I didn't see a posting for the next discussion, but I wanted to get these out of the way. Anyway, here are my summaries:
Dolinsek, I. J., J. W. A. Grant and P. M. Biron. 2007. The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salar. Journal of Fish Biology 70: 206-214.
Kalleberg, E. R. 1958. Observations in a stream tank of territoriality and compensation in juvenile salmon and trout (Salmo salar L. and S. trutta). Report of the Institute of Freshwater Research Drottingholm 39: 55-98.
In a manipulative field experiment, Dolinshek et al. (2007) tested the Kalleberg (1958) hypothesis that for juvenile Atlantic salmon visual isolation reduces territory size and subsequently increases density. Dolinshek et al. (2007) hypothesized that if visual isolation is the primary mechanism controlling density in salmon, and not habitat heterogeneity or habitat quality, changes to a habitat that affect visual isolation should have no effect on non-salmonid density because such fish do not defend territories, but should affect density of coincident salmonids. They manipulated streams by adding or removing boulders from test plots. Boulders were assumed to provide sufficient visual isolation. They found that adding boulders increased salmon density, but had little effect on non-salmonids, thus supporting Kalleberg’s hypothesis.
Elliott, J. M. and M. A. Hurley. 1998. Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream. Journal of Animal Ecology 67: 280-286.
In previous work, Elliott and Hurley (1998) found that one of two extensively documented trout populations studied in the English Lake District was clearly controlled by density-dependent factors in early life stages (competition among individuals that recently emerged from redds). In the second population, which had a lower overall density, this density-dependent relationship was not observed, so they tested whether density-dependence at a later life stage, reproductive females, controlled populations. Specifically, they studied the relationship between how many females laid eggs each year and the number of successfully spawning females that resulted from that year’s recruitment. When female density exceeded 4 per 300 m2 their offspring produced fewer females and eggs. Documentation of later life density-dependence in salmonids is rare and the specific mechanisms remain unknown, though Elliot and Hurley (1998) speculate on a few.
Orth, D.J., and T.J. Newcomb. 2002. Certainties and uncertainties of defining essential habitats of riverine smallmouth bass. Pages 251-264 in M. S. Ridgway and D. P. Phillipp, eds. Black Bass: Ecology, Conservation, and Management. American Fisheries Society, Bethesda, MD.
Sorry to diverge from the Precis approach, but I just could not do this article justice via that summary format. Orth and Newcomb (2002) present concepts germane both to our discussions of habitat ecology and population ecology in stream habitat management.
On Habitat Ecology:
Orth and Newcomb (2002) use the inconsistencies and consistencies of observed habitat associations in Virginia and West Virginia streams to draw conclusions about the physical and biological processes that create and maintain habitats for SMB. For example, physical habitat measures of nest sites (depth, velocity, proximity to banks, etc,) varied by river, but all relationships were related to refugia for both adults and offspring. Nests in deeper habitats with greater cover protected adults from avian prey. Nests were also more common in areas less likely to be affected by violent flows, thus providing flow refugia for eggs. The conceptual connections presented in this example are writ large in Orth and Newcomb (2002) as they look at habitat use for all important life stages of SMB (nesting, early development, juvenile, and adult) and also at habitat needed to sustain a SMB forage base.
On Population Ecology:
In the first portion of their paper, Orth and Newcomb (2002) briefly review some factors known more globally to affect recruitment to and structure of SMB populations. However, in discussion of habitat associations they more narrowly hypothesize links between habitat and population structure, demonstrating the importance of density-independent mechanisms on SMB populations. For example, they hypothesized that SMB population structure is the product of stochastic processes, such as rare and extreme flow events, and habitat quality, such as suitable nest sites. They also discuss the link between habitat for forage and success of populations. For example crayfish density can affect adult SMB density. Thus, habitat quality for crayfish can control SMB populations.
In summary, Orth and Newcomb (2002) expose the danger of the assumption that because an animal appears to be habitat generalist, that population dynamics are not affected by density-independent mechanisms indirectly or directly related to habitat quality.
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In their recent publication “The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salar L.”, Dolinsek et al. studied the changes in Atlantic salmon populations in two Canadian streams after the addition of boulders to increase habitat heterogeneity. The authors applied two treatments and a control to stream habitat (addition of boulders and removal of boulders), recorded fish numbers, species, and ages during day and night snorkeling sessions, and compared differences between the two treatments and control. This study concluded that juvenile salmonids preferred the habitat with additional boulders, but previous studies noted that growth and survival decrease with increased density and future work detailing the impacts of boulder addition on salmonid growth and survival is necessary. The purpose of this study was to test Kalleberg’s (1958) hypothesis that increasing habitat heterogeneity will decrease the territory size of age 0+ Atlantic salmon and lead to increases in population density.
Dolinsek, I. J., J. W. A. Grant, and P. M. Biron. 2007. The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salar L.. Journal of Fish Biology 70: 206-214
Kalleberg, H. 1958. Observations in a stream tank of territoriality and competition in juvenile salmon and trout (Salmo salar L. and S. trutta L.). Report of the Institute of Freshwater Research Drottingholm. 39: 55-98
In association with the study above, Dolinsek et al. completed a study on the behavioral response of Atlantic salmon Salma salar L. to the addition of boulders to a stream, more specifically the effects of visual isolation on territory size and population density. To perform this study, the researchers used GIS to map the surface of the stream bed and the location of each fish during the survey performed in the previous study. With this data they were able to estimate each fish’s field of vision and determine which of the other fish were visible from that location. The researchers concluded that increased habitat heterogeneity increases visual isolation, increases population density, and decreases territory size in juvenile Atlantic salmon. This study was conducted to test Kalleberg’s (1958) hypothesis that increased habitat heterogeneity increases population densities by increasing the visual isolation of individual salmonids.
Dolinsek, I. J., P. M. Biron, and J. W. A. Grant. 2007. Assessing the effect of visual isolation on the population density of Atlantic salmon (Salmo salar) using GIS. River Research Applications 23: 763-774
Kalleberg, H. 1958. Observations in a stream tank of territoriality and competition in juvenile salmon and trout (Salmo salar L. and S. trutta L.). Report of the Institute of Freshwater Research Drottingholm. 39: 55-98
In “The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salarL.” Dolinsek et al. (2007) suggests that the increased presence of large structure increases habitat heterogeneity, decreases visibility for fish, and therefore decreases the size of salmonid territories. The authors used three treatments, boulders-added, boulder-removed, and control to understand the effect of these structures on juvenile Atlantic salmon, finding that treatments with more boulders contained higher densities of salmon. Dolinsek et al. admit that the increased density resulting from increased boulders could be the result of low-velocity refuges and not a function of territory size. The purpose of this article is to understand the effects of boulder additions for the management of salmonids.
Dolinsek, I. J., J. W. A. Grant, and P. M. Biron. 2007. The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salar L.. Journal of Fish Biology 70: 206-214
Elliot and Hurley argue that juveniles in the population of brown trout in Wilfin Beck are not regulated by density-dependent factors while adults are, opposite to the findings in nearby Black Brows Beck in their articlt titled “Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream. The researchers found no evidence of density-dependent mortality in juvenile trout while the number of spawning females produced in each year class was directly related to density, corroborating the authors’ thesis. The authors believe that the lack of density dependence in the juvenile trout is a result of very low densities in comparison to other trout streams and admit some uncertainty in the mechanisms behind the adult population regulation. The purpose of the article was to examine the population ecology of a resident trout stream and compare the findings to populations in well-studied, productive trout streams.
Elliott, J. M. and M. A. Hurley. 1998. Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream. Journal of Animal Ecology 67: 280-286
Sabo and Pauley examine the effects of size and evolutionary history in juvenile interspecific competition in their article titled “Competition between stream-dwelling cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch): effects of relative size and population origin” and predict that cutthroat trout from populations sympatric with coho salmon will compete better than allopatric trout and that cutthroat trout will compete better with salmon of similar size than larger salmon. The researchers used a two factor experiment in which allopatric trout were placed with small and large salmon and sympatric trout were placed in the same two treatments. They found that allopatric trout competed better than sympatric trout and both competed better with the smaller salmon, contradicting their predictions. The authors admit some uncertainty in the extrapolation of their lab experiment to actual situations and are unsure of the mechanism behind this differential ability to compete but hypothesize that stronger intraspecific competitive forces in allopatric populations make them stronger competitors. The authors’ purpose is to understand the nature of competition between salmonid species to get at some of the underlying mechanisms behind previously studied patterns of habitat selection, size, and growth of these species.
Sabo, J.L. and G.B. Pauley. 1997. Competition between stream-dwelling cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch): effects of relative size and population origin. Canadian Journal of Fisheries and Aquatic Science 54:2609-2617.
In “Assessing the effect of visual isolation on the population density of atlantic salmon (Salmo salar) using GIS,” Dolinsek et al 2007 discuss how visual isolation is related to atlantic salmon density. They set up three experimental types: one with 36 boulders, one with all the boulders removed, and one natural habitat. Assessment was done using GIS and they found that greater density was present in the 36 boulder habitat than the other treatment and natural control. Differences occurred between years, but still pointed to the same results. Variation occurred at each test condition by year.
Dolinsek, I.J., P.M. Biron, and J.W.A. Grant. 2007. Assessing the effect of visual isolation on the population density of atlantic salmon (Salmo salar) using GIS. River Research and Applications 23: 763-774.
In “Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream,” J.M. Elliott and M.A. Hurley examine life history traits in relation to density-dependant effects of reproduction on a brown trout population. There was a general increase seen with female size in relation to the number of eggs found in a specific redd, and number of females was usually equal to the quantity of reproductive females present. Year-class reproductive female densities relied heavily on year-class reproduction.
Elliott, J.M., and M.A. Hurley. 1998. Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream. Journal of Animal Ecology 67: 280-286.
In “Nonlinear self-thinning in a stream-resident population of brown trout (Salmo trutta),” Rincon and Lobon-Cervia address weight and density relationships to examine brown trout self-thinning. Resource competition is at the core of this study, mainly habitat in this case, being the driving factor that thins population densities. Size-dependancy became increasingly more important as fish increased in length. Size-selective utilization of resources also affects resource availability and use. Local conditions exert a strong influence on this brown trout population.
Rincon, P.A., and J. Lobon-Cervia. 2002. Nonlinear self-thinning in a stream-resident population of brown trout (Salmo trutta). Ecology 83(7): 1808-1816.
In their research article “Assessing the effect of visual isolation on the population density of atlantic salmon (Salmo salar) using GIS ”, Dolinsek et al (2007) argue that the increase in density of Atlantic salmon observed in boulder-added zones is related to visual isolation rather than the presence of a velocity refuge. The authors support their thesis by conducting an experiment using three treatments: removing the boulders in a portion of the site; addition of boulders to another portion of the site; and then a control, where a portion of the site is left in the natural state. A detailed Digital Elevation Model (DEM) was then created for all the sites with a total station. Variables tested were site velocity, fish velocity and habitat heterogeneity. Dolinsek et al readily admit that while the addition of boulders to the substrate may increase the carrying capacity of a stream, the increase in density in the boulder-added sections was likely due to the redistribution of fish from the other treatments, as well as from outside the study area. The authors’ main purpose is to illustrate the potential of visual isolation as a possible short-term technique to increase salmonid density.
Dolinsek I. J., P. M. Biron and J. W. A. Grant (2007). Assessing the effect of visual isolation on the population density of atlantic salmon (Salmo salar) using GIS, River Research and Applications, 23: 763–774. DOI: 10.1002/rra.1024
D. W. Chapman, in is his journal paper “Food and space as regulators of salmonid populations in streams “, asserts that for stream-dwelling, natural populations of salmonids are mostly regulated in density by a space-food mechanism. More specifically, they argue that there is a minimal spatial requirement present regardless of food supply. They support their thesis via a review of relevant literature on the following topics: unique character of streams, food as a social convention; space and food; exploitation of resources, isolation; and predators and pathogens. Chapman is clear on the fact that even though pathogens and predators are important agents of destruction, the food and space complex is the underlying cause of density regulation. The author’s main purpose is to develop conclusions on the factors regulating salmonid population densities, based on current knowledge on the subject.
Chapman D. W. (1966). Food and space as regulators of salmonid populations in streams, The American Naturalist. No 913, 100: 345-357.
Dolisnek, I. J., W. A. Grant, and P. M. Biron. 2007. The effect of habitat heterogeneity on the population density of juvenile Atlantic salmon Salmo salar L. Journal of Fish Biology. 70: 206-214.
In order to assess the effects of habitat heterogeneity on Atlantic salmon, Dolisnek et al. manipulated boulder density in quadrats in various streams. In the quadrats, they either placed additional boulders (treatment), removed all boulders (treatment), or did nothing (control). They used 2-way ANOVA to determine differences in density between treatment and control sites. The researchers found that age 0 and age 1 Atlantic salmon densities were higher in boulder added quadrats than in boulder removed or control quadrats. They also noticed no difference in non-salmonid density. They attributed this phenomenon to differences in visual requirements between salmonids and non-salmonids
Dolisnek, I. J., P. M. Biron, and J. W. A. Grant. 2007. Assessing the effect of visual isolation on the population density of Atlantic salmon (Salmo salar) using GIS. River Research and Applications. 23: 763-774.
The authors used GIS viewshed analysis to determine the relative importance of visual isolation to Atlantic salmon. They used detailed bed topopgraphy data to construct a digital elevation models (DEM’s). The authors found that increasing boulders decreased the visible portions of the stream for Atlantic salmon. They concluded that increased habitat heterogeneity decreases territory size and increases population density of Atlantic salmon.
Elliot, J. M and M. A. Hurley. 1998. Population regulation in adult, but not juvenile, resident trout (Salmo trutta) in a Lake District stream. Journal of Animal Ecology. 67: 280-286.
The authors posit that populations of young brown trout in Wilfin Beck are not regulated by density dependent factors, but adults are regulated by density dependence. In contrast, juvenile brown trout in Black Brows Beck follow a traditional Ricker stock recruitment curve, and are controlled by density dependence. Each year from 1968 to 1984, redds were excavated and eggs were counted. The authors determined that density dependence did not control trout in Wilfin Beck because their density is not high enough to be a regulating factor.
In their journal article, Bond and Lake argue that the three streams of study are habitat limited and that with appropriate in-stream restoration, such as pool creating and increasing structure and cover, some species of fish may recover. The authors samples sites across multiple creeks affected by a large pulse of sediment and determined who fish presence and abundance varied in a hierarchical manner between creeks, among sites within a creek and within each site. The authors admit two sources of error: that their sampling methods may not be completely accurate with respect to species abundances and large numbers of statistical tests to detect a large number of parameters on fish distributions; however, they felt that patterns across sites, if consistent, were sufficient evidence of effects. The author’s goals were to determine if the sites were indeed habitat limited so that the effects of physical improvements will be an appropriate use of resources in this case.
Bond, N.R. and P.S. Lake. 2003. Characterizing fish-habitat associations in streams as the first stem in ecological restoration. Austral Ecology 28:611-621.
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