It is well documented that animals take risk of predation into account when making decisions about how to behave in particular situations, often trading-off risk against opportunities for mating or acquiring energy. Such an ability implies that animals have reliable information about the risk of predation at a given place and time. Chemosensory cues are an important source of such information. They reliably reveal the presence of predators (or their presence in the immediate past) and may also provide information on predator activity level and diet. In certain circumstances (e.g., in the dark, for animals in hiding) they may be the only cues available. Although a vast literature exists on the responses of prey to predator chemosensory cues (or odours), these studies are widely scattered, from marine biology to biological control, and not well known or appreciated by behavioural ecologists. In this paper, we provide an exhaustive review of this literature, primarily in tabular form. We highlight so...

The scent of death: Chemosensory assessment of predation risk by prey animals

https://www.fs.fed.us/rm/pubs_other/rmrs_2006_cushman_s001.pdf

Effects of habitat loss and fragmentation on amphibians: A review and prospectus

Reports of malformed amphibians and global amphibian declines have led to public concern, particularly because amphibians are thought to be indicator species of overall envi- ronmental health. The topic also draws scientific attention because there is no obvious, simple answer to the question of what is causing amphi- bian declines? Complex interactions of several anthropogenic factors are probably at work, and understanding amphibian declines may thus serve as a model for understanding species declines in general. While we have fewer answers than we would like, there are six leading hypotheses that we sort into two classes. For class I hypotheses, alien species, over-exploitation and land use change, we have a good understanding of the ecological mechanisms underlying declines; these causes have affected amphibian populations negatively for more than a century. However, the question remains as to whether the magnitude of these negative effects increased in the 1980s, as scientists began to notice a global decline of amphibians. Further, remedies for these problems are not simple. For class II hypotheses, global change (including UV radiation and global climate change), contaminants and emerging infectious diseases we have a poor, but improving under- standing of how each might cause declines. Class II factors involve complex and subtle mechanistic underpinnings, with probable interactions among multiple ecological and evolutionary variables. They may also interact with class I hypotheses. Suspected mechanisms associated with class II hypotheses are relatively recent, dating from at least the middle of the 20th century. Did these causes act independently or in concert with pre- existing negative forces of class I hypotheses to increase the rate of amphibian declines to a level that drew global attention? We need more studies that connect the suspected mechanisms underlying both classes of hypotheses with quantitative changes in amphibian population sizes and species numbers. An important step forward in this task is clari- fying the hypotheses and conditions under which the various causes operate alone or together.

/pdf/global-amphibian-declines-sorting-the-hypotheses-4x45l88zki.pdf

Global amphibian declines: sorting the hypotheses

Amphibians are frequently characterized as having limited dispersal abilities, strong site fidelity and spatially disjunct breeding habitat. As such, pond-breeding species are often alleged to form metapopulations. Amphibian species worldwide appear to be suffering population level declines caused, at least in part, by the degradation and fragmentation of habitat and the intervening areas between habitat patches. If the simplification of amphibians occupying metapopulations is accurate, then a regionally based conservation strategy, informed by metapopulation theory, is a powerful tool to estimate the isolation and extinction risk of ponds or populations. However, to date no attempt to assess the class-wide generalization of amphibian populations as metapopulations has been made. We reviewed the literature on amphibians as metapopulations (53 journal articles or theses) and amphibian dispersal (166 journal articles or theses for 53 anuran species and 37 salamander species) to evaluate whether the conditions for metapopulation structure had been tested, whether pond isolation was based only on the assumption of limited dispersal, and whether amphibian dispersal was uniformly limited. We found that in the majority of cases (74%) the assumptions of the metapopulation paradigm were not tested. Breeding patch isolation via limited dispersal and/or strong site fidelity was the most frequently implicated or tested metapopulation condition, however we found strong evidence that amphibian dispersal is not as uniformly limited as is often thought. The frequency distribution of maximum movements for anurans and salamanders was well described by an inverse power law. This relationship predicts that distances beneath 11–13 and 8–9 km, respectively, are in a range that they may receive one emigrating individual. Populations isolated by distances approaching this range are perhaps more likely to exhibit metapopulation structure than less isolated populations. Those studies that covered larger areas also tended to report longer maximum movement distances – a pattern with implications for the design of mark-recapture studies. Caution should be exercised in the application of the metapopulation approach to amphibian population conservation. Some amphibian populations are structured as metapopulations – but not all.

Dispersal and the metapopulation paradigm in amphibian ecology and conservation : are all amphibian populations metapopulations?

Connectivity is a fundamental concept that is widely utilized in spatial ecology. The majority of connectivity measures used in the recent ecological literature only consider the nearest neighbor patch/population, or patches within a limited neighborhood of the focal patch (a buffer). Meta-analysis suggests that studies using nearest neighbor connectivity measures are much less likely to find statistically significant effects of connectivity than studies that use more complex measures. Here we compare simple connectivity measures in their ability to predict colonization events in two large and good-quality empirical data sets. The nearest neighbor distance to an occupied patch is found to be an inferior measure. Buffer measures do much better, but their performance is found to be sensitive to the estimate of the buffer radius. For highly fragmented habitats, the best and most consistent performance is found for a measure that takes into account the size of the focal patch and the sizes of and distances to all potential source populations. When experimenting with reduced data sets, it was discovered that nearest neighbor measures fail to find a statistically significant effect of connectivity for a large range of data set sizes for which the more complex measures still detect a highly significant effect. We conclude that the simplicity of a nearest neighbor measure is not an adequate compensation for poor performance.

https://www.jstor.org/stable/info/3071919

Simple connectivity measures in spatial ecology

From 1988 to 1992 we surveyed the distribution of 14 amphibian species in a set of 37 ponds in southeastern Michigan, USA. Thirty-two of these ponds had been surveyed previously between 1967 and 1974. We found that the distributions of amphibian populations (1988-1992) were strongly related to two habitat characteristics: pond hydroperiod and forest canopy cover. Most species exhibited nonrandom distributions with respect to these pond characteristics. Between surveys, the distribution of each species changed, and most species experienced multiple population colonizations and extinctions. Turnover in the distribution of populations among ponds (estimated via Jaccard's similarity coefficient) averaged nearly 50% among species. The substantial number of species colonizations (40 cases) and extinc- tions (34 cases) between surveys resulted in little net change in number of breeding popu- lations for most species; just four species experienced net changes of more than two popu- lations. Historical information indicated that, for many ponds, hydroperiod and canopy cover changed between surveys. In several cases habitat changes associated with forest succession apparently had negative impacts on amphibian populations. In ponds that now dry each summer and are under closed canopies, two-thirds of the breeding populations present during 1967-1974 were extinct during the recent survey. No population colonizations occurred in these ponds between surveys, in marked contrast to other ponds, in most of which amphibian species richness either was maintained or increased. In addition, tendencies for ponds to experience population colonizations and extinctions also were associated with pond isolation. Our results highlight the volatile nature of amphibian distributions and point to forest suc- cession, via its effects on canopy and hydroperiod, as a potential force shaping the dynamics of amphibian populations.

/pdf/long-term-distributional-dynamics-of-a-michigan-amphibian-57ofm3axfd.pdf

Long-term distributional dynamics of a michigan amphibian assemblage

The potential effects of multiple factors structuring certain larval amphibian communities were studied using a pen experiment in a natural pond. Potential factors (predation and competition from other species) were allowed to act in a stepwise fashion such that their relative importance could be evaluated. Based on a previous study, it was hypothesized that predation by Ambystoma salamander larvae on other larval amphibian species would be the most important factor. Survival of Ambystoma jeffersonianum salamander larvae and Rana sylvatica tadpoles was significantly depressed only by Ambystoma opacum predation. Survival of Ambystoma maculatum salamander larvae was significantly greater in the absence of both A. opacum and A. jeffersonianum predators. The virtual elimination of Hyla chrysoscelis larvae in all treatments also can be largely attributed to Ambystoma predation. Thus, Ambystoma predation was the dominant factor determining larval survival of four amphibian prey species in the experimental communities.

/pdf/an-examination-of-multiple-factors-affecting-community-50omd7hv9t.pdf

An examination of multiple factors affecting community structure in an aquatic amphibian community.

We conducted the first formal quantitative study of the herpetofauna of the Jasper-Pulaski, Willow Slough and LaSalle Fish and Wildlife areas (FWA) in northwest Indiana from 1994–1996 to gather baseline data necessary to determine distribution and status of species and to monitor long-term population trends. We compared our results with those of earlier collectors Chapman Grant, Paul Swanson and Sherman Minton. A total of 339 populations of 13 amphibian species and 78 populations of 22 reptile species were encountered from 1994–1996. Only 9 species were found at all three FWAs and only 11 were commonly encountered. Sixteen new site records and new county records were made while at least 7 species with validated records before 1972 were not found during this survey and may be locally extirpated. The relative abundance of species at Jasper-Pulaski FWA has changed between the 1930s and 1990s with declines of the thirteen most abundant species and increases in some formerly overlooked or rare species...

Spencer A. Cortwright

Papers

Long-term distributional dynamics of a michigan amphibian assemblage

An examination of multiple factors affecting community structure in an aquatic amphibian community.

Historical Changes of Reptiles and Amphibians of Northwest Indiana Fish and Wildlife Properties

Chemically-mediated mate choice in red-spotted newts: Do males select or just detect females?