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Controlling human activities as confounding variable in road studies

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Abstract

Roads cause disturbances to wildlife from the beginning of their construction and once the road is in operation, people usually make use of the habitats, reducing their quality. To this are added the effects caused by light and noise from vehicles. These propagate through the land adjacent to the road causing changes in the fauna's use of the habitat. This led us to ask ourselves what attributes inherent to the road and terrain influence the vertebrate fauna and what factors associated with human activities can be considered as confounding variables for the results interpretation? The study was conducted in proximity of the 40D highway in Mexico. Three paired areas were selected where signs of wildlife presence were recorded during spring and fall from 2018 to 2020 and these data were used as response variable (2108 records of 49 species). We used as explanatory variables the inherent characteristics of the natural terrain and road (e.g., height difference between road and habitat, distance from road), as well as those related to human presence in the habitat (e.g., distance to nearest town). GLM's were adjusted to determine the influence of these on our response variable. We found that the inherent variables of the road and terrain have a significant influence on the number of faunal of hunting interest traces found (p = 0.018, r² = 23.09). The method used allowed us to identify and distinguish the influence that human activities exert on the fauna within the road's influence zone. The differential way in which organisms respond to human presence and activity makes it difficult to isolate this effect from the one we wish to evaluate, such as that of the road. Therefore, it is suggested that the variables used in this study be used as a control measure of this effect in the work carried out in proximity of roads.

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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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Understanding the interactions between predators and prey is essential for predicting the effects of disturbances to ecosystems. Motorways produce changes in the surrounding biotic and abiotic environment and hence have multiple impacts on wildlife. Some species are known to change their activity patterns in the proximity of motorways but the implications for the structure of food webs are unknown. This study analyzes the activity patterns of both mammalian predators and their prey species near nine motorways in attempt to clarify how motorways affect the mammalian community. Habitat structural variables were also sampled to control the effects of microhabitat on relative prey abundance. Our results revealed different activity patterns of both predators and prey near motorways that are independent of structural differences in microhabitat. Both the red fox and small mammals were found to use the zone close to the motorways more frequently, whereas lagomorphs and mustelids were less active there. These differences suggest that motorways favor the population of the predator that is most tolerant of human activity, the red fox, whose activity could have both direct and indirect effects on that of other members of the predator and prey community. On the one hand, the red fox seems to act as “top predator” and mustelids to follow a “safety match” strategy avoiding the area close to the motorway where fox is more active. On the other hand, abundances of prey species are negatively associated with the activity of their most frequent predators. This study is the first to assess how the proximity to motorways affects the activity of mammals in two levels of the food web and opens the field for research to understand the processes driving the detected patterns. Moreover, such effects at the community scale should be taken into account when evaluating the impacts of motorways on the surrounding ecosystems.
Article
Wolf management can be controversial, reflecting a wide range of public attitudes. We analyzed wolf management case histories representing a spectrum of approaches in Canada and the United States. During the early 20th century, wolves were considered undesirable. They were subject to persecution and were extirpated from large areas of their original range. With increased environmental awareness in the 1970s, attitudes toward wolves began to change. Wolf conservation became a focus of public interest, providing conditions that favored regional wolf recovery. However, in regions where livestock production or big-game hunting is valued, wolves have continued to be controlled by management authorities or through the actions of individual citizens. With US wolf populations recovering in the conterminous states, a rule was approved to delist the species from endangered to threatened status under the Endangered Species Act. Notwithstanding the intent of legal instruments, history has demonstrated that societal values ultimately determine the survival of species such as the wolf.
Article
Ecological flows and biological diversity trace broad patterns across the landscape, whereas transportation planning for human mobility traditionally focuses on a narrow strip close to a road or highway. To help close this gap we examined the 'road-effect zone' over which significant ecological effects extend outward from a road. Nine ecological factors-involving wetlands, streams, road salt, exotic plants, moose, deer, amphibians, forest birds, and grassland birds-were measured or estimated near 25 km of a busy four-lane highway west of Boston, Massachusetts. The effects of all factors extended >100 m from the road, and moose corridors, road avoidance by grassland birds, and perhaps road salt in a shallow reservoir extended outwards > 1 km. Most factors had effects at 2-5 specific locations, whereas traffic noise apparently exerted effects along most of the road length. Creating a map of these effects indicates that the road-effect zone averages approximately 600 m in width and is asymmetric, with convoluted boundaries and a few long fingers. We conclude that busy roads and nature reserves should be well separated, and that future transportation systems across landscapes can provide for ecological flows and biological diversity in addition to safe and efficient human mobility.
Article
Naïve zebra danios (Brachydanio rerio) flee from an approaching predator when the angle subtended at the danio's eye by the predator changes at a rate greater than some characteristic threshold value. The hypothesis was tested that this value declines, and hence reactive distance increases, as a function of the number of past experiences with the predator. Artificial predators of two types, a model and a film of an approaching object, were presented to the danios daily and changes in behaviour recorded. The rate of change of visual angle at the time of response to the predator (dα/dt threshold) declined asymptotically with increasing experience. Consequently, flight distance increased asymptotically. The change was not due to growth, maturation, or increased familiarity with the testing situation. The danios apparently associated the visual characteristics of the predator with its subsequent high rate of angular growth and began to respond to these visual characteristics prior to dα/dt exceeding the threshold. The angle of escape was not affected by experience. Escape velocity increased with experience of the film predator, but not with experience of the model predator. No decrement of the learned change in reactive distance was evident after 10 days without experience with the film predator.
Article
Road traffic and the loss of forests are both known to have negative effects on anurans. However, the relative importance of these two predictors is poorly understood because forest cover in the landscape is usually negatively correlated with the density of roads and traffic. To evaluate the independent effects of traffic and forest cover, we selected 36 ponds near Ottawa, Canada, at the center of four landscape types: low forest/low traffic; low forest/high traffic; high forest/low traffic; and high forest/high traffic, where traffic and forest cover were measured within 100–2000 m of the edge of each pond. We surveyed all ponds in 2005 and re-surveyed a 23-pond subset in 2006. The negative association between species richness and traffic density was stronger (partial R2 = 0.34; P < .001) than the positive association of species richness with forest cover (partial R2 = 0.10; P > .05) in the landscape. Three of six common species showed stronger associations with traffic density than with forest cover – Bufo americanus, Rana pipiens, and Hyla versicolor; two species – Pseudacris crucifer and Rana sylvatica – showed stronger associations with forest cover than with traffic; while Rana clamitans showed similar associations with traffic and forest cover. Our results show that the overall negative effect of traffic on anuran populations in northeastern North America is at least as great as the negative effect of deforestation, and also that the relative effects of these two predictors on anuran abundance vary between species.
Article
Dunlin (Calidris alpina) scanning and flocking behavior was studied in two habitats with different predation risk. Mean flock size, time spent scanning, and mean scan duration were higher in rice fields (dhe less profitable and high-risk habitat) than in littoral habitats (the more profitable and low-risk habitat), although vigilance rate was not different between habitats. Increased scanning and flocking behavior probably increase efficency in predator avoidance. The results are explained as behavioral changes to ensure safety in a high predation-risk situation when starvation risk is also present.
Article
1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides insight into the effects that sharp road edges have on biological and social characteristics of small mammal populations, highlighting how such effects vary among species. Our findings have important conservation implications for these threatened species, but are also applicable in a broader context wherever there are abrupt edges caused by linear landscape features.
Article
The conservation of the crop varieties of traditional agriculture in the centers of genetic diversity is essential to provide genetic resources for plant improvement. These resources are acutely threatened by rapid agricultural development which is essential for the welfare of millions. Methodologies for genetic conservation have been worked out which are both effective and economical. Urgent action is needed to collect and preserve irreplaceable genetic resources. Wild species, increasingly endangered by loss of habitats, will depend on organized protection for their survival. On a long term basis this is feasible only within natural communities in a state of continuing evolution, hence there is an urgent need for exploration and clarification of the genetic principles of conservation. Gene pools of wild species are increasingly needed for various uses, from old and new industries to recreation. But the possibility of a virtual end to the evolution of species of no direct use to man raises questions of responsibility and ethics.
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