Cynthia A. Paszkowski

Piscivory and Recruitment: Mechanisms Structuring Prey Populations in Small Lakes

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 de- creasing 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.

Density-Dependent Effects and the Regulation of Crucian Carp Populations in Single-Species Ponds

Crucian carp (Carassius carassius) is often the only fish species present in small ponds of northern Europe. Such populations are typically at high densities and consist primarily of small, relatively slender, and short-lived fish; populations in multispecies assemblages in lakes display opposite traits. Field and laboratory experiments have im- plicated predation as an important mechanism structuring crucian populations in multispe- cies assemblages. To investigate the role(s) of density dependence in structuring pond populations, we manipulated densities of crucians stocked into four sections of a subdivided natural pond in Finland. Mortality of stocked fish during the 3-mo experiment was low (0-11%) and unrelated to density. Growth rates of crucians were both size and density dependent. Larger fish did not noticeably grow in either high- or low-density sections, but growth of smaller size classes was 22% greater in low-density sections. Lower densities and smaller sizes of zoo- plankton, especially of inshore cladocerans that are an important food resource for smaller crucians, indicated that resource limitation caused by exploitation competition was an important density-dependent process restricting growth of small fish in high-density sec- tions. Crucians rely on reserves of glycogen, stored in the liver and muscle, to fuel the over- winter anaerobic metabolism that allows them to maintain populations in ponds where winter hypoxia eliminates other fishes. Liver size was significantly larger and glycogen levels were 82% higher in our low-density pond sections than in high-density sections. At higher, but not lower, densities, relative liver size and glycogen levels decreased with body size; combined with the lack of growth of large fish, this indicates that density-dependent energy limitations contribute to the short life-spans and rarity of large fish that characterize pond populations. An increase in relative body depth can be induced in crucians by the presence of piscivorous fish, reducing vulnerability to predation. It has been proposed that increased body depth incurs a substantial energy cost during swimming and should be restricted to specific size classes in populations sympatric with predators. However, in our experiment, crucians of all sizes became significantly deeper bodied, which contributed to higher con- dition factors in low-density vs. high-density sections. This morphological change, occurring in the absence of piscivores, suggests that energy benefits (accumulation of overwintering reserves) can override any proposed costs for this sluggish, but metabolically unique, fish. Crucian carp successfully reproduced in all sections during the experiment, but growth and recruitment of 0+ fish (young of year) were strongly and negatively related to the numbers of older fish present. The observed density-dependent recruitment was likely caused by starvation-induced mortality and cannibalism; reduced growth observed in 0+ fish would also be expected to cause higher first-winter mortality, reducing further recruit- ment at higher densities. Density dependence has a variety of regulatory effects on pond populations of crucian carp that contribute to their persistence and resilience.

A comparison of sample types varying in invasiveness for use in DNA sex determination in an endangered population of greater Sage-Grouse (Centrocercus uropihasianus)

Obtaining blood and muscle samples is often not feasible in genetic studies on endangered species, therefore researchers must adopt sampling techniques that are less invasive, but yield poorer quality DNA (Taberlet et al. 1999). Noninvasive sampling has increased in avian genetics over the last decade (Pearce et al. 1997; Segelbacher and Steinbru¨ck 2001; Segelbacher 2002), but there has been no thorough comparison of the quality and quantity of DNA produced among sample types. Use of moderately invasive samples, such as mouth swabs (Poschadel and Moïler 2004) and plucked feathers (Taberlet and Bouvet 1991), has also increased, but such samples have not been compared to other types. The purpose of our study was to determine (1) whether DNA could be successfully extracted and amplified from a variety of noninvasive and moderately invasive sample types and (2) which sample types yield the best quality DNA for use in avian DNA sexing based on amplification of the chromo helicase DNA-binding (CHD) gene (Z fragment=224 bp and W fragment=252 bp). We evaluated three under utilized sample types (avian saliva, chick down, and predated eggshell membranes) along with common sample types for use in sex determination. Greater Sage-Grouse (Centrocercus urophasi-anus) are endangered in Canada and the southern Alberta population has declined by 66–92% since the 1970s (Aldridge and Brigham 2003). We collected samples from the Alberta population from 1998–2004. Sample collection protocols and modifications to published DNA extraction protocols using Qiagen DNeasy Ò Tissue Kits and QIAamp Ò DNA Micro Kits (Qiagen, California, USA) are outlined in Table 1. Qiagen DNeasy Ò Tissue Kits were used for all samples with the exception of mouth swabs because low concentration DNA was produced. QIAamp Ò DNA Micro kits were used for mouth swabs and yielded high quality DNA (Table 1). Samples were DNA sexed using the 1237L/ 1272H primer set and PCR cycling conditions from Kahn et al. (1998). Fifteen microlitre PCRs are described in Table 1. PCR products were separated on 3% agarose gels stained with ethidium bromide and visually scored. Low voltage (100 mV) was used for maximum separation and definition of sex-specific bands. All samples were sexed three times to ensure consistent results. Three separate PCRs (modified multiple-tubes approach; Segelb-acher and Steinbru¨ck (2001)) opposed to eight separate PCRs (multiple tubes approach; Taberlet et al. (1999)) were performed for each sample to avoid false typing of individuals with low DNA concentrations. Samples that did not …

δ13C and δ15N Signatures in Muscle and Fin Tissues: Nonlethal Sampling Methods for Stable Isotope Analysis of Salmonids

Abstract Stable isotope analysis has emerged as an important tool in aquatic ecology. For fish, dorsal muscle from sacrificed individuals has traditionally been used in stable isotope studies; however, there are many instances when lethal sampling is undesirable. We evaluated the feasibility of using adipose and caudal fin clips as alternatives to muscle in stable isotope studies for five species of salmonids. Because fish size and water temperature can affect stable isotope ratios, we also determined whether fish length and sampling date affected the difference in isotope signatures between fins and muscle. Biopsied muscle plugs and fin clips were collected from rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, and lake trout S. namaycush as well as lake whitefish Coregonus clupeaformis and pygmy whitefish Prosopium coulterii and analyzed for stable isotopes of carbon and nitrogen. The isotope signatures of both adipose and caudal fins were significantly correlated (0.33 < R 2 < 0.97)...

Effects of prey species composition and habitat structure on foraging by two functionally distinct piscivores

We compared foraging by two piscivores, pike (Esox lucius) and zander (Stizostedion lucioperca), on two prey fishes, crucian carp (Carassius carassius) and rudd (Scardinius erythrophthalmus), in the presence and absence of artificial vegetation in a field enclosure experiment. We found that pike had a higher predation rate than zander in the presence of vegetation, whereas zander had a higher predation rate in the absence of vegetation. In addition, both piscivores selected crucian carp over rudd, resulting in higher survival of rudd in the presence of crucian carp. Behavioral observations of the prey in the presence of artificial vegetation showed that rudd moved rapidly in shoals, spending relatively little time in vegetation, whereas crucian carp moved considerably less and spent more time in vegetation. The presence of either piscivore caused crucian carp, but not rudd, to increase its use of vegetation. In addition, both prey species moved more rapidly in the enclosures when vegetation was absent than when it was present. The increased movements of crucian carp were due to crucians shoaling with rudd. Our data are consistent with the notion that the structure of many European fish assemblages is related to differential vulnerability of prey species as well as differential foraging success ofpiscivores in open water and vegetation.

Population structure and genetic diversity of greater sage-grouse ( Centrocercus urophasianus ) in fragmented landscapes at the northern edge of their range

Range-edge dynamics and anthropogenic fragmentation are expected to impact patterns of genetic diversity, and understanding the influence of both factors is important for effective conservation of threatened wildlife species. To examine these factors, we sampled greater sage-grouse (Centrocercus urophasianus) from a declining, fragmented region at the northern periphery of the species’ range and from a stable, contiguous core region. We genotyped 2,519 individuals at 13 microsatellite loci from 104 leks in Alberta, Saskatchewan, Montana, and Wyoming. Birds from northern Montana, Alberta, and Saskatchewan were identified as a single population that exhibited significant isolation by distance, with the Milk River demarcating two subpopulations. Both subpopulations exhibited high genetic diversity with no evidence that peripheral regions were genetically depauperate or highly structured. However, river valleys and a large agricultural region were significant barriers to dispersal. Leks were also composed primarily of non-kin, rejecting the idea that leks form because of male kin association. Northern Montana sage-grouse are maintaining genetic connectivity in fragmented and northern peripheral habitats via dispersal through and around various forms of fragmentation.

Using Chorus-Size Ranks from Call Surveys to Estimate Reproductive Activity of the Wood Frog (Rana sylvatica)

Abstract Call surveys are a relatively new and efficient technique for detecting the presence of breeding male anurans. Using data from multiple surveys of breeding choruses of Wood Frogs (Rana sylvatica) combined with counts of egg masses on ponds in west-central Alberta we determined (1) the relationship between ranks of chorus size and total number of egg masses in ponds, and (2) number of breeding males in standard chorus-size ranks (1, 2 and 3). Estimates for Rank 3 choruses were based on a formula with number of egg masses present per pond and a fixed male to female ratio of 2:1 calculated from the literature. Calling males were recorded from all ponds that had evidence of female reproductive activity (i.e., egg masses). Generalized linear models suggested that ranks were positively and linearly correlated with the number of egg masses in a pond. In addition, call data from only the second of four sampling periods (each 3–6 days) significantly predicted number of egg masses in ponds, suggesting that timing is important when surveying calling wood frogs. The mean number of chorusing males per rank did not correspond to aural ranks of calling intensity: Rank 1 = 1.3 males, Rank 2 = 3.7 males, and Rank 3 = 118 males. We recommend similar assessments for other widely distributed species to improve our ability to detect and interpret habitat-use patterns and population trends of amphibians through monitoring programs.

Effects of Prey Size, Abundance, and Population Structure on Piscivory by Yellow Perch

Abstract 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 favescens 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, ...

The effects of urbanization on North American amphibian species: Identifying new directions for urban conservation

Urbanization is a pervasive and growing threat to amphibian populations globally. Although the number of studies is increasing, many aspects of basic amphibian biology have not been investigated in urban settings. We reviewed 32 urban studies from North America and quantified the number of species studied and their response to urbanization. We examined existing research on breeding habitats, life-history stages, movement patterns, and habitat use relative to urbanization. We found amphibians as a whole respond negatively to urbanization (69 reported responses were negative, 6 were positive and 35 showed no effect). We caution, however, that many North American species still lack or are associated with conflicting information regarding species-specific responses (e.g., 89 potential responses were unknown). Approximately 40% of all anuran and 14% of caudate species in North America were investigated in the literature; however, the most diverse genera (e.g., Plethodon and Eurycea) were the most understudied likely due to their cryptic terrestrial lifestyles and biases in sampling protocols that assess wetland habitats via call surveys. Research on movement and small scale habitat use was deficient. Adult, juvenile, tadpole, and egg mass life-history stages commonly served as direct measures of species presence and abundance; however, such data do not accurately reflect recruitment into subsequent age classes and population persistence. The lack of data on many North American species may be contributing to poor management of urban amphibian populations and their habitats.

Effects of Forest Harvesting and Fire on Fish Assemblagesin Boreal Plains Lakes: A Reference Condition Approach

Abstract To assess the impacts of forest harvesting and fires on lentic fish assemblages in the Boreal Plains ecoregion (Alberta, Canada), we applied a reference condition approach to 37 lakes in burned, logged, or undisturbed catchments. Fish assemblages in the reference lakes were classified into two types: those dominated by large-bodied piscivores and those dominated by small-bodied fishes. A discriminant function analysis with only two environmental descriptors (lake maximum depth and average slope of the catchment) could correctly predict assemblage type in 84% of reference lakes. Depth likely reflects the influence that winter oxygen concentrations have on fish assemblage type, whereas catchment slope is correlated with a variety of landscape-level features. Although potential effects of forest harvesting and fire can increase the susceptibility of lakes to winter hypoxia (via nutrient enrichment) and alter connectivity to the regional drainage network (via altered hydrology), fish assemblages in 9...