Papers by Cynthia Paszkowski
Crucian carp, a common Eurasian cyprinid fish, shows striking dichotomies in several aspects of i... more Crucian carp, a common Eurasian cyprinid fish, shows striking dichotomies in several aspects of its physiology and ecology, at both the individual and population levels. These dichotomies consistently reflect the communities and ecosystems in which they occur, contrasting crucian carp that occur in "monocultures" (single-species fish assemblages) in ponds with those occurring in multi-species assemblages, primarily in lakes. Dichotomies also occur in the physiological state of individuals between summer and winter. All these dichotomies, involving differences in morphology and population structure, population dynamics and life history, reflect in an integrative way the adaptive strengths and limitations of a unique species. In numerous northern ponds, dense monocultures of crucian carp are sealed in by thick ice and snow to live more than six months in dark, anoxic waters at near freezing temperatures. In summer, these populations experience temperatures of up to 30°C during a relatively brief period of vigorous growth and repeated bouts of reproduction in almost continuous daylight. Crucians in lakes experience a more benign abiotic environment and, with densities that can be orders of magnitude lower than those in ponds, are likely unaffected by intraspecific interactions. However, co-occurring species present a challenging biotic environment. Crucian carp is exceptionally vulnerable to predation and populations persist via three kinds of refugia. Aided by extreme physiological adaptations, crucian carp can be the sole piscine inhabitant of seasonally harsh but productive small ponds, the refugium habitat, where they form dense monocultures of stunted individuals. The structural complexity offered by dense beds of macrophytes in productive larger lakes, the other common habitat (habitat refugium) of crucian carp, ensures survival of a few offspring, even in the presence of piscivores. The risk of predation still remains high for crucians until a certain length (and/or body depth), the size refugium, is attained. Crucian carp's unique anoxia tolerance, accompanied by many exceptional structural and functional features, and the species' suitability for laboratory studies, has recently raised crucian carp to a status of a physiological model species like its relative, the goldfish. Moreover, the dichotomy found in the structure of natural populations has made crucian carp an attractive model for ecological studies in competititon and predation. Crucian carp's resistance to adverse environmental conditions further suggests promising economical use in aquaculture to produce hybrids endowed with higher survival capacity than common carp.
Les modèles pour cette espèce ne donnaient pas de bons résultats et n'ont pas su prévoir l'occurr... more Les modèles pour cette espèce ne donnaient pas de bons résultats et n'ont pas su prévoir l'occurrence avec exactitude. Quant aux modèles pour le Pipit de Sprague, ils se sont avérés les plus puissants d'entre tous et ont montré que l'occurrence de cette espèce était négativement reliée aux dérangements anthropiques. Chez l'ensemble des trois espèces, les caractéristiques du paysage n'étaient pas de bonnes variables pour prévoir leur occurrence et leur abondance. Nos résultats indiquent que le dérangement attribué aux sites de puits et aux infrastructures connexes affecte l'occurrence des certaines espèces et devrait être pris en considération dans les stratégies de conservation d'oiseaux de prairie, particulièrement si des prairies vierges se retrouvent dans la mire du développement énergétique.
Feeding behavior and modeled energetic intake of common loon (Gavia immer) adults and chicks on small lakes with and without fish
Springer eBooks, 2006
We examined the behavior of common loons, Gavia immer (Brü nnich), breeding on small, shallow lak... more We examined the behavior of common loons, Gavia immer (Brü nnich), breeding on small, shallow lakes in central Alberta, Canada that were naturally fishless or contained only small-bodied fishes (minnow lake). For both lake types, adults spent >90%of their time on the nesting lake and >50% of their time foraging. Adult loons on fishless lakes dove more frequently, but dives were of shorter duration than loons on lakes with fish. On two intensively studied fishless lakes, adults fed chicks macroinvertebrates, particularly leeches, whereas on a focal minnow lake, fish made up >70% of prey items delivered by adults. Chicks >36 days of age on a minnow lake spent >50% of their time foraging, whereas older chicks on fishless lakes were highly dependent on food provisioning by adults. Models based on observed foraging patterns indicated that prey size was a better predictor of success in meeting energetic requirements than was feeding behavior (e.g., dive rate, dive success). For most models, estimated energetic intake was higher for loons on minnow lakes than on fishless lakes. Our behavioral observations and model results are consistent with surveys in central Alberta that indicate that breeding Common Loons frequently establish territories on small lakes, but that chicks hatched on lakes completely lacking fish rarely fledge and only if sufficient large invertebrates such as leeches are available.
Horned grebe habitat use of constructed wetlands in Alberta, Canada
Journal of Wildlife Management, Jul 28, 2012
Wetland degradation has resulted in declines in populations of aquatic birds throughout North Ame... more Wetland degradation has resulted in declines in populations of aquatic birds throughout North America. Horned grebe (Podiceps auritus), a migratory diving bird experiencing population decline, may benefit from wetland construction. We examined horned grebe use of borrow pits (ponds created during highway construction) in Alberta, Canada. Our goals were to document patterns of occurrence and breeding success of grebes on borrow pits and to determine if occupied and unoccupied sites differed in local habitat or landscape characteristics. In May 2003 and 2007, 330 constructed ponds were surveyed for horned grebes. We chose 100 occupied and 100 unoccupied ponds for additional surveys in 2007 and 2008, and collected habitat and landscape data for these sites. We used generalized linear mixed model and generalized linear model regression, coupled with Akaike's Information Criterion, to determine which environmental variables were most effective in explaining occurrence of horned grebes. The best model included all measured local and landscape habitat features. Horned grebes occurred on 36% of ponds in May 2003 and 2007, and chicks were produced on 74.5–81.3% of occupied ponds in 2007 and 2008. Grebes occupied larger ponds with more emergent and riparian vegetation and avoided ponds that supported beavers, contained human structures, and were primarily surrounded by forest within 1 km. On ponds with grebe pairs, chicks were produced more often on sites surrounded by more riparian vegetation. We conclude that the construction of small wetlands offers a promising means of increasing breeding habitat for horned grebes and present specific recommendations for breeding pond construction. © 2012 The Wildlife Society.
Avian Conservation and Ecology, 2011
Les modèles pour cette espèce ne donnaient pas de bons résultats et n'ont pas su prévoir l'occurr... more Les modèles pour cette espèce ne donnaient pas de bons résultats et n'ont pas su prévoir l'occurrence avec exactitude. Quant aux modèles pour le Pipit de Sprague, ils se sont avérés les plus puissants d'entre tous et ont montré que l'occurrence de cette espèce était négativement reliée aux dérangements anthropiques. Chez l'ensemble des trois espèces, les caractéristiques du paysage n'étaient pas de bonnes variables pour prévoir leur occurrence et leur abondance. Nos résultats indiquent que le dérangement attribué aux sites de puits et aux infrastructures connexes affecte l'occurrence des certaines espèces et devrait être pris en considération dans les stratégies de conservation d'oiseaux de prairie, particulièrement si des prairies vierges se retrouvent dans la mire du développement énergétique.
Ornithological Science, 2004
We examined habitat use and foraging behavior of male Black-and-white Warblers (Mniotilta varia) ... more We examined habitat use and foraging behavior of male Black-and-white Warblers (Mniotilta varia) in fragments (2-140 ha) of mature forest dominated by trembling aspen (Populus tremuloides) and a similar contiguous forest (Ͼ1000 ha) in central Alberta, Canada. Vegetation structure and composition differed significantly between occupied and unoccupied fragments, and between plots within and outside territories in occupied fragments. Territories in fragments were characterized by a high abundance of willow (Salix spp.), which was the primary foraging site for males in this habitat. Territories in contiguous forest differed significantly in vegetation structure from territories in fragments, and were characterized by a high abundance of trembling aspen trees, which served as the primary forest foraging site. The use of foraging substrates and foraging methods did not differ between individuals in fragments versus contiguous forest. In the boreal mixedwood ecoregion, the Black-andwhite Warbler appears flexible in its habitat use.
ISRN Ecology (print), Sep 16, 2012
The Peace Parkland, Alberta, Canada is part of a continentally important region for breeding and ... more The Peace Parkland, Alberta, Canada is part of a continentally important region for breeding and migrating aquatic birds. As a result of resource development and agricultural conversion, many wetlands have been lost. Road construction in the area results in the creation of borrow pits, <3 ha ponds created when soil is removed to form the road bed. We surveyed 200 borrow pits for aquatic birds in May through August 2007. We examined patterns of occurrence and richness, categorizing ponds based on surrounding landscape type: agriculture (0-33.3% forest within 500 m), mixed habitat (33.4-66.6% forest), and forested (66.7-100% forest). Principal Component Analysis indicated that pond environments differed based on local and landscape features. Twenty-seven species of aquatic birds used borrow pits, with 13 nesting. Nonmetric Multidimensional Scaling and Indicator Species Analysis of birds observed in each month revealed assemblages characteristic of agricultural ponds, including horned grebe, lesser scaup, American coot, and mallard, and of ponds with >33.3% forest, including bufflehead, ring-necked duck, greenwinged teal, and American wigeon. Because borrow pits were used by a variety of dabbling and diving aquatic birds in repeatable assemblages across the breeding season, we propose that these wetlands be integrated into avian conservation strategies.
Population Genetics of Arctic Grayling Distributed Across Large, Unobstructed River Systems
Transactions of The American Fisheries Society, May 2, 2014
AbstractWe investigated the population genetics of Arctic Grayling Thymallus arcticus distributed... more AbstractWe investigated the population genetics of Arctic Grayling Thymallus arcticus distributed throughout several connected river systems in Alberta, Canada. Broad- and fine-scale population structure was examined by genotyping nine microsatellite loci in 1,116 Arctic Grayling captured from 40 sites in the Hay, Peace, and Athabasca River basins. Genetic diversity tended to decline from north to south (allelic richness versus latitude: Spearman's rank correlation rs = 0.793, P < 0.05); the lowest level of diversity was detected in a stocked population. We found significant genetic divergence between and within major river basins (overall genetic differentiation index FST [θST] = 0.13) and strong isolation-by-distance patterns in the Peace River basin (Mantel's r = 0.97, P < 0.001) and Athabasca River basin (Mantel's r = 0.95, P < 0.001). Evidence for gene flow among sites in neighboring rivers (i.e., 25–100 km apart) was common; significant genetic differentiation tended to occur at the subbasin level. ...
The Condor, Aug 1, 2004
We compared trophic ecology of grebes inferred from stable-isotope analysis to that from gut cont... more We compared trophic ecology of grebes inferred from stable-isotope analysis to that from gut contents, and compared isotopic ratios of Red-necked Grebes (Podiceps grisegena) from lakes differing in their food webs. Analyses of different grebe tissues (egg yolk and albumen, pectoral and leg muscle, breast and primary feathers) also allowed us to assess the effectiveness of these tissues at representing grebe trophic relations. Isotopic ratios from pectoral and leg muscles were similar, based on comparisons within individual birds. Enriched values of ␦ 15 N and ␦ 13 C suggested that breast and primary feathers were molted over winter, and therefore reflected a marine food web. Albumen and yolk of grebe eggs and muscle tissues from downy chicks, however, matched isotopic characteristics of the local food web, indicating that female Red-necked Grebes use nutrients from the breeding lake for egg formation. Eggs, therefore, can provide excellent material for isotopic analysis aimed at assessing trophic relations of Red-necked Grebes on breeding lakes. Gut contents and stable isotopes both indicated that grebes from lakes with fish consumed a mixed diet of fish and macroinvertebrates and occupied the highest trophic level, at or above the level of piscivorous fishes. In contrast, grebes from lakes lacking fish occupied a lower trophic position.
Effects of fish density on planktonic communities and water quality in a manipulated forest pond
Hydrobiologia, Oct 1, 1992
We examined the effects of fish on lower trophic levels in a small pond in eastern Finland. The p... more We examined the effects of fish on lower trophic levels in a small pond in eastern Finland. The pond was divided into four sections with plastic curtains and stocked with crucian carp (Carassius carassius); two sections had low (4.45.5 gm-3) and two high (10.413.7 gm-3 ...
Large body size for metamorphic wood frogs in urban stormwater wetlands
Urban Ecosystems, Aug 9, 2015
Constructed wetlands in urban environments may be used by urban amphibian populations for breedin... more Constructed wetlands in urban environments may be used by urban amphibian populations for breeding. Yet, few studies have examined the performance of young-of-the-year from created wetlands even though the success of terrestrial life stages is directly linked to the performance of individuals at the egg and larval stage. We assessed how early-stage amphibians developing within constructed stormwater wetlands compared in body size (one metric of performance) to those in nearby natural wetlands. We conducted surveys for wood frog, Lithobates sylvaticus, larvae and young-of-the-year metamorphs at 13 wetlands located in the City of Edmonton, Alberta, Canada and compared metamorph size (a useful metric for fitness and reproductive success) between constructed stormwater and two types of natural wetlands. We related body size to within-wetland parameters (reflecting water chemistry, thermal regimes and physical characteristics) and used an information-theoretic approach to identify predictors of metamorph body size. Abundances of egg masses, larvae and metamorphs were generally lower at stormwater than natural wetlands. Metamorphs exhibited larger body size in stormwater wetlands compared to natural wetlands. Low metamorph abundances and cool, stable water temperatures best explained large body size in stormwater metamorphs. We propose that with increasing urbanization and associated construction of artificial wetlands, size benefits in early developmental stages may help individuals cope with reduced habitat suitability in the terrestrial environment.
A Comparison of Natural and Restored Wetlands as Breeding Bird Habitat Using a Novel Yolk Carotenoid Approach
Wetlands, Apr 2, 2013
Restored wetlands are commonly assessed as avian breeding habitat using surveys, but data on repr... more Restored wetlands are commonly assessed as avian breeding habitat using surveys, but data on reproductive parameters are needed to better understand how restoration affects wetland-dependent bird populations. A novel way to assess differences in breeding habitat quality is to compare the maternal allocation of carotenoids (i.e., biologically active yellow, orange and red pigments) to egg yolks, which is both diet and habitat dependent. We compared yolk carotenoid concentrations of red-winged (Agelaius phoeniceus) and yellow-headed blackbirds (Xanthocephalus xanthocephalus) that bred in natural, recently restored (i.e., restored ≤ 6 yrs ago) and restored (i.e., restored 9–16 yrs ago) wetlands to determine if restored wetlands provided critical reproductive resources at levels similar to natural sites. We also measured emerging insect abundances, water chemistry, and landscape-level parameters for study wetlands and related these variables to yolk carotenoid concentrations. Moreover, to understand the importance of damselflies to the diet of blackbirds, we measured the carotenoid content of damselflies and compared this to the yolk carotenoid content found in blackbird eggs. Bird abundances were also measured at each wetland to compare the traditional method of assessing breeding habitat to our novel yolk-carotenoid approach. In 2008, red-winged blackbirds in natural wetlands had higher carotenoid concentrations than birds in recently restored wetlands, suggesting that natural wetlands provided better breeding habitats. In 2009 there was a severe drought and we found contrasting results, with red-winged blackbirds in restored wetlands having higher carotenoid concentrations. Adult damselflies contained five carotenoids commonly found in avian tissues, suggesting they are likely an important source of carotenoids for wetland-breeding blackbirds. In contrast to yolk carotenoids, neither avian species richness nor abundance was significantly related to wetland type. Based on model selection results for water chemistry parameters, variation in concentrations of yolk carotenoids in red-winged blackbirds was best explained by conductivity, whereas variation in avian abundance was explained by total nitrogen, and avian species richness by chlorophyll-a concentration. Model selection results for landscape-level parameters revealed that variation in concentrations of red-winged blackbird yolk carotenoids was best explained by percent water in a 500 m buffer and variation in both avian abundance and avian species richness by wetland surface area. Our novel yolk carotenoid approach allowed us to identify differences in breeding bird habitat quality across wetland types, which we failed to detect with traditional bird survey data; our results highlight the need for additional studies comparing methods for assessing wetlands as breeding habitat for wetland-dependent birds.
Complex littoral habitat influences the response of native minnows to stocked trout: evidence from whole-lake comparisons and experimental predator enclosures
Canadian Journal of Fisheries and Aquatic Sciences, Feb 1, 2012
Strong negative effects of introduced predatory fishes on native species are frequently reported ... more Strong negative effects of introduced predatory fishes on native species are frequently reported but may not be universal. Recent research from productive lakes, for example, has documented few serious negative effects. Our objective was to determine how complex littoral habitat mediates the response of adult and young-of-year (YOY) native dace (Chrosomus spp.) and fathead minnow (Pimephales promelas) to the introduction of rainbow trout (Oncorhynchus mykiss) in productive lakes in Alberta, Canada. We first quantified inshore–offshore habitat use of native fish in stocked and unstocked lakes with heavily vegetated littoral zones. We then manipulated the presence or absence of trout and densities of macrophytes within enclosures in an unstocked lake and assessed the behavioral response of native fish. Our whole-lake comparisons revealed that adult and YOY fishes occurred in vegetated inshore areas to a greater extent in stocked relative to unstocked lakes. In the enclosure experiment, native fishes did not respond to the introduction of trout at natural macrophyte densities, but dace significantly reduced their occupation of enclosures with reduced macrophytes once trout were added. Our results suggest that complex littoral macrophyte beds provide important refuge habitat for native fishes, which can potentially mitigate negative effects associated with introductions of a piscivorous predator.
Scale-dependent habitat selection by American Redstarts in aspen-dominated forest fragments
The Wilson Journal of Ornithology, 1999
We examined scale-dependent site occupancy of American Redstarts (Setophaga ruticilla) in forest ... more We examined scale-dependent site occupancy of American Redstarts (Setophaga ruticilla) in forest fragments (2-140 ha in area) dominated by mature trembling aspen (Populus tremuloides) in central Alberta, Canada. Vegetation within territories, both adjacent to and away from nests, differed from vegetation in unoccupied fragments and within occupied fragments outside of territories. Territories contained higher den- sities of willow (SaZix sp.),
An experimental study of body size and food size relations in crucian carp, Carassius carassius
Environmental Biology of Fishes, Apr 1, 1989
Synopsis In dense, single-species assemblages of crucian carp, competition is intense and result... more Synopsis In dense, single-species assemblages of crucian carp, competition is intense and results in populations of stunted fish. To explore mechanisms underlying this competition, we measured handling times, return rates, and prey choice for five sizes of crucian carp feeding on six sizes of a standardized food. Handling times increased with prey size and decreased with fish size. Return rates (dry
Transactions of The American Fisheries Society, Nov 1, 1994
To examine how predator and prey body sizes, prey abundance, and prey population structure affect... more To examine how predator and prey body sizes, prey abundance, and prey population structure affect piscivore-prey interactions, feeding experiments were conducted on large (>190 mm total length, TL) and small (150-189 mm) yellow perch Perca flavescens given small (43-55 mm TL), medium (60-66 mm), and large (71-80 mm) fathead minnows Pimephales promelas as prey. Handling costs suggested that large yellow perch should not discriminate among prey sizes, but small yellow perch should select small fathead minnows over large. Results of feeding trials with only one size of prey were consistent with the cost indications. Large yellow perch consumed similar numbers and biomasses of the three size-classes of fathead minnows in trials with only one size of prey available. Small yellow perch ate more small fathead minnows than medium and more medium than large. Thus, small yellow perch gained less weight with large fathead minnows than with small ones as their prey. When all three prey sizes were available, both large and small yellow perch consistently captured more small fathead minnows than large, even when total prey abundance or the size structure of prey populations varied. Overall consumption by large yellow perch was not affected by prey abundance, but small yellow perch increased consumption at higher abundances by eating more small and medium prey. Increasing the proportion of medium fathead minnows, while decreasing the proportion of large prey, did not affect total consumption by either large or small yellow perch. However, small yellow perch responded to this shift by eating more medium and fewer large fathead minnows. Selection by yellow perch for prey fish smaller than expected based on gape limitations and handling times, and the responses of yellow perch to changes in their prey base under experimental conditions, help explain patterns of predation and coexistence between this piscivore and its prey in nature.
Ecology, Jun 1, 1992
Detecting mechanisms that structure ecological communities often requires investigations at appro... more Detecting mechanisms that structure ecological communities often requires investigations at appropriate spatial and temporal scales. A 15-mo, whole-lake experiment revealed direct and indirect mechanisms by which a fish predator structured its prey population, primarily by affecting recruitment of young-of-the-year (YOY) fish. Piscivorous Eurasian perch (Perca fluviatilis) were added to two of four sections of a divided lake in eastern Finland previously stocked with crucian carp (Carassius carassius). Although the stocked crucians quickly grew beyond vulnerable sizes, recruitment of their offspring through their 1 st yr of life was reduced by 90% in sections with perch. Surviving YOY in predator sections were completely confined to vegetated inshore areas. This restriction to refuges lowered their growth rates in comparison with YOY in predator-free sections, which can further reduce recruitment by prolonging susceptibility to size-limited predation and decreasing energy reserves needed for anaerobic overwintering. In the presence of piscivores, surviving prey subsequently benefit from reduced intraspecific competition, increasing growth rates to achieve large, invulnerable body sizes rapidly. Resulting populations of crucian carp, consisting of relatively few but relatively large individuals, contrast with populations living in the absence of piscivores, which are characterized by high densities of small, stunted individuals. Such divergent population patterns are displayed by a number of prey species in Scandinavia and North America, suggesting that a combination of direct and indirect effects of predation on younger age classes, such as documented for crucian carp, may be common in fish populations of small northern lakes. Detecting these patterns and identifying their underlying mechanisms may often require a combination of extensive and intensive studies.
Effects of watershed disturbance on nutrient inputs and cyanobacterial dynamics in eutrophic lakes of the Canadian Boreal mixed-wood forest: preliminary results
Verhandlungen, Oct 1, 2000
Recent large-scale timber harvesting in the boreal forests of northern Alberta and Québec has pro... more Recent large-scale timber harvesting in the boreal forests of northern Alberta and Québec has prompted concerns over possible impacts on aquatic ecosystems. Watershed disturbances associated with timber harvesting activity should lead to increased nutrient (N and P) Ioadings into srreams and lakes; however, effects of watershed disturbances on aquatic ecosystems are poorly understood, especially for boreal Iakes. In addition, fire events within boreal watersheds are expected to resu!t in similar nutrient loading patterns as timber harvesting disturbances, but direct comparisons berween these disturbance phenomena have never been attempted. We are focusing on comparisons between timber harvesting and fire impacts on the water quality of eutrophic Iakes within boreal mixed-wood watersheds. The objectives of this project are to: (i) develop empirical models describing the influences of forest harvesting and natural disturbances on hydrology, water quality, biodiversity and community structure; (ii) compare an d contrast effects documented for eutrophic lakes in Alberta with effects on the less productive lakes in Quebec; and (iii) ro understand the causal mechanisms of these impacts. Euphotic-zone water quality, phytoplankton, zooplankton, and fisheries community data were colIected monthly from rwo sets of 40 core study lakes in northern Alberta and Québec during July, August and September 1996 and 1997. Stable isotope, cyanobacterial toxin, and littoral and profundal macroinvertebrate samples were also collected for the Alberta study lakes. Lakes with harvested or burned watersheds were compared to undisturbed reference systems, including nine lakes in Alberta with preand post-harvesting data.The water quality of undisturbed Boreal Plain lakes in Alberta was highly variable relative to their Boreal Shield counterparts in Quebéc. Thus, we initially concentrated on idemif}ring key morphometric and watershed parameters linked with water quality variables, such as basin morphometry, watershed topography, soi! types a~d vegetative cover, in undisturbed boreal lakes m Alberta. We found distinct differences between lakes with wetland-dominated watersheds (i.e. large proportions of bogs, fens, and marshes) and uplanddominated systems. Total phosphorus and dissolved organic carbon concentrations in wetland-dominated systems were related to the proportion of wetlands within the watershed, whereas these parameters were related to total watershed area in the upland-dominated systems. Inorganic nitrogen concentrations were related to percentage conifer cover for both watershed types. Cyanobacterial blooms and associated roxins (i.e. microcystin-LR) occurred more frequendy in heavily burned and harvested watersheds in Alberta, compared to reference systems. Microcystin-LR concentrations tended to be highest in lakes with burned watersheds relative to harvested watersheds. Further work o n identif}ring the underlying facrors behind the variability in boreal aquatic ecosystems will help to isolate differences related to watershed disturbance. We hypothesize that the magnitude of aquatic ecosystem response to watershed distur?ance is a function of disturbance type (fire versus ttmber harvesting), the proportion of watersh~d area disturbed, time elapsed since the disturbance event, and lake water residence time. Authors' addresses: E. PREPAS, W. ToNN, D. VITT, C. PAszKowsKI, J. WHITE, K. WoLFSTEIN, L. HALSEY, G. ScRIMGEOUR, K. WESTCOTT, P. DINSMORE, E. BRAUN, J. EVANS, P. McEACHERN, S. REEDYK, University of Alberra, Sustainable Forest Management Nerwork, Deparrment o f Biological Sciences, Edmonton, Alberta, Canada. D. PLANAS, Université du Québec à Montréal, Département de sciences biologiques, Montréal, Quebéc,
Occurrence of the Western Toad and Its Use of ‘Borrow Pits’ in West-Central Alberta
Northwestern Naturalist, Sep 1, 2006
Abstract Populations of western toad (Bufo boreas) have declined or disappeared from much of the ... more Abstract Populations of western toad (Bufo boreas) have declined or disappeared from much of the species' range in the United States. To assess distributions and densities of the western toad in the foothills of west-central Alberta, Canada, we conducted visual surveys of 130 natural water bodies in watersheds encompassing a range of human-disturbance levels in early and late summer 2000. Encounter rates were consistently low throughout the study area (0.2 to 0.3 toads/h) and were one-tenth the rate for the co-occurring wood frog (Rana sylvatica). Pitfall trapping of breeding and non-breeding sites during 2001 and 2002 showed differences in age structures between western toad and wood frog populations and low recruitment of newly metamorphosed juveniles into western toad populations. On ponds, more toads of ≥1 y old were captured than recently emerged juveniles. The difference between the 2 age classes was greater on ‘borrow pits’ (human-created roadside ponds) than on beaver ponds, suggesting that borrow pits might be population sinks providing poor larval habitat. Borrow pits either dried prior to juvenile emergence or had oligotrophic to mesotrophic waters compared to eutrophic conditions in beaver ponds. Pond creation as a mitigation strategy or by-product of road construction may put western toad populations at risk of decline in the foothills of Alberta.
Selective piscivory by perch: Effects of predator size, prey size, and prey species
Verhandlungen, Sep 1, 1991
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Papers by Cynthia Paszkowski