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An Introduction to the Aquatic Insects of North America

AMPHIBIAN DECLINES: THE CONSERVATION STATUS OF UNITED STATES SPECIES. Michael Lannoo (ed.). 2005. University of California Press, Berkeley. ISBN 0-520-235924. XXI + 1094 p. $95.00 (hard cover).—During the past decade and a half, much has been discussed and published on amphibian declines. The new information obtained created a novel field of research in herpetology. The starting point of this new field was the First World Congress of Herpetology, held in Canterbury, England, in 1989, when herpetologists found that the amphibian disappearances they had witnessed individually were not merely rare, local phenomena but rather appeared to be occurring around the globe. The relevance of amphibian declines can be measured not only by the scientific production but also by the extensive coverage by the popular press. The book ‘‘Amphibian Declines: The Conservation Status of United States Species’’ summarizes the advances of this new research field, mainly in the United States. This is an extraordinary book based on the experience of an impressive team of specialists on amphibian declines and conservation, primarily focused on species from the United States. Because North American herpetologists have accumulated detailed data on native amphibians over many years, this book is very thorough. The book is divided into two parts; part one is a collection of 52 essays on conservation written mainly by researchers with extensive experience in amphibian conservation. This first part is divided into an Introduction and chapters titled Declines, Causes, Conservation, Surveys and Monitoring, Education, and Perspective. Part two corresponds to the species accounts for Anura and Caudata. An amazing total of 215 contributors participated in the two parts of the book, producing more than a thousand pages of rich information on amphibian declines and conservation in United States. The essays vary in detail and breadth of coverage, and there is some overlap among some of them, but this is to be expected in a book written by so many scientists. In the Introduction there are five essays that provide a historical perspective on the conservation of amphibians. In the Declines chapter five essays give a historical perspective as well, but there is also specific information on the decline of cricket frogs (Acris crepitans) and a data-rich essay on the decline of the salamanders of the genus Plethodon. Together the essays address all of the relevant topics of conservation and decline in amphibians. For example, the first essay by Tim Halliday addresses the main reasons for amphibian declines, summarizing recent progress that is improving our understanding on the causal factors promoting it. He indicates habitat destruction, climate change, pollution, increased UV-B radiation, and disease as the main factors, but also calls attention to the synergistic action among some of these causes. The necessity of a more ample comprehension of the conservation status of other groups of organisms is also highlighted, given that declines may also be severe in other taxa, such as bivalves. The lack of data on distribution, population structure, and habitat of amphibians makes the task of protection more difficult. In the second essay, Martha L. Crump discusses why some species are in decline while others are not. She compares studies in different parts of the world and concludes that the patterns associated with declines in one assemblage are not necessarily repeated in other assemblages. She did not find a clear pattern of differences (in phylogeny, distribution, habitat, activity, diet, body size, skin characteristics, and life history traits) between declining and non-declining species. She concludes that some species are less able to cope with anthropogenic environmental changes. In Causes, 12 essays adequately cover the main causes that have been proposed or demonstrated to be involved in amphibian declines. Global warming, UV radiation, chemical pollution, parasites and malformations, habitat destruction or alteration, and commercial trade of amphibians are among the treated topics. However, in this chapter some essays are not related to the causes of decline per se, such as the essay on the Lucké renal adenocarcinoma in Northern Leopard Frogs (Lithobates pipiens). In this case there is no evidence that the carcinoma is a factor in frog population decline. In Conservation, 18 essays treat different aspects of amphibian conservation. There are essays on the conservation of specific taxa, such as one on the endangered Houston Toad (Anaxyrus houstonensis) that includes information on the major causes of decline and the politics that play an important role in conservation. The essay on fluctuations in the size of tiger salamander populations provides useful information for understanding the related natural and anthropogenic factors that affect this amphibian. The essay on the Texas spring and cave salamanders (Eurycea) shows that most species have restricted distributions and are threatened by human activities. The essay on the Southwestern desert bufonids indicates that, although these toads escaped the declines experienced by many anurans, some species are being eliminated from some areas as a result of habitat alteration. Two essays raise questions on taxonomic and systematic problems and the conservation status of the amphibians. They call attention to the necessity of clear and workable systems of classification to describe biodiversity, the importance of phylogenetic taxonomies, and the importance of conservation systematics in management and politics. The essay by Karen R. Lips and Maureen A. Donnelly is an exception in the book in that it aims to describe the nature, extent, and possible causes of amphibian declines in the tropics and not in United States. The limitation of this essay is the lack of data on tropical amphibian, which is not the authors’ fault (see below). Other essays in this chapter are on amphibian decline and management, landscape ecology, ecotoxicology, importance of museum collections in amphibian conservation, reserve network, population manipulations of imperiled species, exotic invading species of fish and amphibians and their impacts on the natural systems, and the importance of natural history in the conservation of amphibians. In the Surveys and Monitoring chapter, nine essays cover general and specific aspects, including methodological proposals. Some essays treat the distribution, decline, and monitoring of amphibians from specific places in the United States or from a general program, the North American

Amphibian Declines: The Conservation Status of United States Species

The rapid worldwide emergence of the amphibian pathogen Batrachochytrium dendrobatidis (Bd) is having a profound negative impact on biodiversity. However, global research efforts are fragmented and an overarching synthesis of global infection data is lacking. Here, we provide results from a community tool for the compilation of worldwide Bd presence and report on the analyses of data collated over a four-year period. Using this online database, we analysed: 1) spatial and taxonomic patterns of infection, including amphibian families that appear over- and under-infected; 2) relationships between Bd occurrence and declining amphibian species, including associations among Bd occurrence, species richness, and enigmatic population declines; and 3) patterns of environmental correlates with Bd, including climate metrics for all species combined and three families (Hylidae, Bufonidae, Ranidae) separately, at both a global scale and regional (U.S.A.) scale. These associations provide new insights for downscaled hypothesis testing. The pathogen has been detected in 52 of 82 countries in which sampling was reported, and it has been detected in 516 of 1240 (42%) amphibian species. We show that detected Bd infections are related to amphibian biodiversity and locations experiencing rapid enigmatic declines, supporting the hypothesis that greater complexity of amphibian communities increases the likelihood of emergence of infection and transmission of Bd. Using a global model including all sampled species, the odds of Bd detection decreased with increasing temperature range at a site. Further consideration of temperature range, rather than maximum or minimum temperatures, may provide new insights into Bd-host ecology. Whereas caution is necessary when interpreting such a broad global dataset, the use of our pathogen database is helping to inform studies of the epidemiology of Bd, as well as enabling regional, national, and international prioritization of conservation efforts. We provide recommendations for adaptive management to enhance the database utility and relevance.

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Mapping the Global Emergence of Batrachochytrium dendrobatidis, the Amphibian Chytrid Fungus

Summary
The past decade has seen an explosion in the development and application of models aimed at estimating species occurrence and occupancy dynamics while accounting for possible non-detection or species misidentification.
We discuss some recent occupancy estimation methods and the biological systems that motivated their development. Collectively, these models offer tremendous flexibility, but simultaneously place added demands on the investigator.
Unlike many mark–recapture scenarios, investigators utilizing occupancy models have the ability, and responsibility, to define their sample units (i.e. sites), replicate sampling occasions, time period over which species occurrence is assumed to be static and even the criteria that constitute ‘detection’ of a target species. Subsequent biological inference and interpretation of model parameters depend on these definitions and the ability to meet model assumptions.
We demonstrate the relevance of these definitions by highlighting applications from a single biological system (an amphibian–pathogen system) and discuss situations where the use of occupancy models has been criticized. Finally, we use these applications to suggest future research and model development.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/2041-210X.12100

Advances and applications of occupancy models

Habitat loss and disease are main drivers of global amphibian declines, yet the interaction between them remains largely unexplored. Here we show that paradoxically, habitat loss is negatively associated with occurrence, prevalence, and infection intensity of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in amphibian populations in the tropics. At a large spatial scale, increased habitat loss predicted lower disease risk in amphibian populations across Costa Rica and eastern Australia, even after jointly considering the effect of potential biotic and abiotic correlates. Lower host-species richness and suboptimal microclimates for Bd in disturbed habitats are potential mechanisms underlying this pattern. Furthermore, we found that anthropogenic deforestation practices biased to lowlands and natural vegetation remaining in inaccessible highlands explain increased Bd occurrence at higher elevations. At a smaller spatial scale, holding constant elevation, latitude, and macroclimate, we also found a negative relationship between habitat loss, and both Bd prevalence and infection intensity in frog populations in two landscapes of the Brazilian Atlantic Forest. Our results indicate that amphibians will be disproportionately affected by emerging diseases in pristine environments, and that, paradoxically, disturbed habitats may act as shelters from disease, but only for the very few species that can tolerate deforestation. Thus, tropical amphibian faunas are threatened both by destruction of natural habitats as well as increased disease in pristine forests. To curb further extinctions and develop effective mitigation and restoration programs we must look to interactions between habitat loss and disease, the two main factors at the root of global amphibian declines.

https://www.pnas.org/content/pnas/108/24/9893.full.pdf

Tropical amphibian populations experience higher disease risk in natural habitats

Batrachochytrium dendrobatidis is a fungal pathogen that is receiving attention around the world for its role in amphibian declines. Study of its occurrence patterns is hampered by false negatives: the failure to detect the pathogen when it is present. Occupancy models are a useful but currently underutilized tool for analyzing detection data when the probability of detecting a species is <1. We use occupancy models to evaluate hypotheses concerning the occurrence and prevalence of B. dendrobatidis and discuss how this application differs from a conventional occupancy approach. We found that the probability of detecting the pathogen, conditional on presence of the pathogen in the anuran population, was related to amphibian development stage, day of the year, elevation, and human activities. Batrachochytrium dendrobatidis was found throughout our study area but was only estimated to occur in 53.4% of 78 populations of native amphibians and 66.4% of 40 populations of nonnative Rana catesbeiana tested. We found little evidence to support any spatial hypotheses concerning the probability that the pathogen occurs in a population, but did find evidence of some taxonomic variation. We discuss the interpretation of occupancy model parameters, when, unlike a conventional occupancy application, the number of potential samples or observations is finite.

Using occupancy models to understand the distribution of an amphibian pathogen, Batrachochytrium dendrobatidis

Non-native fish and bullfrogs (Lithobates catesbeianus) are frequently cited as contributing to the decline of ranid frogs in the western United States, so we hypothesized that non-native species, habitat, or a combination of these relate to the probability of local extinction for northern red-legged frogs (Rana aurora) in Oregon, USA. We also hypothesized that the probability of colonization relates to land use, wetland size, or riparian forest. In a 5-yr study, we found no support for an effect of non-native species on northern red-legged frogs. Instead, probability of local extinction decreased with the extent of emergent vegetation and riparian forest. This finding suggests that managers consider the role of habitat when confronting non-native species problems.

Non-native species impacts on pond occupancy by an anuran

Livestock grazing is a common land use across the western United States, but concerns have been raised regarding its potential to affect amphibian populations. We studied the short-term effects of full and partial livestock grazing exclosures on Rana luteiventris (Columbia Spotted Frog) populations using a controlled manipulative field experiment with pre- and posttreatment data (2002-2006). Despite a significant increase in vegetation height within grazing exclosures, we did not find treatment effects for egg mass counts, larval survival, or size at metamorphosis 1-2 years following grazing exclosure installation. Water samples taken in late summer showed concentrations of nitrite, nitrate, ammonia, and orthophosphate that were low or near detection limits across all ponds and years. The results of this experiment do not support a hypothesis that limiting cattle access to breeding ponds will help conserve R. luteiventris populations in our study area. Further research is needed to evaluate regional variation and long-term effects of grazing exclosures on R. luteiventris populations.

Short-Term Effect of Cattle Exclosures on Columbia Spotted Frog (Rana luteiventris) Populations and Habitat in Northeastern Oregon

Incidence of the fungus Batrachochytrium dendrobatidis in amphibian populations along the northwest coast of North America

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2674

Stephanie K. Galvan

Papers

Using occupancy models to understand the distribution of an amphibian pathogen, Batrachochytrium dendrobatidis

Non-native species impacts on pond occupancy by an anuran

Short-Term Effect of Cattle Exclosures on Columbia Spotted Frog (Rana luteiventris) Populations and Habitat in Northeastern Oregon

Incidence of the fungus Batrachochytrium dendrobatidis in amphibian populations along the northwest coast of North America

Disentangling effects of invasive species and habitat while accounting for observer error in a long-term amphibian study.