Ecological limits to human disturbances – A case study involving trails

Human Activity Differentially Redistributes Large Mammals in the Canadian Rockies National Parks 

James Kimo Rogala, Mark Hebblewhite,Jesse Whittington,Cliff A. White,Jenny Coleshill and Marco Musian 
Ecology and Society 16(3): 16.

Burgeoning population is causing irrevocable havoc in many wilderness areas. Parks are susceptible to habitat degradation. Indirect habitat loss is also possible as a result from both natural and anthropogenic disturbances. This new study on the human impact on wildlife in some of Canada’s most popular national parks has identified limits at which trails can be used before ecological disturbance sets in. Even though the thrust is on Canadian Parks the results arrived at has implications for mangers worldwide.

The researchers say human activity on trails and roads may lead to indirect habitat loss, further limiting available habitat. Predators and prey may respond differentially to human activity, which in turn has the potential for disrupting ecological processes

The researchers investigated the relationship between wolf and elk distribution and human activity using fine-scale Global Positioning System (GPS) wildlife telemetry locations and hourly human activity measures on trails and roads in Banff, Kootenay, and Yoho National Parks, Canada. They observed a complex interaction between the distance animals were located from trails and human activity level resulting in species adopting both mutual avoidance and differential response behaviors. In areas < 50 m from trails human activity led to a mutual avoidance response by both wolves and elk. In areas 50 - 400 m from trails low levels of human activity led to differential responses; wolves avoided these areas, whereas elk appeared to use these areas predation refugia. These differential impacts on elk and wolves may have important implications for trophic dynamics.

As human activity increased above two people/hour, areas 50 - 400 m from trails were mutually avoided by both species, resulting in the indirect loss of important montane habitat.

The researchers contend that if park managers are concerned with human impacts on wolves and elk, or on these species’ trophic interactions with other species, they can monitor locations near trails and roads and consider hourly changes of human activity levels in areas important to wildlife.

The researchers sign off with the following words “The circadian cycle has been the finest temporal scale used by previous studies that associate wildlife distribution to human activity. Our research documented that wildlife avoidance occurs at finer spatio-temporal scales than previously studied. We found that wolf and elk selection of locations near trails and roads was dependent on hourly human activity levels and the distance to the human linear feature. A failure to properly address the scale at which wildlife respond to human activity could lead to mistaken conclusions about habitat selection. Proper assessment of the relationship between fine-scale human activity and wildlife distribution may have important implications for animal energy budgets, human-wildlife and predator-prey interactions, ecological trophic cascades, and wildlife viability.”

Theory and practice of conservation – Importance of quantitative recommendations

Quantitative recommendations for amphibian terrestrial habitat conservation derived from habitat selection behavior

Lukas Indermaur and Benedikt R. Schmidt

Ecological Applications 21:2548–2554, Volume 21, Issue 7 (October 2011)

When it comes to practice of conservation there is often a big slip  between the cup and the lip. Conservation managers rarely use scientific information when making decisions.

The grouse of the manger is that conservation scientists rarely provide their knowledge in a way that can directly be used by conservation practitioners. Often the reports are couched in words not understood by the practitioner.

In this paper the researchers show how quantitative recommendations for conservation can be derived.

Past research on terrestrial habitat selection behavior of toads (Bufo bufo and Bufo viridis) showed that wood deposits are a key resource in the terrestrial habitat. The researchers used habitat-dependence analysis to estimate the amount of this key resource, wood deposits, that individual toads require. Based on these estimates they quantified the requirements for wood deposits for a population. The also quantified the area that a population requires.

The researches say although wood deposits vary strongly in size, they found little evidence for size preferences: only one species preferred smallest sizes of wood deposits.

The researchers report all the estimates in a way that can be directly used by conservation managers.

The researchers sign off with the following words “Habitat-dependence analysis is a simple and useful tool to quantify habitat requirements. Provisioning of wood deposits may improve the quality of terrestrial habitat for amphibians. Thereby, managers may increase the carrying capacity of terrestrial habitats and support elevated population densities”

Estimating age when multiple sources of data are available and traditional aging techniques are not practical.

Estimating age from recapture data: integrating incremental growth measures with ancillary data to infer age-at-length

Mitchell J. Eaton and William A. Link

Ecological Applications 21:2487–2497.  Volume 21, Issue 7 (October 2011) 

For answering ecological questions, modeling population demographics, and managing exploited or threatened species estimation of age of individuals in wild populations is of paramount importance. Determining age through the use of growth annuli and growth models are in vogue.

The researcher say many species either do not exhibit physical characteristics useful for independent age validation or are too rare to justify sacrificing a large number of individuals to establish the relationship between size and age.

Many Length-at-age models used in fisheries overlook variation in growth rates of individuals and consider growth parameters as population parameters. More recent models of this genre have taken advantage of hierarchical structuring of parameters and Bayesian inference methods to allow for variation among individuals as functions of environmental covariates or individual-specific random effects.

In this paper the researchers describe hierarchical models in which growth curves vary as individual-specific stochastic processes. They demonstrate how these models can be fit using capture–recapture data for animals of unknown age along with data for animals of known age.

The researchers say they combined these independent data sources in a Bayesian analysis, distinguishing natural variation (among and within individuals) from measurement error. They illustrate using data for African dwarf crocodiles, comparing von Bertalanffy and logistic growth models.

The researchers describe hierarchical models in which growth curves vary as individual-specific stochastic processes, and they show how these models can be fit using capture–recapture data for animals of unknown age along with data for animals of known age. The von Bertalanffy was much better supported than the logistic growth model and predicted that dwarf crocodiles grow from 19.4 cm total length at birth to 32.9 cm in the first year and 45.3 cm by the end of their second year. Based on the minimum size of females observed with hatchlings, the researchers estimated reproductive maturity to be at nine years.

The analysis provides the means of predicting crocodile age, from a single measurement of head length.

The researchers contend that these size benchmarks represent thresholds for important demographic parameters; improved estimates of age, therefore, will increase the precision of population projection models. They say the modeling approach that they present can be applied to other species and offers significant advantages when multiple sources of data are available and traditional aging techniques are not practical.

 

Amur leopard captured on camera in China

Amur leopard has been captured on camera in China for the first time since 1949.

The elusive cat was photographed in a forest in Wangqing County, on the border of Russia and North Korea.

 Photo: credit  Peking University/ World Wildlife Fund 

In April, a video captured five of the elusive leopards in the remote forests of the Russian Far East. Have look at the video.On slow connections it might take couple of minutes for the video to load.

Loss and fragmentation of natural areas and its effect on connectivity

Assessing effects of land use on landscape connectivity: loss and fragmentation of western U.S. forests

 Theobald, David M., Kevin R. Crooks, and John B. Norman

 Ecological Applications, 21:2445–2458.

The accent of this paper is on US, but what is described is of relevance worldwide. The methodology described can be readily modified to examine connectivity for other habitats/ecological systems and for other geographic areas

Loss and fragmentation of natural areas is a big concern for conservation scientists and land managers worldwide. Deleterious effects of land-use change are adversely affecting connectivity and conservation of biodiversity.

The authors of this paper say there is an urgent need to develop practical approaches to identify where important lands are for landscape connectivity (i.e., linkages), where land use constrains connectivity, and which linkages are most important to maintain network-wide connectivity extents. Their effort was to develop an approach that provides comprehensive, quantitative estimates of the effects of land-use change on landscape connectivity and illustrate its use on a broad, regional expanse of the western United States.

The researchers quantified loss of habitat and landscape connectivity for western-forested systems due to land uses associated with residential development, roads, and highway traffic. They examined how these land-use changes likely increase the resistance to movement of forest species in non-forested land cover types and reduce the connectivity among forested habitat patches. They applied a graph-theoretic approach that incorporates ecological aspects within a geographic representation of a network.

The researchers found that roughly one-quarter of the forested lands in the western United States were integral to a network of forested patches. Of course, the lands outside of patches remain critical for habitat and overall connectivity. Using remotely sensed land cover data (ca. 2000), they found 1.7 million km² of forested lands. They estimate that land uses associated with residential development, roads, and highway traffic have caused roughly a 4.5% loss in area (20 000 km²) of these forested patches. Continued expansion of residential land is likely to reduce forested patches by another 1.2% by 2030. They also identified linkages among forest patches that are critical for landscape connectivity. 

The researchers emphasize that their approach can be readily modified to examine connectivity for other habitats/ecological systems and for other geographic areas, as well as to address more specific requirements for particular conservation planning applications

How to clean an oil-slicked penguin

I read this excellent article on how to clean an oil-slicked penguin in BBC online. Biologist Jeremy Gray, volunteering at the Oiled Wildlife Response Centre in Tauranga, New Zealand, after the Rena oil spill, explains in detail the procedure involved. It might come in handy for you. Read it HERE

Wildlife Management - Well-meaning management strategies not based on sound scientific evidence, may go haywires

While managing endangered species wildlife mangers often resort to food supplementation. Even though it has the potential for delivering immediate benefits there could be hidden dangers. This has been proved by recent research on Spanish Imperial Eagle, Aquila adalberti,

Spanish Imperial Eagle, Aquila adalberti, is one of the most endangered birds of prey in the world. For two decades, intensive food supplementation has been used in attempting to improve the breeding productivity of the bird.

The researchers examined the impact of this intensive management action on nestling health, including contamination, immunodepression, and acquisition of disease agents derived from supplementation techniques and provisioned food.

The researchers found that fed individuals were often inadvertently “medicated” with pharmaceuticals (antibiotics and antiparasitics) contained in supplementary food (domestic rabbits). Individuals fed with medicated rabbits showed a depressed immune system and a high prevalence and richness of pathogens as against those with no or safe supplementary feeding using non-medicated wild rabbits. A higher presence of antibiotics (fluoroquinolones) was found in sick when compared to healthy individuals among eaglets with supplementary feeding. This in turn points directly toward a causal effect of these drugs in disease and other health impairments.

The researchers sign off with the following words” This study represents a telling example of well-meaning management strategies not based on sound scientific evidence becoming a “contraindicated” action with detrimental repercussions undermining possible beneficial effects by increasing the impact of stochastic factors on extinction risk of endangered wildlife.

Journal reference

When conservation management becomes contraindicated: impact of food supplementation on health of endangered wildlife

Guillermo Blanco, Jesús A. Lemus, Marino García-Montijano

Ecological Applications

Volume 21, Issue 7 (October 2011) pp. 2469-2477

UK is moving up a notch with landscape level conservation

The future belongs to landscape level conservation. National parks and other wildlife reserves are Ok, but they should never be seen as an end by itself. Many parks across the globe are becoming islands of isolation amidst teeming masses. Managing fragments will not deliver what wildlife requires in the long run.

Realizing the importance of landscape level conservation conservationists in UK are moving in a new direction, with reserves at the centre of a wider, landscape scale approach to protecting wildlife. At the focus is RSPB’s Futurescapes programme.  Within each Futurescape conservationists are working in partnership with farmers, landowners, local authorities and the community to ensure a living space for wildlife.

This effort by RSPB in association with other like-minded people and the local community is worthy of emulation by others.

Otter fecal genotyping studies and population estimation – Guidance for wildlife managers

The first river otter reintroductions in US occurred in Missouri and it is regarded as one of the most successful carnivore recovery programs in history.

The sticking point is that abundance estimates for river otter populations are difficult.  Here the researchers assessed the value of latrine site monitoring as a mechanism for quantifying river otter abundance. Analyses of fecal DNA to identify individual animals were tried.

The researchers say they optimized laboratory protocols, redesigned existing microsatellite primers, and calculated genotyping error rates to enhance genotyping success for a large quantity of river otter scat samples. The also developed a method for molecular sexing.

As a next step the researcher extracted DNA from 1,421 scat samples and anal sac secretions (anal jelly) collected during latrine site counts along 22–34-km stretches. These stretches represented 8–77% of 8 rivers in southern Missouri.

Error rates were low for the redesigned microsatellites. They obtained genotypes at 7–10 microsatellite loci for 24% of samples, observing highest success for anal jelly samples (71%) and lowest for fresh samples (collected within 1 day of defecation)

The team identified 63 otters (41 M, 22 F) in the 8 rivers, ranging from 2 to 14 otters per river. Analyses using program CAPWIRE resulted in population estimates similar to the minimum genotyping estimate. Density estimates averaged 0.24 otters/km.

The researchers used linear regression to develop and contrast models predicting population size based on latrine site and scat count indices, which are easily collected in the field. Population size was best predicted by a combination of scats per latrine and latrines per kilometer.

 The researchers contend that their results provide methodological approaches to guide wildlife managers seeking to initiate similar river otter fecal genotyping studies, as well as to estimate and monitor river otter population sizes.

Journal reference 

River Otter Population Size Estimations using Noninvasive Latrine Surveys

 Rebecca A. Mowry, Matthew E. Gompper, Jeff Beringer, Lori S. Eggert
pg(s) 1625–1636 Journal of Wildlife Management Volume 75 Issue 7

'Chivalrous’ behavior is not exclusive of humans or closely related mammals

I just tread this fascinating paper on insects displaying 'Chivalrous’ behavior.  Well, this is not something from science fiction, it is a fact recently established by scientific research.

Video observations of a wild population of field crickets (Gryllus campestris) by researchers showed males putting their life at risk to protect the females. When a mated pair is out together, males allowed a female priority access to the safety of a burrow, even though it meant increase in the risk of the male being eaten. The researchers say guarding males sire more of their mate's offspring, at a cost of reduced life span. Females benefit from being guarded by dramatically reducing their predation risk.

The usual interpretation of male guarding behavior is an attempt to manipulate females and prevent them from mating with rivals. The new study bucks this belief.

The researchers sign off with the following words” In contrast to conclusions based on previous lab studies, our field study suggests that mate guarding can evolve in a context of cooperation rather than conflict between the sexes.”

Journal reference 

Guarding Males Protect Females from Predation in a Wild insect

Rolando Rodríguez-Muñoz, Amanda Bretman, Tom Tregenza

Current Biology, 06 October 2011

Unexpected ecological impacts of alien species

Colossal Aggregations of Giant Alien Freshwater Fish as a Potential Biogeochemical Hotspot
Stéphanie Boulêtreau, Julien Cucherousset, Sébastien Villéger, Rémi Masson, Frédéric Santoul.
 PLoS ONE, 2011; 6 (10): e25732

Here is a very fascinating paper on the unexpected spin-offs from alien invasion. The researchers report consistent and previously undocumented occurences of aggregations of a giant alien freshwater fish, the Wels catfish (Silurus glanis) in Rhone river and its unexpected functional consequences in recipient ecosystems.

Evidence gathered by the researchers suggests that the mechanism responsible for the observed aggregations were not associated with schooling behavior, reproduction, and foraging or anti-predator behavior. Individuals were active, always swimming, but were not all pointing in the same direction as observed in polarized shoals. No synchronous movements were observed. In the case of schooling fish they maintain a minimum distance between conspecifics. Here the individuals were swimming while rubbing against each other. No mating behaviours were observed and groups occurred throughout the year at temperatures below the spawning threshold. The researchers contend that foraging behaviour was unlikely since no prey was captured and no foraging behaviour was displayed. All individuals were large enough to be released from any predation risk.

The fascinating observation is that defecation and excretion from dense aggregations of fish that rest over coral reefs provide important quantity of nitrogen and phosphorus that subsequently increase the growth rate of corals. The researchers say in some cases fish can translocate nutrients within the ecosystem by feeding in one location while defecating in another.  Heterogenous spatial distribution of fish can also create biogeochemical hotspots, i.e. places where nutrient release by animals exceeds the need of primary producers. The aggregations of alien fish studied by the researchers potentially represent the highest biogeochemical hotspots ever reported for freshwater ecosystems.

The researchers sign off like this "our study is unique in identifying unexpected ecological impacts of alien species. Our findings will be ground breaking news for many scientific fields including conservation biology, ecosystem ecology and behavioral ecology and anyone interested in biological invasion and the potential ecological impacts of alien species. Therefore, we believe that our manuscript will stimulate further research and discussion in these fields."

New Discovery – Jungle crows can identify symbols

Japanese researchers from Utsunomiya University have discovered that crows possess the ability to distinguish between symbols representing different quantities. This works down to the fact that crows have the same numerical cognition ability as humans.

 The birds successfully selected containers containing the highest quantity of food by identifying numbers marked on the lid. The crows were able to pick the correct box 70 percent of the time

When crows could discriminate five items (15 out of 20 correct choices in two blocks of 10 trials each), they received control tests for non-numerical cues such as element configuration, shape, and total filled area and novel quantity (3 versus 5, 4 versus 5, 5 versus 6, 5 versus 7 and 5 versus 8) tests. During training, jungle crows learned the discrimination task relatively quickly.

The crows were responding to quantity. The researchers say Jungle crows selected the familiar larger quantity in smaller sets (3 versus 5 and 4 versus 5) and the novel larger in larger comparisons (5 versus 7 and 5 versus 8) except that of 5 versus 6 quantities.

The researchers say the results suggest that jungle crows have a natural tendency to select the larger quantities and that decisions were affected by the numerical ratio and stimuli magnitude, indicating the use of analogue magnitude mechanism for numerical judgment, as is observed in other animals.

Journal reference 

Quantity discrimination in jungle crows, Corvus macrorhynchos 
Animal behaviour,  Pages 635-64, Volume 82, Issue 4 (October 2011)
Bezawork Afework Bogale, Naoki Kamata, Katano Mioko, Shoei Sugita

Six ways to never get lost in a city again – A nice BBC article

I just read this very nice article “Six ways to never get lost in a city again” and thought it would be nice to share it with you guys.

Are you one of those 'directionally dysfunctional' guys? If so you will find this very useful.

Smart phones, sat-navs or other GPS devices are OK, but they have their limitations. All it takes is a flat battery or a mechanical fault to throw things out of kilter. Natural navigation is what you need under this circumstance. Read the fascinating article HERE

Determining and analyzing multiple ecosystem services across a given spatial scale

Using plant functional traits to understand the landscape distribution of multiple ecosystem services

Sandra Lavorel,Karl Grigulis, Pénélope Lamarque,Marie-Pascale Colace,Denys Garden,Jacky Girel,Gilles Pellet,Rolland Douze

Journal of Ecology

Volume 99, Issue 1, pages 135–147, January 2

This paper deals with the problem of determining and analyzing multiple ecosystem services across a given spatial scale. Presently our understanding of these multiple ecosystem services leaves much to be desired. . The methodology given by the researchers will help us better comprehend the delivery of multiple ecosystem services.

The researcher say in their method spatially explicit single ES models based on plant traits and abiotic characteristics are combined to identify ‘hot’ and ‘cold’ spots of multiple ES delivery, and the land use and biotic determinants of such distributions. They demonstrate the value of this trait-based approach as compared to a pure land-use approach for a pastoral landscape from the central French Alps, and highlight how it improves understanding of ecological constraints to, and opportunities for, the delivery of multiple services.

Vegetative height and leaf traits such as leaf dry matter content were response traits strongly influenced by land use and abiotic environment, which has follow-on effects on several ecosystem properties, and this could therefore be used as functional markers of ES.

The authors’ continue like this  “Patterns of association among ES were related to the dominant traits underlying different ecosystem properties. The functional decoupling between height and leaf traits provided alternative pathways for high agronomic value, as well as determining hot and cold spots of ES. Traditional land uses such as organic fertilization and mowing or altitude summer grazing were also linked with ES hot spots, because functional characteristics supporting fodder production and quality are compatible with species and functional diversity.”
“Analyses of ES using plant functional variation across landscapes are a powerful approach to understanding the fundamental ecological mechanisms underlying ES provision, and trade-offs or synergies among services. Sustainable management of species and functionally diverse grassland could simultaneously aim at conserving biodiversity and locally important ES by taking advantage of correlations and trade-offs among different plant functional traits”.

Social dominance in bank voles depends on the size of their genitals

Researcher Dr Jean-Francois Lemaitre from the University of Liverpool with colleagues in France and Switzerland, studying the social dominance in bank voles, (Myodes glareolus), has come up with the finding that social dominance for bank voles depends on the size of their genitals. 

Dominant males invariably had wider penis bones. The researchers say differences in the genitalia of dominant and subordinate males could be a factor contributing to the fertilisation advantage of dominant males under sperm competition. They also found evidence of positive allometry and a relatively high coefficient of phenotypic variation in the baculum width of male bank voles, consistent with an influence of sexual selection.

The researchers sign off like this” We conclude that dominant male bank voles may benefit from an enlarged baculum under sperm competition and/or cryptic female choice and that differences in penile morphology according to male social status might be important but as yet largely unexplored source of variation in male reproductive success.”

  

Journal reference

Genital morphology linked to social status in the bank vole (Myodes glareolus)

Jean-François Lemaître, Steven A. Ramm, Nicola Jennings and Paula Stockley

Behavioral Ecology and Sociobiology

DOI: 10.1007/s00265-011-1257-4

World’s largest shark sanctuary

Here is some great news. The Marshall Islands government has created the world's largest shark sanctuary

The sanctuary covers nearly two million sq km of ocean. Till now the sanctuary declared by Palau two years ago was the worlds biggest.

Commercial shark fishing and any trade in shark products will be banned. Any fish accidentally caught must be released alive.

Tahrcountry salute the Republic of the Marshall Islands for this magnificent move. The country may be small but the conservation effort is truly MEGA

Another book recommendation

Beyond Naturalness: Rethinking Park and Wilderness Stewardship in an Era of Rapid Change

David N. Cole, Laurie Yung

Island Press

Here is a book worth a read by managers of wilderness areas

The professed purpose of establishing the protected areas is to keep them in their “natural” state. The authors ask what does naturalness mean, particularly as the effects of stressors such as habitat fragmentation, altered disturbance regimes, pollution, invasive species, and climate change become both more pronounced and more pervasive? Ecosystems are not isolated entities they are dynamic systems with interdependencies, complexities, and uncertainties.

The book brings together leading scientists and policymakers to explore the concept of naturalness, its varied meanings, and the extent to which it provides adequate guidance regarding where, when, and how managers should intervene in ecosystem processes to protect park and wilderness values. Innovative ideas about how the areas should be managed are deliberated.

Donald Kennedy President Emeritus and Bing Professor of Environmental Science described the book like this “"Beyond Naturalness is a commentary on how we can preserve the sense of nature under change. The idea of pristine nature innocent of human presence was, we now know, mythical’ but this thoughtful book shows that sound policies can give us a rewarding nature with people in it."

·  Paperback: 304 pages

·  Publisher: Island Press; 1 edition (March 18, 2010)

·  Language: English

·  ISBN-10: 1597265098

·  ISBN-13: 978-1597265096

Book Recommendation

State of the Wild is a biennial series that brings together international conservation experts and writers to discuss emerging issues in the conservation of wildlife and wild places.

This volume has twenty essays intermixed with poetry, and photos that are a treat to the eye. The accent is on how destabilization and war affect wildlife and wild places. Topics discussed include “Can the work of saving wildlife and wild places help ameliorate tensions? Can conservation deepen political understanding? Can conservation help in post-conflict situations?”

Series Editor: Kent Redford
Volume Editor: Eva Fearn
Available in Hardcover and paperback: 264 pages
· Publisher: Island Press (February 2, 2010)

· Language: English

· ISBN-10: 1597266787

· ISBN-13: 978-1597266789

In elephants age does matter in leadership

Leadership in elephants: the adaptive value of age

Karen McComb, Graeme Shannon,Sarah M. Durant,Katito Sayialel,Rob Slotow,Joyce Poole,and Cynthia Moss

Published online before print March 16, 2011, Proc. R. Soc. B 7 November 2011 vol. 278 no. 1722 3270-3276

I found this paper food for thought. It provides the first empirical evidence that individuals within a social group of elephants may derive significant benefits from the influence of an older leader because of their enhanced ability to make crucial decisions about predatory threat, generating what the authors say important insights into selection for longevity in cognitively advanced social mammals.

The value of age is well recognized in human societies, where older individuals often emerge as leaders in tasks that require specialized knowledge. Against this axiom what part do such individuals play in other social species? We have very little knowledge. The information is nebulous. This paper clears the cobweb at least in respect of African elephant (Loxodonta africana).

Here, the researchers used a novel playback paradigm to demonstrate that in African elephants, age affects the ability of matriarchs to make ecologically relevant decisions in a domain critical to survival i.e. the assessment of predatory threat.

Groups consistently adjusted their defensive behaviour to the greater threat of three roaring lions versus one. Against these families with younger matriarchs under-reacted to roars from male lions despite the severe danger they represent.

The researchers say sensitivity to the key threats increases with matriarch age and is greatest for the oldest matriarchs, who are likely to have accumulated the most experience.

On the whole a very good paper

International Year of Forests bibliography

Here is an excellent gesture from publishers Taylor & Francis and Routledg.

 

As part of a celebration of the International Year of Forests, they have compiled a collection of articles entitled “Celebrating Forests for People.”

This collection of articles includes more than 70 online, full-text articles from more than 50 journals. These are available for free to anyone, worldwide.

The full bibliography, with links to individual articles, is available here