased by developing a composite indicator that reflected trends in abundance of several vulnerable species. This indicator provided an overview of their conservation status.
Synthesis and applications. Consistent with the precautionary principle, conservation prioritization and management action should not depend on the statistical significance of recent abundance trends when low power is a consequence of historical depletion. If the conservation prioritization and management of rare and/or vulnerable species have to be predicated on evidence of significant declines, then higher type 1 error rates (falsely detecting a decline) should be acceptable. This is because the costs of type 1 errors are lower than those of type 2 (failure to detect a real decline).