Thesis (M.S.)--University of Guelph, 2001. / Includes bibliographical references. Also available via the Internet.

The object of this field study was to examine Nilsson's hypothesis (Nilsson, 1965, 1967) of interactive segregation as it might apply to feeding and spatial distribution of Cutthroat trout (Salmo clarki clarki) and Dolly Varden (Salvelinus malma) in allopatric and sympatric populations of the two species in small lakes. Salmo clarki clarki living alone changed their depth distribution throughout the summer season but no diel movement was recorded. The changes in food habits closely corresponded with seasonal change in distribution, and a wide variety of food organisms was eaten. Salvelinus malma living alone underwent considerable diel changes in spatial distribution, with the majority caught at the surface during the evening. Their diet consisted primarily of zooplankton and surface-caught insects. Sympatric Salmo clarki clarki and Salvelinus malma were spatially segregated throughout the summer. Cutthroat trout occurred mostly near the surface and in littoral areas and fed in these areas. In contrast, Dolly Varden were mostly benthic in distribution and fed primarily on bottom organisms. By comparing food habits and distribution in allopatric and sympatric situations it was inferred that food competition contributes to the segregation of the species in sympatry. Seasonal differences in food and spatial segregation occur suggesting interactive segregation is a temporary phenomenon. In general, the data support Nilsson's hypothesis of interactive segregation. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.)--Rutgers University, 2009. / "Graduate Program in Ecology and Evolution." Includes bibliographical references (p. 56-76).

The object of this study was to investigate character displacement (Brown and Wilson, 1956) and reduction of phenotypic variability with reduction in niche width (Van Valen, 1965). Dolly Varden from one sympatric (Loon Lake) and two allopatric (Dickson and Foley Lake) populations were compared. Field studies showed that the niche width of sympatric Dolly Varden was less than that of allopatric Dolly Varden owing to food and spatial segregation, confirming results of an earlier study (Andrusak and Northcote, 1971). Character displacement was evident in pyloric caeca numbers and in certain behavioural responses (spatial distribution and feeding) observed in the laboratory. These were accompanied by reduced variability, also apparent in length distributions within year classes, in the sympatric population compared with an allopatric population (Dickson Lake). However, character displacement and reduced variability could not be demonstrated for most morphometric characters, presumably because of the complexity of growth processes involved. Effects of overlapping adjacent year classes and of continuous growth of fish body parts (in contrast to comparable studies with birds) obscured interpretation of such characteristics. / Science, Faculty of / Zoology, Department of / Graduate

Differences in food habits and spatial distribution of sympatric Dolly Varden (Salvelinus malma) and cutthroat trout (Salmo clarki clarki) in a small coastal lake were documented by Andrusak (MS 1968). Segregation was inferred to be of the interactive type hypothesized by Nilsson (1965, 1967). The object of this study was to describe feeding behavior of individuals from these sympatric populations, and to evaluate the importance of food exploitation to the segregation process. Individual and paired fish were studied in the laboratory throughout the spring, summer and autumn. The different food habits were found to be due to a number of basic behavioral and morphological differences between the species. Dolly Varden oriented to and rested on the bottom. Cutthroat rested in the water column and were frequently surface oriented. Searching behavior differed between the species. Dolly Varden swam faster and at relatively constant rates. They sampled "mouthfuls" of substrate as they searched. Trout alternately hovered and cruised, sampling specific items. At low light intensities they were much less successful than the char at finding benthic food items. The mouth of the Dolly Varden is small and "scoop-like" compared to that of the cutthroat, and seems particularly well adapted for benthic feeding. Dolly Varden searched persistently for benthic organisms in the absence and presence of surface insects. Cutthroat rapidly switched from bottom to surface feeding if insects were presented there. The observed differences between species were fully expressed in isolated individuals. There was no evidence of the differences being magnified through interspecific competition. These differences, believed to be inherent, were considered sufficient to keep the species segregated without the involvement of competition. Segregation was concluded not to be of the interactive, type, even though the populations still retained considerable plasticity enabling them to switch diets or habitats when necessary or advantageous. The period of intense competition and food exploitation was considered to have occurred and ended during earlier stages of the coexistence. / Science, Faculty of / Zoology, Department of / Graduate

An analysis of the systematics, zoogeography and evolution of the Dolly Varden char species complex in British Columbia is presented. These features of this species complex and the morphometric statistical procedures used in these analyses have both long been the subjects of strong debate and also have recently seen much renewed interest and work. This thesis assesses both these areas and is divided into those two parts. The first section deals with these three biological topics, and the second section contains a synthesis and exploratory data assessment of the commonly used morphometric techniques and provides some new methodology for understanding their requirements and interpreting their results. PART I 1. The systematics of the Dolly Varden char species complex is examined by using principal component analysis (PCA) to designate typological species groupings and then employing linear discriminant function analysis on a reduced set of significant characters to classify the remaining specimens. This typological distinction is verified with distributional information that reveals no interbreeding of the species in areas of parapatry and sympatry, and with preliminary information regarding intra- and inter- specific crosses, spawning colouration, skull osteology, cytology and embryology. This data is also suggestive of competitive exclusion and character displacement. All these results indicate that the Dolly Varden char species complex in B.C. is composed of two species, Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus). 2. The zoogeography of these two species is analyzed using canonical trend surface analysis (CTS). CTS can potentially separate confounding non-geographic morphometric information from the data and thus could allow historical zoogeograpbic patterns to be inferred from that data which corresponds to geography. Such a reconstruction reveals the possible glacial refuge origins and post-glacial recolonization patterns of these two species for each of the major river drainages in B.C.. 3. The evolution of these two species is assessed through the implementation of PCA to fit the cross-sectional morphometric data to an ontogenetic model. The resultant PCA size and shape vectors effectively portray allometric trends which indicate that Dolly Varden could have evolved from bull trout through neotenic paedomorphosis. This result is supported with data on growth rates and developmental homeostasis. PART II 4. A synthesis of the available but widely scattered and disparate information on the data and statistical requirements for morphometric statistics reveals the analytical problems that can result from not approximating underlying test assumptions. These assumptions are important, but are not appreciated or often assessed. Simple recommendations and rarely used tests for dealing with these requirements are provided. 5. The effectiveness and compatability of four bivariate morphometric techniques (ratios, log₁₀ ratios, allometric regression, regression residuals) are assessed. All methods provide similar but ineffective individual ordination and group separation. Their effects on characters differ greatly and are often unrealistic. None of these methods effectively removes all the confounding allometric size information, but allometric regression will usually be the best bivariate procedure. 6. A similar assessment of four multivariate morphometric procedures (covariance matrix PCA, correlation matrix PCA, shear matrix PCA, size-constrained matrix PCA) is undertaken. Size-constrained PCA results in non-orthogonal vectors that also do not represent the traditional multivariate morphometric size and shape vectors. As well, the character and individual information it provides is unrealistic. The other three techniques result in similar and effective individual ordination, group separation and removal of confounding allometric size information. PCA on a covariance matrix is likely the best multivariate method since it provides the most realistic size adjustment and character information. 7. PCA is often carried out on data which has been previously adjusted through bivariate procedures. An examination of this method demonstrates that it results in no benefits since the multivariate morphometric size and shape vectors are lost, and the data variation is no longer synthesized into only two or three resultant significant vectors. 8. PCA is also performed on mixed character data sets (continuous and discontinuous data). An assessment of this procedure shows that it provides improved group separation, but the representation of characters, individuals and multivariate morphometric size and shape relationships is confounded and unrealistic. There also is a slight reduction in data synthesis. 9. A methodology for back-transforming PCA output into the original and more intuitively comprehensible data scale, format and dimensions is given. This back-transformation also verifies the traditional belief that the first resultant PCA morphometric vector is size and that the second is shape. Separate unconfounded matrices for size and shape information in which only the significant data variation is accounted for can thus be independently back transformed. / Science, Faculty of / Zoology, Department of / Graduate

Laboratory feeding experiments showed that sympatric Dolly Varden charr (Salvelinus malma) were able to locate and consume prey targets at lower irradiance levels than sympatric cutthroat trout (Salmo clarki clarki) but their acuity was poorer. Reaction distance (RD) of both species to artificial and natural prey targets increased as irradiance level increased from a visual irradiance threshold (VIT), an irradiance level below which prey targets were not detected visually (3.0 x 10¹⁴ photons m⁻²s⁻¹ for charr and 3.0 x 10¹⁵ photons m⁻² s⁻¹ for trout) to a saturation irradiance level (SIL) which produced the maximum RD (3.0 x 10¹⁶ photons m⁻² s⁻¹ for charr and 6.6 x 10¹⁸ photons m⁻² s⁻¹ for trout). The VIT and SIL were independent of prey type and prey characteristics in both species. At all irradiance levels greater than the VIT of trout, the RD of trout exceeded that of charr for the same prey type. At a given irradiance level the largest RD in both species occurred in the presence of red irradiance followed in decreasing order by green, yellow and blue irradiance. Reaction distance of trout and charr increased with increases in prey size, movement and contrast. The percent increase in RD was greatest in trout. Between the VIT and the SIL the percent increase in RD was greater at higher irradiance levels in both species. At or above the SIL the percent increase in RD was constant. The central portion of retinas of trout and charr from sympatric and allopatric populations were examined by light microscopy. The two trout populations had a similar density of cone cells and higher than either charr population. Sympatric charr had the lowest cone cell density and allopatric charr intermediate density. Rod cell density showed the opposite trend, being highest in sympatric charr, lowest in sympatric and allopatric trout and intermediate in allopatric charr. The cone cell mosaic, consisting of a regular array of double and single cones, was the same in all four populations. Both cone types were smallest in the two trout populations, largest in the sympatric charr population and intermediate in allopatric charr. The degree of retinal summation was greatest in sympatric charr, least in the trout populations and intermediate in allopatric charr. In summary, histological studies indicated that sympatric and allopatric trout possessed the highest level of visual acuity while sympatric charr were the most sensitive to low irradiance conditions. Foraging velocity of sympatric trout and charr increased as irradiance increased reaching a maximum at the SIL of each species. From foraging velocity, RD and information on the diel irradiance regime in Loon Lake I estimated the volume of water searched visually for two natural prey types by trout and charr on a mid-summer day. Below the VIT, only charr were able to locate and consume buried prey targets, presumably by employing their chemosensory system. Differences in visual and non-visual feeding behaviour in sympatric trout and charr and in retinal structures of sympatric and allopatric trout and charr are generally as expected based on field studies of their vertical distribution and feeding habits. / Science, Faculty of / Zoology, Department of / Graduate

Sympatric populations of Dolly Varden (Salvelinus malma) and cutthroat (Salmo clarki clarki) are spatially and food segregated in Loon Lake, British Columbia. Dolly Varden are found mainly in the lower water column, while cutthroat are found in the middle and upper water column. Zooplankton, the only major prey type found in both diets, appear more important to the cutthroat. The purpose of this study was to determine whether this segregation was due to behavioural interactive processes or genetically based selective processes. This was investigated by the segregation and transferral of the members of the two populations to separate fishless lakes. In addition, field studies examined selective feeding on zooplankton and laboratory studies compared the feeding behaviour and abilities of Dolly Varden and cutthroat on three different types of zooplankton. Little change occurred during the two year sampling period in either the diet or the vertical distribution of the two species, an indication that the fish were not interactively segregated. However, the physical and biological characteristics of the lakes may have reinforced, at least initially, previous behaviour patterns. As a result, more time may be required to properly assess the final results. Laboratory results indicate that primarily Chaoborous larvae and secondarily Daphnia pulex were the preferred prey types to both fish predators, mainly because of their poor escape response when compared to that of Diaptomus kenai. The abundance of these prey types in the diet of lake-caught fish was generally in accordance with the laboratory preferences. These results also demonstrated that cutthroat were more efficient planktivores than were Dolly Varden. / Science, Faculty of / Zoology, Department of / Graduate

Genetic diversity of two salmonid species, Dolly Varden (Salvelinus malma) and coastal cutthroat trout (Oncorhynchus clarki clarki) in Prince William Sound, Alaska were examined at multiple spatial scales with three molecular markers. Pleistocene glaciers covered what is now Prince William Sound 8,000- 12,000 years ago and both species colonized the region subsequently. Because these species have different migratory behavior and historic ranges I expected to see different patterns of genetic diversity within Prince William Sound. Haplotype frequency and nucleotide diversity in sixteen mitochondrial DNA (mtDNA) restriction fragment enzymes combinations in Prince William Sound were higher in Dolly Varden than in coastal cutthroat trout, which were close to fixation. Low estimates of these measures in coastal cutthroat trout may reflect a founder effect resulting from colonization of this region from a single glacial refuge (Cascadia) and low dispersal capacity. To examine if genetic diversity in coastal cutthroat trout was higher in areas of glacial refuge, three additional locations from throughout their distributional range were examined with the same restriction enzymes. Haplotype frequency and nucleotide diversity were lower in areas that were glaciated than estimates of the same measures in a glacial refuge. Again, founder effects during colonization of the three glaciated sites may account for these results. Genetic variation of Dolly Varden and coastal cutthroat trout was also examined within and among populations in Prince William Sound with microsatellites and allozymes. The pattern of genetic variation in coastal cutthroat trout was complex. There was lower genetic diversity within populations that were recently colonized following recent de-glaciation (150-350 ybp). Genetic diversity among some coastal cutthroat trout populations was high, which possibly reflects restricted migration. In other trout populations there was low diversity among populations, possible reflecting historic gene flow. In Dolly Varden, genetic variation among anadromous populations in Prince William Sound was low. There were large differences among resident and anadromous populations. These data provide information for the management for both species, which may reduce the risk of the loss of genetic diversity within local populations. / Graduation date: 2003