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Search Results: 1 - 10 of 19818 matches for " André Desrochers "
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Spatial Aggregation of Forest Songbird Territories and Possible Implications for Area Sensitivity
Julie Bourque,André Desrochers
Avian Conservation and Ecology , 2006,
Abstract: Habitat area requirements of forest songbirds vary greatly among species, but the causes of this variation are not well understood. Large area requirements could result from advantages for certain species when settling their territories near those of conspecifics. This phenomenon would result in spatial aggregations much larger than single territories. Species that aggregate their territories could show reduced population viability in highly fragmented forests, since remnant patches may remain unoccupied if they are too small to accommodate several territories. The objectives of this study were twofold: (1) to seek evidence of territory clusters of forest birds at various spatial scales, lags of 250-550 m, before and after controlling for habitat spatial patterns; and (2) to measure the relationship between spatial autocorrelation and apparent landscape sensitivity for these species. In analyses that ignored spatial variation of vegetation within remnant forest patches, nine of the 17 species studied significantly aggregated their territories within patches. After controlling for forest vegetation, the locations of eight out of 17 species remained significantly clustered. The aggregative pattern that we observed may, thus, be indicative of a widespread phenomenon in songbird populations. Furthermore, there was a tendency for species associated with higher forest cover to be more spatially aggregated [ERRATUM].
Modelling Marten (Martes americana) Movement Costs in a Boreal Forest: Effects of Grain Size and Thematic Resolution
Ophélie Planckaert,André Desrochers
International Journal of Ecology , 2012, DOI: 10.1155/2012/742913
Abstract: We investigated landscape resistance to movements of American marten (Martes americana) based on snow-tracking data. We generated movement cost maps of the study area with different grain size, thematic resolution, and habitat-specific resistance to movements. We compared simulated tracks obtained from resistance maps to real tracks plotted along transects that we surveyed in winters 2004 to 2008 at the Montmorency Forest, Quebec, Canada. Simulated tracks were located at the intersection between least-cost paths simulated across the study area and transects. We used nearest-neighbour distances between simulated and real tracks to assess the performance of resistance maps and estimate landscape resistance parameters. Simulations with specified costs to movement for open areas, young forest, and mature forest performed better than simpler resistance scenarios, suggesting that resistance to marten movements differed among those landscape attributes that were considered. Simulations with a map grain size of 100 m performed significantly better than 5, 25, and 300 m, possibly because of gap crossing avoidance. Model performance (compared to null model) was maximal when resistance to movement in open habitat was set to 20 times higher than in mature forest, but uncertainty around this estimate was large. This research demonstrates that presence-only (point) data can be used to parameterize movements using spatially explicit modelling.
Modelling Marten (Martes americana) Movement Costs in a Boreal Forest: Effects of Grain Size and Thematic Resolution
Ophélie Planckaert,André Desrochers
International Journal of Ecology , 2012, DOI: 10.1155/2012/742913
Abstract: We investigated landscape resistance to movements of American marten (Martes americana) based on snow-tracking data. We generated movement cost maps of the study area with different grain size, thematic resolution, and habitat-specific resistance to movements. We compared simulated tracks obtained from resistance maps to real tracks plotted along transects that we surveyed in winters 2004 to 2008 at the Montmorency Forest, Quebec, Canada. Simulated tracks were located at the intersection between least-cost paths simulated across the study area and transects. We used nearest-neighbour distances between simulated and real tracks to assess the performance of resistance maps and estimate landscape resistance parameters. Simulations with specified costs to movement for open areas, young forest, and mature forest performed better than simpler resistance scenarios, suggesting that resistance to marten movements differed among those landscape attributes that were considered. Simulations with a map grain size of 100?m performed significantly better than 5, 25, and 300?m, possibly because of gap crossing avoidance. Model performance (compared to null model) was maximal when resistance to movement in open habitat was set to 20 times higher than in mature forest, but uncertainty around this estimate was large. This research demonstrates that presence-only (point) data can be used to parameterize movements using spatially explicit modelling. 1. Introduction Habitat selection studies have long assumed that access to habitats is a negligible constraint for animal movements within landscapes [1], but access limitations that are attributable to roadways and forest fragmentation are increasingly recognized [2]. Movement constraints are governed by spatial patterns of resource used to maximize fitness (e.g., access to critical resources and avoidance of predation). They reduce connectivity [3] within the established home range of animals and limit accessibility of habitat patches to dispersing organisms [4], thereby affecting population dynamics. Thus, the occurrence of an animal in a habitat may depend on the surrounding matrix, and the consideration of movement constraints appears to be crucial in the development of habitat selection models [1, 5, 6]. Spatially explicit simulations including least-cost paths [7, 8] have become increasingly popular for modelling optimum movement routes of animals. Least-cost models can simulate animal movements based on the configuration of different spatial features within a heterogeneous landscape, and the hypothetical resistance to
Use of Large Clear-Cuts by Wilson’s Warbler in an Eastern Canadian Boreal Forest
André Desrochers,Jacinthe Tardif,Marc J. Mazerolle
Avian Conservation and Ecology , 2012, DOI: 10.5751/ace-00521-070201
Abstract: Wilson’s Warbler (Cardellina pusilla; WIWA) has been declining for several decades, possibly because of habitat loss. We compared occupancy of territorial males in two habitat types of Québec’s boreal forest, alder (Alnus spp.) scrubland and recent clear-cuts. Singing males occurred in clusters, their occupancy was similar in both habitats, but increased with the amount of alder or clear-cut within 400 m of point-count stations. A despotic distribution of males between habitats appeared unlikely, because there were no differences in morphology between males captured in clear-cuts vs. alder. Those results contrast with the prevailing view, mostly based on western populations, that WIWA are wetland or riparian specialists, and provide the first evidence for a preference for large tracts of habitat in this species. Clear-cuts in the boreal forest may benefit WIWA by supplying alternative nesting habitat. However, the role of clear-cuts as source or sink habitats needs to be addressed with data on reproduction.
From Satellite Imagery to Peatland Vegetation Diversity: How Reliable Are Habitat Maps?
Monique F. Poulin,Denis Careau,Line Rochefort,André Desrochers
Ecology and Society , 2002,
Abstract: Although satellite imagery is becoming a basic component of the work of ecologists and conservationists, its potential and reliability are still relatively unknown for a large number of ecosystems. Using Landsat 7/ETM+ (Enhanced Thematic Mapper Plus) data, we tested the accuracy of two types of supervised classifications for mapping 13 peatland habitats in southern Quebec, Canada. Before classifying peatland habitats, we applied a mask procedure that revealed 629 peatlands covering a total of 18,103 ha; 26% of them were larger than 20 ha. We applied both a simple maximum likelihood (ML) function and a weighted maximum likelihood (WML) function that took into account the proportion of each habitat class within each peatland when classifying the habitats on the image. By validating 626 Global Positioning System locations within 92 peatlands, we showed that both classification procedures provided an accurate representation of the 13 peatland habitat classes. For all habitat classes except lawn with pools, the predominant classified habitat within 45 m of the center of the validation location was of the same type as the one observed in the field. There were differences in the performance of the two classification procedures: ML was a better tool for mapping rare habitats, whereas WML favored the most common habitats. Based on ordinations, peatland habitat classes were as effective as environmental variables such as humidity indicators and water chemistry components at explaining the distribution of plant species and performed 1.6 times better when it came to accounting for vegetation structure patterns. Peatland habitats with pools had the most distinct plant assemblages, and the habitats dominated by herbs were moderately distinct from those characterized by ericaceous shrubs. Habitats dominated by herbs were the most variable in terms of plant species assemblages. Because peatlands are economically valuable wetlands, the maps resulting from the new classification procedure presented here will provide useful information for land managers and conservationists.
Are Boreal Ovenbirds, Seiurus aurocapilla, More Prone to Move across Inhospitable Landscapes in Alberta’s Boreal Mixedwood Forest than in Southern Québec’s Temperate Deciduous Forest?
Marc Bélisle,André Desrochers,Jean-Fran?ois Gobeil,Marc-André Villard
Avian Conservation and Ecology , 2007,
Abstract: Population life-history traits such as the propensity to move across inhospitable landscapes should be shaped by exposure to landscape structure over evolutionary time. Thus, birds that recently evolved in landscapes fragmented by natural disturbances such as fire would be expected to show greater behavioral and morphological vagility relative to conspecifics that evolved under less patchy landscapes shaped by fewer and finer-scaled disturbances, i.e., the resilience hypothesis. These predictions are not new, but they remain largely untested, even for well-studied taxa such as neotropical migrant birds. We combined two experimental translocation, i.e., homing, studies to test whether Ovenbird, Seiurus aurocapilla, from the historically dynamic boreal mixedwood forest of north-central Alberta (n = 55) is more vagile than Ovenbird from historically less dynamic deciduous forest of southern Québec (n = 89). We found no regional difference in either wing loading or the response of homing Ovenbird to landscape structure. Nevertheless, this study presents a heuristic framework that can advance the understanding of boreal landscape dynamics as an evolutionary force.
Winter Responses of Forest Birds to Habitat Corridors and Gaps
Colleen Cassady St. Clair,Marc Bélisle,André Desrochers,Susan Hannon
Ecology and Society , 1998,
Abstract: Forest fragmentation and habitat loss may disrupt the movement or dispersal of forest-dwelling birds. Despite much interest in the severity of these effects and ways of mitigating them, little is known about actual movement patterns in different habitat types. We studied the movement of wintering resident birds, lured by playbacks of mobbing calls, to compare the willingness of forest birds to travel various distances in continuous forest, along narrow corridors (fencerows), and across gaps in forest cover. We also quantified the willingness of Black-capped Chickadees (Poecile atricapillus) to cross gaps when alternative forested detour routes were available. All species were less likely to respond to the calls as distance increased to 200 m, although White-breasted Nuthatches (Sitta carolinensis) and Hairy Woodpeckers (Picoides villosus) were generally less likely to respond than chickadees and Downy Woodpeckers (P. pubescens). Chickadees were as likely to travel in corridors as in continuous forest, but were less likely to cross gaps as the gap distance increased. The other species were less willing to travel in corridors and gaps relative to forest, and the differences among habitats also increased with distance. For chickadees, gap-crossing decisions in the presence of forested detours varied over the range of distances that we tested, and were primarily influenced by detour efficiency (the length of the shortcut relative to the available detour). Over short distances, birds used forested detours, regardless of their efficiency. As absolute distances increased, birds tended to employ larger shortcuts in the open when detour efficiency was low or initial distance in the open was high, but they limited their distance from the nearest forest edge to 25 m. Thus, chickadees were unwilling to cross gaps of > 50 m when they had forested alternatives, yet they sometimes crossed gaps as large as 200 m when no such choice existed. Our results suggest that the presence of corridors enhanced the movement of some, but not all, forest birds, and that even chickadees, which were less sensitive to gap width, preferred not to venture far from forest cover.
Food Provisioning and Parental Status in Songbirds: Can Occupancy Models Be Used to Estimate Nesting Performance?
Aude Catherine Corbani, Marie-Hélène Hachey, André Desrochers
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101765
Abstract: Indirect methods to estimate parental status, such as the observation of parental provisioning, have been problematic due to potential biases associated with imperfect detection. We developed a method to evaluate parental status based on a novel combination of parental provisioning observations and hierarchical modeling. In the summers of 2009 to 2011, we surveyed 393 sites, each on three to four consecutive days at Forêt Montmorency, Québec, Canada. We assessed parental status of 2331 adult songbirds based on parental food provisioning. To account for imperfect detection of parental status, we applied MacKenzie et al.'s (2002) two-state hierarchical model to obtain unbiased estimates of the proportion of sites with successfully nesting birds, and the proportion of adults with offspring. To obtain an independent evaluation of detection probability, we monitored 16 active nests in 2010 and conducted parental provisioning observations away from them. The probability of detecting food provisioning was 0.31 when using nest monitoring, a value within the 0.11 to 0.38 range that was estimated by two-state models. The proportion of adults or sites with broods approached 0.90 and varied depending on date during the sampling season and year, exemplifying the role of eastern boreal forests as highly productive nesting grounds for songbirds. This study offers a simple and effective sampling design for studying avian reproductive performance that could be implemented in national surveys such as breeding bird atlases.
Method to isolate polyribosomal mRNA from scarce samples such as mammalian oocytes and early embryos
Sara Scantland, Jean-Philippe Grenon, Marie-Hélène Desrochers, Marc-André Sirard, Edward W Khandjian, Claude Robert
BMC Developmental Biology , 2011, DOI: 10.1186/1471-213x-11-8
Abstract: The proposed method is based on mixing the extracted oocyte cytoplasm with a preparation of polyribosomes obtained from a non-homologous source (Drosophila) and using sucrose density gradient ultracentrifugation to separate the polyribosomes. It involves cross-linking the non-homologous polyribosomes and neutralizing the cross-linking agent. Using this method, we show that certain stages of oocyte maturation coincide with changes in the abundance of polyribosomal mRNA but not total RNA or poly(A). We also show that the abundance of selected sequences matched changes in the corresponding protein levels.We report here the successful use of a method to profile mRNA present in the polyribosomal fraction obtained from as little as 75 mammalian oocytes. Polyribosomal mRNA fractionation thus provides a new tool for studying gametogenesis and early development with better representation of the underlying physiological status.Gametogenesis and embryonic development in mammals involve several major cellular events marked by an unusual mode of messenger RNA management. In nearly all animal species, mRNA molecules are stored in the developing oocyte until use during maturation or after fertilization [1-8]. These stored mRNAs direct protein synthesis during the period of transcriptional silence, which begins when the germinal stage oocyte reaches its full size [9-13] and lasts until embryonic genome activation [14-16]. In cattle, this size is approximately 120 μm within a follicular antrum 3-5 mm in diameter [10,15,17]. During the period covering the remaining follicular development (i.e. from 3 to 25 mm in antral diameter), the post-LH-surge oocyte maturation, fertilization and the onset of embryonic genome activation, very little genomic transcription occurs. It is generally believed that transcript storage begins in the early stages of oogenesis and may thus last for several weeks. It is also believed that the transcripts are stored in a particulate form [18] and lack the pol
Computational Methodology for the Prediction of Functional Requirement Variations Across the Product Life-Cycle
Guillaume Mandil,Alain Desrochers,Alain Rivière
Physics , 2009,
Abstract: The great majority of engineered products are subject to thermo-mechanical loads which vary with the product environment during the various phases of its life-cycle (machining, assembly, intended service use...). Those load variations may result in different values of the parts nominal dimensions, which in turn generate corresponding variation of the effective clearance (functional requirement) in the assembly. Usually, and according to the contractual drawings, the parts are measured after the machining stage, whereas the interesting measurement values are the ones taken in service for they allow the prediction of clearance value under operating conditions. Unfortunately, measurement in operating conditions may not be practical to obtain. Hence, the main purpose of this research is to create, through computations and simulations, links between the values of the loads, dimensions and functional requirements during the successive phases of the life cycle of some given product. [...]
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