Article

Effects of roads and land use on frog distributions across spatial scales and regions in the Eastern and Central United States

Authors:
  • Tangled Bank Conservation
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Abstract

Understanding the scales over which land use affects animal populations is critical for conservation planning, and it can provide information about the mechanisms that underlie correlations between species distributions and land use. We used a citizen science database of anuran surveys to examine the relationship between road density, land use and the distribution of frogs and toads across spatial scales and regions of the United States. Eastern and Central United States. We compiled data on anuran occupancy collected from 1999 to 2013 across 13 states in the North American Amphibian Monitoring Program, a citizen science survey of calling frogs. These data were indexed to measures of land use within buffers ranging from 300 m to 10 km. The negative effects of road density and development on anuran richness were strongest at the smallest scales (300–1000 m), and this pattern was consistent across regions. In contrast, the relationships of anuran richness to agriculture and forest cover were similar across local scales but varied among regions. Richness had a negative relationship with agriculture/forest loss in the Midwest but a positive relationship with agriculture in the Northeast. Anuran richness was more closely related to primary/secondary road density than to rural road density, and the negative effects of larger roads increased at smaller scales. Individual species differed in the scales over which roads and development affected their distributions, but these differences were not closely related to either body size or movement ability. This study further refines our understanding of the relationship between roads and amphibian populations and highlights the need for research into the specific mechanisms by which roads affect amphibians. Additionally, we find that relationships between land use and species richness can differ substantially across regions, demonstrating that one should use caution in generalizing from one region to another, even when species composition is similar.

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... A literature review identified two relevant landscape-scale variables used to describe P. regilla terrestrial habitat: tree cover (Pearl et al. 2005;Goldberg and Waits 2009;Holzer 2014) and impervious surface cover, which includes buildings, roads, parking lots, and other built features of the urban environment (Rowe and Garcia 2014;Guderyahn et al. 2016). We identified four additional landscape-scale variables with potential to influence P. regilla occupancy based on studies of similar species and probable metapopulation dynamics: percent wetland cover (Johnson et al. 2013), road density (Marsh et al. 2017), number of ponds (Watts et al. 2015), and distance to the nearest pond (Marsh and Trenham 2001). These variables were grouped according to separate hypotheses of terrestrial habitat availability and connectivity (Table 1). ...
... Our findings lend support to two emerging themes in amphibian conservation in developed landscapes: first, that there is a stronger relationship between wetland occupancy and surrounding terrestrial habitat characteristics than with the characteristics of the wetlands themselves (Lehtinen et al. 1999;Quesnelle et al. 2015;Grand et al. 2017); and second, that amphibian occupancy is driven by multiple factors operating at local and landscape scales (Fischer et al. 2015;Johnson et al. 2016;Marsh et al. 2017). We found that wetland occupancy was driven most strongly by the amount of impervious cover within 250 m of a wetland, underscoring the importance of terrestrial habitat availability for P. regilla. ...
... A negative relationship between impervious cover and occupancy has been observed for many aquatic-breeding amphibians (e.g. Knutson et al. 1999;Simon et al. 2009;Marsh et al. 2017) and can be explained by a number of factors. Impervious cover not only displaces essential terrestrial habitat resources, it also limits habitat connectivity by presenting amphibians with barriers to movement and generally high landscape resistance due to risk of desiccation and road mortality. ...
Article
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Pacific chorus frog ( Pseudacris regilla ) populations have persisted despite urban and rural development throughout the species’ range; yet it is possible that P. regilla , like other anurans with which it historically co-occurred, will become extirpated from cities and suburbs if urbanization intensifies as predicted. An improved understanding of the conditions that enable this species to persist in developed landscapes is needed to identify and conserve suitable habitats. We investigated species-habitat relationships for P. regilla in a mixed urban-rural landscape in southwestern British Columbia, Canada, to identify potential criteria for habitat suitability. We conducted repeat auditory surveys of chorusing males at 52 potential breeding wetlands and modeled occupancy at 26 of these sites using local and landscape variables representing competing hypotheses and spatial scales of influence. The models that best explained P. regilla occupancy included a combination of terrestrial habitat and connectivity factors and the presence of non-native predators. We found that the proportion of impervious cover within 250 m of a wetland had the strongest negative impact on occupancy. Our findings suggest that availability of terrestrial habitat adjacent to breeding sites is the primary driver of species presence in the developed landscape. Conservation efforts should seek to limit impervious cover to less than 20% within a 250-m buffer around breeding wetlands. Further, restored and created wetlands in urban and rural areas may be more likely to support P. regilla if they are designed with a seasonal hydroperiod that excludes non-native aquatic predators and are placed in an area of high pond density.
... Researchers (e.g. Vos and Chardon, 1998;Li et al., 2016;Marsh et al., 2017) found the negative impact of roads on frogs. Table 7 Summary of Vuong test for non-nested models. ...
... Soil moisture and roads are also associated with human and vehicle mobility that are important for amphibians (Pellet et al., 2004). On top of effects such as habitat alteration and dispersal barriers acting at the local level or by habitat fragmentation operating at the higher spatial order, roads also induce direct amphibian mortality (Marsh et al., 2017;Vos and Chardon, 1998). Traffic noise associated with urban roads also provides plausible explanations to the reluctance of areas close to the road (Lukanov et al., 2014). ...
... Other literature identified the influence of environmental variables such as land use (Marsh et al., 2017), human population (McKinney, 2002), urban hard surfaces and linear infrastructure (Vos and Chardon, 1998) are on the frog presence. As urban sprawl is growing at an unprecedented rate in Kathmandu (Ishtiaque et al., 2017) that could further threaten the existence of frogs in the valley. ...
Article
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Urbanization and linear infrastructure are reported to influence amphibian assemblages and populations. In areas undergoing rapid infrastructure development and urbanization, the mounting threats to biodiversity are evident. Although protected area coverage and focus on charismatic species conservation are well recognized, non-charismatic species such as amphibians are far from mainstream conservation actions and policies in Nepal. Studies on pattern and distribution of amphibians are limited, as are the roles of environmental variables in amphibian diversity in the urban landscape. This study was designed to assess the frog species richness and correlates of amphibian occurrence in Kathmandu valley. Visual encounter survey of 161 belt transects was carried out in August 2018. Data analysis used two part or Hurdle regression methods where the richness of frogs was considered a response variable. A total of 10 frog species belonging to six families were recorded. The occurrence of frogs was negatively associated with the dry soil conditions and positively associated with increased distance from roads. Occurrence of frogs along road distance gradient depicts the influence of urban infrastructure in amphibian distribution. This entails consideration of systematic conservation planning for rapidly urbanizing areas.
... The cumulative efects of ILTs delineate an 'impact zone' of various widths. The distance of efect can vary from 40 m to 1.5 km with an average of 500 m, depending on the species considered [22][23][24][25][26]. ...
... Increased knowledge of the efects of LTIs on biodiversity, biodiversity protection and legislation has led to the implementation of mitigation measures. The aim of these measures is to enable long-term population viability near the LTI [24,35,37]. The efect of habitat destruction is most often ofset by measures to restore or create new habitats. ...
... Since the 1970s, ecologists have revealed that amphibians are suffering a global decline (Alford et al., 2001;Houlahan et al., 2001). Many studies have also demonstrated that human activities (e.g., urbanization, invasive species, and agricultural activities) could influence amphibian dispersals (Sodhi et al., 2010;Veysey et al., 2011;Marsh et al., 2017;Liu et al., 2018). Anthropogenic activities have brought harmful effects, such as the disturbance in ecological communities via transforming habitats and creating new ones, ultimately leading to the loss of amphibian communities and habitat degradation (Martin and McComb, 2003;Hamer and McDonnell, 2008;Wan et al., 2017). ...
... NB are shown for each species. construction areas, led to a decline of amphibian populations, which was also reported in Europe, Australia, and North America (Pillsbury and Miller, 2008;Marsh et al., 2017;Villasenor et al., 2017). Total road density within each circular area was used as an index of habitat fragmentation degree (Vos and Chardon, 1998). ...
Article
Amphibian declines are caused by multiple stressors at the landscape and local levels, resulting in habitat loss, fragmentation, splits, and degradation. However, the combined effects of different landscape scales on the amphibian declines are poorly understood. We examined the breeding distribution of three frog species, Rana japonica, Rana ornativentris, and Bufo japonicus formosus, along an ecological gradient from urban to mountain areas. The number of egg masses and data on landscape and local variables were collected at 124 sites in Toyota, Okazaki, and Shitara, central Japan. The best model with the lowest value of the Akaike Information Criteria (AIC) was obtained using landscape variables at a 500-m-radius buffer for all three species. The number of egg masses increased with forest area for all frog species. Yet, other variables differently affected the number of egg masses of three species at each site. The egg-mass number of R. japonica was positively affected by the residential region with much vegetation area & elevation difference, and negatively affected by elevation. That of R. ornativentris was positively influenced by the abandoned paddy-field, and negatively influenced by the total road density. Regarding B. japonicus formosus, its egg-mass number was positively affected by the residential region with much vegetation area, and negatively affected by elevation difference. At the local scale, the water area positively affected the number of egg masses of all three species, while the percentage of concrete revetment has negative effects. This study not only assesses how the assemblage of frogs respond to different habitats at multiple spatial scales along the land use gradient (urban-mountain), but also emphasizes the importance of strategic management actions in agricultural landscapes, allowing the maintenance of habitat diversity for amphibians.
... Urbanization also leads to an increase in the coverage of impervious surfaces across developed landscapes which, in turn, can contribute to habitat fragmentation by separating breeding wetlands from important upland habitats [29][30][31][32]. Not only do roads act as barriers between otherwise contiguous habitats, but traffic along these roads has a direct negative, and typically lethal, effect on anuran population [33,34]. Frogs and toads may struggle to navigate even short distances (in relation to their overall dispersal abilities) in urbanized areas [32]. ...
... Frogs and toads may struggle to navigate even short distances (in relation to their overall dispersal abilities) in urbanized areas [32]. Factors such as vehicle collisions, exposure to runoff (salt, oil, etc.), noise, exhaust emissions, and vibrations can all affect anuran populations through either direct mortality or behavior interruptions [34,35]. ...
Article
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Urbanization is among the largest threats to wildlife populations through factors such as fragmentation, isolation, and habitat destruction. Urban open spaces, such as parks and golf courses, have the potential to provide wildlife with suitable habitat within an urbanized matrix. These refugia may be particularly important for amphibians, which represent one of the most endangered and least vagile vertebrate groups on earth. During the spring and summer of 2018, we conducted surveys to determine the presence of anurans at 51 wetland sites within the Piedmont ecoregion of South Carolina. Nearly one-third of these wetlands were located within urban open spaces, one-third in low development areas, and one-third in highly developed areas. Impervious surface and total road length surrounding the wetlands were measured at two scales, a core habitat scale (300 m) and average maximum migration scale (750 m), and we measured several within-wetland habitat variables. Urban Open Space wetlands had levels of surrounding impervious surface similar to High Urbanization wetlands at the larger scale and were intermediate between Low and High Urbanization wetlands at the smaller scale. The total length of road segments occurring within buffers (at both scales) surrounding our study wetlands was higher for Urban Open Space compared to Low and High Urbanization sites. Among the within-wetland variables measured, Low Urbanization sites had higher canopy cover and were more likely to have a terrestrial buffer zone relative to the other categories. Species richness decreased significantly as total road length increased among all wetlands. Wetland category was not a significant driver explaining species richness, but β-diversity was more variable among Urban Open Space wetlands than either Low or High Urbanization wetlands. Urban Open Space wetlands did not appear to increase suitability for anurans relative to High Urbanization wetlands. Urban Open Space wetlands had higher variability in species composition, which was perhaps attributable to the diversity among sites represented in the Urban Open Space category.
... Crowdsourcing can offer an effective solution to gather a mass of observations, as it can provide a large sample size from an extensive area (Devictor et al., 2010;Newman et al., 2011). For example, photographs and metadata submitted by citizen scientists (who are also called community scientists or volunteers) have been used to study animal behaviour (Maritz andMaritz, 2020, Durso et al., 2021;Forti et al., 2022), including habitat use (Marsh et al., 2017). While the primary use of citizen science data is to obtain information on species occurrence, gaining other (often unintended) secondary data, such as behavioural information, can answer many scientific questions . ...
Article
Shelters are microhabitats where animals rest and hide. These microhabitats can be used from short daily periods to long-term estivation or hibernation. Environmental conditions and the phenotypical characteristics of the animal drive habitat selection in relation to shelters. Based on this, climate regions and phylogeny are expected to affect the use of different shelter types. Although shelters are yet to be described for most anuran species, a variety of microhabitats have already been reported as shelter-sites, including dense vegetation, rock crevices, and holes in the ground. In this study, we evaluated photos of frogs for sheltering behaviour from 29 countries in the Americas deposited on the popular citizen-science platform, iNaturalist. We compared the frequency of use of different shelter types identified on the photos among different climate regions and anuran families, also testing possible phylogenetic signals. We identified 11,133 photographs of 378 frog species showing individuals hiding in shelters or in a resting position. We classified observations into 10 shelter types, with live vegetation (24.7%) being the most commonly recorded natural shelter, followed by hole in the ground (11.4%) and tree trunk (11.1%). The use of different shelter types varied between arid and humid climates, and also among different anuran families. We found strong phylogenetic signal for three shelter types (hole in the ground, live vegetation, and water) and the differences in shelter use among taxa suggest a relation with body characteristics. Approximately 47% of observations of threatened and near threatened species were in hole in the ground, while artificial habitat represented only 3.6% of the observations in this group. The daily pattern of shelter use corroborated the nocturnal activity of most species. Our findings also expanded the description of shelter sites for 330 species that had no published information on this behaviour. This study contributes to our current knowledge about animal behaviour and highlights the use of citizen science as an effective approach to understand the natural history of amphibians at a large scale.
... The issue of species distribution modeling has been discussed by many authors, either by the covering of a large area of research thus ensuring high generalizability [10][11][12][13][14][15], by only involving a GIS framework with the creation of a map of species occurrence but without predictions [16][17][18][19], or by using the maximum entropy algorithm for making predictions [20][21][22][23]. The authors have used between two and 20 variables [13,[23][24][25]. ...
Article
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The construction of transport infrastructure is often preceded by an environmental impact assessment procedure, which should identify amphibian breeding sites and migration routes. However, the assessment is very difficult to conduct because of the large number of habitats spread out over a vast expanse, and the limited amount of time available for fieldwork. We propose utilizing local environmental variables that can be gathered remotely using only GIS systems and satellite images together with machine learning methods. In this article, we introduce six new and easily extractable types of environmental features. Most of the features we propose can be easily obtained from satellite imagery and spatial development plans. The proposed feature space was evaluated using four machine learning algorithms, namely: a C4.5 decision tree, AdaBoost, random forest and gradient-boosted trees. The obtained results indicated that the proposed feature space facilitated prediction and was comparable to other solutions. Moreover, three of the new proposed features are ranked most important; these are the three dominant properties of the surroundings of water reservoirs. One of the new features is the percentage access from the edges of the reservoir to open areas, but it affects only a few species. Furthermore, our research confirmed that the gradient-boosted trees were the best method for the analyzed dataset.
... 그러나 오랫동안 인간의 주거지에서 나타나는 일부의 양서류 는 경관 조성의 변화에 내성을 나타내기도 한다 (Hartel et al. 2010). 도시화에 따른 어떤 구체적인 환경의 변화 가 양서류에 영향을 미치는지에 대하여 잘 알려져 있지 않다 (Naito et al. 2012, Marsh et al. 2017 ...
Article
Urbanization is a major driver of global amphibian declines. For the study on the effect of urbanization on amphibians, we compared the growth and the health status of Hyla japonica amphibians collected in the urban areas of Incheon and in the rural area of Gapyeong, Korea. The size and weight of Hyla japonica body in the urban area were smaller than those in the rural area. However, there was no significant difference in their condition factors as a health indicator between the two areas. Our study emphasizes the need for research into the specific mechanism of effects of urbanization on amphibian heath status for the further understanding of the relationship between urbanization and amphibians.
... The combined effects of habitat fragmentation, direct mortality, and other indirect effects (Fahrig and Rytwinski 2009;Jackson and Fahrig 2011;Votsi et al. 2016) demonstrate the crucial need for mitigation of road effects. Furthermore, the road-effect zone is far larger than the footprint of the road itself (Forman 2000;Marsh et al. 2017). Measures taken to mitigate road effects can be costly (Huijser et al. 2008), and as conservation dollars are often limited, efforts should be made to optimize mitigation planning and implementation. ...
Article
Full-text available
The mitigation of road-effects on wildlife, especially road mortality and habitat fragmentation, has become increasingly common in the last 20 years. However, exclusion fencing and habitat connectivity structures can be very costly and several questions remain regarding how to best determine locations that will optimize mitigation success. Based on data collected across several years and across multiple landscapes and taxa, we present a comparative analysis of two methods: road surveys and circuit theory, and review their benefits and challenges to better inform decision making. Road surveys were completed in two locations over three years for large mammals and herpetofauna to identify road crossing hotspots. Circuit theory was also applied to these systems to identify crossing hotspots using habitat resistance models. The location, number and width of hotspots were compared between methods. Hotspot distributions were similar between methods for some herpetofauna, but different for Mammals, and road surveys produced a significantly greater number of smaller hotspots compared to circuit theory, implying that road surveys provide better hotspot resolution. As circuit model complexity increased, the number and width of hotspots decreased, diffusing across the landscape. Road surveys were better at predicting optimal crossing structure location at a local scale; however, circuit theory is less costly, and can be useful at large scales. As both methods can offer valuable information, we argue that the combination of these two approaches provides a strong basis for managers and biologists to make informed decisions about costly mitigation measures, optimizing both conservation benefits and limited funding.
... Noise levels could be high in some highways, especially when heavy trucks make an important portion of the traffic volume (Eigenbrod, Hecnar and Fahrig, 2009). For instance, road density and noise affected frog species richness at the scale of ≤ 5 km in different landscapes in the United States (Marsh, et al., 2016). Other factors that may also affect protected areas within two kilometers of distance are illumination from vehicles at night and chemical pollutants carried by wind and runoff (Forman et al., 2003;Coffin, 2007;Leonard and Hochuli, 2017). ...
Article
Full-text available
Road networks are spatially disposed across landscapes and are differentially used by traffic, generating levels of noise that may negatively affect protected areas. The objective of this study is to quantify the length of road stretches in contact and in close proximity to protected areas, and to investigate differential effects parks may have inrelation to traffic volumes and noise pollution. We measured road networks in proximity to protected areas using a geographic information system and the Atlas of Costa Rica. Noise and traffic volumes were quantified in three protected areas with direct adjacency with roads. We generated environmental sound maps to assess the influence of noise on natural sounds, such as those produced by streams (geophony) and birds (biophony). We recorded biophony close and far to the road in one of the protected areas. We found that 70 protected areas are directly or indirectly affected by road proximity. Noise was greater in roads with higher traffic usage than those with lower traffic usage, but the type of vehicles also influenced noise levels. Noise penetrated the forest with greater levels during the dry season than in the wet season. We found that the amount of biophony in seconds was lower close than far from the road, and that the stream sound was masked by traffic noise. Our results suggest that noise may contribute to habitat degradation through a decrease and loss of natural sounds, decreasing the quality of biodiversity protection. Interdisciplinary action and rigorous planning must be considered to avoid road encroachment on protected areas.
... Genetic studies suggest some amphibian populations are fragmented by roads (Lesbarrères, Primmer, Lodé, & Merilä, 2006). Consequently, roads can lead to regional declines in the distribution of many amphibian species (Cosentino et al., 2014;Marsh et al., 2017). ...
Article
Populations of aquatic-breeding amphibians are declining from habitat loss, fragmentation and degradation. Identifying how populations are affected by landscape barriers such as roads is essential for conservation and requires understanding the processes underpinning species occupancy in fragmented landscapes. Here, I assessed relationships between the occupancy dynamics of the threatened green and golden bell frog (Litoria aurea) and accessible habitat; i.e., the area of breeding and non-breeding habitat around a wetland that can be reached by an amphibian without having to cross a highway. I hypothesised that relationships between occupancy and accessible habitat would be stronger than relationships with the area of extant native vegetation, road density or distance to the highway. I also examined relationships with local habitat variables over a three-year period. Relationships with accessible habitat were stronger and more certain in explaining L. aurea occupancy and colonisation than other landscape variables. Accessible habitat was positively associated with wetland occupancy, which suggests the highway is having a barrier effect on the population. There was a positive relationship between road density and the probability of local extinction. Occupancy rates at highway compensatory ponds increased from near-zero within six months of pond construction, to >30% after 12 months. There was a negative relationship between local extinction and aquatic vegetation cover, highlighting the importance of habitat structure for L. aurea. Urban planners should consider accessible habitat when managing amphibian species in rapidly urbanising landscapes, so that all habitats required throughout a species’ life cycle are protected.
... In fact, many of our samples were obtained from road-killed frogs. High-volume or multi-lane roads may serve as permanent, impenetrable barriers to dispersal, which, along with road mortality, can have considerable impacts on anuran richness and abundance [89,90]. ...
Article
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Cryptic species are a challenge for systematics, but their elucidation also may leave critical information gaps about the distribution, conservation status, and behavior of affected species. We use the leopard frogs of the eastern U.S. as a case study of this issue. We refined the known range of the recently described Rana kauffeldi, the Atlantic Coast Leopard Frog, relative to the region's two other leopard frog species, conducted assessments of conservation status, and improved methods for separating the three species using morphological field characters. We conducted over 2,000 call and visual surveys and took photographs of and tissue samples from hundreds of frogs. Genetic analysis supported a three-species taxonomy and provided determinations for 220 individual photographed frogs. Rana kauffeldi was confirmed in eight U.S. states, from North Carolina to southern Connecticut, hewing closely to the Atlantic Coastal Plain. It can be reliably differentiated in life from R. pipiens, and from R. sphenocephala 90% of the time, based on such characters as the femoral reticulum patterning, dorsal spot size and number, and presence of a snout spot. However, the only diagnostic character separating R. kauffeldi from R. sphenocephala remains the breeding call described in 2014. Based on our field study, museum specimens, and prior survey data, we suggest that R. kauffeldi has declined substantially in the northern part of its range, but is more secure in the core of its range. We also report, for the first time, apparent extirpations of R. pipiens from the southeastern portion of its range, previously overlooked because of confusion with R. kauffeldi. We conclude with a generalized ecological research agenda for cryptic species. For R. kauffeldi, needs include descriptions of earlier life stages, studies of niche partitioning with sympatric congeners and the potential for hybridization, and identification of conservation actions to prevent further declines.
... In fact, many of our samples were obtained from road-killed frogs. High-volume or multi-lane roads may serve as permanent, impenetrable barriers to dispersal, which, along with road mortality, can have considerable impacts on anuran richness and abundance [89,90]. ...
Article
Cryptic species are a challenge for systematics, but their elucidation also may leave critical information gaps about the distribution, conservation status, and behavior of affected species. We use the leopard frogs of the eastern U.S. as a case study of this issue. We refined the known range of the recently described Rana kauffeldi, the Atlantic Coast Leopard Frog, relative to the region’s two other leopard frog species, conducted assessments of conservation status, and improved methods for separating the three species using morphological field characters. We conducted over 2,000 call and visual surveys and took photographs of and tissue samples from hundreds of frogs. Genetic analysis supported a three-species taxonomy and provided determinations for 220 individual photographed frogs. Rana kauffeldi was confirmed in eight U.S. states, from North Carolina to southern Connecticut, hewing closely to the Atlantic Coastal Plain. It can be reliably differentiated in life from R. pipiens, and from R. sphenocephala 90% of the time, based on such characters as the femoral reticulum patterning, dorsal spot size and number, and presence of a snout spot. However, the only diagnostic character separating R. kauffeldi from R. sphenocephala remains the breeding call described in 2014. Based on our field study, museum specimens, and prior survey data, we suggest that R. kauffeldi has declined substantially in the northern part of its range, but is more secure in the core of its range. We also report, for the first time, apparent extirpations of R. pipiens from the southeastern portion of its range, previously overlooked because of confusion with R. kauffeldi. We conclude with a generalized ecological research agenda for cryptic species. For R. kauffeldi, needs include descriptions of earlier life stages, studies of niche partitioning with sympatric congeners and the potential for hybridization, and identification of conservation actions to prevent further declines.
... The combined effects of habitat fragmentation, direct mortality, and other indirect effects Jackson & Fahrig 2011;Votsi et al. 2016) demonstrate the crucial need for mitigation of road effects. Furthermore, the road-effect zone is far larger than the footprint of the road itself Marsh et al. 2017). Measures taken to mitigate road effects can be costly , and as conservation dollars are often limited, efforts should be made to optimize mitigation planning and implementation. ...
Thesis
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Globally, roads are one of the most ubiquitous forms of human infrastructure, and have been identified as a serious conservation concern. Though roads impact wildlife in a variety of ways, their effects are often negative. Perhaps the most concerning threats are habitat fragmentation and mortality via wildlife-vehicle collisions. Attempts to manage the negative effects of roads have had mixed results, and major gaps in our understanding of how roads affect wildlife populations and the effectiveness of strategies to mitigate road-effects remain. Many factors contribute to these gaps, particularly the logistical constraints associated with road-effect monitoring and weak study designs that inhibit strong inferences crucial for effective management. To this end, I approached road-effect mitigation in a holistic way. First, I documented and analyzed the local-scale population and spatial ecologies of large mammals around a newly twinned highway. I found that highway twinning, a common strategy to accommodate increased traffic volume, had little effect on large mammals. Second, I focused on the optimization and evaluation of road-effect mitigation (i.e., exclusion fencing and road crossing structures). I developed a procedure for identifying ideal locations for mitigation features by comparing road monitoring data to landscape resistance models for both large mammals and herpetofauna. Using this approach, I designed a mitigation plan for reptiles and amphibians, which I evaluated using a robust 6-year Before-After-Control-Impact design that included road surveys, trapping, and two methods of monitoring tunnel usage: trail cameras and PIT tag scanners. I found that exclusion fencing was effective for turtles and amphibians but had no impact on the number of snakes detected on the road. Crossing tunnels were well used by reptiles and amphibians and I demonstrated that for turtles, tunnels effectively facilitated connectivity at the population-level. Finally, I investigated the value of outreach as a long-term conservation strategy in the context of road ecology. I demonstrated that outreach programs significantly increase the perceptions of youth concerning their own likelihood to participate in conservation. Further, using a mixed-methods approach, I identified the aspects of outreach that were most effective at eliciting this change, creating broadly applicable guidelines to optimize future outreach endeavors. By addressing knowledge gaps pertaining to each phase of road-effect mitigation, I have provided a structural framework from which the field of road ecology can continue to flourish. My findings have serious implications for wildlife management and conservation because they increase our understanding of road-effects and importantly, how to increase the success of road-effect mitigation.
... We do not suggest that Level One methods replace excellent programs such as the North American Breeding Bird Survey or the Marsh Monitoring Program. Such programs offer long term, data-rich information on the community structure of various ecological indicators for specific sites; these programs can also contribute to regional or national assessments of wetland condition (Cosentino et al., 2014, Marsh et al., 2017. Additionally, these programs involve and motivate citizen scientists in wetland and species conservation. ...
... Other scales shown to be relevant to urban pond ecosystems include 100 m for macroinvertebrates in West Midlands, UK (Thornhill et al. 2017), 100-300 m for wetland birds in eastern Massachusetts, USA (Tavernia and Reed 2010), and 500 m for submerged and floating-leaved macrophytes in Hyogo, Japan (Akasaka et al. 2010). Differences in the scale of influence have also been reported for the same taxonomic group (e.g., amphibians): 200 m in Gresham, Oregon, USA (Guderyahn et al. 2016), 300-1000 m in the Eastern and Central USA (Marsh 2017), and 1 km in southeastern Australia (Villasenor et al. 2017). ...
Article
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Many cities around the world are expanding and this trend in urbanization is expected to sharply increase over coming decades. At the same time, the integration of green and blue spaces is widely promoted in urban development, potentially offering numerous benefits for biodiversity. This is particularly relevant for urban waterbodies, a type of ecosystem present in most cities. However, site managers often lack the knowledge base to promote biodiversity in these waterbodies, which are generally created to provide other ecosystem services. To address this, our review presents guidelines for promoting biodiversity in urban ponds. We found a total of 516 publications indexed in ISI Web of Sciences related to this topic, of which 279 were retained for the purposes of our review. The biodiversity of urban ponds, measured by species richness, appears to be generally lower than in rural ponds; however, urban ponds often support threatened species. Furthermore, if well managed, urban ponds have the potential to support a much greater biodiversity than they currently do. Indeed, this review shows that a range of urban factors can impair or promote pond biodiversity, including many that can easily be controlled by site managers. Local factors include design (surface area, pond depth, banks and margins, shade, shoreline irregularity), water quality (conductivity, nutrients, heavy metals), and hydroperiod and biotic characteristics (stands of vegetation, fish, invasive species). Important regional factors include several indicators of urbanization (roads, buildings, density of population, impervious surfaces, car traffic), and the presence of other wetlands or green spaces in the surrounding landscape. We considered each of these factors and their potential impact on freshwater biodiversity. Taking into account the management measures listed in the publications reviewed, we have proposed a framework for the management of urban ponds, with guidelines to promote biodiversity and other ecosystem services, and to avoid ecosystem disservices or the creation of ecological traps. At the city scale, the biodiversity of a pondscape benefits from a high diversity of pond types, differing in their environmental characteristics and management.
... Surprisingly, we found that populations of both spring and summer breeding species, as well as species that overwinter in soil and in stream beds, were sensitive to observed winter severity, with warmer temperatures and increasing days of snow cover increasing occupancy for many species. This illustrates that changing winter conditions may have long-term consequences for anuran species across a range of breeding phenology and life history characteristics across large spatial scales, in contrast to other investigations (Gibbs & Breisch, 2001;Marsh et al., 2017). ...
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Aim Climate change is an increasingly important driver of biodiversity loss. The ectothermic nature of amphibians may make them particularly sensitive to changes in temperature and precipitation regimes, adding to declines from other threats. While active season environmental conditions can influence growth and survival, effects of variation in winter conditions on population dynamics are less well‐studied. Given that extreme winter temperatures can influence amphibian survival and fitness, we expected that increased winter severity—as measured by variability in winter temperatures and snow cover—would be associated with decreased occupancy, and that populations that experience more severe winters would have the largest sensitivities and show the greatest declines. Location Eastern United States. Time period 2001–2015. Major taxa studied Anurans. Methods We used large‐scale citizen science data from the eastern half of the United States, a diverse biogeographic and climatic region, to assess how variation in winter severity influenced occupancy dynamics (i.e. presence or absence of species across sites and years) of 11 spring and summer breeding anuran species. Results Most species had increased occupancy in years with greater than average snow cover and warmer than average mean winter temperatures. Surprisingly, climatic conditions in winter affected occupancy dynamics of species with varying life history characteristics, including both spring and summer breeding species, those that overwinter under the soil, and those that overwinter in ponds and stream beds. For two wide‐ranging species (Lithobates catesbeianus and Lithobates clamitans), colder winter temperatures reduced occupancy more at northern latitudes, while the association between days of snow cover and latitude was equivocal. Main conclusions As the climate continues to change, expected reductions in snowpack may reduce occupancy of already declining anuran populations, while milder winters may improve overwinter survival for some species. The contradictory impacts of temperature and snow cover illustrate the importance of considering multi‐dimensional impacts of climate change on anuran populations.
... De nombreuses études ont démontré l'impact négatif des routes sur les amphibiens, que ce soit sur la diversité biologique (Eigenbrod et al. 2008a;McKinney 2008), sur l'occupation des mares (Vos and Chardon 1998) ou sur l'abondance spécifique (Fahrig et al. 1995;Carr and Fahrig 2001). Les routes seraient également un facteur important expliquant le déclin des espèces à l'échelle régionale (Cosentino et al. 2014a;Marsh et al. 2017). ...
Thesis
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Identifier, conserver et restaurer un réseau fonctionnel d’habitats favorables à la biodiversité est fondamental face aux enjeux écologiques actuels, en particulier dans des régions fortement anthropisées. Cette thèse vise à identifier des réseaux écologiques régionaux liés aux mosaïques paysagères agricoles à partir d’espèces modèles : les amphibiens. Nous avons réalisé des modèles d’habitat favorable (HSM) pour neuf espèces, essentiellement communes, à l’échelle régionale à partir de données opportunistes. Nous avons constitué un jeu de données indépendant pour l’évaluation à partir de données de sciences participatives filtrées et complétées avec l’aide des réseaux naturalistes. Dans un second temps, nous avons intégré aux HSMs des processus multi-échelles liés aux déplacements. Enfin, nous avons compilé des cartes d’habitat favorables pour créer un indice de favorabilité multi-spécifique que nous avons intégré dans une analyse de connectivité régionale puis confronté au réseau de conservation existant. Ces travaux montrent que des données de sciences participatives peuvent être mobilisées pour améliorer l’évaluation des HSM et que l’intégration de processus multi-échelles est pertinente pour augmenter leur pouvoir prédictif. Enfin, nous avons mis en évidence des distributions multi-spécifiques et identifié des lacunes dans le réseau régional de conservation existant. Ce travail pourra contribuer à l’amélioration des politiques de conservation des amphibiens et des mosaïques agricoles associées et à renforcer les liens entre structures académiques et non-académiques.
... Moreover, we also did not consider possible rises in mortality rates due to habitat destruction for 1987 and 2010 (e.g. direct or traffic mortality; Shine et al. 2004;Van Der Ree et al. 2011;Florencio et al. 2014;Marsh et al. 2017), or loss of individuals' fitness during this process (e.g. population stress). ...
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... The relative distance to roads promoted changes in anuran functional and taxonomic compositions. In general, anuran abundance reduces largely in response to road proximity (Marsh et al., 2017), with ponds near roads also presenting the lower values of diversity (e.g. Cosentino et al., 2014). ...
Thesis
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... We do not suggest that Level One methods replace excellent programs such as the North American Breeding Bird Survey or the Marsh Monitoring Program. Such programs offer long term, data-rich information on the community structure of various ecological indicators for specific sites; these programs can also contribute to regional or national assessments of wetland condition (Cosentino et al., 2014, Marsh et al., 2017. Additionally, these programs involve and motivate citizen scientists in wetland and species conservation. ...
Technical Report
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Modern human societies generate new patterns of noise that may affect acoustic communication in many animal species. Whilst animals have evolved several mechanisms to cope with natural background noise, the rapid increase of anthropogenic alteration of acoustic environment could challenge the potential for adjustments of communicative systems. Because acoustic communication is involved in crucial behaviours, noise pollution can be particularly detrimental in affecting breeding success or survival. I investigated the impact of traffic noise on acoustic communication in a tree frog by way of an experimental approach using noise playback. Traffic noise triggered a decrease of the males’ calling activity, with males being more affected when noise amplitude increased. Additionally, the males’ social situation (calling in chorus versus alone) exerted a strong influence on sensitiveness to noise. Males were only weakly affected by noise pollution when calling in a chorus situation, probably because they were more stimulated and because traffic noise emergence was lower. Moreover results showed that in response to noise playback, males are not able to adjust their temporal or frequency call structures to increase efficiency of the information transfer. Understanding species’ ability to adapt their communicative systems to cope with human-made noise constitutes an important contribution to wildlife conservation.
Article
In light of increasing evidence of declining anuran populations worldwide, an important conservation issue is the extent to which declines are consequences of smaller-scale stresses such as local habitat loss or degradation, or larger-scale stresses such as climate change. Here we show that anuran richness in 77 southeastern Ontario wetlands is negatively correlated with the density of roads on lands within 1 km of the wetland, and positively correlated with the percentage of forest cover. Logistic regression analysis shows that the presence of at least two species, the mink frog (Rana septentrionalis) and the wood frog (Rana sylvatica), is negatively related to road density, while the pickerel frog (Rana palustris) shows significant positive association with adjacent forest cover. These results suggest that in southeastern Ontario, significant conservation gains can be achieved through local land-use planning and management decisions that mitigate the effects of existing roads, minimize the construction of new roads, and discourage further forest conversion on lands adjacent to wetlands.
Article
Abstract A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
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In 1989 at the World Congress of Herpetology, scientists expressed concern that amphibian population declines were more than local phenomena and may be a global issue. In 1994, the North American Amphibian Monitoring Program (NAAMP) — a partnership among state, provincial, academic, and nonprofit groups working regionally to gather monitoring data on amphibian populations — was established. Across North America, amphibians have variable life history and natural history features. Therefore, the original goal of the NAAMP effort was to employ several survey approaches and protocols to ensure that all species could be monitored. The first NAAMP protocol to be implemented was a roadside calling survey, with the goal of monitoring anurans (frogs and toads) that make distinctive vocalizations during courtship. Roadside calling surveys are most useful in regions of North America where all (or most) of the anuran species in an assemblage vocalize in a relatively predictable manner. Further research is needed to confirm or refine the seasonal sampling periods and nightly sampling conditions on a regional basis.
Article
We examined the relationship between the richness of four different wetland taxa (birds, mammals, herptiles, and plants) in 30 southeastern Ontario, Canada wetlands and two anthropogenic factors: road construction and forest removal/conversion on adjacent lands. Data were obtained from two sources: road densities and forest cover from 1:50,000 Government of Canada topographic maps and species lists and wetland areas from Ontario Ministry of Natural Resources wetland evaluation reports. Multiple regression analysis was used to model the relationships between species richness and wetland area, road density, and forest cover. Our results show a strong positive relationship between wetland area and species richness for all taxa. The species richness of all taxa except mammals was negatively correlated with the density of paved roads on lands up to 2 km from the wetland. Furthermore, both herptile and mammal species richness showed a strong positive correlation with the proportion of forest cover on lands within 2 km. These results provide evidence that at the landscape level, road construction and forest removal on adjacent lands pose significant risks to wetland biodiversity. Furthermore, they suggest that most existing wetland policies, which focus almost exclusively on activities within the wetland itself and/or a narrow buffer zone around the wetland perimeter, are unlikely to provide adequate protection for wetland biodiversity.
Article
Urbanization is a growing threat to ecological communities and has become a leading cause of population extirpations in a wide range of taxa. Because the effects of urbanization are often multifaceted, identifying the pathways through which changes in communities occur has remained a persistent challenge. We draw upon metacommunity theory to evaluate competing explanations for the effects of urbanization, focusing on the relative importance of processes at local (e.g. abiotic and biotic characteristics) and regional (e.g. habitat connectivity and dispersal) scales. Over 4years, we sampled 201 wetlands in the Front Range region of Colorado, which is one of the most rapidly developing areas in the USA. Wetlands embedded within urban areas exhibited significantly lower taxonomic richness and diversity compared to those in agricultural or grassland areas. Relative to grassland wetlands, urban wetlands supported a 60% lower richness of amphibians and aquatic reptiles and a 33% lower richness of aquatic insects, molluscs and crayfish. These patterns were associated with changes in biotic factors (introduced fishes and bullfrogs), abiotic factors (nutrients, conductivity and vegetation) and landscape characteristics (road density and surrounding wetland area). The use of an information-theoretic approach and structural equation modelling suggested that the effects of urbanization on richness were mainly driven by changes in road density. Analyses of community composition indicated that discrete communities formed along the urban systems gradient, such that actively dispersing predators associated more negatively with urban system relative to herbivores with passive dispersal. Synthesis and applications. These results highlight the importance of considering both local and regional factors in addressing conservation-related challenges and underscore the benefits of linking conceptual work on metacommunity theory with applied efforts to mitigate the effects of urbanization.
Article
Many groups show higher species richness in tropical regions but the underlying causes remain unclear. Despite many competing hypotheses to explain latitudinal diversity gradients, only three processes can directly change species richness across regions: speciation, extinction and dispersal. These processes can be addressed most powerfully using large-scale phylogenetic approaches, but most previous studies have focused on small groups and recent time scales, or did not separate speciation and extinction rates. We investigate the origins of high tropical diversity in amphibians, applying new phylogenetic comparative methods to a tree of 2871 species. Our results show that high tropical diversity is explained by higher speciation in the tropics, higher extinction in temperate regions and limited dispersal out of the tropics compared with colonization of the tropics from temperate regions. These patterns are strongly associated with climate-related variables such as temperature, precipitation and ecosystem energy. Results from models of diversity dependence in speciation rate suggest that temperate clades may have lower carrying capacities and may be more saturated (closer to carrying capacity) than tropical clades. Furthermore, we estimate strikingly low tropical extinction rates over geological time scales, in stark contrast to the dramatic losses of diversity occurring in tropical regions presently.
Article
With human populations increasing worldwide, habitat destruction and degradation are among the greatest threats facing wildlife. To minimize the impacts of development on aquatic habitats, numerous conservation measures have been implemented, including the use of riparian buffer zones along streams and rivers. We examined the effectiveness of current buffer-zone systems for management of small watersheds in conserving stream-dwelling salamander populations in 10 small streams (draining <40.5 ha) in the western Piedmont of North Carolina. We captured salamanders by means of funnel traps and systematic dipnetting and used a geographic information system to calculate the percentage of disturbed habitat within the watershed of each stream and within 10.7-, 30.5-, and 61.0-m buffer zones around each stream, upstream from our sampling locations. Although the relative abundance of salamanders was strongly inversely proportional to the percentage of disturbed habitat in the entire watersheds (R2 = 0.71 for Desmognathus fuscus and 0.48 for Eurycea cirrigera), we found little to no correlation between the relative abundance of salamanders and the percentage of disturbed habitat present within buffer zones (R2 = 0.06-0.27 for D. fuscus and 0.01-0.07 for E. cirrigera). Thus, conservation efforts aimed at preserving salamander populations in headwater streams must consider land use throughout entire watersheds, rather than just preserving small riparian buffer zones.
Article
For many species, not all required resources are contained in breeding habitat. Such species depend on landscape complementation, i.e., linking together different landscape elements through movement, to complete their life cycles. We suggest that the dichotomous habitat classification of many metapopulation analyses (habitat vs. nonhabitat) masks our ability to detect metapopulation effects for such species. We tested this using a species for which landscape complementation is obligate and metapopulation structure is likely: Rana pipiens, the northern leopard frog. We used breeding chorus survey data to index relative abundance of leopard frogs in 34 'core' ponds and conducted Poisson regression analysis to determine the effects on frog density of local pond habitat, availability of summer habitat (landscape complementation), and number of occupied ponds in the surrounding landscapes (metapopulation structure). All of these factors had statistically significant effects on frog density. However, when summer habitat was not included in the statistical model, the metapopulation structure was no longer significant; i.e., its effect was masked. Our results suggest that one must be cautious in applying the results of metapopulation analyses to species for which the habitat vs. nonhabitat categorization of the landscape is not appropriate. The potential for rescue and recolonization to maintain a regional population must be assessed within the constraints of the entire landscape.
Article
Vehicular traffic can be a major source of mortality for some species. Highly vagile organisms may be at a disadvantage in landscapes with roads because they are more likely to encounter roads and incur traffic mortality. To test this prediction, we assessed the population abundance of two anuran species of differing vagility, the leopard frog ( Rana pipiens, more vagile) and the green frog ( Rana clamitans, less vagile), at 30 breeding ponds. Traffic density, an index of the amount of potential traffic mortality, was measured in concentric circles radiating from the ponds out to 5 km. We conducted multiple linear regressions relating population abundance to traffic density, pond variables, and landscape habitat variables and found that leopard frog population density was negatively affected by traffic density within a radius of 1.5 km. There was no evidence that the presence of vehicular traffic affected green frog populations. These results suggest that traffic mortality can cause population declines and that more vagile species may be more vulnerable to road mortality than less vagile species.
Article
Anthropogenic change such as road construction and subsequent traffic noise in pristine habitats has been shown to be detrimental to a range of vertebrate taxa. The effect of anthropogenic noise on anuran communication is not well known, and has only recently been a topic of investigation. We tested the effect of anthropogenic noise on the calling behaviour of the Amazonian treefrog Dendropsophus triangulum. We performed four experiments. We first presented frogs with the noise of a pre-recorded motorcycle engine, and recorded the call rates of focal frogs for 5 min, then for another 5 min during which they were presented with a broadcast of noise, and again for 5 min post-stimulus. We repeated this experiment using music as the stimulus. We then tested the effect of intermittent engine noise, recording baseline call rate and response to six cycles of intermittent noise. In all experiments, call rates nearly doubled during playbacks. Finally, we compared frogs' responses to anthropogenic noise to responses to chorus noise broadcast at the same intensity; call rates did not differ between treatments. These results demonstrate a clear effect of exogenous noise on male D. triangulum.
Article
Effective monitoring programs are designed to track changes in the distribution, occurrence, and abundance of species. We developed an extension of Royle and Kéry's (2007) single species model to estimate simultaneously temporal changes in probabilities of detection, occupancy, colonization, extinction, and species turnover using data on calling anuran amphibians, collected from 2002 to 2006 in the Lower Mississippi Alluvial Valley of Louisiana, USA. During our 5-year study, estimates of occurrence probabilities declined for all 12 species detected. These declines occurred primarily in conjunction with variation in estimates of local extinction probabilities (cajun chorus frog [Pseudacris fouquettei], spring peeper [P. crucifer], northern cricket frog [Acris crepitans], Cope's gray treefrog [Hyla chrysoscelis], green treefrog [H. cinerea], squirrel treefrog [H. squirella], southern leopard frog [Lithobates sphenocephalus], bronze frog [L. clamitans], American bullfrog [L. catesbeianus], and Fowler's toad [Anaxyrus fowleri]). For 2 species (eastern narrow-mouthed toad [Gastrophryne carolinensis] and Gulf Coast toad [Incilius nebulifer]), declines in occupancy appeared to be a consequence of both increased local extinction and decreased colonization events. The eastern narrow-mouthed toad experienced a 2.5-fold increase in estimates of occupancy in 2004, possibly because of the high amount of rainfall received during that year, along with a decrease in extinction and increase in colonization of new sites between 2003 and 2004. Our model can be incorporated into monitoring programs to estimate simultaneously the occupancy dynamics for multiple species that show similar responses to ecological conditions. It will likely be an important asset for those monitoring programs that employ the same methods to sample assemblages of ecologically similar species, including those that are rare. By combining information from multiple species to decrease the variance on estimates of individual species, our results are advantageous compared to single-species models. This feature enables managers and researchers to use an entire community, rather than just one species, as an ecological indicator in monitoring programs. © 2011 The Wildlife Society.
Article
The Michigan Frog and Toad Survey (MFTS) is an annual volunteer-based anuran census. One major concern with data collected by volunteers is the information's quality and consistency. The goal of this study was to evaluate the effect of observer experience on data quality. Questionnaires and an audio CD with a simulated anuran survey route were mailed to all active volunteers. We were able to determine volunteer demographics and commitment to program; species characteristically missed, misidentified, over- or under-estimated; and influence of volunteer background on data quality. Volunteers were reasonably reliable in their abilities to determine species presence, but there was extensive variability in abundance estimation. Some species were characteristically confused by volunteers, and additional species frequently were recorded even when absent from a site. Prior experience and background had little influence on the ability to identify or estimate abundance of calling anurans. Our results indicate that such survey approaches are easy for volunteers to learn and provide reasonable estimates for species' presence, but do not necessarily estimate abundance well. These results will be used to improve data-collection protocols for the MFTS and better analyze and interpret data collected, and also could be beneficial for other regional amphibian monitoring programs.
Article
Species in biological communities respond to environmental variation si-multaneously across a range of organizational levels. Accordingly, it is important to quantify the effects of environmental factors at multiple levels on species distribution and abundance. Hierarchical methods that explicitly separate the independent and confounded influences of environmental variation across several levels of organization are powerful tools for this task. Our study used a hierarchical approach to partition explained variance in an Oregon Coast Range bird community among plot-, patch-, and landscape-level factors. We used a series of partial canonical ordinations to decompose species–environment relationships across these levels of organization to test four hypotheses about the importance of envi-ronmental control over community structure. We found that plot-level factors were better predictors of community structure than patch-or landscape-level factors. In addition, al-though landscape-level variables contributed substantial independent explanatory power, there was little evidence that patch-level environmental variability provided additional explanation of community structure beyond that provided by plot-and landscape-level factors. At higher levels of the hierarchical analysis, we found that, among plot-level factors, vegetation cover type was as powerful a predictor of community structure as detailed floristics, and more powerful than vegetation structure. At the landscape level, we found that landscape composition and configuration both provided substantial independent ex-planatory power, with landscape composition being the better overall predictor. Our results have a number of implications for sampling, analysis, and conservation. For example, misleading results could be obtained by studies conducted at a single organizational level. Also, the high degree of confounding among several levels of our analysis suggests that there is a lack of independence between the influences of environmental structure at different organizational levels. Due to this confounding, our results suggest that patch-based studies of forest–bird ecological relationships in the Oregon Coast Range may be equivocal. In addition, the power of mapped cover class as a plot-level predictor variable suggests that coarse-filter, multiscale approaches utilizing remote sensing and GIS may be nearly as effective at predicting local patterns as expensive field surveys of habitat conditions at the plot level, and more effective at predicting patterns continuously across large regions.
Article
ABSTRACT  Road mortality is often spatially aggregated, and there is a need for models that accurately and efficiently predict hot spots within a road network for mitigation. We surveyed 145 points throughout a 353-km highway network in New York State, USA, for roadkill of reptiles and amphibians. We used land cover, wetland configuration, and traffic volume data to identify features that best predicted hot spots of herpetofauna road mortality. We resampled 40 points an additional 4 times over 4 years to evaluate temporal repeatability. Both amphibian and reptile road mortality were spatially clustered, and road-kill hot spots of the 2 taxa overlapped. One survey provided a valid snapshot of spatial patterns of road mortality, and spatial patterns remained stable across time. Road-kill hot spots were located where wetlands approached within 100 m of the road, and the best predictor was a causeway configuration of wetlands (wetlands on both sides of the road). We validated causeways as predictors of road mortality by surveying 180 causeways and 180 random points across 5 regions (17,823 km2) of northeastern New York. Causeways were 3 times more likely than random locations to have amphibian and 12 times more likely to have reptile mortality present, and causeways had a 4 times higher total number of amphibian roadkill and 9 times higher reptile roadkill than did random points. We conclude it is possible to identify valid predictors of hot spots of amphibian and reptile road mortality for use when planning roads or when conducting surveys on existing roads to locate priority areas for mitigation.
Article
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.
Article
Landscapes can be described by two essential features: the composition and spatial arrangement of patches. We considered the roles of these basic landscape descriptors by examining how the occurrence of nine amphibian species in breeding ponds was associated with the area of forested habitat and the proximity of ponds to forested habitat. We used visual and call surveys to compare the composition of amphibian assemblages in 116 ponds adjacent to or separated from forest and surrounded by different amounts of forested land. The area of forest and pond adjacency to forest were not associated ( t = −0.13, nisolated = 64, nconnected = 52, p = 0.21), which means these factors can manifest their effects separately. We used logistic regression to test predictions about associations between each species and forest area and to test for associations with pond-forest adjacency. Seven of nine species were associated with forest area. Wood frogs ( Rana sylvatica), green frogs ( Rana clamitans), eastern newts ( Notopthalmus viridescens), spotted salamanders (Ambystoma maculatum), and salamanders of the blue-spotted/Jefferson's complex (Ambystoma laterale/A. jeffersonianum) were more likely to occupy ponds in more forested areas, whereas leopard frogs ( Rana pipiens) and American toads ( Bufo americanus) were negatively associated with forest area. Three species were associated with pond-forest adjacency. Spotted salamanders and salamanders of the blue-spotted/Jefferson's complex were more likely to occupy ponds that were adjacent to forest. In areas with little forest, leopard frogs were more likely to occur in adjacent ponds, but the reverse was true for areas with extensive forests. Our results suggest that the composition of the landscape surrounding breeding ponds is associated with the likelihood of occurrence of most of the species examined and that landscape configuration is also important for a smaller subset of species.
Article
Aim To describe broad-scale geographical patterns of body size for European and North American amphibian faunas and to explore possible processes underlying these patterns. Specifically, we propose a heat balance hypothesis, as both heat conservation and heat gain determine the heat balance of ectotherms, and test it along with five other hypotheses that have a possible influence on body size gradients: size dependence, migration ability, primary productivity, seasonality and water availability. Location Western Europe and North America north of Mexico. Methods We processed distribution maps for native amphibian species to estimate the mean body size in 110 × 110 km cells and calculated eight environmental predictors to explore the relationship between environmental gradients and the observed patterns. We used least squares regression modelling and model selection approaches based on information theory to evaluate the relative support for each hypothesis. Results We found consistent body size gradients and similar relationships to environmental variables within each amphibian group in Europe and North America. Annual potential evapotranspiration, a measure of environmental energy, was the strongest predictor of mean body size in both regions. However, the contrasting responses to ambient energy in each group resulted in opposite geographical patterns, i.e. anurans increased in size from high- to low-energy areas in both continents and urodeles showed the opposite pattern. Main conclusions Our results support the heat balance hypothesis, suggesting that the thermoregulatory abilities of anurans would allow them to reach larger sizes in colder climates by optimizing the trade-off between heating and cooling rates, whereas a lack of such strategies among urodele faunas would explain why these organisms tend to be smaller in cooler areas. These findings may also have implications for the role of climate warming on the global decline of amphibians.
Article
Management of amphibian populations to reverse recent declines will require defining high-quality habitat for individual species or groups of species, followed by efforts to retain or restore these habitats on the landscape. We examined landscape-level habitat relationships for frogs and toads by measuring associations between relative abundance and species richness based on survey data derived from anuran calls and features of land-cover maps for Iowa and Wisconsin. The most consistent result across all anuran guilds was a negative association with the presence of urban land. Upland and wetland forests and emergent wetlands tended to be positively associated with anurans. Landscape metrics that represent edges and patch diversity also had generally positive associations, indicating that anurans benefit from a complex of habitats that include wetlands. In Iowa the most significant associations with relative abundance were the length of the edge between wetland and forest (positive) and the presence of urban land (negative). In Wisconsin the two most significant associations with relative abundance were forest area and agricultural area (both positive). Anurans had positive associations with agriculture in Wisconsin but not in Iowa. Remnant forest patches in agricultural landscapes may be providing refuges for some anuran species. Differences in anuran associations with deep water and permanent wetlands between the two states suggest opportunities for management action. Large-scale maps can contribute to predictive models of amphibian habitat use, but water quality and vegetation information collected from individual wetlands will likely be needed to strengthen those predictions. Landscape habitat analyses provide a framework for future experimental and intensive research on specific factors affecting the health of anurans.
Article
Urbanization negatively affects natural ecosystems in many ways, and aquatic systems in particular. Urbanization is also cited as one of the potential contributors to recent dramatic declines in amphibian populations. From 2000 to 2002 we determined the distribution and abundance of native amphibians and exotic predators and characterized stream habitat and invertebrate communities in 35 streams in an urbanized landscape north of Los Angeles (U.S.A.). We measured watershed development as the percentage of area within each watershed occupied by urban land uses. Streams in more developed watersheds often had exotic crayfish (Procambarus clarkii) and fish, and had fewer native species such as California newts (Taricha torosa) and California treefrogs (Hyla cadaverina). These effects seemed particularly evident above 8% development, a result coincident with other urban stream studies that show negative impacts beginning at 10–15% urbanization. For Pacific treefrogs (H. regilla), the most widespread native amphibian, abundance was lower in the presence of exotic crayfish, although direct urbanization effects were not found. Benthic macroinvertebrate communities were also less diverse in urban streams, especially for sensitive species. Faunal community changes in urban streams may be related to changes in physical stream habitat, such as fewer pool and more run habitats and increased water depth and flow, leading to more permanent streams. Variation in stream permanence was particularly evident in 2002, a dry year when many natural streams were dry but urban streams were relatively unchanged. Urbanization has significantly altered stream habitat in this region and may enhance invasion by exotic species and negatively affect diversity and abundance of native amphibians.
Article
In many respects, amphibian spatial dynamics resemble classical metapopulation models, in which subpopulations in breeding ponds blink in and out of existence and extinction and colonization rates are functions of pond spatial arrangement. This “ponds-as-patches” view of amphibian spatial dynamics is useful in several respects. First, it highlights the importance of regional and landscape processes in determining local patterns of abundance. Second, it offers a straightforward, pond-based approach to monitoring and managing amphibian populations. For many species, however, the ponds-as-patches view may be an oversimplification and metapopulation structure may be more apparent than real. Changes in distribution may be caused by processes other than extinction and recolonization, and most extinctions probably result from deterministic factors, not stochastic processes. In addition, the effects of pond isolation appear to be important primarily in disturbed environments, and in many cases these isolation effects may be better explained by the distribution of terrestrial habitats than by the distribution of breeding ponds. These complications have important implications for both researchers and managers. For researchers, future efforts need to determine the mechanisms underlying patterns of abundance and distributional change and patterns in amphibian populations. For managers, effective conservation strategies must successfully balance metapopulation considerations with careful attention to local habitat quality. Furthermore, translocations and active management may be indispensable tools for conserving amphibians in landscapes containing multiple breeding ponds.
Article
Conversion of forested lands to agriculture or urban/residential areas has been associated with declines in stream and lake water quality. Less attention has been paid to the effects of adjacent land-uses on wetland sediment and water quality and, perhaps more importantly, the spatial scales at which these effects occur. Here we address these issues by examining variation in water and sediment nutrient levels in 73 southeastern Ontario, Canada, wetlands. We modeled the relationship between water and sediment nutrient concentrations and various measures of adjacent land-use such as forest cover and road density, measured over increasing distances from the wetland edge. We found that water nitrogen and phosphorous levels were negatively correlated with forest cover at 2250 meters from the wetland edge, while sediment phosphorous levels were negatively correlated with wetland size and forest cover at 4000 meters and positively correlated with the proportion of land within 4000 meters that is itself wetland. These results suggest that the effects of adjacent land-use on wetland sediment and water quality can extend over comparatively large distances. As such, effective wetland conservation will not be achieved merely through the creation of narrow buffer zones between wetlands and more intensive land-uses. Rather, sustaining high wetland water quality will require maintaining a heterogeneous regional landscape containing relatively large areas of natural forest and wetlands.
Article
The distribution pattern of the tree frog (Hyla arborea) in an intensively used agricultural landscape in Zealand Flanders, was analyzed for effects of habitat fragmentation. The logistic regression models showed that the chance that a pond (potential reproduction site) was occupied by tree frogs depended on three isolation factors. The density of ponds within 750 m of the occupied pond was higher compared to ponds that remained unoccupied during the survey period. Additionally both the density of shrubs as well as the density of high herbs, two terrestrial habitat factors, was higher within 1000 m of occupied ponds. The explanatory value of two different types of isolation measures was compared with logistic regression analysis. It is discussed that Concentric isolation measures, which take size and distance of potential habitat patches in all directions into account, are expected to give a better description of isolation than the more often used 'distance from the nearest habitat patch'.
Article
A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15-20% of the United States is ecologically impacted by roads.